CENOZOIC TERRESTRIAL PALAEOENVIRONEMTAL CHANGE: AN INVESTIGATION OF THE PETROCKSTOWE AND BOVEY BASINS, SOUTH WEST UNITED KINGDOM by MOHAMMED SULEIMAN CHAANDA A thesis submitted to Plymouth University for the partial fulfilment for the degree of DOCTOR OF PHILOSOPHY School of Geography, Earth and Environmental Sciences Faculty of Science and Technology May 2016 Copyright Statement This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rest with its author and that no quotation from the thesis and no information derived from it may be published without the author’s prior consent. Signed: Date: 25-05-2016 CENOZOIC TERRESTRIAL PALAEOENVIRONMENTAL CHANGE: AN INVESTIGATION OF THE BOVEY AND PETROCKSTOWE BASINS, SOUTH WEST UNITED KINGDOM, Mohammed S. Chaanda The Petrockstowe and Bovey basins are two similar pull apart (strike slip) basins located on the Sticklepath – Lustleigh Fault Zone (SLFZ) in Devon, SW England. The SLFZ is one of the several faults on the Cornubian Peninsula and may be linked to Variscan structures rejuvenated in Palaeogene times. The bulk of the basins’ fill consists of clays, silts, lignites and sands of Palaeogene age, comparable to the Lough Neagh Basin (Northern Ireland), which is also thought to be part of the SLFZ. In this study a multiproxy approach involving sedimentary facies analysis, palynological analysis, stable carbon isotope (δ13C) analysis and organic carbon palaeothermometer analyses were applied in an attempt to understand the depositional environment in both basins. A negative carbon isotope excursion (CIE) with a magnitude of 2‰ was recorded at ~ 580 m in the siltstone, silty clay to clay lithofacies in the 13 lower part of Petrockstowe Basin, with minimum δ CTOC values of -28.6‰. The CIE spans a depth of 7 m. Palynological characteristics of this excursion are correlated with the Cogham Lignite in the southern UK, which is the only established PETM section in the UK, and other continental sections to test whether the palynology associated with this CIE can be used to date it. The age model proposed herein correlates the CIE to the Eocene Thermal Maximum -2 (ETM2; ~ 52.5Ma) event. Key pollen and spore assemblages found in the lower Petrockstowe Basin are Monocolpopollenites, Inaperturopollenites, Laevigatisporites, Bisaccate conifer pollen and Tricolporopollenites, which suggest an Eocene age, while those occurring in the upper part of the Petrockstowe and Bovey basins are Arecipites, Inaperturopollenites, Monocolpopollenites, Tricolporopollenites, Sequoiapollenites, and Pompeckjodaepollenites, which have suggested botanical affinities to modern tropical to sub-tropical genera signifying a climate that was frost-free at the time of sediment deposition. This assemblage further suggests that these sediments are Oligocene to middle Oligocene in age. In the upper part of the Petrockstowe Basin, reconstructed mean annual air temperatures (MAT) demonstrate a clear departure from the mean temperature of 24.5oC at 10 m to 19.5oC towards the top of the core, indicating a steady continuous decline similar to the temperature departures seen in the Solent Group in the Hampshire Basin, Isle of Wight, UK which has an establsihed Eocene – Oligocene succession. i CONTENTS Abstract………………………………………………………………………………………..i Contents………………………………………………………………………………………ii List of Figures………………………………………………………………………………...v List of Plates………………………………………………………………………………….x List of Tables…………………………………………………………………………………x Acknowledgements………………………………………………………………………......xi Author’s Declaration……………………………………………………………………….xiv CHAPTER 1 – INTRODUCTION 1.0 Introduction……………………………………………………………………………...1 1.1 Rational………………………………………………………………………....2 1.2 Palaeocene-Eocene climate…………………………………………………......3 1.2.1 Background to the PETM………………………………………......3 1.2.2 Impact………………………………………………………………5 1.2.3 Possible Mechanisms……………………………………………….7 1.3 Eocene Thermal Maximum 2 (ETM-2)………………………………………..12 1.4 Early Eocene Climatic Optimum (EECO) and Eocene Climatic Optimum (MECO)………………………………………………………………………..15 1.5 Eocene – Oligocene Transition………………………………………………..17 1.5.1 Possible mechanisms……………………………………………...18 1.5.2 Impact……………………………………………………………..19 1.5.3 Temperature versus ice volume change…………………………...20 1.6 Location of the study area……………………………………………………..23 1.6.1 General Location………………………………………………….23 1.6.2 Structural control and sedimentary fill of the Petrockstowe and Bovey basins………………………………………………………24 1.6.3 Geological setting of the Petrockstowe Basin…………………….25 1.6.4 Geological setting of the Bovey Basin……………………………30 1.7 Palynology……………………………………………………………………..33 1.8 Aims…………………………………………………………………………...34 2.0 CHAPTER 2 – METHODOLOGY 2.1 Introduction……………………………………………………………………37 2.2 Petrockstowe Basin Logging…………………………………………………..37 2.2.1 Sampling…………………………………………………………..37 2.3 Bovey Basin – South John Acres Lane (SJAL) Quarry……………………….39 2.3.1 Sampling…………………………………………………………..39 2.4 Total Organic carbon (TOC) Stable Isotope Analyses………………………...41 2.5 Organic Geochemistry…………………………………………………………42 2.5.1 Glycerol Dialkyl Glycerol Tetraether (GDGT) Analysis…………42 2.5.2 Branched and Isoprenoid Tetraether Index (BIT)………………...44 ii 2.5.3 Extraction and analysis……………………………………………45 2.6 Palynological sample preparation……………………………………………...48 2.6.1 Removal of silicates and carbonates………………………………48 2.6.2 Heavy liquid separation…………………………………………...49 2.6.3 Oxidized sample preparation……………………………………...49 2.6.4 Mounting of slide………………………………………………….50 2.7 Palynological Slides…………………………………………………………...50 2.8 Taxonomy of selected form genus...…………………………………………..52 3.0 CHAPTER 3 – FACIES ANALYSIS 3.1 Introduction……………………………………………………………………55 3.2 Facies analysis of Petrockstowe 1A and 1B cores and the Abbrook Clay-and- Sand Member and Southacre Clay-and-Lignite Member, Bovey Formation, John Acres Lane Quarry, Bovey Basin………………………………………..56 3.2.1 Description and interpretation of facies…………………………...65 3.3 Facies associations……………………………………………………………..77 3.3.1 Long-lived lake or Lake centre……………………………………77 3.3.2 Ephemeral lake or Lake margin…………………………………...78 3.3.3 Sand filled fluvial channels……………………………………….80 3.3.4 Flood plains……………………………………………………….80 3.4 Facies Association succession and Sequence stratigraphy of Petrockstowe 1A and 1B cores, Petrockstowe Basin……………………………………………..81 3.5 Facies association succession and Sequence Stratigraphy of the Abbrook Clay- and-Sand Member and Southacre Clay-and Lignite member, Bovey Formation, South John Acres Lane Quarry, Bovey Basin………………………………....83 3.6 Correlation of Petrockstowe core and South John Acres Lane Quarry section, Bovey Basin……………………………………………………………………84 3.7 Palaeogeography of the depositional settings in the Bovey and Petrockstowe basins in the Eocene – early Oligocene………………………………………..88 4.0 CHAPTER 4 – PALYNOFACIES AND PALYNOLOGICAL ANALYSIS 4.1 Introduction……………………………………………………………………95 4.2 Palynofacies analysis Results……………………………………………….....98 4.2.1 Petrockstowe Core (1A and 1B), Petrockstowe Basin…………..101 4.2.2 South John Acre Lane Quarry section, Bovey Basin……………107 4.3 Palynology Results………………………………………………………...…112 4.3.1 Palynomorphs…………………………………………………....113 4.3.2 Palynological analysis…………………………………………...115 4.4 Quantitative analysis of Palynological data……………………………….....134 4.5 Age Model……………………………………………………………………135 4.5.1 Is PETM preserved in the lower Petrockstowe Basin?.................135 4.5.2 Is the Eocene – Oligocene boundary preserved in the Bovey and Petrockstowe basins?.....................................................................138 4.6 Palaeoenvironmental Interpretation………………………………………….141 4.6.1 Petrockstowe Basin………………………………………………141 4.6.2 Bovey Basin………………………………………………….......143 13 4.6.3 δ CTOC versus palynofacies relationship in the Petrockstowe Basin……......................................................................................144 iii 13 4.6.4 δ CTOC versus palynofacies relationship in the Bovey Basin……………..........................................................................145 5.0 CHAPTER 5 – TOTAL ORGANIC CARBON (%TOC) AND STABLE CARBON 13 ISOTOPE (δ CTOC) 5.1 Introduction…………………………………………………………………..147 5.2 Percentage Total Carbon (%TOC)…………………………………………...148 5.2.1 Petrockstowe Basin………………………………………………148 5.2.2 Bovey Basin……………………………………………………...148 13 5.3 Stable Carbon Isotope (δ CTOC) record……………………………………...152 5.3.1 Petrockstowe Basin………………………………………………152 5.3.2 South John Acres Lane Quarry section, Bovey Basin…………...154 5.4 Carbon Isotope Excursion (CIE)……………………………………………..156 5.4.1 Petrockstowe Basin………………………………………………156 5.5 Eocene – Oligocene Boundary……………………………………………….159 5.5.1 Conclusion……………………………………………………….161 6.0 CHAPTER 6 – ORGANIC GEOCHEMISTRY 6.1 Introduction…………………………………………………………………..163 6.1.1 Methylation Branched Tetraether / Cyclization Branched Tetraether Ration (MBT’/CBT)……………………………………………..163 6.1.2 Branched and Isoprenoid Tetraether (BIT) index……………….166 6.2 BIT Index, pH, CBT, and MBT’ Results…………………………………….168 6.2.1 Petrockstowe cores 1A & 1B, Petrockstowe Basin……………..168 6.2.2 South John Acres Lane Quarry section, Bovey Basin…………..172 6.3 Reconstructed Mean Annual Air Temperature (MAAT)……………………179 7.0 CHAPTER 7 – SYNTHESIS 7.1 Age Model for the Petrockstowe and Bovey basins………………………….183 7.2 Long-term palaeoenvironmental changes during the Palaeogene in the Petrockstowe and Bovey basins……………………………………………...188 7.3 The ETM-2 in the Petrockstowe Basin………………………………………189 7.4 The E-O boundary