Differentiate allogenic and autogenic controls on the formation of parasequences and depositional sequences of a tide‐ and wave‐dominated carbonate platform (Lower Cretaceous, Kopet‐Dagh Basin, Iran)

Abstract

The carbonate‐dominated successions of the Tirgan Formation (Latest Barremian‐Early Aptian) in the Kopet‐Dagh Basin (Iran) were studied to decipher the tectonic and eustatic sea‐level effects, as well as the autogenic influence on lateral and vertical facies changes, depositional environment, and sequence stratigraphy of the tide‐wave‐dominated sediments at the northern margin of the Neo‐Tethys Ocean. Fourteen facies were identified in the studied sequences, here grouped into five facies associations according to the depositional setting: tidal flat (A), lagoon (B), shoal (C), shallow open‐marine (D), and deep‐open marine (E). A third‐order depositional sequence, including a transgressive system tract (TST) and a highstand system tract (HST) was also identified, along with several medium‐ and small‐scale, thickening‐ and shallowing‐upward cycles (parasequences). The development of the depositional sequence and parasequences of the studied successions of the Tirgan Formation were controlled by interactions between allogenic (tectonic and eustasy) and autogenic factors (wave and tidal hydrodynamic regimes). The allogenic factors mainly affected the stacking pattern and parasequence development of the TST deposits in the lower part of the Tirgan Formation, characterized mainly by the deep‐open marine association. Autogenic factors display a main influence on the stacking pattern and formation of the HST deposits and related parasequences, characterized by shallow open‐marine‐lagoon–shoal associations developed in the upper part of the Tirgan Formation. The tectono‐sedimentary model for the evolution of the tide‐wave‐dominated carbonate platform represented by the Tirgan Formation may be useful for further studies on sedimentary basin evolution or palaeogeographic reconstructions of the Neo‐Tethys margin.