138 The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms

The Cretaceous-Paleogene boundary interval witnessed extreme geological events: the Chicxulub impact and Deccan Traps volcanism, and a biological catastrophe. New proxy-records, coupled with numerical modelling, unravel the mechanisms driving the environmental change and mass extinction.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 304A

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

Paper number: 138-9
Program: Technical Sessions
Time: 3:40 PM – 4:00 PM

Authors

Abstract

The Cretaceous-Paleogene (K-Pg) boundary represents the latest of the five major mass extinctions in Earth´s history. Previous biomarker studies at distal K-Pg sites have observed limited 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 ~300 cm-thick K-Pg boundary interval at the Caravaca distal section (SE Spain), spanning ~25 kyr before to ~220 kyr after the K-Pg event. We analysed the section’s biostratigraphy and explored: i) changes in organic matter composition and provenance using a range of apolar (n-alkanes, acyclic isoprenoids, steranes and hopanes) biomarkers; ii) detrital inputs using trace elemental ratios (K/Al, Ti/Al, Ir/Al ratios); iii) productivity changes using major and trace elemental ratios and percentages (Ba/Ti, Ca/Al and % of Ca CO3); and iv) environmental changes using stable oxygen isotopic compositions of inorganic carbon and stable carbon isotopic compositions of both bulk (inorganic carbon-δ13Ccarb, organic carbon-δ13CTOC) components and high-molecular-weight n-alkanes(δ13CHMW).

Changes in the organic matter abundance and provenance, isotopic composition and in the trace element distributions were observed, mainly in the post-impact ejecta layer and boundary clay layer (representing ca. <10 kyr after impact). Although the mass accumulation rates show a decrease and slow recovery of biomarkers abundance after K-Pg, an increase in marine productivity (pristane and phytane; LMW n-alkanes) is recorded from 6 kyrs before to 10 kyrs after K-Pg mass extinction. Intriguingly, a co-eval variation in thermal maturity indices (C31 hopane and CPI), an increase in some inorganic terrestrial/extraterrestrial input ratios (Ti/Al, Ir/Al), and the anomalous excursion in the organic carbon isotope record (δ13CTOC) suggest a combination of reworked organic matter (erosive event) with a minimum effect in the marine phytoplankton community through the impact event. This erosive event mainly related to the remobilization of older marine organic matter (with less thermal maturity), located in upper and shallow shelfs, has been also detected in other studied distal Cretaceous-Paleogene sections such as Agost, in Spain, and Mid-Waipara, in New Zealand. Thus, this is the first time that we can reconstruct at high-resolution primary productivity evolution by biomarkers through the Cretaceous-Paleogene boundary.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412554

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