Response of a Passive Continental Margin Carbonate Slope to Closing of a Mesozoic Ocean Basin--Mayhah Formation and Qumayrah Facies of Muti Formation, Oman: ABSTRACT

Abstract

The Jurassic to Cretaceous Mayhah Formation formed along the passive continental margin slope between the extensive shallow-marine Arabian carbonate platform and the deep-oceanic Hawasina basin (South Tethys Sea). Near Wadi Qumayrah, it is overlain by preorogenic and synorogenic sediments of the Cretaceous Qumayrah facies of the Muti Formation. These strata record the response of the platform margin to Late Cretaceous basin closing. Redeposited Jurassic oolitic calcarenite, megabreccia, and other calcirudite formed an apron along an east-facing platform margin. Redeposited limestone and slump deposits become uncommon upsection, suggesting basinal sedimentation; perhaps this basin developed ramp-like margins along which mass movements were unlikely. A well-documented Tithonian to Early Cretaceous drowning of the platform led to the deposition of bedded chert in this marginal basin. The chert is primarily silicified limestone, indicating a shallower depositional setting (above the CCD) than for equivalent red radiolarian chert at the type locality, Jebel Sumeini. Basinal carbonate sedimentation became reestablished in the post-Valaginian. In the uppermost Mayhah Formation, slump deposits and intraformational breccias indicate steepening of the slope, perhaps due to tectonic downbowing associated with basin closing. Cenomanian to Coniacian chert and siliceous mudstone of the Qumayrah facies formed below the CCD. This could signify tectonically inducedmore » deepening of the ocean basin, upwelling in a relatively narrow ocean basin, and/or shallowing of the CCD. Calcirudite and calciturbidite in the unit were derived from an uplifted shelf edge and local coeval rudist banks. A thick, lenticular synorogenic megabreccia may have been derived from adjacent eroded anticlines.« less