Response of Shallow-Marine Ecosystem to Cretaceous-Paleogne Boundary in Baluchistan Baisn (eastern Tethys, Pakistan)

TheCretaceous–Paleogene (K–Pg) mass extinction (ca. 66 Ma)was a profound climatic event that affected both deep and shallow marine ecosystems. Following the K–Pg mass extinction, the early Paleocene recovery period represents an important phase for Larger Benthic Foraminiferal (LBF) evolutionDuring this time, LBF taxa with simple and smaller tests rapidly evolved into more complex and larger test forms and progressively increased in diversity. Several new genera originated in the early Paleocene and later broadly diversified at the species level. Despite its importance, the response of shallow-marine biotic environments tothe K–Pg eventparticularly within theSouthern Himalayan carbonate platform succession (Eastern Tethys, Pakistan)remains unexplored. Based onbiostratigraphic, chemostratigraphic, and sedimentological data, this study provides, for the first time, an integratedLBF and calcareous plankton biostratigraphyfrom a shallow-marine environment across the K–Pg boundary interval. The studiedDunghan Formationconsists of a35 m-thick shallow-marine sequence of thin- to thick-bedded limestones, in whichfive distinct microfacies typesare identified, representing aninner–outer ramp depositional environmentNotably, we observed achange in LBF assemblages constraining theK–Pg boundaryto the upper part of theSiderolites–Orbitolites–Omphalocyclus wackestone microfaciesAbove the boundary, we observed a striking shift fromSiderolites–Orbitolites–Omphalocyclus assemblagesto Smoutina–Rotalia–Lockhartia dominated assemblages, which suggest asea-level rise. Concurrently, severalMaastrichtian index LBF taxa (e.g., Omphalocyclus macroporus, Lepidorbitoides blanfordi and Siderolites denticulatus) disappear, while Danian index taxa(e.g., Elazigina dienelli, Pararotalia tuberculifera, Smoutina cruysi, and Lockhartia cushmani) began to proliferate. In addition, importantcalcareous plankton biozonesare identified, including theMicula murusand Lithraphidites quadratus assemblage (NP25)followed byThoracosphaera operculata and Watznaueria barnesiaeassemblage (NP1), theCruciplacolithus tenuis assemblage (NP2),the Heliolithus kleinpellii and Prinsius bisulcus assemblage (NP3), andSphenolithus primus (NP4).The extinction of calcareous plankton across theK–Pg boundarywas abrupt and catastrophic, associated withhumid and warm event linked togreenhouse conditionsThe extinction level is overlain by a unit corresponding toNP1 (earliest Danian)which suggest asea-level riseassociated with increased humidity, marked by an increase infecal pellets and glauconiteindicating alow sedimentation rate.