The Paleocene-Eocene Thermal Maximum (PETM, ∼56 Ma) marks a rapid, intense warming event at the Paleocene-Eocene boundary. However, the terrestrial record of the PETM is limited, and its paleoenvironmental impacts are debated. This study examines the effects of the PETM on terrestrial lake environments using mineralogical, inorganic and organic geochemical analyses of the Paleocene Kongdian Formation’s organic-rich rocks from the Bohai Bay Basin. Findings show that global PETM warming drove regional aridification and evaporation, while carbonate isotopic signals (negative δ13C, positive δ18O) are consistent with enhanced hydrological cycling and salinity fluctuations, reflecting the interplay between global climate forcing and local hydrological responses. Nutrient influx during the PETM boosted paleoproductivity. Arid-adapted organisms like Podocarpidites and Ephedripites also became present. The PETM experienced heightened seasonal variance and climatic extremes, with elevated temperatures causing increased evaporation and salinity during dry seasons, indicating greater aridity. Seasonal precipitation likely intensified due to monsoonal rains or the tropical convergence zone’s northward movement. Pollen from the Bohai Bay Basin indicates both significant episodic precipitation and increased aridity, reflecting complex climatic interactions. Increased detrital kaolinite content during the PETM suggests intensified physical weathering and erosion in kaolinite-bearing catchment areas, driven by episodic heavy rainfall. Our sedimentological observations (e.g., laminated shale cyclicity and detrital mineral assemblages) indicate sporadic heavy rainfall events, enhancing physical weathering and altering detrital sediment mineral content in the Bohai Bay Basin.

The Palaeocene–Eocene Thermal Maximum (PETM) was a global extreme climatic event, but it is relatively unknown from lower latitudes or equatorial regions in comparison to mid- and high latitudes. The present study provides the first clay mineralogical evidence of the PETM and subsequent hyperthermal events in a near-equatorial region represented by the Akli Formation in the Barmer Basin, India. The 32 m-thick succession of the Akli Formation shows abrupt changes in smectite and kaolin abundances preceding, during and succeeding the PETM event. Within the studied section, the kaolin content increases from 5–8% pre-PETM to 30–35% during the PETM, and then again decreases to 5–6% during the post-PETM period. The smectite, however, is marked by a corresponding decrease and its transformation into kaolin in acid weathering conditions. The transformation of the smectite is first marked by hydroxy interlayering and then transformation into kaolin during the PETM. The transformation of smectite into kaolin also resulted in extensive precipitation of iron oxide in sediments. The clay mineralogical changes in the Palaeocene–Eocene transition sediments of the Akli Formation were caused by 3–5°C warming and a 25–50% increase in rainfall during the hyperthermal events. Unusually high charcoal (~20%) fragments during the Palaeocene–Eocene transition also suggest warming and widespread biomass burning during the PETM in the lower latitudes.

The Palaeocene–Eocene Thermal Maximum (PETM) is one of the most important Cenozoic climatic events shaping modern biodiversity, yet reconstructions of its palaeobiomes remain controversial. Here we describe Gesomyrmex gallicus sp. nov., a new, extinct species of the ant genus Gesomyrmex Mayr, 1868, based on minor and major workers preserved in the early Eocene amber of Oise, France. Although there are only seven known extant species in the genus, all confined to warm and humid forests of SE Asia, the fossil record of Gesomyrmex indicates that the genus once radiated across Eurasia. The new species therefore provides direct evidence that this radiation likely co-occurred with the PETM. This observation constrains palaeoclimatic reconstructions of the Early Eocene by requiring the presence of an extensive, homogeneous and interconnected rainforest-like biome across palaeo-Eurasia, a scenario otherwise corroborated by pollen assemblages. The phases of regression of warm and humid forests and the widening of dry biomes probably occurred later during the Eocene, in between hyperthermals, and were probably less extensive than some computer models predicted.

If an industrial civilization had existed on Earth many millions of years prior to our own era, what traces would it have left and would they be detectable today? We summarize the likely geological fingerprint of the Anthropocene, and demonstrate that while clear, it will not differ greatly in many respects from other known events in the geological record. We then propose tests that could plausibly distinguish an industrial cause from an otherwise naturally occurring climate event.