Turonian-Maastrichtian biostratigraphy and isotope stratigraphy of the Kopet-Dagh Basin deposits, northeastern Neo-Tethys, Iran

Abstract

Planktonic foraminiferal biostratigraphy and isotope stratigraphy analyses of Turonian-Maastrichtian deposits have been carried out in the western part of the Kopet-Dagh Basin. The identification of the planktonic foraminiferal assemblages has led to the recognition of twelve Upper Cretaceous zones (Helvetoglobotruncana helvetica Zone to the Contusotruncana contusa-Abathomphalus mayaroensis zone) from the Tethyan realm. The obtained stable carbon isotope profile correlates with other reference curves, revealing many Late Cretaceous events including the Hitchwood, Navigation, Light Point, East Cliff, White Fall, Late Campanian Event (LCE), Campanian-Maastrichtian Boundary Event (CMBE), Middle Maastrichtian Event (MME) and KPg Events (KPgE). The Turonian-Maastrichtian deposits of the studied area represent severe changes in sedimentation rate and several hiatuses and condensed intervals, which mostly coincide with lithological boundaries. The data indicate a general shallowing -upwards in association with the Late Cretaceous tectonics of the Kopet-Dagh Basin. The reconstruction of the age model allows a discussion of the results in terms of changes in palaeoenvironmental conditions (eutrophic vs. oligotrophic).