Carbonate Facies of the Shale Unit of the Lalun Formation: New Findings in Tuyeh-Darvar Area (Southwest of Damghan)

The shale unit of the Lalun Formation in Tuyeh-Darvar area (Southwest of Damghan) is unconformably underlain by the sandstone unit and is gradationally overlain by Top Quartzite unit of the Lalun Formation. The shale unit of the Lalun Formation is composed of siliciclastic facies and two carbonate horizons (less than two meters thick) in the lower part of the shale unit. These carbonate horizons include dolomitized microbialite and ooide grainstone facies, which were deposited in a estuary environment of the northwestern passive margin of Gondwana, following late Early Cambrian mass extinction.