Geochemical study of the Cretaceous–Tertiary boundary succession exposed at Duhok Dam area (eastern Tethys): Northern Iraq

Abstract

This article is concerned primarily with the variation in chemistry across the bluish gray marlstone sediments of the uppermost Maastrichtian/lowermost Danian exposed at the Dohuk Dam suburb area of Dohuk City, about 60 km north of Mosul. This succession was sampled at intervals of 0.10 m and the samples were investigated by various techniques, including detailed study of index fossils in the CF2, CF1, Po, and Pα biozones, grain size analysis by the hydrometer method, mineralogical analysis by XRD, chemical analysis of 48 major and trace elements by XRF, loss on ignition, rare earth element, iridium and gold analysis by instrumental neutron activation, investigation of micro-size constituents by SEM, and stable isotope analysis of deltaC13 and δ18O by conventional mass spectrometry. The K-T boundary was identified on the basis of planktonic foraminifera assemblage investigation and the global negative shift of δ13C. Warming conditions and highstand sea levels were deduced from the decreasing trend of oxygen isotope ratios and grain size variation, with a short interval of cooling and sea regression which precedes the K-T boundary. There is a gradual decrease of carbonate and an increase in the accumulation rate of detritus towards the K-T boundary. Sediments enriched in heavy trace elements precede those enriched in light major elements. Different scenarios are discussed to account for the observed variations.