Sequence Stratigraphy of Lower Carboniferous Rocks in Bakhshi Section, East-Central Iran

Abstract

The deposits of Lower Carboniferous rocks in Kalmard Block are characterized by Gachal informal formation, showing various properties in different outcrops. These deposits (in Gachal formation) are composed chiefly of carbonate, evaporite and siliciclastic rocks. This formation commonly hosts 190 m sandstone, limestone, dolomitic limestone and dolomite as well as a small amount of shale and marl in the Bakhshi section. It unconformably underlies Devonian deposits (Rahdar formation) while lateritic soils of lower Permian (Chili formation) are depicted overlying an erosional unconformity above this formation. The mixed carbonate-evaporite-siliciclastic sequence of Gachal formation is made up of three third-order depositional sequences, separated from each other by Type 1 sequence boundary (SB1). Siliciclastic and evaporite deposits include LST system tract, whereas carbonate microfacies involve TST and HST system tracts, separated from each other by MFS. The depositional sequences identified in Gachal formation point to the Lower Carboniferous age, conforming to upper Kaskaskia supersequence. The upper erosional boundary between Gachal and Chili formations complies with the global-scale sea level fall.