Sedimentary aspects of the Eo-Alpine cycle on the northeast edge of the Arabian Platform (Oman Mountains)

Abstract

Abstract The northeast edge of the Arabian Platform in the Oman Mountains is represented by the autochthonous unit that crops out in the two windows of Jabal Akhdar and Saih Hatat, beneath and in front of the Hawasina and Samail nappes. The Eo-Alpine orogenic cycle began in the Late Permian with extension on the margin of Gondwana and ended in the Campanian with the formation of a subduction-obduction-type mountain range, the Oman Mountains of the Late Cretaceous. During this cycle, long periods of stable shelf sedimentation were interrupted by tensional tectonic episodes, often accompanied by volcanism and subsidence of the platform, passing into the bathyal domain. Deposition during the Permian to Campanian occurred during five main sedimentary cycles. In the Late Permian (Murghabian), a widespread marine transgression covered the edge of Gondwana in a tensional setting. The ‘Fusulinid Sea’ transgression was followed by the deposition, lasting until the Triassic, of a thick regressive sequence, the Akhdar Group, which was terminated by emergence and weathering in a continental environment. The next sedimentary cycle, represented by the Sahtan Group, began in the Pliensbachian, when the Oman Mountains area formed an inner carbonate shelf, and ended in the early Tithonian. The entire margin of the platform was profoundly affected, in the late Tithonian, by extension, listric faulting and foundering into the bathyal domain, with deposition of the Kahmah Group (Maiolica-type deposits: calpionellid-bearing micrite), and rapid retreat of the continental slope by about 250 km. Renewed carbonate shelf deposition then prograded SSW-NNE across the foundered part, though this was still incomplete when the latest Aptian-Albian transgression took place. At the Cenomanian-Turonian boundary, the shelf underwent profound reorganization with the development of the Muti (intrashelf) Basin, in which the Aruma Group was deposited, and the Masqat-Musandam High which provided the detritus filling the Muti Basin on the continentward side and the Hawasina Basin on the oceanic side. Fragments from the advancing nappe were redeposited in the Muti Basin only from the Campanian on, and it was only during this period that a flysch trough became superimposed on part of the Muti Basin. The closure of the Muti Basin was affected with the emplacement of the nappes on the platform and the subsequent deposition of cover formations over both nappes and the autochthon from the late Maastrichtian onward.