High-resolution biostratigraphic analysis of the Cretaceous-Paleogene Boundary in the Kurdistan Region (NW Iraq)

Abstract

A stratigraphical challenge has long been associated with the debatable K/Pg boundary-transition in Iraq, particularly in the high folded zone of the western Zagros fold-thrust belt (Kurdistan Region). However, dissensions regarding the boundary have remained controversial. Because of differing interpretations most of the previous studies considered it as a hiatus and/or erosional surface. Here, we present a high-resolution investigation of the planktonic foraminiferal biostratigraphy across the K/Pg boundary from three sections (Per Fat, Xezava, and Behere) within the Dohuk and Zakho areas of the Kurdistan Region of Iraq. The contact zone shows a lithostratigraphic resemblance and is represented by the upper part of the Shiranish Formation (late Maastrichtian) with the overlying Aaliji Formation (Danian), positioned in a continuous pelagic marlstone that exhibits a change in color from pale blue of the Cretaceous (Shiranish Formation) to light brown at the base of the Paleogene (Aaliji Formation). The biostratigraphic investigations across the studied interval reveal three Upper Cretaceous zones: Pseudoguembelina hariaensis p.p. (CF3) Interval Zone, Pseudoguembelina palpebra (CF2) Interval Zone, and Plummerita hantkeninoides (CF1) Total Range Zone. Four main zones and three subzones of the Danian are recorded: Guembelitria cretacea (P0) Partial Range Zone, Parvularugoglobigerina eugubina (Pa) Total Range Zone, Parasubbotina pseudobulloides (P1) Partial Range Zone (Globoanomalina archaeocompressa (P1a) Partial Range Subzone, Subbotina triloculinoides (P1b) Interval Subzone, Globanomalina compressa - Praemurica inconstans (P1c) Interval Subzone, and Praemurica uncinata p.p. (P2) Interval Zone. High biostratigraphic resolution indicates a complete K/Pg transition with no hiatus at the three studied localities in the Dohuk and Zakho areas.