Juergen Thurow

Global Neoproterozoic petroleum systems: the emerging potential in North Africa

Abstract The Neoproterozoic Eon is relatively poorly known from a petroleum perspective, despite the existence of producing, proven and potential plays in many parts of the world. In tectonic, climatic and petroleum systems terms, the Neoproterozoic to Early Cambrian period can be divided into three distinct phases: a Tonian to Early Cryogenian phase, prior to about 750 Ma, dominated by the formation, stabilization and initial break-up of the supercontinent of Rodinia; a mid Cryogenian to Early Ediacaran phase (c. 750–600 Ma) including the major global-scale ‘Sturtian’ and ‘Marinoan’ glaciations and a mid Ediacaran to Early Cambrian (c. post 600 Ma) phase corresponding with the formation and stabilization of the Gondwana Supercontinent. There is increasing evidence that deposition of many mid to late Neoproterozoic (to Early Palaeozoic) organic-rich units was triggered by strong post-glacial sea level rise on a global scale, following the ‘Snowball Earth’ type glaciations, coupled with basin development and rifting on a more local scale. Fieldwork in North Africa including the Taoudenni Basin in Mauritania, Algeria and Mali; the Anti-Atlas region of Morocco and the Cyrenaica, Kufra and Murzuk basins in Libya has added to the understanding of reservoir, source and seal relationships and confirmed the widespread presence of Precambrian stromatolitic carbonate units of potential reservoir facies. Current research on the chronostratigraphy, distribution and quality of source rocks, controls on reservoir quality and distribution of seals in the Precambrian–Early Cambrian hydrocarbon plays throughout South America, North Africa, the Middle East and the Indian Subcontinent is documented in this Special Publication.

Geology and hydrocarbon potential of Neoproterozoic–Cambrian Basins in Asia: an introduction

In 2005, the Maghreb Petroleum Research Group (MPRG), University College London, initiated a major research programme focused on the relatively poorly understood Neoproterozoic petroleum systems of the world. A series of research projects were undertaken to understand the generation and entrapment of hydrocarbons in this unique geological time interval, which is dominated by several episodes of global glaciations and post-glacial transgressions, coupled with basin development and rifting on a more local scale (Craig et al. 2009). The research started with a field-based study of the Neoproterozoic sequences in North Africa (Libya, Morocco and Mauritania) and northern India (Rajasthan and Jammu & Kashmir). A series of international conferences, with field excursions/workshops, were run in parallel with the research programmes. The first of these was held at the Geological Society of London in November 2006 and the proceedings were published in 2009 in Geological Society London, Special Publication 326, entitled, ‘Global Neoproterozoic Petroleum Systems: the emerging potential in North Africa’ (Craig et al. 2009). The second international conference was held at the University of Jammu in 2008 with a focus on the Neoproterozoic petroleum systems of Asia, including India, Pakistan, Oman, China and Siberia (Bhat et al. 2008) (Fig. 1). This current volume contains some of the papers presented at the Jammu conference, in addition to new research on the geology and hydrocarbon potential of the Neoproterozoic–Cambrian basins of Asia. A third and concluding conference and an associated third Geological Society Special Publication will focus on the Neoproterozoic petroleum systems in regions of the world not covered in the previous volumes (mainly North and South America, western and southern Africa and Australia) and will complete the project to provide a global synthesis of the Neoproterozoic petroleum systems. The present volume contains fifteen papers covering the Neoproterozoic petroleum systems of India (Ojha, Ram, Kumar and Majid et al.), Pakistan and (Jamil & Sheikh and Siddiqui), Oman (Cozzi et al.), China (Turner) and Siberia (Howard et al.). The remaining five papers concentrate on various aspects of Neoproterozoic geology and palaeobiology, including stratigraphy (Tewari) and tectonics (Mishra & Mukhopadhyay) of the NW Himalaya, salt tectonics in Oman (Smith), acritarchs in Oman (Butterfield & Grotzinger) and the palaeobiology of the Vindhyan succession in central India (Sharma & Shukla). This Introduction provides a synthesis of the key conclusions in a palaeogeographic context, but for details the reader is referred to the relevant articles in this volume.

Geology and Hydrocarbon Potential of Neoproterozoic-Cambrian Basins in Asia

This volume provides a comprehensive overview of the geology and hydrocarbon potential of the major Neoproterozoic–Cambrian basins of Asia from Oman, across the Middle East and the Indian Subcontinent, to China and SE Siberia, along with new research on the region. Many of these areas (e.g., Oman, Bikaner–Nagaur Basin in India, South China and SE Siberia) host prolific Neoproterozoic–Cambrian petroleum systems with giant to supergiant fields. Three key elements: (1) tectonic stability, (2) relatively late phase of hydrocarbon generation and (3) presence of an effective evaporite seal, seem to be critical for the development of effective Neoproterozoic–Cambrian petroleum systems. These key elements appear of less consequence for the development of ‘unconventional’ hydrocarbons, and the future prospectivity in many of these basins may lie in the exploration for, and production of, shale gas and shale oil directly from the thermally mature, organic-rich source rocks. This volume follows on from the successful Geological Society SP326 on African basins and documents hydrocarbon exploration potential of basins in Asia that until now were poorly understood and documented.

Acquiring High to Ultra-High Resolution Geological Records of Past Climate Change by Scientific Drilling

Scientific drilling on land and sea has played a key role in advancing our knowledge of climate change. It has helped to demonstrate the effects of orbital variations on climate, revealed evidence for extreme warm events in the past and for the timing of Antarctic ice growth, and provided insights into the hydrologic balance of lake systems around the world. Now, with attention increasingly focused on the likely manifestation of future climate change, the challenge to understand past climates at societally relevant, high-resolution timescales has become ever more critical.

Hydrocarbon source potential of the Proterozoic Sirban Limestone Formation, NW Himalaya, Jammu

The Proterozoic Sirban Limestone Formation (SLFm) crops out as detached allochthons in the northwest Himalaya (Jammu region, India) and has its coeval equivalents laterally disposed in the west in Salt Range, in the northwest in Abbotabad (Pakistan) and in southeast in Himachal Pradesh (India). The oil and gas occurrences have been reported from the Proterozoic successions globally and the hydrocarbon potential of the SLFm cannot be ruled out.The interbedded shales and algal laminated dolostones within the SLFm have yielded microflora comparable to those reported in the North African Neoproterozoic sandstones and the Late Proterozoic carbonates of the giant oil and gas fields of the Siberian Platform. The SLFm contains a rich and diverse biota comprising ~ 10% of the rock volume in thin section. The rich organic assemblage justified a hydrocarbon source potential analysis of the SLFm, tested in this study by Rock Eval (RE) pyrolysis.RE pyrolysis yielded a total organic carbon (TOC) content of 0.02 to 1 wt. % with very low Hydrogen Index (HI) values for the shales and TOC content averaging 0.02 wt. % for the dolostones. The organically lean shales and dolostones exhibit Tmax values indicative of immature to post mature stage. But, since these values are for the samples with complex thermal and tectonic history the results may be unreliable. The highly altered organic matter and kerogen present in the SLFm had the potential to generate hydrocarbons and presently indicates no significant source potential. This study is important for understanding the hydrocarbon occurrences in the SLFm particularly in light of the recent oil and gas discoveries from the coeval Proterozoic successions.