Implication of glaucony in sequence-stratigraphic interpretation of the Aitamir Formation (south of Agh-Darband) in eastern Kopet-Dagh basin

Abstract:
      Aitamir Formation (Lower to Upper Cretaceous) is exposed in eastern Kopet-Dagh basin in the northeast Iran. This formation is composed of sandstone, shale, siltstone and carbonate facies. Green grains of glaucony are present with different amount in lithofacies. Based on these lithofacies and characteristics of glaucony grains is interpreted that the Aitamir Formation was deposited in a shallow open marine environment. With sea level fluctuations caused that, these sediments to be deposited in lagoon to shallow open marine environments. Based on analysis of glaucony grains and bioclasts frequency and vertical change in lithofacies, transgressive system tract (TST), high stand system tract (HST), maximum flooding surface (MFS) and condensed section (CS) were identified in four measured stratigraphic sections from east to west. In Karizak section (eastern section), four depositional sequences with three MFS, in Derazab and Shorab sections (middle sections), five depositional sequences with four MFS and in Cale- Shah Mohammad section (western section), six depositional sequences with five MFS were identified. In all depositional sequences, sequence boundaries are type 2 (SB2). Comparison between interpreted sea level changes in transgressive and regressive sequences in this formation with eustatic sea level curve show a relatively good correlation.