Evolution of the primary productivity recovery at the Cretaceous-Paleogene boundary at the Caravaca distal section (Spain)

Abstract

The Cretaceous-Paleogene boundary represents the latest of the five major mass extinctions in Earth's history. Previous biomarker studies at distal K-Pg sites have suggested transient changes; however, the lack of high-resolution and extended records limits our understanding of the mechanisms and duration of post-impact biotic recovery. We performed a multiproxy analysis at continuous cm-scale resolution across an ∼300 cm-thick K-Pg boundary interval at the Caravaca distal section (SE Spain) that spans ∼22 kyr before to ∼220 kyr after the K-Pg event. We analysed the section's biostratigraphy and explored changes in organic matter composition (n-alkanes, acyclic isoprenoids, steranes and hopanes), trace elemental ratios and concentrations (K/Al, Ti/Al, Ba/Ti, Ca/Al, Ir and CaCO3), and isotopic compositions of both bulk (δ13Ccarb, δ13Corg) and high-molecular-weight n-alkanes (δ13CHMW). Changes in the organic matter abundance and provenance, isotopic composition and in trace element distributions were observed, mainly in the post-impact ejecta layer and boundary clay layer (representing ca. ∼10 kyr after impact). Although many biomarker mass accumulation rates exhibit a decrease and slow recovery after the K-Pg, an increase in some putative marine productivity biomarkers (pristane and phytane; LMW n-alkanes) is recorded from 5 kyrs before to 30 kyrs after the K-Pg mass extinction. Intriguingly, a co-eval variation in some inorganic terrestrial/extraterrestrial input (Ti/Al, K/Al, Ir) and some biomarker proxies with an anomalous excursion in the organic carbon isotope record (δ13Corg) suggest transient change in organic matter, perhaps reflecting an erosive event associated with the impact. This erosive event appears to be related to the remobilization of less thermally or diagenetically altered terrestrial organic matter, making it analogous to but distinct from studied distal Cretaceous-Paleogene sections such as Agost, in Spain, and Mid-Waipara, in New Zealand which were characterised by remobilization of thermally mature organic matter. Thus, with our novel high-resolution primary productivity evolution results, we can evidence for first time, heterogeneity on biomarker's responses in distal the Cretaceous-Paleogene boundary sites.