SEA LEVEL CHANGE, BIOGEOGRAPHY AND PALEOSALINITY OF THE ABDERAZ FORMATION (TURONIAN – SANTONIAN) AT DERAZ-AB SECTION, NE IRAN

  • Mohsen Allameh Associate Professor, Department of Geology and Petroleum Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Keywords: Kopeh-Dagh sedimentary basin, Planktonic foraminifera, Depositional environment

Abstract

The Abderaz Formation (Late Turonian – Late Santonian) is investigated in this work at Deraz-Ab section, where a thickness of 400 m, comprised of light grey shale and marls, is exposed. The aim of the present study is to determine the Paleobathymetry and paleosalinity of the depositional environment based on planktonic foraminifera assemblages. Three swarming morphotypes, suggested by Leckie in 1987 are followed, in addition to the ratio of planktonic to benthic foraminifera to determine the sedimentation depth. Statistical study of the morphotype groups of planktonic foraminifera shows that they are of shallow water forms (SWF) and deep water forms (DWF). The planktonic to benthic ratio is high indicating specific conditions of oligotrophy and sedimentation in a relatively deeper marine condition. Salinity is considered minimum in the Coniacian and maximum in the Coniacian – Santonian boundary. Comparing planktonic assemblages recovered from the formation with those of Cretaceous biogeographical provinces indicate a close similarity with those of the Tethyan province.

Published
2021-05-29
Section
Articles