Abstract A global larger foraminiferal turnover (LFT), first identified in the Pyrenees in 1960, occurred around the Paleocene-Eocene boundary. It is characterized by the replacement of Paleocene assemblages dominated by Glomalveolina and Lockhartia (west and east Tethys, respectively), with others typified by Eocene Alveolina and Nummulites. Its relationship with the Paleocene-Eocene Thermal Maximum (PETM), a brief interval of global warming, has been debated at length. This study confirms that the LFT was triggered by the PETM. In the Pyrenean Basin the primary driver of the LFT was the influx of over 100 km3 of predominantly fine-grained siliciclastic sediment into the sea during the PETM, which disrupted the previous long-lasting oligotrophic conditions. Unlike other K-strategists, Alveolina and Nummulites adapted to the new ecological conditions, radiating and expanding during the Eocene. Although no comparable siliciclastic influx occurred in the Tethys Ocean, the LFT also coincided with the PETM in Slovenia and Egypt (western Tethys). The link between both events is attributed to adaptations to fluctuating nutrient levels and increased coastal water productivity. In Pakistan and the Himalayas (eastern Tethys), the replacement of Paleocene assemblages appears to have been gradual, leading to the notion that the LFT was not linked with the PETM, but rather resulted from natural evolution. A re-evaluation of the data demonstrates that before the global warming Alveolina and Nummulites were minor components of the assemblages, but that they rapidly evolved and diversified during the relatively short interval of the PETM, a shift also observed in the Pacific Ocean.

Abstract Glaucony, an Fe-rich mineral typically formed through marine authigenesis under specific physicochemical conditions, serves as a crucial indicator for reconstructing ancient marine settings. In the Eastern Black Sea region (Northeast Türkiye), glaucony-bearing limestone (GBL) strata have been discovered within uppermost Lower Cretaceous carbonates. However, the specific controls governing GBL formation have remained largely unexamined. This study presents the first comprehensive sedimentological and geochemical data to reconstruct the prevailing palaeoenvironmental conditions during the deposition of these GBL strata. The GBL strata exhibit a packstone texture, primarily comprising skeletal fragments transported from an adjacent inner carbonate platform, along with calcispheres and sponge spicules. The defining characteristic of this lithofacies is the pervasive presence of abundant, authigenic glaucony displaying ellipsoidal to reniform morphologies. Geochemical proxies, including Ce/Ce* ratios and V/(V + Ni) values, imply oxygen-depleted conditions during deposition. Furthermore, Sr/Cu and Sr/Ba ratios, coupled with elevated Al, Rb, Zr and Nb, suggest relatively humid, warm to mesothermal conditions. A slight enrichment in light rare earth elements (LREEs), positive Eu anomalies, depleted Y/Ho and Zr/Hf ratios, and elevated Sm/Yb ratios collectively point to a probable hydrothermal influence. Our integrated sedimentological and geochemical approach suggests that the observed Fe enrichment during the Albian period likely stems from a complex interplay of factors. These include hydrothermal activity associated with syn-sedimentary tectonic regimes and intensified continental weathering driven by prevailing palaeoclimatic conditions. These factors, in conjunction with basin subsidence and distinct palaeoenvironmental conditions, facilitated the deposition of the GBL during the Mid-Cretaceous sedimentary evolution of the Tethys basin.