Paleozoic tectono-stratigraphic framework of the Arabian Peninsula

Abstract

Thick Paleozoic succession of siliciclastics and carbonates is well exposed and penetrated in the greater Arabian Basin. The succession included source, reservoir, and seal rocks. Though, oil and gas have been discovered in sandstone and limestone reservoirs in these rocks in several oilfields in the basin, the tectonic history of this succession has not been fully understood yet.The Paleozoic succession of the basin is severely affected by series of major climatic and tectonic events which have caused facies change and major stratigraphic breaks. The major tectonic movements have resulted in dividing the Paleozoic succession into mega-depositional cycles. The succession is subdivided into pre- and syn-climatic and tectonic events representing well defined depositional cycles separated by regional unconformities. These mega-depositional cycles are well preserved in basinal or less tectonically affected areas where boundaries between the respective cycles are marked by possible hiatus. In more tectonically active areas, the Paleozoic succession is less preserved and boundaries between the cycles are more complicated due to longer periods of erosion by later movements and/or non-deposition. Minor stratigraphic breaks within the mega cycles subdivide them into smaller sub-cycles.Following the deposition of the Late Caradocian Quwarah member of the Qasim Formation the area went through a gentle uplift and tilt probably related to the Taconic tectonic movements, and a drop of sea level due to glaciation. Thick succession of the Quwarah, Ra'an, Kahfah, and Hanadir members of the Qasim Formation and the Risha and Sajir members of the Saq Formation were eroded and deep paleo-valleys incised in outcrops of the two formations. Glacial and periglacial deposits of the Zarqa and/or Sarah Formations were unconformably rest on older units from Ordovician to Precambrian.The second main event occurred during Late Silurian where the pre-existing successions, mainly on paleo-highs, were affected by tectonic movements synchronous with the Acadian tectonic phase of the Caledonian tectonic movements. The Early Devonian Tawil Formation unconformably rests on eroded Silurian and Late Ordovician deposits of the Sharawra, Qusaiba, and Sarah Formations in the Qusayba Depression in central Arabia.The third main event is a regional tectonic movement contemporaneous with the Hercynian tectonic movement which have reached its maximum phase in the Late Carboniferous. Earlier successions from Carboniferous to Precambrian were affected and the Permo-Carboniferous Shajara Formation unconformably rests on all underlying Paleozoic rock units in central Arabia and other paleo-highs. The Shajara rests on the Devonian Jubah, Jauf and Tawil Formations, the Silurian Sharawra, Qusaiba, and Uqlah Formations, the Ordovician Sarah, Zarqa, and Qasim Formations, the Cambro-Ordovician Saq Formation, and finally rests on Precambrian Basement complex in central Arabia.The Paleozoic outcrops in central Arabia offer an excellent geologic window documents the influence of the three tectonic movements. The Baq'a and Buraydah quadrangles show excellent outcrops of the glacial related deposits and the merge of the sub-Zarqa/Sarah unconformity, sub-Tawil unconformity, and sub-Shajara unconformity. The three unconformities represent the Taconic, Acadian (Caledonian), and Hercynian events, respectively.