Abstract 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.

Abstract 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

Abstract The Indian Proterozoic Super Basins were part of the Northern Rim of Gondwanaland prior to its break-up along six major radial fractures. The Proterozoic rocks of these basins are extensively exposed in the northern as well as the southern parts of the Indian Peninsula. Based on recently conducted geochemical and seismic surveys within these basins, followed by well drilling in the Son Valley, Ganga Valley, and the Bikaner–Nagaur basin, it is concluded that hydrocarbons have been generated within these basins and conditions conducive to hydrocarbon accumulation exist within them. The discovery of gas within Son Valley has indicated the existence of an active Mesoproterozoic petroleum system that is likely to have continued up to Infracambrian times. Based on the correlation of Indian Proterozoic Super Basins with their analogous Chinese and Australian basins, it appears that elements of a similar petroleum system exist within these basins, together with the possibility of an active Ordovician–Silurian petroleum system within the northernmost Ganga Valley Vindhyans, where sedimentation continued up to the lower Devonian. Modelling and empirical data show that the Chambal Valley, as well as the probably trap-concealed Vindhyans, underwent intense wrenching during Neoproterozoic times, accompanied by good entrapment conditions. Even the peninsular SW Cuddapah Superbasin also appears worth exploring as an element of the Meso–Neoproterozoic petroleum system.

Abstract The burgeoning oil and gas consumption in India in recent years has necessitated looking into the Proterozoic basins of India, which are sparsely explored and have a scanty knowledge base. The rationale for hydrocarbon exploration in Indian Proterozoic basins is derived from the fact that they have large basinal areas, wide geographical distribution, varied geotectonic setting and sedimentary fill. The favourable tectonic settings of these basins, pronounced biological activity, known hydrocarbon gas seepages, and subsurface commercially viable oil and gas shows in the Bikaner–Nagaur and Vindhyan basins and analogous basins throughout the world necessitate proactive exploration strategies in these basins. The basins of Bikaner–Nagaur, Vindhyan, Cuddapah and Chhatishgarh include thick Neoproterozoic/basal Lower Palaeozoic (Cambrian) successions, in addition to Palaeoproterozoic and Mesoproterozoic sequences. The Neoproterozic sediments in these basins incorporate thick successions of shale, limestone and sandstone. These successions have rich organic matter of high-quality cyanophycean (stromatolites, acritarchs and filamentous algae) affinity that is proven to be high-quality (type one) source material for hydrocarbon generation and also involved in later structurization. However, the Neoproterozoic sedimentary pack in the Bhima–Kaladgi basins is comparatively less thick, and appears to have less prospectivity. The available geological and source-rock data are reassessed for their hydrocarbon prospectivity in order to help in planning a strategy for exploration in these basins.

Abstract In the central and western part of India, the Neoproterozoic deposits are identified in the Vindhyan and Marwar Basins. The Vindhyan Basin consists of two sub-basins; one in the eastern part and the other in the western part. The basic problem with the Vindhyan Basin is the correlation of the eastern part with the western part, as the two areas show different stratigraphic successions and the outcrops in the eastern part are not traceable in the western part. In this paper, an attempt is made to suggest intrabasinal correlation within the Vindhyan Basin on the basis of stromatolites, carbon isotope data, microbial mats, fossils and lithology. The Marwar Supergroup is developed in the western Rajasthan and unconformably overlies the Malani Igneous Suite, which has previously been dated as 779–681 Ma. On the basis of the available fossil records, the Jodhpur Group has been assigned an Ediacaran age and the Precambrian–Cambrian boundary is suggested within the Bilara Group. As both the Maihar Sandstone of the eastern part of the Vindhyan Basin and the Jodhpur Sandstone of the Marwar Supergroup have been assigned an Ediacaran age, these have been correlated.

Abstract The Upper Bhander Sandstone is dominantly composed of quartzarenites. The basal and top portions are sandstones, with the middle section comprising thinly bedded shales with interlayer silt and sandstone units. The sandstone units are composed of several varieties of quartz, feldspar, micas, rock fragments and heavy minerals. The Upper Bhander Sandstone was deposited in a transgressive phase and later modified by tidal processes and wave- and storm-dominated processes in a tide-influenced Barrier Beach Complex of the shallow marine environment. This study reveals that, during mechanical compaction, a rearrangement of grains took place and point and long contacts were formed. The early silica cementation and shallow burial resulted in high primary porosity. This phase was followed by chemical compaction and the replacement of silica cement by iron cement (Fe-cement) under the deep burial phase of these sandstones. Dissolution of Fe-cement and feldspars resulted in secondary porosity development. Quartz overgrowths are better developed on coarse- to medium-sized grains than on fine-sized grains. These observations suggest a progressive compaction, which initiated at the sediment–water interface and continued till deep burial diagenesis in a rapidly subsiding basin. The existing optical porosity of the Upper Bhander Sandstone is 4% and the minus cement porosity is 18%.

Abstract Over time, Neoproterozoic rocks in Pakistan have intermittently attracted the interest of oil and gas exploration companies. However, despite these rocks having been penetrated by nearly 40 wells and being exposed in various parts of Pakistan, no serious efforts have yet been made to investigate their reservoir potential. Neoproterozoic rocks are exposed along the outer periphery of the Salt Range and Nagar Parker in Pakistan and in Rajasthan (India). Surface and subsurface data suggest a good correlation between outcrops in Rajasthan and wells in the Punjab Platform. However, the Neoproterozoic of the Punjab Platform seems to be somewhat different from that in Potwar, suggesting the existence of a kind of barrier or palaeo-high, separating the two basins. Proterozoic stromatolite found in a number of Himalayan sequences seems to be correlatable with similar facies encountered in other parts of the world, such as in the Abalog-1 and Yarba-1 wells in the Toudeni Basin in Mauritania and Mali, respectively. Glacial Pokhran boulder beds (representing snowball Earth) in the Hazara Basin, and reportedly in Pokran and Lawan across the border in India, also correlate with similar Neoproterozoic facies found in other parts of the world. Neoproterozoic offers a complete petroleum system. Regional data demand that the Neoproterozoic reservoir potential be re-evaluated, and a proper understanding of basinal configuration may play a vital role in future exploration success in this region.

Abstract During the Late Neoproterozoic to Early Mesozoic the Indian Plate was part of Pangaea, the Palaeo supercontinent, with the African Plate to the west, as interpreted by various authors. At the same time, the Indian Plate was juxtaposed with the Central Iranian Plate, which separated it from the Arabian Plate in the vicinity of present-day Oman, c. 800 Ma ago. Between 612 and 200 Ma (Late Neoproterozoic to the end of the Triassic) these plates remained firmly attached. The changing configuration of the plates from 200 Ma to the present are provided in this paper. The Neoproterozoic–Cambrian rocks are recorded along the eastern border of Pakistan with India, extending into the Indian Territory and comprising part of the Neoproterozoic–Cambrian basin (Lower Indus Basin). The southern part of the Lower Indus Basin, from the Thar Platform in the east, deepens westwards towards Karachi (embayment) and the Kachhi Foredeep, where the Neoproterozoic–Cambrian succession is likely to be deep-seated. However, c. 5 km uplift of the Kirthar Fold Belt (KFB) across the Western Boundary Thrust (WBT) and the subsequent erosion have exposed the Middle Jurassic Chiltan Limestone, particularly in the central region of the KFB (Landsat images and domal structures with Jurassic outcrops are described in this paper) The limestone rests over older strata, with a possible presence of that of Neoproterozoic–Cambrian age, which is interpreted to be at drillable depth.

Abstract The vast amount of new lithostratigraphic, chemostratigraphic and geochronologic data from the Huqf Supergroup (Sultanate of Oman) has established it as the Cryogenian (850–635 Ma) and Ediacaran (635–542 Ma) reference section for the Neoproterozoic of the Middle East Region. A direct litho- and chemostratigraphic comparison of the Huqf Supergroup of Oman with the supposed time-equivalent succession of the Marwar Supergroup in western Rajasthan (India) reveals remarkable affinities in facies evolution and chemostratigraphic signature through time. Ara Group equivalent strata are also found in the Salt Range Formation of Pakistan, which shows an almost identical repetition of evaporites and carbonates with six to seven basin refreshening–desiccation cycles, comparing well with the A0–A6 Ara Group stratigraphy of the South Oman Salt Basin. These similarities bring out a consistent picture of a cratonic setting for the Marwar Supergroup of West Rajasthan, changing into a more open marine setting towards Pakistan until Oman, suggesting an assembly of Oman–Pakistan and India ‘terrains’ prior to being accreted to the Arabian shield sometime after 650 Ma. From a petroleum exploration perspective, key success factors when pursuing the Late Neoproterozoic plays in the Salt Basins of India, Pakistan and Oman are source rock maturity, charge preservation and seal integrity.

Abstract Recent contraction in the NW Tarim Basin, China, has exhumed a thick (2–3 km) sequence of Upper Neoproterozoic to Lower Palaeozoic sediments that provide a unique insight into the early evolution of the basin. The sedimentary sequence was examined in outcrop and consists of a lower, 500-m-thick fluvial–lacustrine clastic and volcanic succession, conformably overlain by a 2000-m-thick shallow marine carbonate succession which records a major rifting event that initiated in the Late Neoproterozoic. This rifting event probably corresponds to the break-up of East Gondwana and the separation of the Tarim Block from a conjugate margin equivalent in NW Australia. The generation and infilling of rift basins creates a number of potential hydrocarbon plays, although analysis of individual play elements indicates a relatively high risk, despite the prevalence of hydrocarbons derived from the same rift sequence elsewhere in the basin.

Abstract The Siberian Platform covers an area of c. 4.5 million km 2 in the East Siberia region of Russia, up to 3.5 million km 2 of which is prospective for hydrocarbons. We review the Archaean to Neoproterozoic evolution of the Siberian Platform and the potential oil and gas resources of Riphean, Vendian and Infracambrian sediments. The Riphean was dominated by passive margin sedimentation and was intensely deformed during the Baikalian orogeny. Vendian strata record a clastic transgressive sequence and the eventual re-establishment of carbonate platform sedimentation. The late Vendian–early Cambrian is characterized by carbonate deposition including thick salt horizons, which form a regional seal. Hydrocarbon maturation and migration from Riphean and Vendian source rocks occurred during the late Neoproterozoic and Early Palaeozoic, indicating that hydrocarbon reservoirs on the Siberian Platform may have hosted their reserves over a remarkable period of geological time. Despite many years of hydrocarbon exploration in East Siberia, many regions remain under-explored, and aspects of the proven hydrocarbon systems are poorly understood. There are undoubtedly more major discoveries to be made in the region, and the Infracambrian succession of the southern Siberian Platform therefore represents an irresistible target for further hydrocarbon exploration.

Abstract Two sedimentary lithotectonic zones are traditionally recognized in the northwestern Himalayan frontal fold–thrust belt in the Nahan salient: the Lesser Himalaya Zone (LHZ) and the Sub-Himalaya Zone (SHZ). The LHZ is made up of a sequence of Proterozoic to Early Cambrian rocks and the SHZ is made up of Cenozoic rock sequences, which were deposited subsequent to the India–Asia collision. Serial balanced cross-sections show that the structural geometries become increasingly complex from independent ramp anticlines near the foreland through imbricate fan/duplex to stacked-up horses towards the hinterland. Sequential restoration suggests a structural evolution in which a foreland propagating, in-sequence thrusting event was followed by out-of-sequence thrusting in an approximately break-back style. During the out-of-sequence movement, some of the ramps formed during in-sequence thrusting were repeatedly reactivated, leading to very complex structural geometries, particularly in the LHZ. In such a complexly deformed terrain, a rigorous structural modelling approach, combined with a robust geochemical and geochronological database, should be used to carry out calibrated petroleum system modelling, and thus reduce exploration risk.

Abstract The paper reviews the age, location and extent of the late Neoproterozoic to Early Cambrian evaporite basins in the Middle East, NW India and Pakistan. The stratigraphic section discussed includes the largest inorganic negative δ 13 C excursion known (in the Shuram Formation); six cycles of alternating evaporites and carbonate (Ara Formation) and a unique formation in the middle of the Ara known as the Al Shomou silicilyte, which is a major hydrocarbon source. Tuff/volcanic horizons within the Ara are very well dated, with a precision of <0.15 myr. Extensional faulting was contemporaneous with the deposition of the evaporites, creating basins that at times showed density stratification and anoxia. The Buah Formation, which underlies the Ara, provides an insight into the development of Ediacaran carbonate ramp systems in the absence of bioturbation. A reconstruction of Gondwana brings the Ara and the Hormuz evaporites close to the evaporites of NW India and Pakistan, but leaves a small gap between them, which was probably occupied by a continental sliver, mostly likely part of the Lut block of central Iran. The Ara-Hormuz basins lie on the edge of a major continental collision between India and east Africa that was part of the amalgamation of east Gondwana.

Abstract Extensive subsurface sampling of the Huqf Supergroup in the Sultanate of Oman has yielded microfossil assemblages of Cryogenian, Ediacaran and Early Cambrian age. Microfossils have been recovered from most stratigraphic units in the Huqf, including Marinoan-equivalent horizons of the Ghadir Manqil Formation (Cryogenian Abu Mahara Group), the Masirah Bay, Shuram and Buah formations of the Ediacaran Nafun Group, and the A3 (latest Ediacaran) and A6 (Early Cambrian) cycles of the Ara Group. Despite the extensive recovery of leiosphaerid acritarchs from the Shuram Formation, there is no indication of the large acanthomorphs typical of other early–middle Ediacaran assemblages. This absence suggests a relatively young (post-extinction) depositional age for the Shuram; however, the signal is complicated by local deep-water conditions and the facies-specific distribution of Proterozoic microfossils. A shallower-water sequence of undivided Nafun Group sediments preserves sphaeromorphic acritarchs in association with filamentous microfossils, fragmentary vendotaenids and possible vaucheriacean algae.

Abstract The breakup of Rodinia resulted in the formation of rift basins and passive margins c. 650 Ma. Major palaeoclimatic vents such as Neoproterozoic global glaciation (known as ‘snowball Earth’; Hoffman et al. 1998 ) followed by global warming have been recorded on different continents, including the Indian Lesser Himalaya (Blaini–Krol Cryogenian–Ediacaran Period). The reconstruction of the Rodinia supercontinent ( Powell et al. 1993 ; Li et al. 2003 ) and the palaeoposition of India (including Lesser Himalaya–Southern China shelf facies, Tewari 2010 ) strongly suggest that a connection of the Lesser Himalayan Neoproterozoic sedimentary basins with Rodinia must have existed. Early Earth possibly witnessed its most extreme climatic fluctuations during the mid late Neoproterozoic between 750 and 550 Ma. Palaeoglaciers even reached the equator c. 635 Ma, covering the whole Earth. Evidence from Australia, Africa, Antarctica, South America, South China and the Indian Lesser Himalaya suggest that there may have been three or more palaeoglacial events during this 200 million year interval. The global decline of Meso-Neoproterozoic stromatolites, biotic evolution, diversification, extinctions and the discovery of Ediacaran life following the cold climate are of great significance. Carbon isotopic excursions from all pink cap carbonates from the Lesser Himalaya capping the Blaini glacial diamictites have shown strong negative excursions, whereas the overlying Ediacaran Krol carbonates are characterized by a positive shift in carbon isotope ratios ( Tewari 2010 ). In the Lesser Himalayan Krol belt, extending from the Solan in Himachal to Nainital in Uttarakhand Lesser Himalaya, the Upper Krol Formation (Krol D Member, Auden, 1934 , 1937 ) is a typical Ediacaran (terminal Neoproterozoic) microbial carbonate sedimentation facies. Krol D contains Ediacaran metazoan fossils and abundant microbial structures in the form of columnar, domal and stratified stromatolites. Peloids, oncoids and microphytolites are also microbially formed structures. Carbonate grainstones and packstones are common in Krol D, and the allochemical constituents are intraclasts, ooids, coated grains, peloids, microbial grains and catagraphs. A diagenesis and cathodoluminescence study of the Krol ooids has been done in detail for the first time. The sedimentary structures present in the non-stromatolitic Krol carbonates include bird's eye, cross beddings, symmetrical ripples and shallow channel structures. An intertidal to supratidal carbonate ramp depositional environment with some moderate currents and intermittent periods of exposure has been suggested for the Upper Krol carbonates of the Lesser Himalaya. A moderate to high content of organic matter (kerogen) in the Neoproterozoic microbial fossils indicates the presence of probable hydrocarbon source rocks.

Abstract An abundant well-preserved assemblage of annulated carbonaceous compressions and impressions has been recorded from the intra-cratonic argillaceous sedimentary sequence of the Bhima basin in south India. Impressions and carbonaceous compressions recorded in the Hulkal Formation belong to annulated forms similar to the previously reported Sinosabellidites huainanensis , Protoarenicola baiguashanensis and Pararenicola huaiyuanensis from China. This paper discusses the diversity, systematics, affinity, biostratigraphical potential and global significance of these remains. The previously proposed worm-like body fossil affinity for these organisms, based on similarity with the Chinese assemblage, has been reinterpreted as with pre-Ediacaran epibenthic organisms. Fresh investigations of the Indian assemblage of such specimens reveal their close proximity to the algal affinity. The occurrence of global marker events, such as phosphatization, the presence of complicated annulated carbonaceous remains in the Hulkal Formation and the absence of stromatolites in the carbonate sequences of the Bhima basin, collectively indicate a Neoproterozoic, possibly pre-Sturtian age for the Bhima Group.

Abstract Neoproterozoic successions are major hydrocarbon producers around the world. In North Africa, large basins with significant surface outcrops and thick sedimentary fills are widespread. These basins are now emerging as potential sources of hydrocarbons and are attracting interest from geological researchers in academia and the oil and gas industry. This volume focuses on recent developments in the understanding and correlation of North African basin fills and explores novel approaches to prospecting for source and reservoir rocks. The papers cover aspects of petroleum prospectivity and age-equivalent global petroleum systems, Neoproterozoic tectonics and palaeogeography, sequence stratigraphy, glacial events and global climatic models, faunal and floral evolution and the deposition of source rocks. The broader aim of this volume is to compare major environmental change, the emergence of life, the global carbon cycle and the implications for hydrocarbon exploration of well-studied Neoproterozoic successions worldwide.