Depositional systems and sequence stratigraphy analysis of the Upper Callovian to Tithonian sediments in the Central and Western Kopet‐Dagh Basin, Northeast Iran

Abstract

Upper Callovian to Tithonian (late Jurassic) sediments represent an important hydrocarbon reservoir in the Kopet‐Dagh Basin, NE Iran. These deposits consist mainly of limestone, dolostone, and calcareous mudstone with subordinate siliciclastic interbeds. Detailed field surveys, lithofacies and facies analyses at three outcrop sections were used to investigate the depositional environments and sequence stratigraphy of the Middle to Upper Jurassic interval in the central and western areas of the basin. Vertical and lateral facies changes, sedimentary fabrics and structures, and geometry of carbonate bodies resulted in recognition of various carbonate facies related to tidal flats, back‐barrier lagoon, shelf‐margin/shelf‐margin reef, slope and deep‐marine facies belts. These facies were accompanied by interbedded beach and deep marine siliciclastic petrofacies. Field surveys, facies analysis, parasequences stacking patterns, discontinuity surfaces, and geometries coupled with relative depth variation, led to the recognition of six third‐order depositional sequences. The depositional history of the study areas can be divided into two main phases. These indicate platform evolution from a rimmed‐shelf to a carbonate ramp during the late Callovian–Oxfordian and Kimmeridgian–Tithonian intervals, respectively. Significant lateral and vertical facies and thickness changes, and results obtained from regional correlation of the depositional sequences, can be attributed to the combined effect of antecedent topography and differential subsidence related to local tectonics. Moreover, sea‐level changes must be regarded as a major factor during the late Callovian–Tithonian interval. Copyright © 2015 John Wiley & Sons, Ltd.