Combined geophysical and tectonostratigraphic models to characterize Jurassic synrift petroleum systems in the Shushan Basin, northern Egypt

Source rock evaluation and nature of hydrocarbons in the Khalda Concession, Shushan Basin, Egypt's Western Desert

Integrated organic petrographic and geochemical analyses were made on organic-rich marine carbonate and mixed clastic-carbonate rocks of Middle–Late Jurassic and Early Cretaceous age from the Shushan Basin, Egypt to evaluate their hydrocarbon potential. Analyses allowed the identification of depositional settings, paleoclimate, and three third order genetic stratigraphic sequences (SQ) with deposits assigned to highstand (HST), lowstand (LST) and transgressive systems tracts (TST). Deposition of the source rocks in the rifting Shushan Basin resulted from the interaction between Neotethyan sea level changes, tectonic, and climate. The good reducing conditions developed during the Neotethyan Middle–Late Jurassic (Bajocian–Kimmeridgian) second order sea level rises and the climatically induced carbonate sedimentation resulted in the deposition of the organic-rich carbonates of the Khatatba Formation (SQ 1, early–middle TST) in inner–middle shelf settings under anoxic–dysoxic conditions. The Late Jurassic (late Kimmeridgian) uplifting resulted in the deposition of the organic-lean mixed clastic–carbonate strata of the Masajid Formation (SQ 1, latest TST) in the same shelfal and reducing conditions, which experienced a notable dilution of organic matter. The late TST deposits of SQ 1 are good to very good oil-producing source rocks, where they show average good to very good generative potential of late mature (late oil-to early wet gas-window) highly oil-prone organic matter. The Early Cretaceous (Valanginian–Albian) uplifting associated with the rifting of the Shushan Basin overprinted the Neotethyan late Valanginian–Hauterivian second order sea level rises, Aptian second order highstand sea level, and Albian second order sea level rise. The coeval climatic shift toward more humid conditions resulted in the clastic-dominated deposition of the organic-lean regressive units of SQ 2 (HST and LST of Alam El Bueib, Alamein, and Dahab formations) and SQ 3 (HST and LST of the lower–upper Kharita Formation) in marginal marine settings under anoxic–dysoxic to oxic conditions. The HST and LST deposits of the SQ 2 and SQ 3 show poor to good organic richness of early–mid mature (early–peak oil-window) oil/gas-prone and gas/oil-prone organic matter, respectively and exhibit average fair oil source rock potential with no gas generation.

Seismic stratigraphic techniques permit identification of Late Triassic, Jurassic, and Early Cretaceous eustatically controlled sequences in strata from the North American Gulf Coast and West Africa. Several distinct sequences are remarkably persistent from the Florida Panhandle around the perimeter of the Gulf Coast into northern Mexico, a distance of over 1,500 miles. Their identification requires the integration of seismic data with lithologic, environmental-facies, biostratigraphic, radiometric, and well log information. A comparison with strata of comparable age in offshore West Africa indicates the same sequences can be recognized there. The sequences in North America and Africa are interpreted to be eustatically controlled because they occupy the same time-stratigraphic positions and display coastal onlap patterns similar to those previously recognized by us elsewhere in the world. Gulf Coast eustatic cycles and the formations occurring within them are: (1) Late Triassic--Eagle Mills Formation; (2) Early Jurassic--known only from southern Mexico and not identified in the study area; (3) Middle Jurassic (Bajocian-Bathonian)--Werner Anhydrite-Louann Salt interval; (4) Late Middle Jurassic (Callovian)--Norphlet Formation; (5) Late Jurassic (Oxfordian-Kimmeridgian)--Smackover-Buckner-Haynesville Formations; (6) Late Jurassic-Early Cretaceous (Tithonian-Berriasian)--most of the Cotton Valley Group; and (7) Early Cretaceous (Valanginian)--a restricted wedge seen only in a basinward position. West African eustatic cycles are (1) Late Triassic; (2) Early Jurassic; (3) Middle Jurassic; (4) Early Late Jurassic (Oxfordian-Kimmeridgian); (5) Late Jurassic-Early Cretaceous (Tithonian-Berriasian); and (6) Early Cretaceous (Valanginian). Further refinement may show additional sequences in Middle Jurassic and Late Jurassic intervals.

Palynofacies analysis and palaeoenvironmental reconstruction of the Upper Cretaceous sequence drilled by the Salam-60 well, Shushan Basin: Implications on the regional depositional environments and hydrocarbon exploration potential of north-western Egypt

An integration of palynomorph and palynofacies data from the Shushan-1X well is used to infer the paleoenvironmental conditions of the Valanginian to Middle Cenomanian (Cretaceous) section of the western Shushan Basin, northern Egypt. The data obtained contribute significantly to the depositional history of the basin. The low diversity of dinoflagellate cyst assemblages, along with the dominance of land-derived spores and pollen, suggest restricted (marginal) marine environments, in contrast to their coeval representatives from the Tethyan Realm. Open marine (inner shelf) environments developed at a few horizons in the Dahab and Bahariya formations, partly contemporary with the global Aptian and Cenomanian eustatic cycles. These environments were relatively more offshore than those described in the eastern and southeastern parts of the basin. The study of total palynological organic matter (TPOM) has contributed largely to these established environmental settings. It has also allowed the recognition of redox (suboxic to anoxic) conditions and the impact of a large magnitude of terrigenous influence.

Hydrocarbon potential of the Albian-early Cenomanian formations (Kharita- Bahariya) in the North Western Desert, Egypt: A review

Shushan Basin is one of the coastal basins in the northern part of the Western Desert of Egypt that is characterized by its high oil and gas potential. Rock-Eval pyrolysis, biomarker properties, and stable carbon isotopes of crude oils and related source rocks revealed two types of extracts, A (Alam El-Bueib and Abu Roash-G) and B (Khatatba Formation), and two families of crude oils, I and II of similar δ13C carbon isotope composition. Fair correlation can be made between type A extracts abd Bahariya crude oils, where the similar biomarker properties among them, as C30 moretane ratio < 10% and [20S/(20S+20R)] C29ααα sterane < 0.5, suggest that these crude oils were generated from terrestrial land plants influenced at a low thermal maturity level. Meanwhile, type B extracts and Alam El-Bueib crude oils are genetically related and bear the same terrestrial source input generated at a higher thermal maturity level than those of Alam El-Bueib and Abu Roash–-G source rocks as evidenced from higher C 30 moretane ratio > 10% and [20S/(20S+20R)] C 29ααα sterane > 0.5. Organic rich rocks with excellent potential to generate mainly oil are present in the Middle Jurassic Khatatba Formation that entered the late mature stage of oil and gas generation window at vitrinite reflectance measurements between 1.0 and 1.3 Ro% during the Late Cretaceous. Meanwhile, a good to fair source of rocks of Alam El-Bueib and Abu Roash-G Member are located within the early to mid-mature stages of the oil generation window between vitrinite reflectance 0.5 to 1.0 Ro%, at time varying from Late Cretaceous to Late Eocene. The similarities in biomarker characteristics of crude oils and source rock extracts, in addition to the geologic occurences, are related to the stratigraphic as well as structural entrapment elements, which play an important role during the hydrocarbon accumulations in Shushan Basin.

ABSTRACTThe Ordos Basin, situated in the western part of the North China Craton, preserves the 150-million-year history of North China Craton disruption. Those sedimentary sources from Late Triassic to early Middle Jurassic are controlled by the southern Qinling orogenic belt and northern Yinshan orogenic belt. The Middle and Late Jurassic deposits are received from south, north, east, and west of the Ordos Basin. The Cretaceous deposits are composed of aeolian deposits, probably derived from the plateau to the east. The Ordos Basin records four stages of volcanism in the Mesozoic–Late Triassic (230–220 Ma), Early Jurassic (176 Ma), Middle Jurassic (161 Ma), and Early Cretaceous (132 Ma). Late Triassic and Early Jurassic tuff develop in the southern part of the Ordos Basin, Middle Jurassic in the northeastern part, while Early Cretaceous volcanic rocks have a banding distribution along the eastern part. Mesozoic tectonic evolution can be divided into five stages according to sedimentary and volcanic records: Late Triassic extension in a N–S direction (230–220 Ma), Late Triassic compression in a N–S direction (220–210 Ma), Late Triassic–Early Jurassic–Middle Jurassic extension in a N–S direction (210–168 Ma), Late Jurassic–Early Cretaceous compression in both N–S and E–W directions (168–136 Ma), and Early Cretaceous extension in a NE–SW direction (136–132 Ma).

The Søgne Basin in the Danish‐Norwegian Central Graben is unique in the North Sea because it has been proven to contain commercial volumes of hydrocarbons derived only from Middle Jurassic coaly source rocks. Exploration here relies on the identification of good quality, mature Middle Jurassic coaly and lacustrine source rocks and Upper Jurassic – lowermost Cretaceous marine source rocks. The present study examines source rock data from almost 900 Middle Jurassic and Upper Jurassic – lowermost Cretaceous samples from 21 wells together with 286 vitrinite reflectance data from 14 wells. The kerogen composition and kinetics for bulk petroleum formation of three Middle Jurassic lacustrine samples were also determined.Differences in kerogen composition between the coaly and marine source rocks result in two principal oil windows: (i) the effective oil window for Middle Jurassic coaly strata, located at ∼3800 m and spanning at least ∼650 m; and (ii) the oil window for Upper Jurassic – lowermost Cretaceous marine mudstones, located at ∼3250 m and spanning ∼650 m. A possible third oil window may relate to Middle Jurassic lacustrine deposits. Middle Jurassic coaly strata are thermally mature in the southern part of the Søgne Basin and probably also in the north, whereas they are largely immature in the central part of the basin. HImax values of the Middle Jurassic coals range from ∼150–280 mg HC/g TOC indicating that they are gas‐prone to gas/oil‐prone. The overall source rock quality of the Middle Jurassic coaly rocks is fair to good, although a relatively large number of the samples are of poor source rock quality.At the present day, Middle Jurassic oil‐prone or gas/oil‐prone rocks occur in the southern part of the basin and possibly in a narrow zone in the northern part. In the remainder of the basin, these deposits are considered to be gas‐prone or are absent. Wells in the northernmost part of the Søgne Basin / southernmost Steinbit Terrace encountered Middle Jurassic organic–rich lacustrine mudstones with sapropelic kerogen, high HI values reaching 770 mg HC/g TOC and Ea‐distributions characterised by a single dominant Ea‐peak. The presence of lacustrine mudstones is also suggested by a limited number of samples with HI values above 300 mg HC/g TOC in the southern part of the basin; in addition, palynofacies demonstrate a progressive increase in the abundance and areal extent of lacustrine and brackish open water conditions during Callovian times. A regional presence of oil‐prone Middle Jurassic lacustrine source rocks in the Søgne Basin, however, remains speculative.Middle Jurassic kitchen areas may be present in an elongated palaeo‐depression in the northern part of the Søgne Basin and in restricted areas in the south.Upper Jurassic – lowermost Cretaceous mudstones are thermally mature in the central, western and northern parts of the basin; they are immature in the eastern part towards the Coffee Soil Fault, and overmature in the southernmost part. Only a minor proportion of the mudstones have HI values &gt;300 mg HC/g TOC, and the present‐day source rock quality is for the best samples fair to good. In the south and probably also in most of the northern part of the Søgne Basin, the mudstones are most likely gas‐prone, whereas they may be gas/oil‐prone in the central part of the basin. A narrow elongated zone in the northern part of the basin may be oil‐prone. The marine mudstones are, however, volumetrically more significant than the Middle Jurassic strata.Possible Upper Jurassic – lowermost Cretaceous kitchen areas are today restricted to the central Søgne Basin and the elongated palaeo‐depression in the north.

Hydrocarbon potential and depositional paleoenvironment of a Middle Jurassic succession in the Falak-21 well, Shushan Basin, Egypt: Integrated palynological, geochemical and organic petrographic approach

The Orientation of Small Muddy Clasts in Turbidites: Paleocurrent Indicators on a Jurassic Carbonate Slope, Tunisia

Upper Triassic to Upper Jurassic strata in the western and northern Sichuan Basin were deposited in a synorogenic foreland basin. Ion–microprobe U–Pb analysis of 364 detrital zircon grains from five Late Triassic to Late Jurassic sandstone samples in the northern Sichuan Basin and several published Middle Triassic to Middle Jurassic samples in the eastern Songpan–Ganzi Complex and western and inner Sichuan Basin provide an initial framework for understanding the Late Triassic to Late Jurassic provenance of western and northern Sichuan Basin. For further understanding, the paleogeographic setting of these areas and neighboring hinterlands was constructed. Combined with analysis of depocenter migration, thermochronology and detrital zircon provenance, the western and northern Sichuan Basin is displayed as a transferred foreland basin from Late Triassic to Late Jurassic. The Upper Triassic Xujiahe depocenter was located at the front of the Longmen Shan belt, and sediments in the western Sichuan Basin shared the same provenances with the Middle–Upper Triassic in the Songpan–Ganzi Complex, whereas the South Qinling fed the northern Sichuan Basin. The synorogenic depocenter transferred to the front of Micang Shan during the early Middle Jurassic and at the front of the Daba Shan during the middle–late Middle Jurassic. Zircons of the Middle Jurassic were sourced from the North Qinling, South Qinling and northern Yangtze Craton. The depocenter returned to the front of the Micang Shan again during the Late Jurassic, and the South Qinling and northern Yangtze Craton was the main provenance. The detrital zircon U–Pb ages imply that the South and North China collision was probably not finished at the Late Jurassic.

The study area is located in the zone of junction of the In’yali-Debin synclinorium and the Omulevka terrane (Kolyma-Omolon microcontinent of the Verkhoyansk-Kolyma fold belt). The main tectonic structure is the Momontai syncline made of Middle Jurassic clastic rocks overlain by Upper Jurassic volcanic and volcaniclastic rocks of the Uyandina-Yasachnaya volcanic arc. The Au and Au-Ag occurrences known here are confined to NE-trending faults and hosted in subvolcanic and volcanogenic rocks, mainly rhyolites and dacites. The studied Middle Jurassic rocks are found to be characteristic of near-shore shelfal environments changing, in certain time intervals, to deltaic conditions of sedimentation. The presence in the conglomerates and sandstones of large poorly rounded quartzite and carbonate fragments and of mudstone and volcanite pebbles indicates a proximal provenance of the clastics. For the first time we established a sharp angular unconformity between the intensely deformed Middle Jurassic and Upper Jurassic rocks in the region. Relations between the Late Jurassic subvolcanic deposits and the host rocks were studied. The carried out structural and tectonophysical investigations showed that folding occurred in two deformation stages. During the first stage, the Middle Jurassic clastic rocks were draped into small recumbent to isoclinal folds, cylindrical and parallel-type, with a NW strike. Cleavage is rare. The structural paragenesis of bedding-plane detachment faults, thrusts, normal faults, and strike slip faults is found to have formed in a single stress field together with the development of folds of the first deformation stage. The intensity of the first-stage folding increases from west to east. Restored are axes of paleostresses responsible for the formation of fold-and-thrust structures of the first deformation stage. The Upper Jurassic volcanogenic-sedimentary strata were deformed into superposed large, simple, open folds of the second stage, which exhibit sublatitudinal orientation. They associate with small-scale thrusts and, rarely, strike-slip faults. It is recognized that in the late Middle Jurassic or the early Late Jurassic the region was affected by intense folding which produced tectonic structures of NW strike. Accumulation of the Late Jurassic volcanogenic rocks and intrusion of subvolcanic deposits occurred on/into the earlier deformed Middle Jurassic rocks.

Taxonomic affinities of the putative titanosaurs from the Late Jurassic Tendaguru Formation of Tanzania: phylogenetic and biogeographic implications for eusauropod dinosaur evolution

Jurassic northward migration of Mexico, which lay on the southern part of the North America plate, resulted in temporal evolution of climate-sensitive depositional environments. Lower–Middle Jurassic rocks in central Mexico contain a record of warm-humid conditions, indicated by coal, plant fossils, and compositionally mature sandstone deposited in continental environments. Paleomagnetic data for central Oaxaca and other regions of central and eastern Mexico indicate that Lower and Middle Jurassic rocks were deposited at near-equatorial paleolatitudes. In the Late Jurassic, the Gulf of Mexico formed as a subsidiary basin of the Atlantic Ocean when the Pangea supercontinent ruptured. Upper Jurassic strata across Mexico, including eolianite and widespread evaporite deposits, indicate dry-arid conditions. Available paleomagnetic data (compaction-corrected) from southern and northeast Mexico for Upper Jurassic strata indicate deposition at ~15°N–20°N. As North America moved northward during Jurassic opening of the Atlantic Ocean, different latitudinal regions experienced coeval Middle–Late Jurassic climatic shifts. Climate transitions have been widely recognized in the Colorado Plateau region. The plateau left the horse latitudes in the late Middle Jurassic to reach temperate humid climates at ~40°N in the latest Jurassic. Affected by the same northward drift, the southern end of the North America plate represented by central Mexico gradually reached the arid horse latitudes in the late Middle Jurassic as the Colorado Plateau was leaving them. As a result, Late Jurassic epeiric platforms developed in the circum–Gulf of Mexico region after a long period of margin extension and were surrounded by arid land masses. We propose that hydrocarbon source-rock deposition was facilitated by arid conditions and wind-induced coastal upwelling.