# Integrated biostratigraphy of the Maastrichtian-Danian sequence in the southern Tethys with insights into paleoenvironmental implications

## TL;DR

This study analyzes fossil records from Egypt to understand ancient environmental changes around the time of the Cretaceous-Paleogene boundary in the southern Tethys region.

## Contribution

The paper provides new insights into paleoenvironmental conditions and biostratigraphic zones in the Maastrichtian-Danian sequence of the southern Tethys.

## Key findings

- Calcareous nannofossil analysis identified four main biostratigraphic zones with a hiatus at the K/Pg boundary.
- Three intervals of varying oxygen levels were identified, indicating dysoxic to anoxic conditions.
- Climatic shifts and biotic productivity patterns were linked to Deccan trap volcanic phases and oceanic changes.

## Abstract

The Cretaceous-Paleogene (K/Pg) sequence offers a global perception of the paleoecological evolution in the southern Tethys realm. High-resolution calcareous nannofossil and dinoflagellate cyst analyses were conducted on subsurface Maastrichtian-Danian deposits in the Western Desert of Egypt, to characterize the paleo-conditions. The calcareous nannofossil analysis retrieved four main biostratigraphic zones (UC18-UC20, and NP4). A hiatus at the K/Pg boundary resulted in absence of most Danian nannofossil zones (NP1-NP3). The palynofacies assemblages discriminated three intervals of varying oxygen levels: dysoxic, proximal suboxic-anoxic shelf, and distal suboxic-anoxic basin incorporated by oligo-eutrophic conditions. The species diversity and relative abundance patterns of sensitive nannofossil indicators during this interval are attributed to significant climatic shifts. The surface waters during the Maastrichtian experienced a general cooling trend, interrupted by two warming episodes that may be correlated with the Deccan traps’ two phases (1&2). The biotic productivity indices and geochemical proxy (P, Sr/Al& P/Al) showed that during the earliest Maastrichtian high productivity prevailed, whereas during middle and late Maastrichtian a fluctuating pattern appeared. Statistically, multivariate techniques discriminated the retrieved taxa into five groups, each characterizing a depositional environment and climatic trend. Further, the palynomorphs analysis classified the Maastrichtian-Danian sequence into three offshore environments. A more refined understanding of climatic upheavals is essential for future studies to assess their potential role in driving biotic changes across the K/Pg boundary.

The online version contains supplementary material available at 10.1038/s41598-025-24036-1.