Middle Cambrian Marine Transgressive-Regressive Depositional System of the Peri-Gondwana Terranes: An Example from Miqrat Formation of the Haushi-Huqf Region, Oman

Abstract

The Miqrat Formation is the uppermost lithostratigraphic unit of the Mahatta Humaid Group (Haima Supergroup) that crops out in the Huqf region of central Oman. The formation is among the complex, deep tight gas reservoirs in the interior Oman Salt Basin. The formation has been previously interpreted as deposits of interconnected ephemeral playa lakes, aeolian dunes, and wet and dry sabkha environments. Lithologic reevaluation of the rocks in the Huqf region unveils new geologic information that allows reassessment of the spatial and temporal distribution of the depositional facies and the construction of the updated and improved depositional model. The Miqrat Formation can be stratigraphically divided into three informal members. The lowermost member is about 80-m-thick section characterized by coarsening-upward cycles of dark brown to reddish-brown mudstones to sandy siltstones that grade to fine-grained sandstones. The sandstones show parallel to low-angle cross lamination and wave ripples, whereas the mudstone and siltstone interbeds display large-scale desiccation cracks. The middle member contains about 40-m-thick light-brown to buff, fine- to coarse-grained sandstone containing low- to high-angle tabular to trough cross-bedding and wave ripples. Near the uppermost part of this unit, the sandstone contains Thalassinoides trace fossils, which are reported here for the first time, indicating the deposition in the marine system—subtidal environments. The uppermost member of the formation is poorly exposed interval and lithologically appears to be similar to that of the lower member. The sedimentary properties and trace fossils suggest that the formation accumulated in a marginal marine setting characterized by tidally-influenced supratidal to intertidal environments (lower and upper members) and subtidal (middle member) depositional setting. This interpretation may further indicate a possibly 3rd-order sea level change represented by initial low sea level (lower member) through relatively higher sea level (middle member) and lastly back to lower sea level (upper member).