Biostratigraphy of the Late Campanian–Maastrichtian of the Duwi Basin, Red Sea, Egypt

Abstract

Abstract During the Late Campanian, sea-level fluctuation occurred in the form of two chert bands and the topmost conglomeratic phosphate beds (CF8a zone). A great transgression event occurred associated with the global warming (CF8b zone) trend indicated by large double-keeled foraminifera as Globotruncana aegyptiaca Nakkady of oligotrophic conditions. Through the event of CF6/CF5 zones, a gradual increase in the relative abundance of Gublerina rajagopalani Govindan and Planoheterohelix planata (Cushman) and other heterohelicids have been shown to tolerate and thrive in a wide range of environmental conditions as in high-stress environments. Sea-level fall at the CF6 zone and the overlying CF5 boundary marked a warming climate for the Middle Maastrichtian Event. In the latest CF4 records, the beginning of the decrease in planktic/benthic ratio, globotruncanids, rugoglobigerinids, and heterohelicids indicating a fall in sea level coincided with the CF4/CF3 and the development of dark grey shales in a regressive regime. The observed low abundance of planktic specimens may be due to the presence of pyrite with black shale interval suggesting low oxygen condition. The latest zones CF3, CF2, and CF1 are generally characterized by heterohelicids blooms specially Planoheterohelix globulosa (Ehrenberg), and a gradual decrease in diversity associated with the warming phase before the K/Pg boundary event, implying high biotic stress to even absent of Guembelitria cretacea species through CF3–CF1 zones. Pseudotextularia elegans (Rzehak) occurs in the zones CF4 and CF2 warming of phases 1 and 2 of Deccan Trap Volcanic. The absence of P. elegans (Rzehak) in the zone (CF3) is postulated due to a tectonic cause (maximum cooling of Deccan Trap Volcanic) whereas its absence in the zone (CF1) was due to regression of phase 2.