The Persian Gulf Basin: Geological history, sedimentary formations, and petroleum potential
ABSTRACT The Persian Gulf Basin is the richest region of the World in terms of hydrocarbon resources. According to different estimates,
the basin contains 55–68% of recoverable oil reserves and more than 40% of gas reserves. The basin is located at the junction
of the Arabian Shield and Iranian continental block that belong to two different (Arabian and Eurasian) lithospheric plates.
Collision of these plates at the Mesozoic/Cenozoic boundary produced the Zagros Fold Belt and the large Mesopotamian Foredeep,
which is a member of the Persian Gulf Basin. During the most part of the Phanerozoic, this basin belonged to an ancient passive
margin of Gondwana, which was opened toward the Paleotethys Ocean in the Paleozoic and toward the Neotethys in the Mesozoic.
Stable subsidence and the unique landscape-climatic conditions favored the accumulation of a very thick sedimentary lens of
carbonate rocks and evaporites (up to 12–13 km and more). Carbonate rocks with excellent reservoir properties are widespread,
while the evaporites play the role of regional fluid seals. Organicrich rocks, which can generate liquid and gaseous hydrocarbons
(HC), are present at different levels in the rock sequence.
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ABSTRACT: Lowermost Silurian organic-rich (`hot') shales are the origin of 80–90% of Palaeozoic sourced hydrocarbons in North Africa and also played a major role in petroleum generation on the Arabian Peninsula. In most cases, the shales were deposited directly above upper Ordovician (peri-) glacial sandstones during the initial early Silurian transgression that was a result of the melting of the late Ordovician icecap. Deposition of the main organic-rich shale unit in the North African/Arabian region was restricted to the earliest Silurian Rhuddanian stage (acuminatus, atavus and probably early cyphus graptolite biozones). During this short period (1–2 m.y.), a favourable combination of factors existed which led to the development of exceptionally strong oxygen-deficiency in the area. In most countries of the study area, the post-Rhuddanian Silurian shales are organically lean and have not contributed to petroleum generation. The distribution and thickness of the basal Silurian `hot' shales have been mapped in detail for the whole North African region, using logs from some 300 exploration wells in Libya, Tunisia, Algeria and Morocco. In addition, all relevant, accessible published and unpublished surface and subsurface data of the lower Silurian shales in North Africa and Arabia have been reviewed, including sedimentological, biostratigraphic and organic geochemical data. The lowermost Silurian hot shales of northern Gondwana are laterally discontinuous and their distribution and thickness were controlled by the early Silurian palaeorelief which was shaped mainly by glacial processes of the late Ordovician ice age and by Pan-African and Infracambrian compressional and extensional tectonism. The thickest and areally most extensive basal Silurian organic-rich shales in North Africa occur in Algeria, Tunisia and western Libya, while on the Arabian Peninsula they are most prolific in Saudi Arabia, Oman, Jordan and Iraq. The hot shales were not deposited in Egypt, which was a large palaeohigh at that time. The depositional model presented may help in better understanding the source potential of the basal Silurian shales in less-explored regions of North Africa and Arabia including Morocco, northern Niger and the Kufra Basin in southeast Libya.Earth-science Reviews - EARTH-SCI REV. 01/2000; 49(1):121-200.
Article: Tethyan margins in space and time[show abstract] [hide abstract]
ABSTRACT: Rifting processes, leading to sea-floor spreading, are characterized by a sequence of events: transtensive phase of extension with syn-rift volcanism; simple shear extension accompanied by lithospheric thinning and asthenospheric up-welling and thermal uplift of the rift shoulder and asymmetric volcanism. The simple shear model of extension leads to an asymmetric model of passive margin: a lower plate tilted block margin and an upper plate flexural, ramp-like margin. Both will be affected by thermal contraction and subsidence, starting soon after sea-floor spreading.Based on these actualistic models Tethyan margins are classified as one type or the other. Their evolution from the first transtensional phase of extension to the passive margin stage are analyzed. Four main rifting events are recognized in the Tethyan realm: an episode of lower Paleozoic events leading to the formation of the Paleotethys; a Late Paleozoic event leading to the opening of the Permotethys and East Mediterranean basin; an early Mesozoic event leading to the opening of the Pindos Neotethys and a Jurassic event related to the opening of the Alpine/Atlantic Neotethys.Type margins are given as example of each rifting event: Northern Iran (Alborz) as a type area for the Late Ordovician to Silurian rifting of Paleotethys.Northern India and Oman for the Late Carboniferous to early Permian rifting of Permotethys.The East Mediterranean (Levant, Tunisia) as a Late Carboniferous rifting event.The Neotethyan rifting phases are separated in two types: an eastern Pindos system found in Turkey and Greece is genetically linked to the Permotethys with a sea-floor spreading delayed until middle Triassic; a western Alpine system directly linked to the opening of the central Atlantic is characterized by a Late triassic transtensive phase, an early to Middle Liassic break-away phase and, following sea-floor spreading, a thermal subsidence phase starting in Dogger.Problems related to the closure of the Paleozoic oceanic domains are reviewed. A Late Permian, early Triassic phase of “docking” between an European accretionary prism (Chios) and a Paleotethyan margin is supported by recent findings in the Mediterranean area. Back-arc rifting within the European active margin led to the formation of marginal seas during Permian and triassic times and will contribute to the closure of the Paleozoic oceans.Palaeogeography, Palaeoclimatology, Palaeoecology. 01/1991;
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ABSTRACT: Triassic strata of the northern part of the Arabian plate mark the establishment of the Neo-Tethys passive margin. This ocean first opened in the western part of the Mediterranean region directly after the Hercynian orogeny. The strata were deposited on a shallow carbonate platform surrounded by clastic-evaporitic lagoons and continental fluvial and eolian settings. The rocks are divided be- tween continental clastics (such as the Budra and the Ga'ara for- mations), continental-marine clastics and evaporites (such as the Mohilla, Abu Ruweis, Beduh, and Baluti formations) and epiconti- nental marine facies (such as the Saharonim, Salit, and Kurra Chine formations). These settings are comparable to those of the German Triassic and have matching lithofacies and eustatic sea level changes. The succession has been divided into four ''high-frequency'' sequences dominated by highstand systems tract carbonates and highstand sys- tems tract-lowstand systems tract evaporites and clastics: the Mu- lussa Formation, the Kurra Chine dolomite and oolitic limestones, the clastics in the Euphrates -Anah graben in Syria and Iraq, and the Triassic buildups in the northern parts of the Levant form at- tractive hydrocarbon reservoirs when they are overlain by the Triassic- Jurassic evaporite sequence and are in communication with Silurian source rocks. In Syria, the Kurrachine Formation contains both source and reservoir rocks. On the Aleppo plateau, this formation is believed to lie at the beginning of the thermal maturation window, whereas in the areas of Jebbissa, Soukhne, and Souedie, it is in the mature or overmature windows. The Triassic strata produced fair amounts of light oil, gas, and condensates from some fields in Syria and Iraq with a high potential of gas and condensate accumulations in the Levant region.Aapg Bulletin - AAPG BULL. 01/2004; 88(4):515-538.