Middle Cenozoic unconformities in the Waihao Valley, South Canterbury Basin, New Zealand

Table of Contents

Abstract

Acknowledgements

Table of Contents

List of Tables

List of Figures

Chapter 1 Introduction
1.1 Previous work on New Zealand Cretaceous and Cenozoic basins
1.2 Purpose of thesis
1.3 Unconformities
1.4 Eocene - Oligocene unconformities in New Zealand
1.5 Global Mid - Oligocene unconformity
1.6 Marshall unconformity

Chapter 2 Methodology
2.1 Field work
2.1 Micropaleontology
2.2 Sedimentary petrology
2.2 Scanning Electron Microscope (SEM)

Chapter 3 Data & Results
3.1 Geology of the lower Waihao Valley
3.2 Dons Hole
3.3 McCullochs Bridge
3.4 Dyer Farm quarry
3.5 Waihao River Walkway - "Cabbagetree Gully”
3.6 Waimate Gorge (local Torlesse Terrane basement)

Chapter 4 Discussion
4.1 Eocene unconformities
4.2 Oligocene unconformities
4.3 Facies - and thickness variations in the Kokoamu Greensand
4.4 Provenance
4.5 Regional context of Zealandia in the Eocene - Oligocene
4.6 Future work

Chapter 5 Conclusions

Appendix A Petrological and petrophysical data
A.1 Modal mineralogical composition and magnetic susceptibility

Appendix B Micropaleontological data
B.1 Micropaleontological data

References

Abstract

This thesis presents descriptions and interpretations of stratigraphic sections in the lower Waihao Valley, southern Canterbury Basin. The aim of this reconnaissance study was to describe and interpret the age, origin and significance of previously identified unconformities in the Eocene - Oligocene sedimentary succession. Four sections were logged and sampled for foraminiferal biostratigraphy. Sedimentary petrological - and petrophysical analysis was carried out to understand the provenance and lithological variations to either confirm or contradict previous local paleoenvironmental interpretations.

Eocene strata in the lower Waihao Valley consist of Bortonian to Kaiatan age (ca. 42.6 - 36.7 Ma) Waihao Greensand and Kaiatan to Runangan? age (ca. 39.1 - 34.6 Ma) Ashley Mudstone. Oligocene strata in the lower Waihao Valley consist of lower Whaingaroan age (ca. 34.6 - 29.8 Ma) Earthquakes Marl, upper Whaingaroan to Duntroonian age (ca. 29.8 - 25.2 Ma) Kokoamu Greensand, and Duntroonian to Waitakian age (ca. 27.3 - 21.7 Ma) Otekaike Limestone. Four locations were investigated in the study area: Dons Hole, McCullochs Bridge, Dyer Farm quarry, and Waihao River Walkway (“Cabbagetree Gully”). Local Torlesse metasedimentary basement rocks were investigated at the Waimate Gorge quarry to supplement provenance analysis of the sedimentary strata.

Major results are as follows: One Eocene unconformity and two Oligocene unconformities are identified. One Oligocene unconformity is particularly significant as it represents a new location of the regional Mid - Oligocene Marshall unconformity, which was identified with confidence to represent a hiatus of at least 2.5 Ma.

One Eocene unconformity was identified at Dons Hole: A burrowed disconformity at the top of the Waihao Greensand (Otaio Limonitic Member) is established to be of Kaiatan age (ca. 39.1 - 36.7 Ma). Two Oligocene unconformities were identified in a measured section at Dyer Farm quarry: (1) A strongly burrowed disconformity, separating the lower Whaingaroan Earthquakes Marl (ca. 29.8 - 27.3 Ma) from the Duntroonian Kokoamu Greensand (ca. 27.3 - 25.2 Ma), shows significant age - and lithological changes, and confidently represents a new location of the regional Mid - Oligocene Marshall unconformity in Zealandia. (2) A fossiliferous horizon in the basal Duntroonian to Waitakian Otekaike Limestone (ca. 27.3 - 21.7 Ma) was identified as a diastem. It represents a short-time, high - energy storm - wave deposit (tempestite).

Local Duntroonian Kokoamu Greensand bed thickness and facies variations were recorded at Dyer Farm quarry and Waihao River Walkway (“Cabbagetree Gully”) - ca. 3 km apart. These lateral variations in deposition rate and facies are associated with either local changes in water depth or sediment supply.

Provenance analysis shows that the terrigenous influx in the Eocene - Oligocene strata was probably derived from nearby Torlesse Terrane metasedimentary rocks of Permian age and Cretaceous to Eocene Taratu Formation, suggested by the occurrence of abundant polycrystalline quartz grains. The parautochthonous glauconite in the Eocene - Oligocene strata in the lower Waihao Valley indicates a slow sediment deposition rate in a marine shelf environment and confirms previous local paleoenvironmental interpretations of the southern Canterbury Basin.

The outcome of this thesis is the lithostratigraphy and chronostratigraphy of the lower Waihao Valley, a confident identification of a new location of the regional Mid - Oligocene Marshall unconformity representing a hiatus of at least 2.5 Ma, and the confirmation of local Eocene - Oligocene paleoenvironmental interpretations, which add valuable contributions to the wider southern Canterbury Basin geology.

Keywords: Torlesse metasedimentary rocks, Waihao Greensand, Otaio Limonitic Member, Ashley Mudstone, Earthquakes Marl, Kokoamu Greensand, Otekaike Limestone, biostratigraphy, lithostratigraphy, chronostratigraphy, quartz grain provenance, Marshall unconformity, disconformity, diastem, tempestite, Notorotalia spinosa, parautochthonous glauconite, lower Waihao Valley, South Canterbury Basin, Zealandia

Acknowledgements

I would like to thank the University of Otago for granting me an International Master's Research Scholarship for 2019 to undertake my M Sc thesis.

I would particularly like to express my appreciation to my supervisor Prof R Ewan Fordyce, Geology Department, University of Otago, and my informal advisor Dr. Nick Mortimer, GNS Science, Dunedin, for their valuable and constructive suggestions during this research work. Contributions from Brent Pooley and Stephen Read from the Geology Department, University of Otago, are acknowledged for making thin sections and helping with graphics. Assistance in grammar review and / or field assistance provided by Samantha Allan, Rachel Seidner, Natalie Knupfer, Rico Menzel, Lachie Scarsbrook, Erin Weightman, and Caroline Wilsher was greatly appreciated. I want to thank the landowner of Dyer Farm quarry, Henry Arthur Dyer, for access to his property. The stratigraphic columns were made with Sed Log (Version 3.1), distributed by the Royal Holloway University of London, Department of Earth Sciences, London, UK.

Furthermore, I would like to convey my heartfelt thanks to my parents, Erika and Klaus - Dieter Piekarski, and grandparents, Irmgard and Heinz Schelte, for financially supporting my M Sc studies in New Zealand.

List of Tables

Table 1-1 Different types of unconformities, according to Dunbar & Rodgers (1957) and Neuendorf et al. (2011)

Table 3-1 Eocene - Oligocene lithostratigraphic nomenclature for the geological formations of the southern Canterbury Basin

Table 5-1 Modal mineralogical composition and magnetic susceptibility values of the samples. The modal mineralogical composition accounts only for clasts identified with point counting (no matrix)

Table 5-2 Identified foraminifera in the sedimentary Eocene - Oligocene strata of the lower Waihao Valley, southern Canterbury Basin. The red marked species are the age - diagnostic foraminifera (Hornibrook et al. 1989, Pearson 2006)

List of Figures

Figure 1-1 Bathymetric map showing the continent Zealandia with New Zealand Cretaceous to Cenozoic sedimentary basins. The red star shows the location of the study area (lower Waihao Valley) in the southern Canterbury Basin. Graphic annotated by author. Source: GNS Science, Lower Hutt, New Zealand (http://gns.cri.nz)

Figure 1-2 The New Zealand Geological Timescale, Version 2015/1 (based on Cooper 2004, with incooperated revised ages from Cohen et al. 2014 and Raine et al. 2015). Source: GNS Science, Lower Hutt, New Zealand

Figure 1-3 New Zealand Geological Timescale, Version 2015/1, with highlighted age range of the exposed Eocene - Oligocene strata in the study area. The red ovals show the absolute dates given to the International units and the blue ovals show the absolute dates given to the New Zealand stages. The obvious differences add another difficulty in precise age determination of the Cenozoic strata. The blue circle “29.8 Ma” marks the boundary between the lower Whaingaroan (ca. 34.6 - 29.8 Ma) and the upper Whaingaroan (ca. 29.8 - 27.3 Ma). Graphic based on Raine et al. (2015). Source: GNS Science, Lower Hutt, New Zealand

Figure 1-4 The different types of unconformities, according to Dunbar & Rodgers (1957)

Figure 1-5 The correlation of unconformities across different Cretaceous - Cenozoic sedimentary basins on the South Island of New Zealand. The graphic shows the correlation of several Eocene - Miocene unconformities across different sedimentary basins, incl. the Canterbury Basin (Canterbury) and the Great South Basin (Otago). Graphic annotated by author. Source: Lever (2007)

Figure 3-1 Topographic map with the location of the lower Waihao Valley in the South Canterbury Basin. The map was made using Arc GIS Pro (ESRI)

Figure 3-2 Topographic map showing the five study locations in the lower Waihao Valley. The map was made using Arc GIS Pro (ESRI)

Figure 3-3 Geological map of the lower Waihao Valley (fig. 3-1, 3-2). (1): Dyer Farm quarry, (2): Waihao River Walkway / McCullochs Bridge, (3): Squires Farm, (4): The Earthquakes. The map was made using Arc GIS Pro (ESRI). Source of geological map: Geological Map of New Zealand, 1:250.000 (QMAP), GNS Science, Lower Hutt, New Zealand Geological data from Heron (2014)

Figure 3-4 Location of Dons Hole. Source: Google Earth (22.11.2019)

Figure 3-5 Stratigraphic column of the sedimentary strata at Dons Hole

Figure 3-6 The top of the Waihao Greensand (Otaio Limonitic Member) at Dons Hole. Figure for scale. The bedding dips downstream in the direction of the photographer

Figure 3-7 Thin section image of the top of the Waihao Greensand (Otaio Limonitic Member) at Dons Hole, OU 86409, XPL. (1) = polycrystalline quartz, (2) = Fe oxide - coated allochthonous glauconite, (3) = vermicular, autochthonous glauconite

Figure 3-8 Fossil log Araucariaceae sp. (ca. 1.70 m long specimen), partly silicified and burrowed by Teredo sp., in the top of the Waihao Greensand (Otaio Limonitic Member). Identification based on personal communication with Mathew Vanner, MSc Geology, Geology Department, University of Otago, Dunedin, NZ

Figure 3-9 The disconformity within the top of the Waihao Greensand (Otaio Limonitic Member), showing an abrupt lithological change and abundant phosphatization and burrowing

Figure 3-10 Ashley Mudstone at Dons Hole.

Figure 3-11 Thin section image of the Ashley Mudstone at Dons Hole, OU 86410, XPL. The thin section shows glauconite grains (greenish) and quartz + feldspar grains (white/grey)

Figure 3-12 Location of the stratigraphic section at McCullochs Bridge on the Waihao River Source: Google Maps (22.11.2019)

Figure 3-13 Stratigraphic column of the sedimentary succession at McCullochs Bridge. This is a composite section with data from Ayress (1995), obtained at the exact same location at McCullochs Bridge

Figure 3-14 Ashley Mudstone at McCullochs Bridge during the river lowstand in summer (January 2019). Figure for scale

Figure 3-15 Thin section image of the Ashley Mudstone at McCullochs Bridge, OU 86411 (J40/f0250), XPL. (1) = dark basaltic scoria fragment, (2) = zeolites - infilled planktic foraminifera void

Figure 3-16 The location of the measured section at Dyer Farm quarry. Source: Google Earth (22.11.2019)

Figure 3-17 Stratigraphic column - measured section - of the sedimentary succession at Dyer Farm quarry

Figure 3-18 The Earthquakes Marl at the Dyer Farm quarry with sample locations.

Figure 3-19 Thin section image of the Earthquakes Marl at Dyer Farm quarry, OU 86402 (J40/f0242), PPL. It shows abundant greyish-white siliciclastic grains (quartz + feldspar) and yellowish-brown altered glauconite grains

Figure 3-20 The disconformity at the base of the Kokoamu Greensand at Dyer Farm quarry

Figure 3-21 Detailed view of the examined disconformity at the base of the Kokoamu Greensand at Dyer Farm quarry

Figure 3-22 Thin section image of the Kokoamu Greensand at Dyer Farm quarry, OU 86405 (J40/f0245), XPL. (1) = allochthonous glauconite, (2) = polycrystalline quartz, (3) = bioclasts (benthic foraminifera)

Figure 3-23 Notorotalia spinosa, SEM - Image, OU 86405 (J40/f0245). Image taken by Dr. Marianne Negrini, Geology Department, University of Otago

Figure 3-24 The base of the Otekaike Limestone with the echinoderm - rich diastem at Dyer Farm quarry. Figure for scale

Figure 3-25 Detailed image of the echinoderm - rich diastem, interpreted as a storm - wave deposit (tempestite) at the base of the Otekaike Limestone at Dyer Farm quarry. A sample, OU 86407 (J40/f0247) has been taken from the horizon (sampled directly at the tip of the lead pencil)

Figure 3-26 Thin section image of the Otekaike Limestone at Dyer Farm quarry, OU 86408 (J40/f0248), XPL. (1) = bioclast, (2) = allochthonous glauconite, (3) = polycrystalline quartz

Figure 3-27 The location of the stratigraphic section of the Waihao River Walkway ("Cabbagetree Gully”). Source: Google Earth (22.11.2019)

Figure 3-28 Stratigraphic column of the sedimentary succession at Waihao River Walkway ("Cabbagetree Gully”). This is a composite section including data from Ward & Lewis (1975), obtained at the nearby Waihao Forks location

Figure 3-29 The sedimentary succession at Waihao River Walkway ("Cabbagetree Gully”). It shows the sharp contact between the massive facies and the nodular facies of the Kokoamu Greensand. The Otekaike Limestone is exposed further to the right-hand side (fig. 3­30). Photo was taken by Prof. R Ewan Fordyce in 2012

Figure 3-30 The sedimentary succession (to the right of fig. 3-29) showing all three formations

Figure 3-31 Thin section image of the massive facies of the Kokoamu Greensand at Waihao River Walkway ("Cabbagetree Gully”), OU 86413 (J40/f0251), XPL. (1) = allochthonous glauconite, (2) = vermicular, autochthonous glauconite, (3) = siliciclastic grains (polycrystalline quartz + feldspar)

Figure 3-32 Thin section image of the nodular facies of the Kokoamu Greensand at Waihao River Walkway ("Cabbagetree Gully”), OU 86414 (J40/f0252), XPL. (1) = allochthonous glauconite, (2) = polycrystalline quartz

Figure 3-33 The Otekaike Limestone at Waihao Forks, described by Ward & Lewis (1975). The outcrop shows (1) = abundant cross - bedding and (2) = channelling across the width of the whole outcrop. Photo taken by Prof R Ewan Fordyce in 2012

Figure 3-34 Location of the small aggregate quarry in the south-end of the Waimate Gorge. The thick black line outlines the Torlesse Supergroup exposed in the Waimate Gorge and further to the north of the image (compare fig. 3-3). Source: Google Earth (22.11.2019).

Figure 3-35 The small aggregate quarry in the south-end of the Waimate Gorge, showing the active quarry face of around 21 m in height (August 2018).

Figure 3-36 Thin section image of the Torlesse metasedimentary basement rock (quartzo - feldspathic sandstone - greywacke), Waimate Gorge quarry, OU 86415, XPL. (1) = polycrystalline quartz, (2) = sericitized feldspar, (3) = dark rock fragment, (4) = prehnite, (5) = pumpellyite

Figure 4-1 Eocene - Oligocene lithostratigraphy of the lower Waihao Valley, South Canterbury Basin, showing the thickness of exposed strata

Figure 4-2 Eocene - Oligocene chronostratigraphy of the lower Waihao Valley, South Canterbury Basin. Three unconformities are identified: (1) = A disconformity in the Waihao Greensand (Otaio Limonitic Member) at Dons Hole, (2) The Marshall unconformity at Dyer Farm quarry separating Earthquakes Marl from Kokoamu Greensand, (3) A diastem in the basal Otekaike Limestone at Dyer Farm quarry. The unconformable contact separating the Ashley Mudstone from the Earthquakes Marl at McCullochs Bridge (Ayress 1995) is marked as uncertain (?) as no investigations were made during this study

Figure 4-3 Paleogeographic reconstruction of Zealandia during the Kaiatan (ca. 39.1 - 36.7 Ma) The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

Figure 4-4 Paleogeographic reconstruction of Zealandia during the Runangan (ca. 36.7 - 34.6 Ma) The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

Figure 4-5 Paleogeographic reconstruction of Zealandia during the lower Whaingaroan (ca. 34.6 - 29.8 Ma). The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

Figure 4-6 Paleogeographic reconstruction of Zealandia during the Duntroonian (ca. 27.3 - 25.2 Ma). The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

Figure 4-7 Paleogeographic reconstruction of Zealandia during the Waitakian (ca. 25.2 - 21.7 Ma). The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

Figure 4-8 Ternary diagram showing the modal mineralogical composition (vol%) of the Eocene - Oligocene strata in the lower Waihao Valley, South Canterbury Basin. (1): Eocene Waihao Greensand and Ashley Mudstone at Dons Hole, (2): Eocene Ashley Mudstone at McCullochs Bridge, (3): Eocene to Oligocene Earthquakes Marl at Dyer Farm quarry, (4): Oligocene Kokoamu Greensand at Dyer Farm quarry, (5): Oligocene Kokoamu Greensand at Waihao River Walkway ("Cabbagetree Gully”), (6): Oligocene Otekaike Limestone at Dyer Farm quarry. The calcite content is taken from the acid measurements (tab. 5-1: CaCO3 content with mud absent). The ternary diagram was made using Petrograph (Version 2.0)

Figure 4-9 Paleogeographic reconstruction of oceanic current patterns in the Southern Ocean in the Eocene (A) and Oligocene (B). Source: Nelson et al. 2004. Figure based on Kamp et al. 1990 and Nelson & Cooke 2001

Chapter 1 Introduction

1.1 Previous work on New Zealand Cretaceous and Cenozoic basins

The Canterbury Basin is one of several sedimentary basins in Zealandia of Cretaceous to Cenozoic age, as shown in fig. 1-1 (Field & Browne 1989, King et al. 1999, Lever 2007, Fulthorpe et al. 2011).

Editorial Note: Figure 1-1 was removed due to copyright issues.

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Figure 1-1 Bathymetric map showing the continent Zealandia with New Zealand Cretaceous to Cenozoic sedimentary basins. The red star shows the location of the study area (lower Waihao Valley) in the southern Canterbury Basin. Graphic annotated by author. Source: GNS Science, Lower Hutt, New Zealand ( http://gns.cri.nz )

Development of New Zealand Cretaceous and Cenozoic basins is related to the evolution of Zealandia, which has been influenced by eustatic sea-level changes, sediment supply, non­deposition, erosion, local tectonics, and plate boundary activity (Vella 1965, Haq 1987, Hayward 1990, Forsyth 2001, Lever 2007). The Taranaki Basin on the western part of the North Island of New Zealand (fig. 1-1) is well-known for its hydrocarbon resources and contains a Late Cretaceous to Early Miocene sedimentary succession, associated with the transgression caused by the Tasman Sea rifting due to the separation of Zealandia from Gondwana in the Late Cretaceous (Jenkins 1987, Hayward 1990, King et al. 1999). According to Hayward (1990), rapid subsidence occurred in the Late Oligocene to Early Miocene in the Taranaki Basin due to progradation associated with the obliquely extensional boundary between the Pacific and the Indian Plates. The Great South Basin in the south eastern part of the South Island of New Zealand (fig. 1-1) contains a Cretaceous to Cenozoic sedimentary succession and has been unsuccessfully explored for petroleum resources (McMillan & Wilson 1997, Killops et al. 1997, King et al. 1999).

The Cretaceous to Cenozoic Canterbury Basin in the mid-southern part of the South Island of New Zealand (fig. 1-1) has been explored for petroleum resources since the 1960s and several wells have been drilled (Killops et al. 1997). According to Field & Browne (1989), the petroleum wells Clipper - 1 (1984) and Galleon - 1 (1985) found gas and condensate in Late Cretaceous coal measure sands. In the South Canterbury Basin, previous work focussed on paleontological and sedimentological aspects such as Eocene molluscs (Maxwell 1992), Oligocene penguins (Fordyce & Jones 1990, Fordyce & Thomas 2011, Ksepka et al. 2012), sedimentary petrology (Riddolls 1968, Browne & Field 1985), and reconstruction of paleocurrents (Ward & Lewis 1975). Dating of the Eocene and Oligocene strata has been carried out using ostracods (Ayress 1993, Ayress 1995), foraminifera (Hornibrook 1961, Hornibrook et al. 1989, Hornibrook 1996), and strontium isotopes (Fulthorpe et al. 1996, Graham et al. 2000, Nelson et al. 2004). Despite the above work, many unresolved issues exist both at a regional and local level, especially related to the precise dating of unconformities (Lewis & Belliss 1984, Lever 2007). The unresolved issues include the identification of unconformable surfaces and investigations to get to know the nature, precise age, and origin of these surfaces in order to correlate them inter-regionally throughout Zealandia's sedimentary basins (Lever 2007).

The Canterbury Basin, located at the eastern margin of the South Island of New Zealand as shown in fig. 1-1, consists of a several km - thick Cretaceous to Cenozoic sedimentary sequence, which includes non-marine - and marine strata (Browne & Field 1985, Field & Browne 1989, Forsyth 2001). Previous work on Canterbury Basin geology comprises measured bio - and lithostratigraphic sections onshore as well as offshore petroleum exploration wells, multichannel seismic, and IODP research surveys (Allan 1927, Gage 1957, Riddolls 1968, Browne & Field 1985, Field & Browne1989, Maxwell 1992, Fulthorpe et al. 2011, Tinto 2010).

According to Vella (1965) and Loutit & Kennett (1981), the basin comprises a tectonically controlled, transgressive - regressive megacycle. The basement is formed by Torlesse metasedimentary rocks of late Paleozoic to Mesozoic age, laterally grading into the Haast Schist to the southeast of the region (Field & Browne 1989, Ford et al. 1999). The erosion surface on top of the basement - Waipounamu Erosion Surface - is mostly unconformably overlain by Cretaceous-Cenozoic sediments, forming a gently - dipping surface (Landis et al. 2008). Broadly speaking, the strata above the Waipounamu Erosion Surface are oldest in the east and progressively young to the west (Nelson 1978, Landis et al. 2008). The Waitaki-Waimate District - part of the South Canterbury Basin - exposes Cenozoic rocks, in places overlain by Pleistocene to Holocene terrace gravels and loess (Gage 1957, Maxwell 1992, Heron 2014).

Following the break-up of Gondwana in the Mid - Cretaceous, Zealandia separated from Australia and Antarctica and drifted away towards its isolated position in the South Pacific Ocean (Carter & Norris 1976, Forsyth 2001, Fulthorpe et al. 2011). Shallow dips of most Late Cretaceous strata suggest tectonic stability during Late Cretaceous and most of the Cenozoic, unlike most of New Zealand (Browne & Field 1985, Forsyth 2001). Transgression occured during the Late Cretaceous and Early Cenozoic, and local subsidence leads to the formation of sedimentary basins (Field & Browne 1989). Paleogene marine sedimentary rocks comprise thin, bioclastic to glauconitic strata, and lacked coarse terrigenous material. The land was probably distant and / or low relief (Field & Browne 1989, Fulthorpe et al. 2011).

According to Forsyth (2001), transgression continued into the Eocene. The Eocene strata consist mostly of neritic calcareous mudstone (Maxwell 1992, Ayress 1995). Volcanism in the southern Canterbury Basin, associated with the formation of graben structures, occurred around Oamaru (Waiareka - Deborah Volcanics) during the Late Eocene to Early Oligocene (Kaiatan to Whaingaroan (ca. 39.1 - 27.3 Ma), according to Gage (1957), Field & Browne (1989), and Thompson et al. (2014). Sporadic igneous activity included shallow submarine Surtseyan - style volcanoes forming pillow-lavas, tuffs, breccias, and pyroclastic surge deposits (Field & Browne 1989, Mortimer et al. 2014, Thompson et al. 2014). This volcanic activity formed shallow shoals that supported the formation of limestones and partially isolated the southern Canterbury Basin to the east as a bathymetric barrier (Mortimer et al. 2014, Thompson et al. 2014).

The maximum transgression during the Oligocene almost drowned the whole continent of Zealandia and formed extensive glauconitic and bioclastic limestone deposits (Ward & Lewis 1975, Field & Browne 1989). Regression occurred during the Miocene and continues to the present day (Gage 1957, Averes 2018). Besides, North Otago and South Canterbury are affected by regional uplift and deposition of significant quantities of coarse terrigenous sediment from the rising ranges along the site of the present Southern Alps (Forsyth 2001). According to Field & Browne (1989) and Fulthorpe et al. (2011), this Early Miocene sandstone - siltstone succession forms a prograding continental shelf wedge containing numerous channel structures, as shown in offshore seismic sections. The later Neogene is dominated by terrigenous rocks and non-fossiliferous rocks (Riddolls 1968, Field & Browne 1989).

Field & Browne (1989) and Lever (2007) mention several unconformities in various sections across different basins on the South Island of New Zealand, but some unconformities either lack precise dating or detailed stratigraphic logging. Difficulties in precise dating are related to correlating unconformities of varying extent across the basins (Lever 2007). Furthermore, changes in the New Zealand Stages of the New Zealand Geological Timescale (fig. 1-2, 1-3) and correlating these to absolute dates and international units of the International Geological Timescale add another difficulty in dating sedimentary strata and associated unconformities in Zealandia's Cretaceous to Cenozoic basins (Cooper 2004, Lever 2007, Cohen et al. 2014).

Editorial Note: Figure 1-2 was removed due to copyright issues.

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Figure 1-2 The New Zealand Geological Timescale, Version 2015/1 (based on Cooper 2004, with incooperated revised ages from Cohen et al. 2014 and Raine et al. 2015). Source: GNS Science, Lower Hutt, New Zealand

Editorial Note: Figure 1-3 was removed due to copyright issues.

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Figure 1-3 New Zealand Geological Timescale, Version 2015/1, with highlighted age range of the exposed Eocene - Oligocene strata in the study area. The red ovals show the absolute dates given to the International units and the blue ovals show the absolute dates given to the New Zealand stages. The obvious differences add another difficulty in precise age determination of the Cenozoic strata. The blue circle "29.8 Ma” marks the boundary between the lower Whaingaroan (ca. 34.6 - 29.8 Ma) and the upper Whaingaroan (ca. 29.8 - 27.3 Ma). Graphic based on Raine et al. (2015). Source: GNS Science, Lower Hutt, New Zealand

1.2 Purpose of thesis

This thesis aims to contribute to resolving some of the outstanding issues by closely investigating the nature of contacts in the exposed Eocene - Oligocene sedimentary strata of the lower Waihao Valley and recognizing unconformable surfaces. Sedimentary petrological - and petrophysical investigations add additional information about lithological changes to either confirm or contradict previous local paleoenvironmental interpretations (e.g. Field & Browne 1989, Ayress 1993). Observations and interpretations of a well - exposed Eocene - Oligocene sedimentary succession in the lower Waihao Valley, part of the South Canterbury Basin, were carried out to determine the origin, age, and setting of the unconformities. Reconstructing local basin evolution and establishing the chronostratigraphy gives insight whether there is a suspected association with the “Marshall unconformity”, the regional Mid - Oligocene unconformity in New Zealand (Findlay 1980, Carter 1985, Fulthorpe 1996). In order to address the aims, fieldwork to identify and measure selected localities with known or suspected unconformities was carried out to establish bio- and lithostratigraphic sections. Attention was paid to dating the succession using age-relevant key species of benthic and planktic foraminifera, which were extracted from selected sedimentary rock samples (Hornibrook 1961, Jenkins 1975, Hayward 1986). The variability in petrographic - and petrophysical properties was measured using modal mineralogical composition and magnetic susceptibility to recognize the provenance and local lithological variations in formations (Weltje & van Eynatten 2004). This data will contribute to local paleoenvironmental interpretations. Assessing the significance of the unconformities after data processing, places these local data and interpretations in a regional context and therefore contributes insights into wider southern Canterbury Basin geology.

1.3 Unconformities

The definition of the different types of unconformities (fig.1.4 and tab. 1-1) is based on the well-cited and authoritative literature of Dunbar & Rodgers (1957) and additional definitions by Neuendorf et al. (2011). In this thesis I am following these definitions to analyse the exposed unconformities in the Eocene - Oligocene strata of the lower Waihao Valley.

An unconformity is defined as a “temporal break in a stratigraphic sequence resulting from a change in regimen that caused deposition to cease for a considerable span of time” (Dunbar & Rodgers 1957, p. 118). The unconformity itself is a “surface separating the unconformable units” (Dunbar & Rodgers 1957, p. 118). Unconformities occur throughout the geological record and can have global, regional, or local extent (Neuendorf et al. 2011). In comparison to a conformable contact, an unconformable contact shows significant changes in time and / or lithology (Dunbar & Rodgers 1957, Neuendorf et al. 2011). The colloquial “time gap” is recognized as a “hiatus” (= gap in the geological record) by missing strata (Neuendorf et al. 2011). According to Dunbar & Rodgers (1957), this hiatus can be either caused by erosion or nondeposition and the unconformity might change character from proximal to distal parts in a sedimentary basin. To determine the hiatus recognized by missing strata, precise dating of the units below and above an unconformable contact is essential. Dating of calcareous sedimentary rocks can be done using microfossils like foraminifera and ostracods (e.g. Hornibrook 1961, Hornibrook et al. 1989, Ayress 1993, Ayress 1995). There are various reasons which can cause unconformities, ranging from global sea-level changes, local tectonics, oceanic currents to volcanic activity (Dunbar & Rodgers 1957, Nichols 2009, Neuendorf et al. 2011).

The different types of unconformities are shown in fig. 1-4 and are described in detail in tab. 1­ 1.

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Figure 1-4 The different types of unconformities, according to Dunbar & Rodgers (1957)

Table 1-1 Different types of unconformities, according to Dunbar & Rodgers (1957) and Neuendorf et al. (2011)

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1.4 Eocene - Oligocene unconformities in New Zealand

Several authors compared the local and regional extent of Cenozoic unconformities throughout the South Island of New Zealand (Jenkins 1975, Jenkins 1987, Lewis 1992, Lever 2007). Previous work by Lewis & Belliss (1984) addressed two Oligocene unconformities in the Waitaki Valley (South Canterbury Basin), ca. 20 km SW of the lower Waihao Valley: (1) an older unconformity of upper Whaingaroan or early Duntroonian age resting on lower Whaingaroan Earthquakes Marl, which might be associated with the regional Mid - Oligocene Marshall unconformity; and (2) a younger unconformity of Waitakian age shows paleokarst features, indicative for regional emergence due to eustatic sea-level fall. Jenkins (1987) correlated the Oligocene unconformities at The Earthquakes in the Waitaki Valley (South Canterbury Basin), first described by Lewis & Belliss (1984), by comparing their planktonic foraminiferal ranges with the unconformities found in the drill core of the Deep Sea Drilling Project (Site 593) in the Tasman Sea (Latitude 40° 30. 47'5 Longitude 167° 40. 47'E).

As seen in fig. 1-5, Lever (2007) correlated several unconformities of varying extent (some local, some regional) throughout several Cretaceous to Cenozoic sedimentary basins on the South Island of New Zealand (e.g. Canterbury Basin, West Coast Basins, Southland Basins). As most of the successions are condensed sections, it is sometimes unclear if there are one or several unconformable surfaces in the strata (Browne & Field 1986, Fulthorpe et al. 1996, Lever 2007).

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Figure 1-5 The correlation of unconformities across different Cretaceous - Cenozoic sedimentary basins on the South Island of New Zealand. The graphic shows the correlation of several Eocene - Miocene unconformities across different sedimentary basins, incl. the Canterbury Basin (Canterbury) and the Great South Basin (Otago). Graphic annotated by author. Source: Lever (2007)

As seen in fig. 1-5, Early - and mid - Oligocene unconformities are known to be present in western and eastern offshore areas of the South Island, in Canterbury, Southland, and some West Coast sections (Watkins & Kennett 1972, Jenkins 1987, Lewis 1989, Lever 2007).

1.5 Global Mid - Oligocene unconformity

The globally widespread Mid - Oligocene unconformity (Rupelian-Chattian unconformity), separates the Early Oligocene (Rupelian stage) - ca. 33.9 - 28.1 Ma - from the Late Oligocene (Chattian stage) - ca. 28.1 - 23.03 Ma - in the North Sea Basin and the Atlantic Coastal Plains (Harris & Zullo 1992, De Man 2004, Simaeys 2004, De Man 2010) (fig.1.3).

The Rupelian-Chattian boundary is associated with the “Oligocene Glacial Maximum” (ca. 27.3 to 26.8 Ma) (Liu et al. 2004). Global cooling and associated glacio-eustatic sea-level fall due to Antarctic ice-sheet growth occurred during this phase, recognized by lowering of sea surface temperatures (SST) based on deep-sea benthic foraminiferal 518 O events (De Man & Simaeys 2004, Harris & Zullo 1991). In the basal Chattian, global warming induced a significant sea­level rise (“Late Oligocene Warming Event”) (De Man & Simaeys 2004).

In the southern North Sea Basin, glauconitic Chattian sands unconformably overlie upper Rupelian silty clays (De Man 2004, Simaeys 2004). The resulting hiatus marks a significant change in paleotemperature and paleobathymetry (De Man et al. 2010). The age determination in the North Sea Basin and the Atlantic Coastal Plains has been done using key species of foraminifera (De Man 2004, Harris & Zullo 1991).

1.6 Marshall unconformity

A regional Mid - Oligocene unconformity in New Zealand - Marshall unconformity - is still subject to controversy regarding its age, origin and type of unconformity (e.g. Carter et al. 1982, Findlay 1980, Fulthorpe et al. 1996, Tinto 2010).

The type location of the Marshall unconformity is Squire's Farm in South Canterbury, ca. 22 km N of the lower Waihao Valley, where lower Whaingaroan sedimentary strata is paraconformably overlain by Duntroonian sedimentary strata (Carter & Landis 1972, Fulthorpe et al. 1996, Lever 2007). The Marshall unconformity occurs as a heavily burrowed paraconformity at McCullochs Bridge in the lower Waihao Valley, according to Fulthorpe et al. (1996).

Dating unconformities in the Eocene - Oligocene strata of the Canterbury Basin is reasonably difficult due to locally poor preservation of foraminifera, mostly associated with abundant bioturbation (Fulthorpe et al. 1996). Furthermore, difficulties in correlation of formations on a local to regional scale occur due to the lack of timescale precision (fig. 1-3). The definition of New Zealand Stages in the New Zealand Geological Timescale (fig. 1-2, 1-3) are generally based on biostratigraphy and exposed to evolving changes in the age range of microfossil species due to new investigations (e.g. Ayress 2016). The absolute dates in the New Zealand Geological Timescale are based on Sr isotopes (e.g. Graham et al. 2000, Campbell et al. 2004). According to Fulthorpe et al. (1996), the Marshall unconformity encompasses a hiatus of 2 - 4 Ma (ca. 32 - 29 Ma) based on Sr isotope dating of Squires Farm section, but the total time gap may range up to 15 Ma due to gentle warping or sediment starvation (Mc Millan & Wilson 1997, Fulthorpe et al. 1996, Campbell et al. 2004). McMillan & Wilson (1997) reports the Marshall unconformity in the Burnside quarry, (U/C10), in Dunedin, where Eocene sedimentary strata is unconformably overlain by Oligocene sedimentary strata.

Carter & Landis (1972) argued that the unconformity is “a single unconformity, traced throughout the South Island of New Zealand and parts of Australia” (Carter & Landis 1972, p. 12), whereas Findlay (1980) stated that the Marshall unconformity was “one of many extensive paraconformities in the region” (Findlay 1980, p. 125). Carter (1985) interpreted the Marshall unconformity as a “time of greatly reduced sedimentation or nondeposition “(Carter 1985, p. 363).. .“marked by a heavily burrowed, partly phosphatized omission surface in the underlying Concord Greensand Formation” (Carter 1985, p. 360). According to Fulthorpe et al. (1996), the “paraconformable surface occurs as a simple bedding plane with no evidence of erosion” (Fulthorpe et al. 1996, p. 74).

The Marshall unconformity can be traced offshore into the Great South Basin as it coincides with a prominent seismic reflector, recognized in at least three offshore exploration wells (Field & Browne 1989, Fulthorpe et al. 1996, McMillan & Wilson 1997, Fulthorpe et al. 2011).

The origin of the Marshall unconformity is still in discussion (e.g. Fulthorpe et al. 2011, Tinto 2010). The opening of the Tasmanian Gateway in the Southern Ocean in the Early Oligocene coincides roughly with the onset of the Antarctic Circumpolar Current (ACC), which derived cooler waters due to west-wind drift, resulting in strong bottom water currents (Watkins & Kennett 1972, Exon et al. 2002, Scher & Martin 2006, Burgess et al. 2008). Fulthorpe et al. (1996), Fulthorpe et al. (2011) and Tinto (2010) argued that this could be responsible for the widespread nondeposition during the proposed hiatus of 3-4 Ma, represented by missing strata of the Marshall unconformity.

Chapter 2 Methodology

2.1 Field work

Fieldwork (11 days in total) was carried out from April 2018 to May 2019 with several field assistants from the Geology Department, University of Otago, in the study area of the lower Waihao Valley. The reconnaissance field work involved measuring sections using tape and Jacob's staff for bio - and lithostratigraphy at selected localities, including sampling of rocks for foraminiferal biostratigraphy and sedimentary petrology. Flat, smooth surfaces were sampled using a geological hammer. The sampling density varied per location, but the aim was to get a sample every few meters, where possible. Variations in facies and lithology were observed and unconformities identified and logged. Petrophysical properties of the strata were measured using a magnetic susceptibility meter Bartington MS-2 in the field. Global Positioning System (GPS) Coordinates using the World Geodetic System (WGS84) as its reference coordinate system were measured and regarded in the field using the GPS device Noyafa NF - 178. The GPS coordinates were measured at the base of the stratigraphic sections or at the exact sample location. Sedimentary and metamorphic rock samples were given OU numbers issued by Geology Department, University of Otago, and microfossil samples were given FRED fossil record numbers, issued by GNS Science, Lower Hutt, New Zealand. The FRED (Fossil Record Electronic Database) is a computer database for the New Zealand Fossil Record File (NZ - FRF). It comprises information about fossil localities in New Zealand, Southeast Pacific Islands and the Ross Sea, Antarctica, and is jointly managed by Geoscience Society of New Zealand, Wellington, NZ, and GNS Science, Lower Hutt, NZ (https://fred.org.nz, 14.11.2019).

2.1 Micropaleontology

Foraminifera were extracted from the rock samples to date the sedimentary rocks. This involved the use of different chemicals (mostly alkaline salts) depending on the rock and fossil type (Jenkins 1971, Haynes 1981). Key species of benthic and planktic foraminifera are a useful tool to determine the age of sedimentary strata, as they are common in calcareous marine rocks. During fieldwork in 2018 and 2019, representative samples were collected to extract foraminifera for age determination. The oven-dried samples were broken into small chunks. For processing, about 80 g of the sample was used.

Foraminifera were extracted from mudstones and soft glauconitic limestones using Sodium hexametaphosphate (SHMP) (Na 6 P 6 Ö i8 ) (Haynes 1981, Hornibrook et al. 1989). The sample was heated in a solution of 10g/l SHMP for 30 to 90 min until the rock starts disaggregating. After this process, the material was washed and sieved using a 150 gm wet sieve, before dried under a heat lamp. The sieve was washed after each sieving to avoid contamination of the samples and therefore soaked in methylene blue (C16H18CIN3S) to stain remaining foraminifera and distinguish them as contamination.

For some mudstones and soft glauconitic limestones, Hydrogen peroxide (H 2O 2) was used (Jenkins 1971, Hayward 1990). 10 ml of H2O2 were added to the simmering SHMP - solution within the last 10 min of the process to increase the rate of disaggregation. It was done under a fume hood as the vapours were irritant. H2O2 was also used as a pre-treatment for well- cemented glauconitic limestones to disaggregate them partly.

Sodium thiosulfate (Na 2S 2O 3) was used to disaggregate calcareous sandstone (Haynes 1981). 300g of Na2S2Ü3 (crystals) were placed in a cooking pot and heated until melted. The limestone chunks were then placed in the melted thiosulfate. After mixing the sample with the chemical, the mixture was cooled rapidly by placing the pot in ice water. After the reagent has recrystallized, the whole process was repeated several times (ca. 8-9 runs) until the limestone was fully disaggregated.

A 60 % acetic acid - solution (CH 3COOH) was used to extract foraminifera from well- cemented glauconitic limestone (St Clair 1935, Lirer 2000, Rodrigues 2011). This acetolysis method is risky as the CaCO3 - shelled foraminifera can easily be destroyed during the process (Lirer 2000). CH3COOH reacts with the micritic cement in well-cemented limestones which helps to disaggregate them (Rodrigues 2011). The chemical reaction between this weak acid and the CaCO3 occurs slowly and can easily be monitored under a fume hood:

Abbildung in dieser Leseprobe nicht enthalten

It was helpful for the identification process, to separate the benthic and planktic foraminifera of every sedimentary rock sample using the “floating-method” after the extraction process (Jenkins 1971, Jenkins 1975, Haynes 1981).

The chloro-trihalomethane (THM) chloroform (CHCl3) was used to separate pristine foraminifera from permineralized foraminifera (Haynes 1981, Hornibrook et al. 1989). Chloroform is a colourless organic component which has a higher density than H2O. It was 14 necessary to work under a fume hood due to the toxic vapours. 0.3 l of CHCh was stirred with processed material (ca. 10 g) in a small dish. Well-preserved hollow foraminifera float to the top of the dense chloroform. By decanting the mixture with a filter paper, the floating planktic foraminifera were trapped in it and therefore secured for identification process.

The benthic and planktic foraminifera were picked using a Zeiss Binocular Transmitted Light Microscope with 10 x, and 63 x magnification and a small paintbrush (Hornibrook 1961). To avoid contamination, the brush was washed after each sample in distilled water. Micropaleontological Plummer cells were used to store the foraminifera and consist of numbered sections on a cardboard tray where the samples can be fixed with a water-soluble glue - guar gum - (Hornibrook 1961, Hornibrook 1996). Water-soluble green ink (Phthalocyanine green G) was used to make critical identifiable surface features more prominent and therefore helps to identify the species (Haynes 1981).

2.2 Sedimentary petrology

To help reconstruct the basin evolution, sedimentary petrological - and petrophysical data were obtained from the rock samples (Field & Browne 1989, Weltje & van Eynatten 2004). The petrological - and petrophysical data set, including the values for the modal mineralogical composition (vol% + wt%), and the magnetic susceptibility of the sedimentary rock samples are listed in the Appendix A, tab. 5-1.

Standard 30 pm - thin sections (not polished, unstained, embedded in undyed epoxy resin) were produced from representative sedimentary and metamorphic rock samples. Epoxy impregnation was used as a standard method for sectioning friable and porous sedimentary rocks, especially mudstones and glauconitic limestones.

To estimate the modal mineralogical composition, point counting was used for all sedimentary rock samples. The approach was to identify 300 mineral grains per sample in representative thin sections via automated point count stage using a petrographic microscope Olympus BH- 2. Detrital sand grains and bioclasts between 63 pm and 500 pm were counted, to estimate the modal mineralogical composition (vol%). Silt - and mud-sized grains were counted as “matrix”. The errors of this method are misidentification of grains and failing to capture the heterogeneity of the sample.

To obtain the CaCO 3 content, rock samples were processed using acid dissolution with a 33% hydrochloric acid - solution (HCL). 100 g of oven-dried, fine-powdered sample was weighed before the acid dissolution process and reweighed after it to obtain the weight difference.

Powdered samples were used to increase the reaction surface for the acid. As HCI is corrosive and the chlorine vapours are harmful, the process was done under a fume hood. The samples were placed in the HCL for around 1 hour to dissolve the CaCO3.

The errors of this method are based on the chemical reaction as the weight difference does not only account for the amount of dissolved CaCOß.

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Some bioclasts are partly dolomitized. Dolomite is an anhydrous Ca-Mg carbonate mineral which is insoluble in HCL. Even though dolomite is not regarded as calcium carbonate, it leads to errors and differences in the total CaCO3 content, especially in well-cemented glauconitic limestones. The CaCOß within the calcareous matrix and/or cement and bioclasts of the sample is dissolved, leaving a residue of detrital quartz, detrital feldspars, detrital micas, and glauconite behind.

For the accuracy of the compatibility between point count data (vol%) and chemical data (wt%), there should be a density correction. However, the reconnaissance nature of this study, the imprecision in point counting, and the overlap of calcite density (2.71 g/cm 3) with the range of other minerals of variable density means that it was not regarded as necessary.

Magnetic susceptibility was used to track the amount of terrestrial influx due to the abundance of terrestrially - derived magnetic minerals such as ferrimagnetic magnetite (FeßO4) (Weltje & van Eynatten 2004). Magnetite is common in igneous and metamorphic rocks and at least in trace amounts also in the detrital heavy mineral fraction of sedimentary rocks (Weltje & van Eynatten 2004). During the fieldwork in December 2018, a magnetic susceptibility meter Bartington MS-2 was used for 10 secs on each measured sedimentary rock sample. The secondary oxidation, represented in the examined Eocene - Oligocene sedimentary succession by iron oxides and iron hydroxides, can interfere with the measurements (Dekkers 1978). Unfortunately, the whole succession is heavily weathered and contains abundant secondary oxidation. Heavily oxidized patches were avoided during measurements.

2.2 Scanning Electron Microscope (SEM)

A Scanning Electron Microscope (SEM) was used to produce high-resolution images of the identified foraminifera showing species-specific surface features. A Zeiss Sigma VP Field Emission Scanning Electron Microscope with an acceleration voltage (electron high tension) of 15 kV produces high-resolution surface images by scanning the surface of the sample with a focussed electron beam in a high vacuum chamber. The foraminifera samples are embedded in an aluminium disk and then coated with pure graphite for conductivity. Secondary electrons (SE), generated as an ionization product due to inelastic interactions between the primary electron beam and the surface of the specimen, are used to image the surface topography of foraminifera.

Chapter 3 Data & Results

3.1 Geology of the lower Waihao Valley

The study area is the lower Waihao Valley - part of the southern Canterbury Basin (fig. 3-1, 3­2). The lower Waihao Valley is located ca. 60 km N of Oamaru and 10 km SW of Waimate. The geology consists of late Paleozoic and Mesozoic Torlesse Terrane metasedimentary basement rocks, and a Cretaceous to Cenozoic sedimentary strata as shown in fig. 3-3 (Allan 1927, Srinivasan 1966, Riddolls 1968, Browne & Field 1985, Maxwell 1992).

Editorial Note: Figure 3-1 was removed due to copyright issues.

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Figure 3-1 Topographic map with the location of the lower Waihao Valley in the South Canterbury Basin. The map was made using Arc GIS Pro (ESRI)

Editorial Note: Figure 3-2 was removed due to copyright issues.

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Figure 3-2 Topographic map showing the five study locations in the lower Waihao Valley. The map was made using Arc GIS Pro (ESRI)

The geological map of the lower Waihao Valley (fig. 3-3) shows part of this strata along the banks of the Waihao River.

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Figure 3-3 Geological map of the lower Waihao Valley (fig. 3-1, 3-2). (1): Dyer Farm quarry, (2): Waihao River Walkway / McCullochs Bridge, (3): Squires Farm, (4): The Earthquakes. The map was made using Arc GIS Pro (ESRI). Source of geological map: Geological Map of New Zealand, 1:250.000 (QMAP), GNS Science, Lower Hutt, New Zealand. Geological data from Heron (2014)

The Torlesse Supergroup (fig. 3-3: Permian - Triassic metasedimentary rocks) typically comprises beds of indurated quartzo - feldspathic sandstone (greywacke), semi - schist, siliceous pelagites, and argillite around the edge of the South Canterbury Basin. The age of the Torlesse Supergroup ranges in South Canterbury from Permian to Triassic (Field & Browne 1989, Forsyth 2001). Ford et al. (1990) identified conodonts (e.g. Mesogondolella bisselli) of Early Permian age (ca. 288.5 - 251.5 Ma) from siliceous pelagites at nearby Meyers Pass, Hunters Hills, ca. 25 km N of the study area of this thesis.

The Eocene (Kaiatan - Runangan) sedimentary succession shows submarine basaltic eruptions and the accumulation of calcareous glauconitic sediments on wave-planed volcanic platforms (Gage 1957). During the Oligocene (lower and upper Whaingaroan), marine planation of volcanoes occurred (Maxwell 1992). In the Duntroonian, there was very slow subsidence associated with the abundant accumulation of glauconitic sediments, indicative for slow sedimentation (Maxwell 1992, Mortimer et al. 2014). The Waitakian represents an interval of increasing current activity, possibly associated with small-scale changes in oceanic circulation pattern in the Southern Ocean (Ward & Lewis 1975, Nelson 1978, Field & Browne 1989).

The Eocene - Oligocene lithostratigraphic nomenclature of the Canterbury Basin has been given different names based on location in the literature (e.g. Allan 1927, Gage 1957, Riddolls 1968, Ward & Lewis 1975, Carter 1985, Field & Browne 1989). The New Zealand Stratigraphic Lexicon (www.data.gns.cri.nz/stratlex) (10.09.2019) was used to compile the different lithostratigraphic names used in this thesis (see tab. 3-1).

Table 3-1 Eocene - Oligocene lithostratigraphic nomenclature for the geological formations of the southern Canterbury Basin

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Lithostratigraphic nomenclature based on McKay (1887), Park (1905) and Gage (1957) was used to grant consistency of used terminology for geological formations in this thesis (see tab. 3-1).

Taratu Formation (fig. 3-3: Cretaceous - Eocene sedimentary rocks) in the South Canterbury Basin consists of conglomerates, coal measures, kaolinitic clays, sandstones, and siltstones with local quartz pebble horizons. It is diachronous as it varies from upper Cretaceous (Haumurian) to Eocene (Waipawan) (ca. 83.6 - 52.0 Ma) (Forsyth 2001). The depositional environment was non-marine, paralic and fluvial (Field & Browne 1989, Middlemiss 1999).

Kauru Formation (fig. 3-3: Cretaceous - Eocene sedimentary rocks) in the South Canterbury Basin commonly occurs as a well-cemented calcareous sandstone, locally with fossiliferous conglomerate near the base (Brown & Field 1985). It overlies the Broken River Formation and underlies the Waihao Greensand (Riddolls 1968, Maxwell 1992). The presence of coarse clasts suggests a deposition on a coastal beach ridge or storm breaker zone on the shoreface (Brown & Field 1985, Forsyth 2001). It is of Paleocene (Teurian) to Eocene (Porangan) age (ca. 66.0 - 42.6 Ma), according to Fordyce & Thomas (1990) and Forsyth (2001).

Waihao Greensand (fig. 3-3: Eocene - Oligocene sedimentary rocks) consists of muddy glauconitic siltstones and sandstones with locally occurring phosphatised nodules and concretions (Gage 1957, Maxwell 1992). It overlies the Taratu Formation usually with the intervening Kauru Formation, according to Riddolls (1968) and Fordyce & Thomas (1990). The Waihao Greensand forms a succession of at least 60 m in thickness (Browne & Field 1985, Maxwell 1992). There are several unconformities within this formation (Srrinivasan 1966, Field & Browne 1989, Maxwell 1992). Most of the formation is Bortonian (ca. 42.6 - 39.1 Ma), but the top of the Waihao Greensand (= Otaio Limonitic Member) is of Kaiatan age (ca. 39.1 - 36.7 Ma), according to Srinivasan (1966), Fordyce et al. (1985), and Maxwell (1992). According to Browne & Field (1985) and Srinivasan (1966), it was deposited in a outer shelf setting. Maxwell (1992) and Ayress (1995) estimated the paleo water depth to be 150 - 200 m, based on fossil assemblages of molluscs and ostracods. A transgression could have occurred during the Bortonian and /or Kaiatan (Maxwell 1992).

Ashley Mudstone (fig. 3-3: Eocene - Oligocene sedimentary rocks) is a calcareous glauconitic silty mudstone with a thin, dark greyish tuff bed (Kapua Tuff), according to Riddolls (1968), Field & Browne (1989), Maxwell (1992). According to Coombs & Jillett (1995), some foraminifera are infilled with euhedral Ca - rich clinoptilolite which permineralized the voids of hollow planktic foraminifera. These secondary zeolites (clinoptilolite, phillipsite) are most likely derived from the Kapua Tuff (Coombs & Jillett 1995). The thickness of the Ashley Mudstone including the Kapua Tuff is approximately 60 m near McCullochs Bridge (Srinivasan 1966, Riddolls 1968). The depositional environment is outer shelf to bathyal and the formation is of Kaiatan to Runangan? age (ca. 39.1 - 34.6 Ma), according to Browne & Field (1985), Maxwell (1992), and Ayress (1995).

Earthquakes Marl (fig. 3-3: Eocene to Oligocene sedimentary rocks) is a thin moderately indurated, glauconitic marl which is locally sandier and highly glauconitic at the base at its type locality, The Earthquakes, in the Waitaki Valley (Gage 1957, Riddolls 1968). Furthermore, it occurs as greyish muddy sandstones, micritic limestones, and calcareous siltstones throughout the Canterbury Basin (Browne & Field 1985). This formation unconformably overlies the Ashley Mudstone (Ayress 1995). The depositional environment is an outer shelf setting or deeper, according to the abundant planktic foraminifera (Maxwell 1992). It is of lower Whaingaroan age (ca. 34.6 - 29.8 Ma), according to Gage (1957).

Kokoamu Greensand (fig. 3-3: Eocene - Oligocene sedimentary rocks) is a massive to dm - bedded, calcareous greensand, glauconitic siltstone, or glauconitic limestone with abundant macro - and microfossils (brachiopods, vertebrates, and foraminifera) in places (Gage 1957). The base is commonly a burrowed unconformity (Field & Browne 1989). It grades up into the overlying Otekaike Limestone (Gage 1957). This contact is unconformable in places (Lever 2007). The Kokoamu Greensand is of upper Whaingaroan to Duntroonian age (ca. 29.8 - 25.2 Ma) (Browne & Field 1986, Ayress 1993). It is interpreted as a mid - to inner shelf setting, with a shallowing trend towards inner shelf at the transition to the Otekaike Limestone (Ayress 1993).

Otekaike Limestone (fig. 3-3: Eocene - Oligocene sedimentary rocks) is a cemented, massive to dm - bedded bioclastic glauconitic limestone with concretionary horizons and common trace fossils (Browne & Field 1985, Field & Browne 1989). It is of Duntroonian to Waitakian age (ca. 27.3 - 21.7 Ma), according to Hornibrook et al. (1989) and Ayress (2006). The transition between Kokoamu Greensand and Otekaike Limestone is characterized by a decrease in siliciclastic sediment and an increase in biogenic carbonate, which causes the limestone to be more cemented (Riddolls 1966, Ward & Lewis 1975). Locally, this formation is current-bedded and contains large-scale cross - bedding, parallel bedding and channeling (Ward & Lewis 1975). Cross - bedding indicates that shallow water with vigorous currents existed (Riddolls 1968, Ward & Lewis 1975, Ayress 2006).

At the Waihao River, two types of paleocurrent directions are recognised. The interpreted paleocurrent directions are foresets to the E-NE and scour channels to the N-NE, according to Ward & Lewis (1975). Macrofossils like brachiopods, molluscs, echinoids and bryozoans are mostly present in damaged condition due to vigorous current action during deposition (Ward & Lewis 1975). The bioclastic limestone becomes muddy in top and grades into the Mount Harris Formation (Maxwell 1992). The deposition of the limestone was characterized by only minor amounts of land-derived sediment and an abundance of biogenic carbonate (Riddolls 1966, Riddolls 1968). It is inferred to be a mid - to inner shelf setting (Ward & Lewis 1975, Ayress 2006).

Mount Harris Formation (fig. 3-3: Miocene - Pliocene sedimentary rocks) is a succession of glauconitic, slightly to moderately calcareous siltstones and mudstones with interbedded, partly concretionary, sandstone (Riddolls 1968, Maxwell 1992). The mineralogy consists of angular quartz, calcite, and glauconite (Riddolls 1966). Locally this formation contains well-preserved molluscs and rich foraminiferal faunas (Maxwell 1992). The maximum thickness of this formation is 600 m and it is mostly conformably overlying the Otekaike Limestone (Field & Browne1989). This formation is unconformably overlain by the Elephant Hill Gravels, according to Riddolls (1966). The depositional environment is mid -to outer shelf (Field & Browne 1989). It is of Waitakian to Altonian age (ca. 25.2 - 15.9 Ma), according to Riddolls (1968) and Ayress (2006).

For clarifying the sedimentary petrology, ambiguous terms like “greensand”, “marl”, and “greywacke” are replaced by clearly descriptive petrological terms such as “glauconitic limestone” or “calcareous glauconitic mudstone”.

3.2 Dons Hole

Dons Hole is a natural outcrop on the erosion bank of a pool in the Waihao River (fig. 3-4), about 7 km upstream from SH1 and 6 km south of Waimate (Fordyce et al. 1985, Maxwell 1992).

Editorial Note: Figure 3-4 was removed due to copyright issues.

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Figure 3-4 Location of Dons Hole. Source: Google Earth (22.11.2019)

Dons Hole features a 19.5 m thick Late to Middle Eocene sedimentary succession, consisting of glauconitic sandstones and siltstones (Waihao Greensand, Ashley Mudstone), as shown in fig. 3-5 (Fordyce et al. 1985).

The exposed sedimentary succession at Dons Hole is only slightly calcareous. The ages are identified using previous data from Srinivasan (1966), Fordyce et al. (1985) and Maxwell (1992). None of the sedimentary units shows structural deformation.

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Figure 3-5 Stratigraphic column of the sedimentary strata at Dons Hole

The top of the Waihao Greensand (Otaio Limonitic Member) consists of 14.5 m glauconitic sandstone and siltstone. The rock is brownish-green, shows dm-bedding, and strong bioturbation. Fe-oxide - stained phosphate pellets and granules are abundant and distributed across the width of the whole outcrop (fig. 3-6, 3-7).

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Figure 3-6 The top of the Waihao Greensand (Otaio Limonitic Member) at Dons Hole. Figure for scale. The bedding dips downstream in the direction of the photographer

The glauconitic sandstone (sample: OU 86409) is fine-grained, poorly-sorted and clast- supported (fig. 3-7). The mineralogy is dominated by subrounded to rounded glauconite (67 vol%). 85 % of the glauconite shows pelletal / rounded textures, which is interpreted as allochthonous glauconite, originating at a distance from its formation (Seed 1965, Banerjee et al. 2016). These grains are coated with amorphous iron oxides and iron hydroxide, such as goethite and limonite (fig.3-7). Minor vermicular glauconite is grown in-situ, as indicated by a layered structure (fig. 3-7) and interpreted as autochthonous glauconite (15 %) (Seed 1965, Banerjee et al. 2016). Rare feldspathic grains show a high grade of sericite alteration. As seen in fig. 3-7, occasionally oversized subrounded to rounded, polycrystalline quartz granules (24 vol%) occur. The matrix is muddy and partly consists of sericite. The CaCO3 content is low with only 9 wt% (fig. 3-5, tab. 5-1). Due to the low CaCOß content, no calcareous micro - or macrofossils are present at this location, but calcareous fossils are reported from this formation at nearby locations, e.g. McCullochs Bridge (Srinivasan 1966, Fordyce et al. 1985, Maxwell 1992). The magnetic susceptibility is 0.02 (fig. 3-5, tab. 5-1), indicative for a small amount of magnetic minerals derived from the provenance.

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Figure 3-7 Thin section image of the top of the Waihao Greensand (Otaio Limonitic Member) at Dons Hole, OU 86409, XPL. (1) = polycrystalline quartz, (2) = Fe oxide - coated allochthonous glauconite, (3) = vermicular, autochthonous glauconite

Fossilized wood Araucariaceae sp. was found in the top of the Waihao Greensand (Otaio Limonitic Member), as shown in fig. 3-5, 3-8.

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Figure 3-8 Fossil log Araucariaceae sp. (ca. 1.70 m long specimen), partly silicified and burrowed by Teredo sp., in the top of the Waihao Greensand (Otaio Limonitic Member). Identification based on personal communication with Mathew Vanner, MSc Geology, Geology Department, University of Otago, Dunedin, NZ.

In addition, Fordyce et al. (1985) reports a large, incomplete nut and a partial skeleton of a bony fish (teleost) from the Waihao Greensand at Dons Hole. Srinivasan (1966), Fordyce et al. (1985) and Maxwell (1992) interpret an Kaiatan age (ca. 39.1 - 36.7 Ma) for the top of the Waihao Greensand (Otaio Limonitic Member) and the base of the Ashley Mudstone, according to calcareous fossils found in these formations at nearby localities, e.g. McCullochs Bridge.

At 14.45 m above the stratigraphic base of the section at Dons Hole (fig. 3-5, 3-9), a burrowed horizon distributed across the width of the whole outcrop marks a lithological change from a glauconitic siltstone to a glauconitic sandstone. According to the definitions of different types of unconformities (fig. 1-4 and tab. 1-1), this prominent burrowed horizon was identified as a disconformity. As seen in fig. 3-9, the “contact between the two stratified rock units is an uneven surface of appreciable relief’ (Dunbar & Rodgers 1957, p. 124). Abundant bioturbation consisting of vertical and horizontal burrows up to 12 cm, occurs (fig. 3-9). The horizon shows phosphatization, consisting of abundant cm - sized, Fe - oxide coated phosphatic nodules distributed across the width of the outcrop (fig. 3-9).

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Figure 3-9 The disconformity within the top of the Waihao Greensand (Otaio Limonitic Member), showing an abrupt lithological change and abundant phosphatization and burrowing

The contact between the top of the Waihao Greensand (Otaio Limonitic Member) and the base of the Ashley Mudstone at Dons Hole is conformable (fig.3-10).

The Ashley Mudstone at Dons Hole (sample: OU 86410) consists of glauconitic sandstone (fig. 3-5). The rock is light greenish to grey, lacks bedding, and has a thickness of 5 m (fig. 3­5, 3-10). It shows dm - bedding, bioturbation and phosphate granules distributed across the width of the outcrop.

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Figure 3-10 Ashley Mudstone at Dons Hole

The glauconitic sandstone is fine-grained, poorly - sorted and clast-supported (fig. 3-11). The mineralogy consists of abundant coarse subrounded glauconite (65 vol%). 88 % of the glauconite shows pelletal / rounded textures, which is interpreted as allochthonous glauconite, originating at a distance from its formation (Seed 1965, Banerjee et al. 2016). Minor vermicular glauconite (12%) is grown in-situ, as indicated by a layered structure and interpreted as autochthonous glauconite (Seed 1965, Banerjee et al. 2016). Furthermore, a moderate amount of angular to subangular polycrystalline quartz and feldspar grains (22 vol%) is present. Minor detrital components are epidote and muscovite (less than 1 vol%), set in a muddy matrix. The magnetic susceptibility is 0.01. The glauconitic sandstone is only slightly calcareous (13 wt%) (fig. 3-5, tab. 5-1).

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Figure 3-11 Thin section image of the Ashley Mudstone at Dons Hole, OU 86410, XPL. The thin section shows glauconite grains (greenish) and quartz + feldspar grains (white/grey).

No calcareous macro - and microfossils are preserved in the Ashley Mudstone at Dons Hole. Fordyce et al. (1985) report fossil wood, a small shark teeth, and a deformed nautiloid (Aturia sp. ?) from the Ashley Mudstone at Dons Hole. Calcareous fossils found at nearby locations, e.g. McCullochs Bridge, suggest a Kaiatan to Runangan ? age (ca. 39.1 Ma - 34.6 Ma) for the Ashley Mudstone in the lower Waihao Valley (Srinivasan 1966, Fordyce et al. 1985, Maxwell 1992, Ayress 1995). The base of the Ashley Mudstone, as seen in Dons Hole, is of Kaiatan age (ca. 39.1 - 36.7 Ma) (Fordyce et al. 1985).

In summary, the succession exposed at Dons Hole represents sedimentary rocks of Kaiatan age (ca. 39.1 - 36.7 Ma) and a succession of glauconitic sandstones and siltstones. A burrowed disconformity occurs within the top of the Waihao Greensand (Otaio Limonitic Member). Lack of foraminifera in the whole exposed sedimentary strata at Dons Hole makes dating of collected sedimentary rock samples using calcareous foraminifera impossible, therefore ages are inferred from strata using previous work at nearby locations (e.g. McCullochs Bridge) by Srinivasan (1966), Fordyce et al. (1985), Maxwell (1992) and Ayress (1995).

3.3 McCullochs Bridge

McCullochs Bridge (fig.3-12) is a well-known fossil locality on the erosional bank of the Waihao Valley, around 200 m downstream from the bridge (Srinivasan 1966, Maxwell 1992, Ayress 1995, Pearson 2006). Most of the outcrops are not accessible nowadays due to dense vegetation, so published data (Srinivasan 1966, Field & Browne 1989, Ayress 1995) has been used to complete the stratigraphic column of this location in addition to observations made for this thesis.

Editorial Note: Figure 3-12 was removed due to copyright issues.

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Figure 3-12 Location of the stratigraphic section at McCullochs Bridge on the Waihao River. Source: Google Maps (22.11.2019)

McCullochs Bridge features a Late Eocene sedimentary succession of 10.7 m of Ashley Mudstone unconformably overlain by Earthquakes Marl, according to Ayress (1995). None of the sedimentary units shows structural deformation.

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Figure 3-13 Stratigraphic column of the sedimentary succession at McCullochs Bridge. This is a composite section with data from Ayress (1995), obtained at the exact same location at McCullochs Bridge

The Ashley Mudstone at McCullochs Bridge is a greenish-grey calcareous glauconitic mudstone, shows indistinct dm-bedding and bioturbation (fig. 3-13, 3-14). The total thickness of the Ashley Mudstone is 9.25 m (fig. 3-13). Abundant macrofossils (mostly molluscs) occur. Minor secondary alteration (limonite) is present.

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Figure 3-14 Ashley Mudstone at McCullochs Bridge during the river lowstand in summer (January 2019). Figure for scale

As shown in fig. 3-15, a calcareous glauconitic mudstone from the Ashley Mudstone is fine­grained, well-sorted and matrix-supported (up to 45%). The mineralogy consists of dark basaltic scoria fragments in the lower 2.25 m measured above base of the stratigraphic section (fig. 3­13). Fine sand-sized glauconite (up to 33 vol%) is parautochthonous. 88 % of the glauconite shows pelletal / rounded textures, which is interpreted as allochthonous glauconite, originating at a distance from its formation (Seed 1965, Banerjee et al. 2016). Minor vermicular glauconite (12 %) is grown in-situ, as indicated by a layered structure and interpreted as autochthonous glauconite (Seed 1965, Banerjee et al. 2016). Furthermore, very fine angular polycrystalline quartz and feldspar grains (29-33 vol%), and micas (less than 1 vol%) are present, set in a muddy to silty calcareous matrix (35 - 38 wt%). Abundant foraminifera, partly phosphatized, occur (fig.3-15). The magnetic susceptibility is 0.01 - 0.02, indicative of some terrigenous influx (fig. 3-13, tab. 5-1).

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Figure 3-15 Thin section image of the Ashley Mudstone at McCullochs Bridge, OU 86411 (J40/f0250), XPL. (1) = dark basaltic scoria fragment, (2) = zeolites - infilled planktic foraminifera void

According to Coombs & Jillett (1995), some planktic foraminifera tests contain zeolite minerals such as euhedral high Ca - clinoptilolite, and phillipsite. This is confirmed as shown in fig. 3­15. The occurence of these zeolite minerals replacing voids of planktic foraminifera, indicates that “the unit has been buried to a depth not greater than ca. 1000 m at temperatures of not more than a few tens of degrees” (Coombs & Jillett 1995, p.263).

The “Kapua Tuff” (Field & Browne 1989, Maxwell 1992, Ayress 1995) was not distinguishable in this outcrop during the fieldwork in 2018 and 2019, but the angular basaltic scoria particles within the Ashley Mudstone (fig. 3-13) are indicative for a nearby source.

As shown in fig. 3-12 and tab. 5-2, well-preserved and abundant foraminifera occur throughout the stratigraphic section at McCullochs Bridge. Globigerapsis index, Globorotalia aculeata, Sphaeroidina variablilis, and Cancris compressa occur based on own sample identifications and reported by Ayress (1995). These indicate a Kaiatan to Runangan (?) age (ca. 39.1 Ma - 34.6 Ma).

The uppermost 2 m of the Ashley Mudstone at McCullochs Bridge are decalcified as reported by Ayress (1995); therefore the Runangan age of the formation is uncertain (Ayress 1995). A burrowed unconformity reported as separating the Ashley Mudstone from the overlying Earthquakes Marl (limestone) by Ayress (1995) was not accessible during the fieldwork in 2018 and 2019, and therefore no investigations on this unconformity were made (fig. 3-13). Fulthorpe et al. (1996) reports the Marshall unconformity, separating the underlying Earthquakes Marl (limestone) from the overlying Kokoamu Greensand, as a burrowed paraconformity at McCullochs Bridge. This unconformity was not recognized during the field work in 2018 and 2019 either at McCullochs Bridge or at the nearby Waihao River Walkway (“Cabbagetree Gully”) (fig. 3-12, 3-27).

In summary, the sedimentary succession at McCullochs Bridge represents Ashley Mudstone of Kaiatan to Runangan (?) age (ca. 39.1 Ma - 34.6 Ma), unconformably overlain by lower Whaingaroan (?) Earthquakes Marl (ca. 34.6 - 29.8 Ma), according to Ayress (1995). Unfortunately, the burrowed unconformity between the Ashley Mudstone and the Earthquakes Marl reported by Ayress (1995) is not exposed nowadays due to dense vegetation, so a recognition of the type of unconformity, precise dating, and detailed stratigraphic logging was not possible. The Marshall unconformity, reported as a burrowed paraconformity at McCullochs Bridge by Fulthorpe et al. (1996) was not exposed either and therefore investigations on it could not be made.

3.4 Dyer Farm quarry

The disused Dyer Farm quarry is a cliff face produced by quarrying of limestone in the 19 th century, according to a personal statement of the landowner Henry Arthur Dyer (fig. 3-16).

Editorial Note: Figure 3-16 was removed due to copyright issues.

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Figure 3-16 The location of the measured section at Dyer Farm quarry. Source: Google Earth (22.11.2019)

The measured section at Dyer Farm quarry features a well-exposed sedimentary succession of 16.6 m, with Earthquakes Marl at the bottom, separated from overlying Kokoamu Greensand by a burrowed disconformity (fig. 3-17). The Kokoamu Greensand is overlain by well- cemented Otekaike Limestone, separated by an echinoderm-rich diastem, which occurs at the base of the Otekaike Limestone (fig. 3-17). None of the sedimentary units shows structural deformation.

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Figure 3-17 Stratigraphic column - measured section - of the sedimentary succession at Dyer Farm quarry

The Earthquakes Marl consists of fine calcareous sandstone which is slightly glauconitic in places. The rock is greenish-yellow, lacks bedding, and has a thickness of 6.8 m (fig. 3-17, 3­18). It shows few sedimentary structures, except minor bioturbation at the top. Fragments of macrofossils (molluscs, brachiopods, annelids) and small phosphate granules are present and distributed throughout the unit.

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Figure 3-18 The Earthquakes Marl at the Dyer Farm quarry with sample locations

A sandstone sample from the Earthquakes Marl at Dyer Farm quarry is fine-grained, well-sorted and matrix- supported. As shown in fig. 3-17, the detrital mineralogy is dominated by abundant angular to subrounded polycrystalline quartz and feldspar grains (53-58 vol%). Furthermore, it consists of subrounded to rounded glauconite (7-9 vol%) and muscovite (less than 1 vol%), set in a silty to muddy calcareous matrix (35 - 38 wt%). The magnetic susceptibility varies between 0.01 and 0.02 (fig.3-17, tab. 5-1), indicative for abundant terrigenous influx.

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Figure 3-19 Thin section image of the Earthquakes Marl at Dyer Farm quarry, OU 86402 (J40/f0242), PPL. It shows abundant greyish-white siliciclastic grains (quartz + feldspar) and yellowish-brown altered glauconite grains

Foraminifera are sparse and poorly preserved within this unit. As shown in fig. 3-17 and tab. 5­2, Notorotalia stachei, Globigerina euapertura, and Globigerina angiporoides occur and are consistent with a lower Whaingaroan age (ca. 34.6 - 29.8 Ma). Furthermore, Anomalinoides orbiculus, Cibicides karreriformis, Globigerina labiacrassata, Bulimina forticosta, Globocassidulina pseudocrassa, and Chiloguembelina ototara are present.

A strongly burrowed horizon of ca. 30 cm between 6.8 m and 7.1 m in the measured section represents an unconformity at the base of the Kokoamu Greensand (fig. 3-17, 3-20, 3-21). The horizon shows abundant vertical and horizontal burrows (Thalassinoides sp.), which are filled with glauconitic sediment. Sampling occurred between the infilled burrows to avoid sampling reworked sediment. Given its appearance as a erosional contact, represented by abundant bioturbation between the upper and lower unit, as shown in fig. 3-21, and the abrupt change in fossil record and lithology, it was identified as a disconformity (fig. 1-4 and tab. 1-1).

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Figure 3-20 The disconformity at the base of the Kokoamu Greensand at Dyer Farm quarry

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Figure 3-21 Detailed view of the examined disconformity at the base of the Kokoamu Greensand at Dyer Farm quarry.

This disconformity can be traced across the width of the whole outcrop at Dyer Farm quarry. The hiatus represented by missing strata lies between the lower Whaingaroan (ca. 34.6 - 29.8 Ma) and the Duntroonian (ca. 27.3 - 25.2 Ma) and is therefore at least 2.5 Ma.

The Kokoamu Greensand is a greenish to brown, massive, sandy glauconitic limestone, which lacks bedding, with a thickness of 7.2 m (fig. 3-17). It shows abundant glauconite-infilled burrows, phosphate granules, and macrofossils (molluscs, brachiopods, annelids, cetacean and/or penguin bones). Towards the top, calcareous dm-sized nodules and small scours are present and found across the width of the whole outcrop. Secondary mineralization (limonite) is present in the shape of brownish tubes and diffuse patches.

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Figure 3-22 Thin section image of the Kokoamu Greensand at Dyer Farm quarry, OU 86405 (J40/f0245), XPL. (1) = allochthonous glauconite, (2) = polycrystalline quartz, (3) = bioclasts (benthic foraminifera)

The glauconitic limestone is fine to medium-grained, moderately to poorly - sorted and clast- supported. As seen in fig. 3-22, the mineralogy consists of abundant subrounded to rounded glauconite (28 - 32 vol%). 79 % of the glauconite shows pelletal / rounded textures, which is interpreted as allochthonous glauconite, originating at a distance from its formation (Seed 1965, Banerjee et al. 2016). Minor vermicular glauconite (21 %) is grown in-situ, as indicated by a layered structure and interpreted as autochthonous glauconite (Seed 1965, Banerjee et al. 2016). A moderate amount of angular to subrounded polycrystalline quartz and feldspar grains of 14 - 21 vol% is present and set in a silty to muddy calcareous matrix (fig. 3-22). The CaCOß content varies between 51 and 54 wt% and the magnetic susceptibility varies between 0.00 to 0.02, showing some amount in terrigenous influx (fig. 3-17, tab. 5-1) (Dekkers 1978).

Foraminifera are abundant and well-preserved within the Kokoamu Greensand at Dyer Farm quarry (fig. 3-17, tab. 5-2). As shown in fig. 3-17, Notorotalia spinosa (fig. 3-23) and Globigerina euapertura are consistent with a Duntroonian age (ca. 27.3 Ma - 25.2 Ma). Furthermore, Globigerina labiacrassata, Melonis dorreeni, Anomalinoides orbiculus, Anomalinoides fasciatus, Cassidulina cuneata, Cibicides thiara, Cibicides perforatus, Chiloguembelina cubensis, and Cyclammina incisa occur.

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Figure 3-23 Notorotalia spinosa, SEM - Image, OU 86405 (J40/f0245). Image taken by Dr. Marianne Negrini, Geology Department, University of Otago.

The base of the Otekaike Limestone at Dyer Farm quarry is marked by a distinct accumulation horizon of sea urchin spines and -plates of possibly Histocidaris sp. and crinoids. Abundant dm-sized calcareous nodules and concretions occur above and below this ca. 35 cm thin fossiliferous horizon (fig. 3-24, 3-25).

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Figure 3-24 The base of the Otekaike Limestone with the echinoderm – rich diastem at Dyer Farm quarry. Figure for scale

The fragments of echinoids and crinoids are cm-sized, show jagged edges, and are randomly orientated throughout this horizon at Dyer Farm quarry (fig. 3-24, 3-25). No colonization and / or overgrowth by sessile organisms (e.g. oysters, worms) is visible on the fossil fragments, which is indicative for a short break in sedimentation, represented by a “rapidly deposited individual bed” (Dunbar & Rodgers 1957, p.131). These observations coincide with the jagged edges of the echinoid - and crinoid fragments, indicating a high - energy environment. According to Dunbar & Rodgers (1957), Myrow & Southard (1996) and Nichols (2009), this deposit is interpreted as a small diastem, represented in the stratigraphy by a storm - wave deposit (tempestite). A tempestite can be caused by either a strong storm or a tsunami event (Myrow & Southard 1996, Nichols 2009, Boggs Jr. 2011). A strong storm or tsunami event can disturb pre-existing sediment and redeposit it in shallow waters (Dunbar & Rodgers 1957, Nichols 2009). The horizon (fig. 3-24, 3-25) is scoured and shows significant changes in age from Duntroonian (ca.27.3 - 25.2 Ma) to Waitakian (ca. 25.2 - 21.7 Ma).

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Figure 3-25 Detailed image of the echinoderm - rich diastem, interpreted as a storm - wave deposit (tempestite) at the base of the Otekaike Limestone at Dyer Farm quarry. A sample, OU 86407 (J40/f0247) has been taken from the horizon (sampled directly at the tip of the lead pencil)

The sample taken within the echinoderm - rich diastem, OU 86407 (J40/f0247), at 14.45 m measured above base of the measured section at Dyer Farm quarry (fig. 3-17), is moderately glauconitic (40 vol%). 78 % of the glauconite shows pelletal / rounded textures, which is interpreted as allochthonous glauconite, originating at a distance from its formation (Seed 1965, Banerjee et al. 2016). Minor vermicular glauconite (22 %) is grown in-situ, as indicated by a layered structure and interpreted as autochthonous glauconite (Seed 1965, Banerjee et al. 2016).

OU 86407 (J40/f0247) shows a small amount of polycrystalline quartz and feldspar grains (5 vol%). The calcareous matrix contains abundant bioclasts and the CaCOß content is 55 wt% (fig. 3-17). The magnetic susceptibility is 0.02, indicative of some terrigenous influx (Dekkers 1978). Phosphate nodules are cm-sized, randomly orientated in the horizon, and occur rarely. Small, cm-sized fragments of cetacean and / or penguin bones are present, but rare. Abundant secondary mineralization (limonite) occurs throughout this horizon.

The Otekaike Limestone at the top of the measured section at Dyer Farm quarry (fig. 3-17, 3­26) is a well-cemented, bioclastic glauconitic limestone at the top of the exposed section, represented by the samples OU 86407 (J40/f0247) and OU 86408 (J40/f0248). It is diffuse - bedded to massive, light greyish-yellow, with a thickness of 2.5 m (fig. 3-26). It shows minor bioturbation and abundant scouring and small cross-beds across the width of the outcrop. Macrofossils are not visible.

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Figure 3-26 Thin section image of the Otekaike Limestone at Dyer Farm quarry, OU 86408 (J40/f0248), XPL. (1) = bioclast, (2) = allochthonous glauconite, (3) = polycrystalline quartz

A bioclastic glauconitic limestone sample from the upper Otekaike Limestone at Dyer Farm quarry is fine - to medium-grained, moderately - to poorly - sorted and clast-supported (fig. 3­26). The non - carbonate mineralogy is dominated by abundant glauconite (36 - 40 vol%). 77 % of the glauconite shows pelletal / rounded textures, which is interpreted as allochthonous glauconite, originating at a distance from its formation (Seed 1965, Banerjee et al. 2016). Minor vermicular glauconite (23 %) is grown in-situ, as indicated by a layered structure and interpreted as autochthonous glauconite (Seed 1965, Banerjee et al. 2016). Furthermore, angular to subangular polycrystalline quartz and feldspar (3-5 vol%), and muscovite (less than 1 vol%), set in a calcareous matrix, occur (fig. 3-17, 3-26). The CaCOß content, represented mostly by abundant bioclasts, varies between 55 and 61 wt%. The magnetic susceptibility is 0.01 - 0.02, indicating some terrigenous influx, as shown in fig. 3-17 and tab. 5-1 (Dekkers 1978).

Foraminifera in the upper Otekaike Limestone at Dyer Farm quarry are sparse, but well- preserved. As shown in fig. 3-17 and tab. 5-2, the base of the Otekaike Limestone shows a Duntroonian to Waitakian age (ca. 27.3 - 21.7 Ma). Notorotalia spinosa and Globigerina brazieri are indicative for a Duntroonian to Waitakian age in sample OU 86407 (J40/f0247), while the first appearance of Globoquadrina dehiscens in sample OU 86408 (J40/f0248) indicates a Waitakian age (ca. 25.2 - 21.7 Ma). Furthermore, Anomalinoides orbiculus, Cibicides perforatus, Melonis dorreeni, Guembelitria triseriata, and Lenticulina loculosa occur .

In summary, the succession exposed at the disused Dyer Farm quarry represents sedimentary rocks of lower Whaingaroan, Duntroonian, and Waitakian age, and furthermore a transition from terrigenous-rich sedimentary rocks to terrigenous - poor carbonates. The age ranges from upper Whaingaroan (ca. 34.6 - 29.8 Ma) to the Waitakian (ca. 25.2 - 21.7 Ma). The lower Whaingaroan Earthquakes Marl (calcareous sandstone) is separated from the Duntroonian Kokoamu Greensand (glauconitic limestone) by a strongly burrowed disconformity. The absence of upper Whaingaroan sedimentary rocks (ca. 29.8 - 27.3 Ma) indicates non-deposition or erosion of these strata and are responsible for the hiatus of at least 2.5 Ma. The Duntroonian to Waitakian Otekaike Limestone is separated from the Duntroonian Kokoamu Greensand (glauconitic limestone) by a diastem, representing a short-time, high - energy storm-wave deposit (tempestite), either caused by a strong storm or tsunami event.

3.5 Waihao River Walkway - "Cabbagetree Gully”

The Waihao River Walkway, managed by the Waimate City Council (WCC), runs along the south bank of the Waihao River, between McCullochs Bridge and the Black Hole (a swimming hole) (fig. 3-27).

Editorial Note: Figure 3-27 was removed due to copyright issues.

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Figure 3-27 The location of the stratigraphic section of the Waihao River Walkway ("Cabbagetree Gully”). Source: Google Earth (22.11.2019)

The exposed sedimentary succession at Waihao River Walkway (“Cabbagetree Gully”) features a Mid - to late Oligocene sedimentary succession of 28.5 m. It shows the massive facies of the Kokoamu Greensand at the bottom, gradationally grading into the nodular facies of the Kokoamu Greensand, and overlain by the Otekaike Limestone. The Otekaike Limestone is not accessible at the Waihao River Walkway, therefore published data (Ward & Lewis 1975) from a nearby location at Waihao Forks (GPS Coordinates: 44 ° 47'35.0016 “ S 170° 55'57. 1764 “E) was used to complete the stratigraphic column (fig. 3-28). None of the sedimentary units shows structural deformation.

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Figure 3-28 Stratigraphie column of the sedimentary succession at Waihao River Walkway ("Cabbagetree Gully"). This is a composite section including data from Ward 8i Lewis (1975), obtained at the nearby Waihao Forks location

The sedimentary succession at Waihao River Walkway (“Cabbagetree Gully”) is shown in fig. 3-28, 3-29, 3-30. The stratigraphic column was measured at the position of the two figures in fig. 3-29.

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Figure 3-29 The sedimentary succession at Waihao River Walkway ("Cabbagetree Gully”). It shows the sharp contact between the massive facies and the nodular facies of the Kokoamu Greensand. The Otekaike Limestone is exposed further to the right-hand side (fig. 3­30). Photo was taken by Prof. R Ewan Fordyce in 2012

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Figure 3-30 The sedimentary succession (to the right of fig. 3-29) showing all three formations

The massive facies of the Kokoamu Greensand consist of glauconitic limestone (fig.3-28, 3­31). The rock is greenish-grey, lacks bedding, shows abundant bioturbation, and has a thickness of 9.5 m (fig. 3-29, 3-30). Fragments of macrofossils (molluscs, brachiopods, annelids, cetacean and / or penguin bones) are present and distributed randomly throughout the sedimentary succession at Waihao River Walkway (“Cabbagetree Gully”).

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Figure 3-31 Thin section image of the massive facies of the Kokoamu Greensand at Waihao River Walkway ("Cabbagetree Gully”), OU 86413 (J40/f0251), XPL. (1) = allochthonous glauconite, (2) = vermicular, autochthonous glauconite, (3) = siliciclastic grains (polycrystalline quartz + feldspar)

A thin - sectioned glauconitic limestone sample (OU 86413 (J40/f0251)) of the massive facies of the Kokoamu Greensand at this location is medium-grained, moderately-sorted and clast- supported (up to 85%). As shown in fig. 3-31, the mineralogy consists of abundant rounded glauconite (33 vol%). 80 % of the glauconite shows pelletal / rounded textures, which is interpreted as allochthonous glauconite, originating at a distance from its formation (Seed 1965, Banerjee et al. 2016). Minor vermicular glauconite (20 %) is grown in-situ, as indicated by a layered structure and interpreted as autochthonous glauconite (Seed 1965, Banerjee et al. 2016). In addition, angular to subangular polycrystalline quartz and feldspars (15 vol%), and minor epidote (less than 1 vol%) occur, set in a calcareous matrix. The CaCO3 content, mostly derived from bioclasts, is 52 wt%. The magnetic susceptibility is 0.02, indicative for a large amount of terrigenous influx (fig.3-28, tab. 5-1) (Dekkers 1978).

Foraminifera in the massive facies of the Kokoamu Greensand at the Waihao River Walkway (“Cabbagetree Gully”) are abundant and well-preserved. As shown in fig. 3-28 and ta. 5-2, Notorotalia spinosa and Globigerina euapertura occur and are indicating a Duntroonian age (ca. 27.3 Ma - 25.2 Ma). Furthermore, Anomalinoides orbiculus, Melonis dorreeni, Cibicides thiara, and Buliminapupula are present. The massive facies of the Kokoamu Greensand grades into the nodular facies of the Kokoamu Greensand (fig. 3-29 and 3-30).

The nodular facies of the Kokoamu Greensand consist of glauconitic limestone (fig. 3-28, 3-32). The rock is greenish to grey, shows indistinct dm-bedding, calcareous nodules and concretions, scours, cross - beds, bioturbation, and has a thickness of 10 m (fig. 3-28). Macrofossils (molluscs, brachiopods, annelids, cetacean and / or penguin bones) occur randomly oriented at the bottom of the unit. Abundant secondary alteration (limonite) is present and distributed across the whole width of the outcrop.

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Figure 3-32 Thin section image of the nodular facies of the Kokoamu Greensand at Waihao River Walkway ("Cabbagetree Gully”), OU 86414 (J40/f0252), XPL. (1) = allochthonous glauconite, (2) = polycrystalline quartz

The glauconitic limestone is medium-grained, moderately - sorted and clast-supported (up to 75 %). As seen in fig. 3-32, the mineralogy consists of abundant subrounded to rounded glauconite (34 vol%) which are partly altered. 88 % of the glauconite shows pelletal / rounded textures, which is interpreted as allochthonous glauconite, originating at a distance from its formation (Seed 1965, Banerjee et al. 2016). Minor vermicular glauconite (22 %) is grown in­situ, as indicated by a layered structure and interpreted as autochthonous glauconite (Seed 1965, Banerjee et al. 2016). In addition, angular to subangular polycrystalline quartz and feldspar (13 vol%), and micas (less than 1 vol%) occur, set in a calcareous silty matrix. The CaCO3 content, mostly derived from abundant bioclasts, is 53 wt%, and the magnetic susceptibility is 0.01, indicating less terrigenous input than in the massive facies of the Kokoamu Greensand at Waihao River Walkway (“Cabbagetree Gully”) (fig. 3-28, tab. 5-1) (Dekkers 1978).

The abundant calcareous nodules and concretions in the nodular facies of the Kokoamu Greensand at Waihao River Walkway (“Cabbagetree Gully”) are ovoid, spherical, and of irregular shape. They are distributed as nodular - to concretionary patches along the dm - sized bedding planes (fig. 3-29, 3-30). The calcareous nodules and concretions represent secondary sedimentary features, formed due to the precipitation of CaCO3 cement infilling cavities between mineral grains (Nichols 2009, Boggs Jr. 2011). These replacement bodies were formed before the lithification of the sediment during the diagenesis (Boggs Jr. 2011).

Foraminifera in the nodular facies of the Kokoamu Greensand at Waihao River Walkway (“Cabbagetree Gully”) are abundant and well-preserved. As shown in fig. 3-28 and ta. 5-2, Notorotalia spinosa and Globigerina euapertura are consistent with a Duntroonian to Waitakian age (ca. 27.3 Ma - 21.7 Ma). Furthermore, Anomalinoides orbiculus, Melonis dorreeni, Cibicides perforatus, Uvigerina maynei, and Gaudryina quadrazea occur.

The Otekaike Limestone is not accessible at the Waihao River Walkway as the outcrop consist of a steep, inaccessible cliff (fig. 3-28, 3-30). Therefore, published data (Ward & Lewis 1975) from a nearby location at Waihao Forks (GPS coordinates: 44 ° 47' 35.0016 “S 170 ° 55'57. 1764”E), ca. 1.8 km W of the Waihao River Walkway (“Cabbagetree Gully”), is used to complete the stratigraphic column (fig. 3-28, 3-33). The thickness of the Otekaike Limestone at Waihao River Walkway (“Cabbagetree Gully”) is ca. 9 m, according to fig. 3-28. Ward & Lewis (1975) used the stratigraphic name “Arno Limestone” for the Otekaike Limestone, as shown in tab. 1-2.

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Figure 3-33 The Otekaike Limestone at Waihao Forks, described by Ward & Lewis (1975). The outcrop shows (1) = abundant cross - bedding and (2) = channelling across the width of the whole outcrop. Photo taken by Prof R Ewan Fordyce in 2012

According to Ward & Lewis (1975), the bioclastic Otekaike Limestone is strongly bedded, and contains abundant calcareous nodules and concretions (fig. 3-33). Furthermore, bioturbation is common and distributed throughout the unit (Ward & Lewis 1975). The rock is light yellowish - brown, well-cemented, and “large-scale cross-beds and scour channels are common in the lower part of the unit; some scour channels are filled with greensand” (Ward & Lewis 1975, p. 881).

According to the thin section description of sample UC 6694 by Ward & Lewis (1975), the bioclastic glauconitic limestone is fine-grained and well - sorted and the mineralogy consists of abundant subrounded to rounded parautochthonous glauconite (= containing both allochthonous and autochthonous grains), and very fine angular to subangular quartz, and feldspar. In addition, “volcanic rock fragments, amphiboles, and muscovite are present, set in a calcareous matrix” (Ward & Lewis 1975, p. 888).

According to Smith et al. (1989), the CaCOß content at the base of the Otekaike Limestone at Waihao Forks is 78 wt% at sample J40/s14 (see FRED Database, GNS Science, Lower Hutt, NZ). At the top of the Otekaike Limestone at Waihao Forks, the CaCO3 content is 72 wt% at sample J40/s13 (see FRED Database, GNS Science, Lower Hutt, NZ). Some bioclasts show signs of micritization, according to Ward & Lewis (1975). The age of the Otekaike Limestone is Duntroonian to Waitakian (ca. 27.3 - 21.7 Ma), based on foraminifera biostratigraphy (Hornibrook 1961, Hornibrook et al. 1989, Hornibrook 1996), ostracod biostratigraphy (Ayress 1993, Ayress 2006) and Sr isotope dating (Fulthorpe et al. 1996, Graham et al. 2000, Nelson et al. 2004). Micropaleontological data obtained from the nearby Dyer Farm quarry in this reconnaissance study confirms the Duntroonian to Waitakian age of the Otekaike Limestone (see Chapter 3.4).

In summary, the sedimentary succession exposed at the Waihao River Walkway (“Cabbagetree Gully” ) represents sedimentary strata of Duntroonian to Waitakian age (ca. 27.3 Ma - 21.7 Ma) and a transition from terrigenous-rich sedimentary rocks to terrigenous - poor carbonates. The Kokoamu Greensand shows two different facies: a massive facies and a nodular facies. The massive facies grades sharp into the nodular faices of the Kokoamu Greensand at Waihao River Walkway (“Cabbagetree Gully”). The Otekaike Limestone is not accessible at the Waihao River Walkway (“Cabbagetree Gully”) due to steep cliffs, therefore published data (Ward & Lewis 1975) from nearby Waihao Forks was used to complete the stratigraphic column (fig.3- 28). As seen in fig. 3-28, no unconformity was recognized at the Waihao River Walkway (“Cabbagetree Gully”).

3.6 Waimate Gorge (local Torlesse Terrane basement)

The small aggregate quarry off Hakataramea Highway No. 82 between Waihao Forks and Waimate in the south-end of the Waimate Gorge (fig. 3-34), consists of slightly metamorphosed quartzo - feldspathic sandstone (greywacke) of the Torlesse Supergroup.

Editorial Note: Figure 3-34 was removed due to copyright issues.

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Figure 3-34 Location of the small aggregate quarry in the south-end of the Waimate Gorge. The thick black line outlines the Torlesse Supergroup exposed in the Waimate Gorge and further to the north of the image (compare fig. 3-3). Source: Google Earth (22.11.2019)

In hand specimen, the sample taken in the small aggregate quarry (OU 86415) is a greyish, structureless (isotropic), and fine-grained quartzo - feldspathic sandstone (fig. 3-36). Abundant dark rock fragments, probably mudstone or argillite, as well as generally angular to subangular quartz and feldspar grains are visible. Small quartz veins are visible and distributed randomly thoughout the outcrop. No jointing occurs. Bedding is present in places, but indistinct.

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Figure 3-35 The small aggregate quarry in the south-end of the Waimate Gorge, showing the active quarry face of around 21 m in height (August 2018)

In thin section (fig. 3-36), the fine grain-size is confirmed and the texture of the sample is inequigranular. The mineralogy consists of abundant polycrystalline angular quartz and angular feldspar grains, as shown in fig. 3-36. Minor detrital components are muscovite, chlorite, epidote, biotite, and amphiboles, set in a matrix of silt or clay. Prehnite and pumpellyite, replacing detrital minerals, are present as small grains (fig. 3-36).

In this unstained thin section, it is hard to distinguish between quartz and untwinned plagioclase. The matrix consists presumably of clastic mud. The larger feldspars are commonly highly altered due to sericitization (fig. 3-36).

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Figure 3-36 Thin section image of the Torlesse metasedimentary basement rock (quartzo - feldspathic sandstone - greywacke), Waimate Gorge quarry, OU 86415, XPL. (1) = polycrystalline quartz, (2) = sericitized feldspar, (3) = dark rock fragment, (4) = prehnite, (5) = pumpellyite

In summary, OU86415 is a slightly metamorphosed, indurated quartzo - feldspathic sandstone (greywacke), dominated by detrital features. Foliation in terms of pressure-solution veins or mica alignment does not occur. The presence of small secondary grains of prehnite and pumpellyite (fig. 3-36) suggest that it is a slightly metamorphosed sedimentary rock and / or low-grade metamorphic rock (equivalent to prehnite - pumpellyite facies). The occurrence of clasts containing perthitic feldspars suggest a plutonic provenance of the rock. No calcareous fossils (bioclasts) occur in OU 86415, but internal casts (“steinkerne”) of Atomodesma sp. were found in sample J40/f9512 and sample J40/f9514 (see FRED Database, GNS Science, Lower Hutt, NZ) at nearby locations. Atomodesma sp is indicative for a Permian age of ca. 288.5 - 251.5 Ma, according to Ford et al. (1990).

Torlesse metasedimentary rocks as represented by OU 86415 are the plausibly source of the detrital mineral grains (mostly polycrystalline quartz and feldspar) recognised in the Eocene - Oligocene sedimentary succession of the lower Waihao Valley (fig. 3-3, 3-5, 3-13, 3-17, 3-28). There are also other options for provenance, such as Taratu Formation (compare 3.1), containing abundant reworked polycrystalline quartz and feldspar (Field & Browne 1989, Middlemiss 1999).

Chapter 4 Discussion

Three unconformities are identified in the Eocene - Oligocene strata of the lower Waihao Valley, South Canterbury Basin (fig. 4-1, 4-2).

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Figure 4-1 Eocene - Oligocene lithostratigraphy of the lower Waihao Valley, South Canterbury Basin, showing the thickness of exposed strata.

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Figure 4-2 Eocene - Oligocene chronostratigraphy of the lower Waihao Valley, South Canterbury Basin. Three unconformities are identified: (1) = A disconformity in the Waihao Greensand (Otaio Limonitic Member) at Dons Hole, (2) The Marshall unconformity at Dyer Farm quarry separating Earthquakes Marl from Kokoamu Greensand, (3) A diastem in the basal Otekaike Limestone at Dyer Farm quarry. The unconformable contact separating the Ashley Mudstone from the Earthquakes Marl at McCullochs Bridge (Ayress 1995) is marked as uncertain (?) as no investigations were made during this study.

The Eocene - Oligocene strata in the lower Waihao Valley, South Canterbury Basin, ranges from glauconitic sandstone, siltstone, and mudstone in the Kaiatan to Runangan? (ca. 39.1 - 34.6 Ma), to calcareous sandstone in the lower Whaingaroan (ca. 34.6 - 29.8 Ma), followed by glauconitic and bioclastic glauconitic limestones in the Duntroonian to Waitakian (ca. 27.3 - 21.7 Ma) (fig.3-3, 3-5, 3-13, 3-17, 3-28).

4.1 Eocene unconformities

As seen in fig. 4-1, 4-2, two unconformities are present in the Eocene part of the sedimentary succession in the lower Waihao Valley. A burrowed, partly phosphatized disconformity occurs in the top of the Waihao Greensand (Otaio Limonitic Member) at Dons Hole and can be traced across the width of the whole sedimentary succession (fig.3-5, 3-9). The type of unconformity, as shown in fig. 1-4 and tab. 1-1, is identified as a disconformity because the contact is parallel to strata, but it shows a significant erosional surface of appreciable relief with strong bioturbation (fig. 1-4, tab. 1-1). On examination for this study, the over - and underlying units (= glauconitic sandstones and siltstones) were found to be only slightly calcareous and obtained samples contained no foraminifera (fig. 3-5, tab. 5-1). Therefore, a precise age determination to establish the time represented by missing strata using calcareous foraminifera is not possible at Dons Hole. The Kaiatan age (ca. 39.1 - 36.7 Ma) of the Waihao Greensand and Ashley Mudstone at Dons Hole is based on previous work at nearby locations, e.g. McCullochs Bridge, by Srinivasan (1966), Fordyce et al. (1985) and Maxwell (1992). As shown in fig. 3-7, the Waihao Greensand contains Fe oxide - stained glauconite and abundant quartz granules. These subrounded to rounded quartz granules show a polycrystalline texture (fig. 3-7) and are most likely derived from Torlesse metasedimentary rocks as exposed in a small aggregate quarry in the Waimate Gorge (compare Chapter 3.6).

As shown in fig. 3-7, the Fe - oxide stained, partly phosphatized glauconite grains are parautochthonous. Parautochthonous glauconite consist both of in-situ grown (autochthonous) glauconite and transported (allochthonous) glauconite (Seed 1965, McCouchie & Lewis 1980, McMillan 1994, Banerjee et al. 2014). Based on the point counting data of OU 86409, 85 % of the glauconite in the Waihao Greensand is allochthonous and 15% is autochthonous. McMillan & Wilson (1997) mention a partly phosphatized disconformity within the late Bortonian to early Kaiatan in the W. tabulatum zone at the Waihao River. According to Lever (2007), phosphatization is indicative for condensed sections caused by sediment starvation on a submerging shelf. Browne & Field (1985) suggest an outer shelf setting for the Waihao Greensand in the South Canterbury Basin, which agrees with additional work by Maxwell (1992) and Ayress (1995) estimating the paleo water depth to around 150 - 200m, based on fossil assemblages of molluscs and ostracods. The abundant content of parautochthonous glauconite found in OU 86409 at Dons Hole thus confirms an outer shelf setting for the top of the Waihao Greensand (Seed 1965, Banerjee et al. 2016), as indicated in fig. 4-3.

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Figure 4-3 Paleogeographic reconstruction of Zealandia during the Kaiatan (ca. 39.1 – 36.7 Ma). The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

According to observations by Ayress (1995), a burrowed unconformity occurs at the base of the Earthquakes Marl at 9.25 m measured above the base of the stratigraphic section of McCullochs Bridge (fig. 4-1, 4-2). According to Ayress (1995), the uppermost 2m of the Ashley Mudstone at the unconformable contact with the Earthquakes Marl at McCullochs Bridge are decalcified, as shown in fig. 3-13. Ayress (1995) inferred the age of the strata to be of Runangan? age (ca. 36.7 - 34.6 Ma). No further study on this unconformity has been done in previous work and not in this study either as, elsewhere, the unconformity is not exposed anymore (overgrown by dense vegetation). Browne & Field (1985), Maxwell (1992) and Ayress (1995) suggest an outer shelf to bathyal setting for the Kaiatan to Runangan? age (ca. 39.1 - 34.6 Ma) Ashley Mudstone (fig. 4-4). This thesis is not able to contribute to further interpretations about the local paleoenvironment of the Runangan age due to the lack of exposure at McCullochs Bridge.

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Figure 4-4 Paleogeographic reconstruction of Zealandia during the Runangan (ca. 36.7 – 34.6 Ma). The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

4.2 Oligocene unconformities

In the Oligocene part of the sedimentary succession in the lower Waihao Valley, two unconformities occur in a measured section at Dyer Farm quarry (fig. 4-1, 4-2). These will be discussed in further detail as one of the unconformities was confidently identified as a new recognized exposure of the regional Mid - Oligocene Marshall unconformity in New Zealand.

A burrowed disconformity occurs at the base of the Kokoamu Greensand at 7 m measured above base in the measured section at Dyer Farm quarry (fig. 3-17). The disconformity is marked by an erosional contact showing abundant strong bioturbation (fig. 3-20, 3-21). Some extensive horizontal burrows reach down to ca. 35 cm into the underlying unit (Earthquakes Marl). Some of the burrows are identified as decapod crustacean - generated burrows of Thalassinoides sp. which are indicative of a near - shore, shallow marine mid - to inner shelf environment (e.g. Ward & Lewis 1975, Field & Browne 1989). Furthermore, there is paleontological evidence represented by an abrupt change in the fossil record, which is indicative for missing time represented by missing strata (fig. 1-4, tab. 1-1). According to the erosional contact represented by abundant strong bioturbation and the paleontological evidence, this unconformity was identified as a disconformity (fig. 1-4, tab. 1-1). Lower Whaingaroan strata (Earthquakes Marl) is unconformably overlain by Duntroonian strata (Kokoamu Greensand) (fig. 4-2). As shown in fig. 4-2, the upper Whaingaroan (ca. 29.8 - 27.3) is not exposed at the measured section of Dyer Farms quarry. Therefore, the missing time represented by missing strata shows a hiatus of at least 2.5 Ma. The missing strata can either be related to erosion or non-deposition (Dunbar & Rodgers 1957, Neuendorf et al. 2011).

Carter & Landis (1972) describe the type location of the Marshall unconformity at Squire's Farm in South Canterbury, ca. 22 km N of the lower Waihao Valley, where lower Whaingaroan sedimentary strata is paraconformably overlain by Duntroonian sedimentary strata. The succession at Squires's Farm was dated by Fulthorpe et al. (1996) using Sr isotopes and the hiatus was estimated to be ca. 2-4 Ma at this location. According to Lewis & Belliss (1984), the contact between the lower Whaingaroan Earthquakes Marl and the Duntroonian Kokoamu Greensand is disconformable at Kokoamu Cliffs and The Earthquakes - both locations in the Waitaki Valley, ca. 27 km to the SW of Dyer Farm quarry. Jenkins (1987) correlated these sedimentary successions with the Deep-Sea Drilling Project (Site 593) in the Tasman Sea using planktonic foraminiferal ranges and interpreted this unconformity as the regional Mid - Oligocene Marshall unconformity (compare Chapter 1.6). The hiatus of the Marshall unconformity between the lower Whaingaroan Earthquakes Marl and the Duntroonian Kokoamu Greensand is estimated to be ca. 2 Ma, according to Jenkins (1987). The disconformity separating the lower Whaingaroan Earthquakes Marl from the Duntroonian Kokoamu Greensand at Dyer Farm quarry was therefore identified with confidence as a new recognized location of the regional Mid - Oligocene Marshall unconformity. At Dyer Farm quarry, the Marshall unconformity represents a hiatus of at least 2.5 Ma (fig. 4-2).

Fulthorpe et al. (1996) identified the Marshall unconformity as a burrowed paraconformity, separating the underlying Earthquakes Marl from the overlying Kokoamu Greensand, at McCullochs Bridge. During the fieldwork in 2018 and 2019, this paraconformity could not be recognized at McCullochs Bridge, as the exposure of the Earthquakes Marl is heavily overgrown by dense vegetation (fig.3-13). Furthermore, Fulthorpe et al. (2011) identified the Marshall unconformity as a paraconformity in Hole U1352C in the offshore South Canterbury Basin during the IODP Expedition 317. Tinto (2010) identified the Marshall unconformity as a paraconformity in a sedimentary drill core from Cave, South Canterbury - ca. 50 km N of Dyer Farm quarry. The Marshall unconformity can therefore either occur as a disconformity (e.g. Dyer Farm quarry, Kokoamu Cliffs, The Earthquakes) or as a paraconformity (e.g. Squire's Farm, Cave, IODP Expedition 317 - Hole U1352C), depending on the location in the sedimentary basin. The nature of unconformities can change laterally throughout different parts of a sedimentary basin, due to variations in water depth, current strength, and sediment supply (Nichols 2009, Boggs Jr. 2011, personal comment from Browne, G., GNS Science, Lower Hutt, NZ via email on 20.12.2018).

At the new recognized exposure of the Marshall unconformity at Dyer Farm quarry, the underlying calcareous sandstone (Earthquakes Marl) is of lower Whaingaroan age (ca. 34.6­29.8 Ma), given the last occurrences of the key foraminiferal species Notorotalia stachei and Globigerina angiporoides (fig. 3-17, tab. 5-1). As shown in fig. 3-17 and 3-19, the Earthquakes Marl is rich in siliciclastic grains (quartz + feldspar = 53 - 58 vol%). The quartz grains are mostly polycrystalline, which is indicative for a metamorphic origin (Weltje & van Eynatten 2004). These quartz grains are most likely derived from local Torlesse metasedimentary rocks as exposed in the Waimate Gorge (compare Chapter 3.6). This confirms previous petrological studies on Oligocene strata in the Canterbury Basin by Smith et al. (1989) and Mortimer & Strong (2014). Maxwell (1992) suggested an outer shelf setting or deeper for the Earthquakes Marl in the southern Canterbury Basin, according to the abundant planktic foraminifera found in the Earthquakes Marl at The Earthquakes, Waitaki Valley - ca. 27 km SW of the lower Waihao Valley. The foraminifera in the Earthquakes Marl at Dyer Farm quarry do not match this trend, instead they are sparse and poorly preserved. The abundant content of siliciclastic grains (53 - 58 vol%), magnetic susceptibility values between 0.01 and 0.02, and the small amount of glauconite (7 - 9 vol%), as shown in fig. 3-17 and tab. 5-1, coincides with an outer shelf setting or deeper with a moderate to large amount of terrigenous influx (fig. 4-5).

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Figure 4-5 Paleogeographic reconstruction of Zealandia during the lower Whaingaroan (ca. 34.6 – 29.8 Ma). The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

At the exposure of the Marshall unconformity at Dyer Farm quarry, the overlying glauconitic limestone (Kokoamu Greensand) is of Duntroonian age (ca. 27.3 - 25.2 Ma), given the last occurrence of the key foraminiferal species Globigerina euapertura and the first occurrence of Notorotalia spinosa (fig. 3-17, 3-23, tab. 5-1). As shown in fig. 3-17 and 3-22, the Kokoamu Greensand contains a large amount of parautochthonous glauconite (28-32 vol%) with 21% autochthonous and 79% allochthonous grains, and a moderate amount of siliciclastic grains (quartz + feldspars = 14 - 21 vol%). The Kokoamu Greensand is named a “greensand” due to the abundant greenish glauconite grains, which are indicative for slow sedimentation rates (e.g. Field & Browne 1989, Smith et al. 1989, Thompson & Bassett 2014). At Dyer Farm quarry and the Waihao River Walkway - “Cabbagetree Gully”), the Kokoamu Greensand is a glauconitic limestone (fig.3-22, 3-31, 3-32). According to local paleoenvironmental interpretations of ostracod assemblages, an mid - to inner shelf setting for the Kokoamu Greensand in the southern Canterbury Basin is suggested by Ayress (1995), as shown in fig.4-6, which coincides with the large amount of parautochthonous glauconite found in the Kokoamu Greensand at Dyer Farm quarry and Waihao River Walkway (“Cabbagetree Gully”) (Banerjee et al. 2016).

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Figure 4-6 Paleogeographic reconstruction of Zealandia during the Duntroonian (ca. 27.3 - 25.2 Ma). The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

A diastem occurs in the basal Otekaike Limestone, at 14.45m measured above base in the measured section at Dyer Farm quarry (fig. 3-17, 4-1, 4-2). This is because it shows a notable interruption in sedimentation, represented by a ca. 35 cm thick fossiliferous horizon with coarse angular fossil fragments (fig. 3-24, 3-25). As shown in fig. 3-25, this fossiliferous horizon consists of abundant angular fragments of echinoids and crinoids (ca. 86 vol%), randomly intermingled and without any sign of colonization by sessile organisms like oysters or worms (Dunbar & Rodgers 1957), set in a calcareous glauconitic matrix. The angular shape of the fossil fragments is indicative of a rapid deposition and burial (Myrow & Southard 1996, Nichols 2009) (fig. 1-4, tab. 1-1). An appropriate explanation is a short-time, high-energy storm-wave deposit - a tempestite (Myrow & Southard 1996). A tempestite is caused by either a strong storm or a tsunami event (Myrow & Southard 1996). It usually occurs just below the wave - base in a shallow shelf setting (Nichols 2009). The time gap represented by this diastem is short and probably deposited within several hours due to the angularity of the fossil fragments and the lack of colonization by sessile organisms (Dunbar & Rodgers 1957, Myrow & Southard 1996, Nichols 2009). The exact time missing represented by this short interruption in sedimentation is not distinguishable by foraminiferal biostratigraphy, as the dating precision of foraminifera is only to the Stage level of the New Zealand Geological Timescale (fig. 1-2, 1­3).

Previous work by Lewis & Belliss (1984) described a thin basal macrofossil shell - bed, lying on the base of the Otekaike Limestone at Kokoamu Cliffs, Waitaki Valley, with “larger macrofossil clasts including cetacean bones than in the remainder of the formation (Lewis & Belliss 1984, p.264). Lever (2007) mentions a paraconformity of Duntroonian to Waitakian age, occurring in South Canterbury and in the West Coast basins. Ward & Lewis (1975) linked the current - bedded Otekaike Limestone at Waihao Forks, ca. 1.8 km W of the Waihao River Walkway (“Cabbagetree Gully”), with increasing presence of ocean current activities, caused by oceanic changes in the Southern Ocean such as the opening and later deepening of the Tasmanian Gateway and the onset of the proto - Antarctic Circumpolar Current (ACC).

Ayress (1993) suggest a shallowing trend in the basal Otekaike Limestone towards an inner shelf setting (fig. 4-7). An inner shelf setting would coincide with the abundant parautochthonous glauconite (36 - 40 vol%), as shown in fig. 3-17 and tab. 5-1, and the occurrence of storm-wave deposits (Dunbar & Rodgers 1957, Myrow & Southard 1996, Nichols 2009). Furthermore, a CaCOß content of 55 - 61 wt% coincides with the interpretation of the Otekaike Limestone representing a shallow cool-water carbonate platform (Smith et al. 1989, Thompson & Bassett 2014). Small cross - beds and bedding at the top of the diastem, as shown in fig. 3-24, are indicative for current activity (e.g. Ward & Lewis 1975, Thompson & Bassett 2014).

The underlying Kokoamu Greensand is of Duntroonian age (ca. 27.3 - 25.2 Ma), given the last occurrence of the key foraminiferal species Globigerina euapertua and the first occurrence of Notorotalia spinosa (fig. 3-17, 4-2, tab. 5-1). The overlying glauconitic bioclastic limestone (Otekaike Limestone) is of Waitakian age (ca. 25.2 - 21.7 Ma), given the key foraminiferal species Notorotalia spinosa and the first occurrence of Globigerina brazieri and Globoquadrina dehiscens (fig. 3-14, 4-2). Abundant calcareous nodules and concretions occur both in the Duntroonian Kokoamu Greensand and the Duntroonian to Waitakian Otekaike Limestone (fig. 3-17, 3-28).

Figure 4-7 Paleogeographic reconstruction of Zealandia during the Waitakian (ca. 25.2 – 21.7 Ma). The blue star marks the approximate position in the South Canterbury Basin. Source: Kamp et al. 2015

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4.3 Facies - and thickness variations in the Kokoamu Greensand

The Duntroonian Kokoamu Greensand shows significant variations in thickness and facies between the measured section at Dyer Farm quarry and the Waihao River Walkway (“Cabbagetree Gully”), ca. 3 km apart (fig. 3-17, 3-28, 4-1). The Kokoamu Greensand is a glauconitic limestone at both locations (fig. 3-17, 3-28). The massive Kokoamu Greensand at Dyer Farm quarry is 7.2 m thick. At the Waihao River Walkway (“Cabbagetree Gully”), the Kokoamu Greensand has a total thickness of 19.5 m and consists of a massive facies (9.5 m thickness) and a nodular facies (10 m thickness) (fig. 4-1). As shown in fig. 3-29 and 3-30, the abundant calcareous nodules and concretions in the nodular facies of the Kokoamu Greensand at Waihao River Walkway (“Cabbagetree Gully”), distributed as nodular - to concretionary patches along the dm - sized bedding planes, are secondary replacement bodies formed due to the precipitation of CaCO3 cement infilling cavities between mineral grains (Nichols 2009, Boggs Jr. 2011).

Bed thickness variations due to lateral variation in deposition rate and facies are most likely responsible for the local variations in thickness and facies of the Kokoamu Greensand between the sedimentary successions at Dyer Farm quarry and the Waihao River Walkway (“Cabbagetree Gully”). This is unlikely to be due to erosion because the only evidence for erosion found within the Kokoamu Greensand is in the top of the nodular facies at Waihao River Walkway (“Cabbagetree Gully”), represented by indistinct dm - bedding and small scours (fig. 3-29, 3-30). These features increase in size and abundance in the overlying Otekaike Limestone as described by Ward & Lewis (1975) at nearby Waihao Forks location. It is important to mention that intense bioturbation, which occurs in the Kokoamu Greensand at Dyer Farm quarry and Waihao River Walkway (“Cabbagetree Gully”), can overprint sedimentary structures such as current bedding, cross - beds and scours (Nichols 2009). Local thickness - and facies variations in the Kokoamu Greensand are either caused by local changes in water depth or sediment supply (Browne & Field 1989, personal comment of Browne, G., GNS Science, Lower Hutt, NZ, via email on 20.12.2018). According to Lever (2007), huge thickness variation can be observed over short distances in all sedimentary basins on the South Island of New Zealand.

4.4 Provenance

To obtain the provenance of the terrestrially - derived siliciclastic grains (quartz + feldspars) found in the Eocene - Oligocene sedimentary rock samples in the lower Waihao Valley, the aggregate quarry in the Waimate Gorge was sampled (compare Chapter 3.6). As shown in fig. 4-8, the lower Whaingaroan Earthquakes Marl at Dyer Farm quarry contains a large amount of siliciclastic grains (quartz + feldspar) and the Duntroonian Kokoamu Greensand at Dyer Farm quarry and the Waihao River Walkway (“Cabbagetree Gully”) a moderate amount of siliciclastic grains. The other Eocene - Oligocene strata contains low amounts of siliciclastic grains (fig. 4-8). The Waimate Gorge quarry exposes local basement consisting of Torlesse metasedimentary rocks (fig. 3-3). Quartz grain provenance shows that the quartz grains in the quartz sand and the quartz granules recognized in the Eocene - Oligocene strata is polycrystalline and therefore indicative of a metamorphic origin (Weltje & van Eynatten 2004). The Torlesse metasedimentary rocks (see Chapter 3.6) were identified as the most likely source of the angular to subangular quartz grains, present in the quartz sand - and silt of the Eocene - Oligocene strata. The angular to subangular shape of the quartz grains generally indicates little transport and therefore a nearby source (Weltje & van Eynatten 2004). This supports Field & Browne (1989), Smith et al. (1989), and Mortimer & Strong (2014) suggesting Torlesse landmasses to the west as the most likely source of the quartz-rich nature of the Eocene - Oligocene sedimentary rocks in the southern Canterbury Basin. However, it is not diagnosed, as no prehnite or pumpellyite grains are recognized in the Eocene - Oligocene strata of the study area, which were expected to be found in the strata as the Torlesse metasedimentary rocks are of a prehnite - pumpellyite metamorphic facies (see Chapter 3.6).

The subrounded to rounded, polycrystalline quartz granules identified in the top of the Waihao Greensand (Otaio Limonitic Member) at Dons Hole (fig. 3-7) suggest that the quartz and other clastic grains can also be derived from the nearby Taratu Formation (see Chapter 3.1), which is exposed in the Waihaorunga Valley - ca. 20 km NW of the study area (Middlemiss 1999). The Taratu Formation contains abundant reworked polycrystalline quartz pebbles from the Haast Schist, according to Field & Browne (1989). The subrounded to rounded shape of the quartz granules in the Waihao Greensand (fig. 3-7) is indicative for abrasion during transportation which suggest that the most likely source for these granules are the reworked quartz pebbles of the Taratu Formation (Middlemiss 1999, Weltje & van Eynatten 2004, Nichols 2009).

Abbildung in dieser Leseprobe nicht enthalten

Figure 4-8 Ternary diagram showing the modal mineralogical composition (vol%) of the Eocene - Oligocene strata in the lower Waihao Valley, South Canterbury Basin. (1): Eocene Waihao Greensand and Ashley Mudstone at Dons Hole, (2): Eocene Ashley Mudstone at McCullochs Bridge, (3): Eocene to Oligocene Earthquakes Marl at Dyer Farm quarry, (4): Oligocene Kokoamu Greensand at Dyer Farm quarry, (5): Oligocene Kokoamu Greensand at Waihao River Walkway ("Cabbagetree Gully”), (6): Oligocene Otekaike Limestone at Dyer Farm quarry. The calcite content is taken from the acid measurements (tab. 5-1: CaCO3 content with mud absent). The ternary diagram was made using Petrograph (Version 2.0)

4.5 Regional context of Zealandia in the Eocene - Oligocene

During the Eocene - Oligocene, Zealandia was influenced by various regional-scale changes in oceanic circulation of the Southern Ocean, as shown in fig. 4-9 (Exon et al. 2002, Nelson et al. 2004, Scher & Martin 2006). These changes led to the creation of various tectonism - or paleoclimate - related unconformities (Field & Browne 1989, Lever 2007).

As shown in fig. 4-9, the onset of the proto-ACC (Antarctic Circumpolar Current) and the opening of oceanic gateways (e.g. Tasmanian Gateway, Drake Passage) in the Eocene - Oligocene transition (EOT) created erosive bottom currents, which are described as being responsible for the Marshall unconformity (Fulthorpe et al. 1996, Tinto 2010, Fulthorpe et al. 2011). According to Ward & Lewis (1975) and Fulthorpe et al. (1996), the outer continental shelf of Zealandia was directly affected by the eastward - flowing current system as indicated by the current-bedded Otekaike Limestone. According to Exon et al. (2002) and Lever (2007), the shallow opening of the Tasmanian Gateway at around 33.5 Ma (lower Whaingaroan) enabled warm surface waters to flow eastwards from the Indian Ocean into the Pacific Ocean. The opening of the Drake Passage at around 29 Ma at the boundary between the lower and upper Whaingaroan, caused the deepening of the Tasmanian Gateway (Scher & Martin 2006, Lever 2007). That enabled cold bottom water to flow through the gateway which developed erosive currents (Scher & Martin 2006). These currents were strong enough to reach the extensive continental shelf of Zealandia (Fulthorpe et al. 1996, Lever 2007, Fulthorpe et al. 2011).

Figure 4-9 Paleogeographic reconstruction of oceanic current patterns in the Southern Ocean in the Eocene (A) and Oligocene (B). Source: Nelson et al. 2004. Figure based on Kamp et al. 1990 and Nelson & Cooke 2001

Abbildung in dieser Leseprobe nicht enthalten

A maximum transgression and the associated maximum inundation of Zealandia during the Oligocene to Miocene (Waitakian to Otaian stage, ca. 25.2 Ma - 18.7 Ma), resulted in extensive cool-water shelf carbonate platforms, far away from terrigenous influx (Ayress 2006, Mortimer & Strong 2014, Thompson et al. 2014, Thompson & Bassett 2014). The depositional regime changed to prograding sedimentary wedges during the Miocene (Field & Browne 1989, Lever 2007).

4.6 Future work

Future work should focus on further identification and precise dating of unconformable surfaces in Zealandia's Cretaceous - Cenozoic sedimentary basins to get to know their variations in nature across different basins. This will give implications to reconstruct paleoenvironments on a regional scale. The use of foraminifera was chosen in this thesis by recommendation of my supervisor, Prof R Ewan Fordyce. For future investigations, I would recommend producing a biostratigraphy based on both foraminifera and ostracods. The use of ostracod biostratigraphy (e.g. Ayress 1993, Ayress 2006) might define the age of the strata as well as give some additional information to help reconstruct local paleoenvironmental settings in the Cenozoic of New Zealand. Due to the limited time for this thesis, no work on ostracod biostratigraphy was done in this reconnaissance study. Further investigations at locations suspected to expose the Marshall unconformity in the Great South Basin (e.g. McMillan & Wilson 1997) and identifying the time missing represented by missing strata will contribute to a better understanding of the nature and extent of the Marshall unconformity in New Zealand. As secondary mineralization can interfere with the magnetic susceptibility measurements (Dekkers 1978), I recommend using a small core drill to obtain unweathered samples and measure the magnetic susceptibility in the lab.

Chapter 5 Conclusions

The Cenozoic strata of the southern Canterbury Basin contains several unconformities whose precise age, nature, and origin is uncertain (e.g. Field & Browne 1989, Lever 2007). The new data and interpretations from this study confirm the presence of three unconformities in the Eocene - Oligocene sedimentary succession of the lower Waihao Valley, South Canterbury Basin (fig. 4-1 and 4-2). Biostratigraphic, petrological and petrophysical data add insights into local paleoenvironmental and wider basin interpretations. One of the Eocene unconformities is significant in terms of stratigraphic breaks as it was identified with confidence to be the regional Mid - Oligocene Marshall unconformity, representing a hiatus of at least 2.5 Ma.

An Eocene unconformity was examined at one location - Dons Hole (fig. 3-2, 3-3, 3-5). Here, a burrowed, partly phosphatized disconformity occurs in the top of the Waihao Greensand (Otaio Limonitic Member) within only slightly calcareous glauconitic sandstones and siltstones (fig. 3-5, 4-1, 4-2). The phosphatization and the abundant parautochthonous glauconite is indicative of a condensed section and most likely caused by sediment starvation in an outer shelf setting with slow sedimentation rates and paleo water depths of 150 - 200 m (Ayress 1995, Lever 2007, Banerjee et al. 2016). The Kaiatan age (ca. 39.1 - 36.7 Ma) of this unconformity was inferred using previous work at nearby locations by Srinivasan (1966), Fordyce et al. (1985) and Maxwell (1992). The sedimentary succession at Dons Hole was not very informative in terms of age determination of unconformities representing the age span of missing strata, but petrological and petrophysical data confirmed previous local paleoenvironmental interpretations of the Kaiatan age in the southern Canterbury Basin.

Two Oligocene unconformities were examined at one location - Dyer Farm quarry (fig. 3-2, 3-3, 3-17). The measured section at Dyer Farm quarry exposed a strongly burrowed disconformity, separating lower Whaingaroan Earthquakes Marl (ca. 34.6 - 29.8 Ma) from Duntroonian Kokoamu Greensand (ca. 27.3 - 25.2 Ma) (fig. 3-20, 3-21, 4-1, 4-2). Significant lithological variations and abrupt changes in the fossil record between the underlying Earthquakes Marl (calcareous sandstone) and the overlying Kokoamu Greensand (glauconitic limestone) are identified (fig. 3-17). This disconformity at Dyer Farm quarry (fig. 3-20, 3-21, 4.2) is identified with confidence as the regional Marshall unconformity (compare Chapter 1.6), because previous work by Carter & Landis (1972), Lewis & Belliss (1984), Fulthorpe et al. (1996), and Tinto (2010) present similar abrupt changes in the fossil record of the lower Whaingaroan / Duntroonian strata at other locations in the southern Canterbury Basin, which were identified as the Marshall unconformity. The upper Whaingaroan (ca. 29.8 - 27.3 Ma) is not exposed at Dyer Farm quarry, either due to erosion or non - deposition. Therefore, the hiatus represented by the missing strata is of at least 2.5 Ma (fig. 4-2). The local paleoenvironment of the lower Whaingaroan Earthquakes Marl in the southern Canterbury Basin was suggested to be outer shelf or deeper by Maxwell (1992), which is confirmed in the present reconnaissance study by the large amount of siliciclastic grains and the small amount of glauconite and CaCOß, as shown in fig. 3-17 and tab. 5-1 (Banerjee et al. 2014). The local paleoenvironment of the Duntroonian Kokoamu Greensand in the South Canterbury Basin was suggested to be a mid - to inner shelf setting with slow sedimentation rates by Ayress (1993), which is confirmed in the present study by the moderate amount of siliciclastic grains and the large amount of parautochthonous glauconite and CaCOß (fig. 3-17, tab. 5-1).

Higher in the succession of the measured section at Dyer Farm quarry, another unconformity is present in the basal Otekaike Limestone. It is identified as a diastem (fig. 3-17, 3-24, 4-2). This diastem was interpreted as a local storm-wave deposit (tempestite) causing a short interruption in sedimentation due to reworking of sediments by storm waves in a shallow inner shelf setting. The angularity of the fossil fragments and the lack of colonization by sessile organisms indicates a short-time event and a rapid burial (Myrow & Southard 1996). The tempestite was most likely deposited within several hours by either a strong storm or tsunami event. The exact time missing is not distinguishable with foraminiferal biostratigraphy as the dating precision using foraminifera is only to the Stage level of the New Zealand Geological Timescale (fig. 1­2, 1-3). A diastem caused by a tempestite at the base of the Duntroonian to Waitakian Otekaike Limestone indicates a local shallow inner shelf setting as suggested by Field & Browne (1989) and Ayress (2006). According to Smith et al. (1989) and Banerjee et al. (2016), this coincides with the large amount of parautochthonous glauconite and CaCOß. The small scours and cross - beds at the top of the basal Otekaike Limestone at Dyer Farm quarry are evidence for a local high-energy paleoenvironment with erosive oceanic currents (fig. 3-24), as suggested by Ward & Lewis (1975). The sedimentary succession at Dyer Farm quarry was the most informative location in the present reconnaissance study as this is a new recognized location for the regional Mid - Oligocene Marshall unconformity. A hiatus of at least 2.5 Ma was identified with confidence (fig. 4-2).

Oligocene Kokoamu Greensand bed thickness varies from 7.2 m at Dyer Farm quarry to 19.5 m at Waihao River Walkway (“Cabbagetree Gully”) - a lateral distance of ca. 3 km (fig. 4-1). At the latter locality, the Kokoamu Greensand consists of two different facies - a thick, massive and a thick, nodular facies (fig. 3-29, 3-30), whereas at Dyer Farm quarry only a thin, massive facies is present (fig. 3-20). The abundant calcareous nodules and concretions in the nodular facies of the Kokoamu Greensand at Waihao River Walkway (“Cabbagetree Gully”) are secondary replacement bodies due to the precipitation of CaCO3 cement infilling cavities between mineral grains along the dm - sized bedding planes and occurred before the lithification of the sediments during the diagenesis.

The comparatively large, local thickness and facies variations are most likely caused by either change in water depth or sediment supply (Field & Browne 1989). The sedimentary successions at Waihao River Walkway (“Cabbagetree Gully”) and McCullochs Bridge (fig. 3-13, 3-28), ca. 1.5 km apart, are the least informative locations in this study as part of the outcrops are not accessible, but petrological and petrophysical data obtained from the exposed strata at these locations confirmed previous local paleoenvironmental interpretations of the Kaiatan and Waitakian in the southern Canterbury Basin.

Sand and silt content, along with above - background magnetic susceptibility measurements from the Eocene - Oligocene sedimentary strata indicate terrigenous influx (fig. 4-8, tab. 5-2). The angular to subangular siliciclastic grains (quartz + feldspar) in the sand - and silt fraction of the strata are probably derived from local Torlesse metasedimentary rocks of Permian age, whereas quartz granules in some of the Eocene strata can be derived from the Cretaceous to Eocene Taratu Formation (Middlemiss 1999). The polycrystalline texture of both quartz sand - silt and quartz granules in the Eocene - Oligocene strata is indicative for a metamorphic origin. This confirms previous interpretations about quartz provenance by Smith et al. (1989) and Mortimer & Strong (2004). The application of quartz grain provenance and magnetic susceptibility on the Eocene - Oligocene strata was evaluated as least informative as the quality of the results is low and does not add a lot of information to the southern Canterbury Basin geology.

As this thesis investigates only a very small window into the past - ca. 8 km - as shown in fig. 3-1, 3-2, 3-3, and consist of a limited dataset due to small, partly inaccessible outcrops, paleoenvironmental interpretations on a regional scale were limited to discussing previous work (e.g. Ward & Lewis 1975, Field & Browne 1989). Nevertheless, the confident identification of a new location of the regional Mid - Oligocene Marshall unconformity at Dyer Farm quarry, representing a hiatus of at least 2.5 Ma, and the confirmation of local Eocene - Oligocene paleoenvironmental settings in the lower Waihao Valley adds valuable contributions to the wider southern Canterbury Basin geology.

A.1 Modal mineralogical composition and magnetic susceptibility

Table 5-1 Modal mineralogical composition and magnetic susceptibility values of the samples. The modal mineralogical composition accounts only for clasts identified with point counting (no matrix)

Abbildung in dieser Leseprobe nicht enthalten

Appendix B Micropaleontological data

B.1 Micropaleontological data

Table 5-2 Identified foraminifera in the sedimentary Eocene - Oligocene strata of the lower Waihao Valley, southern Canterbury Basin. The red marked species are the age - diagnostic foraminifera (Hornibrook et al. 1989, Pearson 2006)

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