oa Biomarker-Based Reconstruction of Palaeoenvironmental Changes During the Lome from the Baltic Basin

The Late Ordovician–Early Silurian interval was marked by significant climatic and sea-level fluctuations, culminating in the Late Ordovician Mass Extinction (LOME), one of the Phanerozoic’s ““Big Five”” extinction events. Despite extensive research, the precise mechanisms driving this extinction remain incompletely understood. This study examines paleoenvironmental changes in the shallow shelf of the Baltic Basin (Lithuania, Rietavas-1 well), leveraging biomarkers as molecular proxies to reconstruct ocean chemistry and biogeochemical conditions during LOME deposition.

A multi-proxy biomarker approach is employed, analyzing steranes, hopanes, n-alkanes, parent and alkylated aromatic compounds, and isorenieratane derivatives to assess shifts in microbial communities and primary productivity. Steranes and hopanes provide insights into eukaryotic and prokaryotic contributions to organic matter, while n-alkane distributions distinguish terrestrial from aquatic inputs. Elevated isorenieratane concentrations indicate euxinic photic zone conditions, which are associated with the second extinction pulse and linked to marine transgression, global warming, and the expansion of anoxic waters.

To further elucidate the environmental drivers of LOME, biomarker data are integrated with geochemical proxies, including d¹³Ccarb, mercury concentrations, and trace element distributions. This comprehensive approach enhances our understanding of the complex interplay between climatic and oceanographic factors in shaping one of Earth’s most profound biotic crises.