Silurian and Devonian Source Rocks and Crude Oils from the Western Part of Libya: Organic Geochemistry, Palynology and Carbon Isotope Stratigraphy
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Silurian and Devonian source rocks and crude oils from the western part of Libya: organic geochemistry, palynology and carbon isotope stratigraphy Mohamed M. A. Elkelani Utrecht Studies in Earth Sciences 71 LPP Contributions Series No. 42 Utrecht 2014 Utrecht Studies in Earth Sciences 71 Members of the dissertation committee Prof. dr. Jack J. Middelburg Utrecht University, The Netherlands Prof. dr. Henk Brinkhuis Royal NIOZ & Utrecht University, The Netherlands Prof. dr. Appy Sluijs Utrecht University, The Netherlands Prof. dr. Thomas Wagner University of Newcastle, School of Civil Engineering and Geosciences, United Kindom Dr. Erik W. Tegelaar Shell Global Solutions B.V., Rijswijk, The Netherlands ISSN 2211-4335 LPP Contributions Series No. 42 ISBN 978-90-6266-380-4 Contact: Mohamed M.A. Elkelani [email protected] [email protected] Cartography and figures: Communication & Marketing (8750), Faculty of Geosciences, Utrecht University Printed in the Netherlands by WPS, Zutphen. Copyright © 2014 Mohamed M.A. Elkelani. All rights reserved. No part of this publication may be reproduced in any form, by print or photo print, microfilm or any other means, without written permission by the author. Silurian and Devonian source rocks and crude oils from the western part of Libya: organic geochemistry, palynology and carbon isotope stratigraphy Organische geochemie, palynologie en koostofisotopenstratigrafie van aardoliemoedergesteenten uit het Siluur en Devoon van westelijk Libië en daaruit gevormde aardolie (met een samenvatting in het Nederlands) PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof. dr. G.J. van der Zwaan, ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op woensdag 28 januari 2015 des middags te 12.45 uur door Mohamed M.A. Elkelani geboren op 10 december 1965 te Tripoli, Libië Promotoren: Prof. dr. G. J. Reichart Prof. dr. ir. J. S. Sinninghe Damsté Co-promotor: Dr. ir. K. G. J. Nierop This Research was funded by Shell Exploration & Production Libya GmbH Libyan Petroleum Institute (LPI), Tripoli, Libya National Oil Corporation (NOC), Tripoli, Libya Dedicated to: My father and my mother, my wife and my children: Raihan, Ragad, Anas, and Raneem. This work is dedicated to the soul of my sister “Mawada” who has traveled without saying Good-bye. 6 Contents Chapter 1: General introduction and synopsis 9 Chapter 2: Stable carbon isotope and palynological records from the Silurian 21 “hot” shale in Libya Mohamed M.A. Elkelani, Gert-Jan Reichart, Jaap S. Sinninghe Damsté, Bas van de Schootbrugge, Zwier Smeenk Chapter 3: Carbon isotope chemostratigraphy and palynology of Late Devonian 71 black shales from the eastern Murzuq Basin, Libya Mohamed M.A. Elkelani, Jaap S. Sinninghe Damsté, Philippe Steemans, Gert-Jan Reichart, Zwier Smeenk Chapter 4: Palaeodepositional reconstruction and thermal maturity of the early 109 Silurian Tanezzuft shales in Libya Mohamed M.A. Elkelani, Gert-Jan Reichart, Jaap S. Sinninghe Damsté, Klaas G.J. Nierop Chapter 5: Application of diamondoids in maturity assessment and oil to source 141 rock correlation in the Libyan Ghadamis Basin Mohamed M.A. Elkelani, Gert-Jan Reichart, Klaas G.J. Nierop, Jaap S. Sinninghe Damsté, Erik W. Tegelaar, Rolande Dekker References 165 Summary in English (Samenvatting in het Nederlands) 179 Aknowledgements 187 Curriculum Vitae 189 7 8 General introduction and synopsis 9 1. The Middle Palaeozoic 1 The source rocks for most North African petroleum reservoirs, which together form one of the largest sources of petroleum globally, were deposited during the Middle Palaeozoic era. The Palaeozoic, ranging from 542 to 251 Ma, covers about 290 Myr, which exceeds the combined duration of the Mesozoic and Cenozoic eras. During this long time interval Earth experienced a large range of different environmental, paleogeography and climate conditions. Most of the Palaeozoic, from the Cambrian to the Carboniferous, has commonly been regarded as a global greenhouse period with high atmospheric pCO2 (Pages et al., 2006; Berner, 1994), interrupted by major but relatively short-lived ice ages in the Late Ordovician, in the Late Devonian and in the Early Carboniferous (Loydell et al., 2009). The Middle Palaeozoic, comprising the Silurian and the Devonian, is characterized by a generally warm climate sandwiched between the Ordovician and Late Devonian ice ages. These climatic changes probably profoundly affected sedimentation, hence the geological record spanning this interval, both through changes in sea level and by affecting oceanic circulation. The Palaeozoic is characterized by substantial episodes of black shale (i.e., rocks with a total organic carbon content exceeding 1% by weight) deposition, hence representing a common sediment type for that time interval. In many localities geological sections spanning this time interval consist of intercalated carbonates and shales. These regular changes between carbonate and shales probably reflect shallowing/deepening of the depositional environment due to sea-level fluctuations, related to either local tectonics or global changes. Interest in the organic-rich deposits of the Palaeozoic primarily reflects the economic importance of the hydrocarbons potentially generated from them (Wignall, 1991). Still, these black shales also attracted much attention from scientists due to their association with sea-level change and mass extinctions (Loydell, 2009). Black shales potentially provide important records for reconstructing past changes in climate and ocean circulation. Overall processes involved in black shale formation can typically be considered to be the product of increased biological productivity and/ or enhanced organic matter preservation (Tyson, 1995). However, as climate and paleogeography in the Palaeozoic differed considerably from today, it is necessary to independently determine the processes responsible for the deposition of the Palaeozoic black shales in North Africa. 1.1. The Silurian succession in North Africa During Palaeozoic times, the Saharan platform was part of the northern passive margin of the Gondwana supercontinent. The tectonic setting of this craton was remarkably calm from Cambrian to Devonian times, while deformation progressively increased during Upper Devonian and Carboniferous times, announcing the late Carboniferous Hercynian compression. The glaciations at the end of the Ordovician-Silurian have been studied extensively because of the associated major extinction event, and also because it was characterized by widespread graptolitic black shale deposition (Lüning et al., 2000; Armstrong et al., 2005). The late Ordovician glaciations lasted only a relatively short period (approximately 1.0 Myr), superimposed on an otherwise warm episode of Earth’s climate (Brenchley et 10 al., 1994; Kump et al., 1999). Baltica, and to some extent, Laurentia, occupied tropical and subtropical latitudes, their geological record is at that time dominated by carbonate deposits (Berner and Kothavala, 2001). In contrast, the area that now comprises Libya drifted across the South Pole and was regularly covered by an extensive ice cap (Fig.1). Baltica Rheic Ocean Iapetus Ocean China Laurentia Libya South Pole Gondwana 60˚ 30˚ 8750 Fig. 1. Late Ordovician paleogeographical reconstruction for the Southern hemisphere at the end of the Ordovician with the location of Libya, Ghadamis and Murzuq Basin indicated (modifi ed after Ghienne and Deynoux, 1998; Scotese and Mckerrow, 1991). Th e early Silurian period was a time of global sea-level rise resulting from the melting of the ice cap that, amongst others, covered the massifs of Hoggar and Tibisti and was characterized by extensive deposition of black shales on the North African Gondwanan margin from Rhuddanian to early Wenlock times. In Libya, the Silurian sequence has been divided lithologically into two major units: Tanezzuft and Akakus. Th ese two formations represent the entire Early to Late Silurian succession in western Libya. On the other hand, the basal Tanezzuft is generally interpreted as being the major local source rock for the petroleum found in that area, the upper part of Tanezzuft and the Akakus formation provide potential reservoir rocks. In North Africa and Arabia, the organic rich shale often occurs at or near the base of the Silurian shale unit. Th is black shale has been termed “hot” shale based on its high natural radioactivity (> 150 API) and this term is used extensively in the Palaeozoic of North Africa and Arabia (Lüning et al., 2000). In Libya, the Silurian succession comprises well-laminated mainly light and dark grey shales, which lie above a sharp lithology boundary with the sandstones of the Memouniat Formation. Locally this sandstone is well developed as a separate unit, especially near the top of the sequence. In parts other 11 of areas, such as the Nafusah Uplift and near the Al Qarqaf Arch, the Silurian sequence 1 is missing due to late Hercynian erosion. In the western part of Libya these organic- rich shales form the basal part of the Tanezzuft Formation, which sourced most of the hydrocarbons in the Ghadamis and Murzuq basins discovered there to date. The Ghadamis Basin extends between Libya, Algeria, and Tunisia, with the depo- center close to the triple junction between the countries (Boote et al., 1998). It covers an area of 250,000 km2, with the Al Qarqaf Arch defining the southern edge of this basin and the northeastern margin being the