A southern hemisphere mid-latitude climate record across the K-Pg boundary from the Bajada del Jagüel section, Argentina

VELLEKOOP, J.; WOELDERS, L.; SMIT, J; CASADÍO, S.; SPEIJER, R.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

Cricyt

The Cretaceous-Paleogene (K-Pg) boundary represents one of the most significant geological transitions in Earth history, being characterized by one of the largest mass extinction events related to the impact of a large extraterrestrial body. Although the K-Pg boundary is characterized by rapid major global change, an accurate reconstruction of these climate changes proves to be challenging. Major extinctions amongst traditionally applied biotic proxy-carriers, e.g. planktic foraminifera, hamper accurate temperature reconstructions and consequently, the resulting records are often contradictory. Marine dinoflagellates that produce organic dinocysts survived the K-Pg mass-extinction relatively unscathed. Therefore, they are ideally suited for reconstructing pre- and post-extinction marine conditions and combined with biomarker-based quantitative temperature proxies such as TEX86 they can potentially resolve the enigmatic climate evolution across the K-Pg boundary. While these techniques have been applied on multiple Northern Hemisphere sites, very few records are so far available from the Southern Hemisphere, so environmental consequences of this impact on Southern Hemisphere environments is still poorly understood. Among the few Southern Hemisphere localities with potentially sufficient temporal resolution across the K-Pg boundary are several outcrops in Argentina, which so far have attracted relatively little attention. One of these is the Bajada del Jagüel section in the Neuquén Basin. To provide insight in Southern Hemisphere biological and environmental changes across the K-Pg boundary, we have applied a multiproxy study on the Bajada del Jagüel section, integrating: (1) quantitative dinocyst analysis, (2) quantitative planktic and benthic foraminifera analysis (3) stable carbon and oxygen isotope analyses, and (4) the quantitative temperature proxy TEX86. Our results show that at Bajada del Jagüel, the K-Pg transition is stratigraphically condensed but complete. The δ18O and TEX86 records show that the last 2 million years of the Cretaceous are characterized by multiple warming and cooling phases, with average sea surface temperatures (SSTs) varying between 23°C and 29°C. Within the boundary layer SST briefly drop to