Larger Benthic Foraminifera across the Cretaceous/Paleogene boundary and their implications for the India–Eurasia collision: Insights from Baluchistan Basin, Pakistan (Eastern Neo-Tethys)

The end of the Cretaceous period (66.04 Ma) was punctuated by a mass extinction event with the disappearance of nearly 75% of all species. Despite its relevance, the extinction in shallow marine environments is still not fully understood. The present study examines the changes in the Larger Benthic Foraminiferal (LBF) assemblages across the Cretaceous/Paleogene (K/Pg) boundary in the Dunghan Formation, N-E Baluchistan Basin, Pakistan (Eastern Neo-Tethys). The Mehrab Tangi section is known for having one of the most extensive and well-preserved K/Pg transitions deposited in a shallow marine environment in this part of the Eastern Neo-Tethys. Thus, the biotic change in the LBF assemblages can be attributed to two distinct phases, namely the pre-K-Pg phase and the post-K-Pg phase. The pre-K/Pg phase is identified by the presence of the Maastrichtian Omphalocyclus-Orbitoides-Lepidorbitoides assemblages, while the post-K/Pg phase is marked by the Danian Rotalia-Lockhartia assemblages. Based on the composition of LBF assemblages and sedimentological characteristics, five distinct microfacies are identified, which represent different paleoenvironments within the inner-outer ramp. The initial phase of the post-K/Pg period is characterized by the presence of the Rotalia-Lockhartia wackstone, which indicates a rise in sea level. This rise is accompanied by a significant increase in glauconite mineral and fecal pellets, indicating a high rate of sedimentation during the earliest Danian. The K/Pg boundary event had a significant impact on the composition of LBF assemblages in shallow marine deposits globally. This event led to the extinction of several LBF Maastrichtian species, including Omphalocyclus macroporus, Lepidorbitoides blanfordi, Lepidorbitoides minor, Orbitoides media, and Orbitoides apiculate, followed by the appearance of important Danian LBF species such as Rotalia hensoni, Rotalia orientalis, Smoutina cruysi, Lockhartia cushmani, and Lockhartia diversa. The presence of a 1.5-meter-thick laterite band below the Maastrichtian Omphalocyclus-Orbitoides-Lepidorbitoides assemblages provides strong evidence for the onset of the collision between the Indian and Eurasian plates in this region of the Neo-Tethys. Based on detailed and accurate biostratigraphic data, we speculate that the Indian-Eurasian plate collision commenced during the middle Maastrichtian age rather than at the Maastrichtian/Danian boundary as previously suggested in studies conducted in the Himalayas, Eastern Neo-Tethys.