Biostratigraphy and palaeoceanography of the early Turonian–early Maastrichtian planktonic foraminifera of NE Iraq

Rawand B N Jaff,Sarah Lee,Fadhil Lawa,Ian P Wilkinson,Jan Zalasiewicz,Mark Williams

doi:10.1144/jmpaleo2014-020

Abstract

The Upper Cretaceous Kometan and Shiranish formations of the Kurdistan region, NE Iraq, yield diverse planktonic foraminiferal assemblages, with a total of 93 species, which enable recognition of nine biozones and two subzones spanning the early Turonian to late early Maastrichtian. Sequential changes in planktonic foraminiferal assemblages map discrete intervals within the Kometan and Shiranish formations that suggest dominantly warm, nutrient-poor marine surface and near-surface conditions during the mid-Turonian to late Coniacian, latest Santonian, and late Campanian, and cooler more nutrient-rich surface and near-surface waters in the early Turonian, early to late Santonian, early Campanian and early Maastrichtian. These intervals appear to correlate with changes in water masses from other regions of the Cretaceous palaeotropics, and with a phase of global, early Maastrichtian climate cooling. The major intra-Campanian truncation surface between the Kometan and Shiranish formations, recognized from the foraminiferal biostratigraphy, represents a lowstand that appears to equate with regional tectonics and ophiolite obduction across the NE margin of the Arabian Plate.

Highlights

The evolution of planktonic foraminifera from the Turonian to the early Maastrichtian is characterized by increasing species richness and morphological complexity (Hart, 1999; Premoli Silva & Sliter, 1999)
This paper presents a revised and refined planktonic foraminiferal biozonation for the early Turonian to early Maastrichtian interval of NE Iraq and recognizes palaeontological changes that suggest warmer more nutrient-poor marine surface conditions during the mid-Turonian to late Coniacian, latest Santonian, and late Campanian, and cooler more nutrient-rich surface waters in the early Turonian, early to late Santonian, early Campanian and early Maastrichtian
The Kometan and Shiranish formations are the most widespread lithostratigraphic units of the early Turonian–early Maastrichtian-aged succession in NE Iraq and contain rich and diverse planktonic foraminiferal assemblages that can be used for high-resolution biostratigraphy and to examine regional palaeoceanographic change (Fig. 2)

Summary

Introduction

The evolution of planktonic foraminifera from the Turonian to the early Maastrichtian is characterized by increasing species richness and morphological complexity (Hart, 1999; Premoli Silva & Sliter, 1999) This overall trend shows a short period of rapid diversification in the Turonian with the appearance of complex morphotypes (marginotruncanids), followed by a longer period of stasis interrupted in the Santonian by the disappearance of marginotruncanids and the diversification of another group of morphologically complex taxa, the globotruncanids (Petrizzo, 2002). The globotruncanids reached their maximum species diversity in the late Campanian–early Maastrichtian (Premoli Silva & Sliter, 1999). This paper presents a revised and refined planktonic foraminiferal biozonation for the early Turonian to early Maastrichtian interval of NE Iraq and recognizes palaeontological changes that suggest warmer more nutrient-poor marine surface conditions during the mid-Turonian to late Coniacian, latest Santonian, and late Campanian, and cooler more nutrient-rich surface waters in the early Turonian, early to late Santonian, early Campanian and early Maastrichtian

Materials And Methods

H: Highest occureance

Conclusion