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Home , Geology of Saudi Arabia

Sedimentary Cover of the Kingdom (Geo 385) Sedimentary Geology of (Geo 385)

• Sedimentary cover rocks in the Arabian Plate range in age from to . • They reach a thickness of about 8000 m. Sedimentary Cover of the Kingdom (Geo 385) Student Learning Objectives: ▪ Develop an understanding of : • Sedimentary basins of Saudi Arabia • stratigraphic units - successions of the Arabian shelf - Mesozoic successions of the Arabian shelf - successions of the Arabian shelf • Sedimentary cycles • Intra-basin stratigraphic correlations • Biostratigraphy • Major Structural trends • Economic geology of the cover rocks Geologic Time Scale Note that the major subdivisions such as eons represent major developments in the Earth’s history. The three eras (Paleozoic, Mesozoic and Cenozoic) are all contained within Phanerozoic eon (largely defined by fossil preservation in the life record). Periods are defined by major evolutionary changes, such as the evolution of early fish in the period (505-435 Ma ago) of the Paleozoic era (545- 245 Ma). Why do you think that the more recent portion of the geologic time scale has greater detail (defined by epochs)? Age numbers based on absolute age dates Textbook and further reading 2019

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2015 Geology of Arabian plate Geology of Arabian plate

• Arabian plate is one of the youngest of the 10 or more plates that make up the present-day surface of the Earth. • Arabian plate is a small plate surrounded by African plate to the west, Eurasian plate to the north and east and Indian plate to the south. Boundaries of Arabian plate

• Convergent boundary (Collision) between Arabian plate and the Eurasian Plate. • Divergent boundary between Arabian plate and African plate along the Red Sea and Gulf of Aden. • Transform boundary along Gulf of Aqaba-Dead Sea and Owen fracture zone. Boundaries of Arabian plate Red Sea divergence and Dead Sea Transform Geology of Arabian plate

• The Arabian Platform (Shelf), which occupies 2/3 of the Arabian Plate; the other 1/3 is Arabian platform occupied by the Arabian Shield

Arabian Shield Sedimentary Cover of the Kingdom (Geo 385)

• Sedimentary cover rocks in the Arabian Plate range in age from Cambrian to Quaternary. • They reach a thickness of about 8000 m. Sedimentary Cover of the Kingdom

The Phanerozoic sedimentary sequence of Saudi Arabia consists of more than 8,000 m of sandstone and carbonate rock units with subordinate shale and anhydrite ranging in age from Cambrian (Tang et al., 2016) to Recent (Powers et al. 1966). Arabian Shield • The oldest portions of the Arabian plate formed in the middle to late (800-650 Ma) when a series of island arcs and micro-continental fragments accreted against the northeastern margin of the Pan African craton to form the Gondwana super-continent. • The Late development of the Arabian Plate played an important role in the subsequent tectonics that inherited their tectonic weaknesses. • Eight terranes (crustal blocks) are recognized: the Midyan, Hijaz, Ha'il, Afif, Ar Rayn, Ad Dawadimi, Jiddah, and Asir terranes. • Collision of the initial blocks occurred around 690 Ma. The resulting suture zones are marked by intense deformation and by ultrabasic rocks interpreted as ophiolites. Complex terrane fabric of the Arabian Shield and Eastern Arabia (by Al Husseni 2000) Sedimentary Geology of Saudi Arabia

Geologic traverse (A-‐B) shows the sedimentary Successions of the Arabian Shelf through Saudi Arabia to Qatar (Konert, 2001) Sediment thickness of the Arabian Plate, estimated from compiled drill hole, gravity, and seismic reflection data (Al-Amri et al., 2017) Sedimentary Geology of Saudi Arabia

(Konert et al., 2001)

Depth of basement in the Arabian Plate Sedimentary Cover of the Kingdom • The outcrops of the Phanerozoic rock units make curved belts flanking the eastern margin of the Arabian Shield and thicken toward the Arabian Gulf.

In the subsurface, all Phanerozoic formations generally dip at 1°–3° towards the northeast, east and southeast following the Arabian Shield basement rocks’ Generalized geology of the (USGS, 1963) configuration. Sedimentary Cover of the Kingdom Sedimentary Cover of the Kingdom

• The lithological characteristics of the Phanerozoic sequence are relatively consistent throughout central and eastern Saudi Arabia. • The Paleozoic formations generally consist of siliciclastic units. • The Mesozoic and Cenozoic formations consist mainly of carbonate and anhydrite, with minor shale and sandstone units in the Middle . Sedimentary Cover of the Kingdom Unconformities

• The sedimentary sequence of Saudi Arabia constitutes several regional unconformities of which the most significant and aerially extensive are the Pre-Unayzah, pre-Marrat, pre-Aruma, and pre-Neogene unconformities. • Except for the pre-Marrat unconformity, which was caused by the global marine regression of the Early Jurassic (Haq and Al-Qahtani 2005), all these major unconformities are a result of uplift and erosion during tectonic events. • This uplifting had caused differential erosion of the underlying rock units with the maximum erosion over major anticlines such as the Ghawar Anticline. Sedimentary Cover of the Kingdom Unconformities

• The unconformities play important roles in the development of the hydrocarbon and aquifer systems of eastern Saudi Arabia. • For example, they form hydrocarbon traps flanks of anticlines such the Jauf gas play on the flanks of the Ghawar anticline (Wender et al. 1998). • They also cause cross-formational flow of groundwater in aquifers (BRGM 1977). Sedimentary Cover of the Kingdom Major Structural trends Geology of Arabian plate

English, J.M.; Lunn, G.A.; Ferreira, L.; Yacu, G. Geologic evolution of the Iraqi Zagros, and its influence on the distribution of hydrocarbons in the Kurdistan region. AAPG Bull. 2015, 99, 231–272. • Geologic data from oil and gas fields and from aquifers provided valuable information on stratigraphic units acting as top seals for hydrocarbon traps and aquifer systems. • These seals are mainly shales in the Paleozoic and Cretaceous siliciclastic sequences, anhydrite within the Mesozoic carbonate sequence, and anhydrite, marl, and shale units in the Cenozoic

sequence. Regional water salinity and groundwater flow in central and eastern Saudi Arabia (modified after MAW 1984) • The hydrocarbon province of central and eastern Saudi Arabia constitutes two major petroleum systems; the Paleozoic and Jurassic petroleum systems (Pollastro 2003). Each system includes regionally extensive source rock facies and multi reservoirs and seals pairs. • A relatively minor hydrocarbon system exists in the lower Jilh Formation (Jenden et al. 2004).

http://www.geoexpro.com/geoscience/whysomuchoil/ • Oil-rich countries in southwest Asia includes Saudi Arabia, Iraq, Syria, Kuwait, Iran, Bahrain, Qatar, United Arab Emirates (UAE), Oman, and Yemen. • These countries together have an area of 5.1 million square kilometers or about 3.4% of Earth’s land surface, but they possess 60% of world’s known oil reserves and 41% of natural gas reserves.

http://www.geoexpro.com/geoscience/whysomuchoil/ http://www.geoexpro.com/geoscience/whysomuchoil/ Sedimentary Cover of the Kingdom

The Hydrostratigraphical units of Paleozoic, Mesozoic and Cenozoic of Saudi Arabia. Geology of Arabian plate