Late Maastrichtian climatic shifts and faunal upheavals at DSDP Site 525A (South Atlantic): Understand the K-Pg boundary crisis in the long-term perspective

The extensively studied Cretaceous-Palaeogene (K-Pg) boundary mass extinction of planktic foraminifera (~66 Ma) has been linked with two catastrophic triggers: the Chicxulub impact (Gulf of Mexico) and Deccan volcanism (India). All the studies of the past three decades have focused on the climate shifts and faunal stress at the K-Pg boundary, and in the final ~200 ky preceding it. However, it is critical to study the events that precede the age and influence of Deccan volcanism to gain perspective on the true magnitude of the biotic crisis at the boundary. This study presents a new high-resolution (at 20-cm intervals) climate and faunal dataset of the entire late Maastrichtian record at the DSDP Site 525A (Walvis ridge, South Atlantic). The DSDP Site 525A offers a relatively continuous sediment record of the late Maastrichtian with near-pristine planktic foraminifera for faunal and stable isotopic analyses, excellent magnetostratigraphy and potential for cyclostratigraphy.

            Our results reveal sediments spanning biozones CF1 through CF7 of the Maastrichtian, a duration of ~6 myr. The updated biozone boundaries have been used to infer the relative ages of the observed faunal and climate shifts. The seven important late Maastrichtian climatic events (E1-7) are clearly identified in stable isotopic (δ¹³C and δ¹⁸O) records of planktic (Rugoglobigerina rugosa) and benthic foraminifera (Cibicidoides cf.). Of these, events E-2, E-4 and E-6 represent relatively warmer climate, whereas events E-1, E-3, E-5 and E-7 are colder climate. Events E-2, E-4 and E-7 correspond to the globally recognized Deccan warming event, mid-Maastrichtian event (MME) and Campanian-Maastrichtian Boundary Event (CMBE), respectively. Based on isotope records, the late Maastrichtian corresponds with four climate shifts. Faunal analysis reveals these events are bracketed within four biozones (CF1-4) and have a species richness of ~50 planktic foraminifera. The census analysis reveals a slightly decreasing diversity in E-4 followed by a uniform diversity in E-3. Further, E-2 witnessed a sharp fall in the diversity trend that reduced to an all-time low of ~20%. Most planktic species (globotruncanids) get extinct in E-2 following the diversity drop. However, Hedbergella spp., Pseudoguenbelina costulata, P.  hariaensis, Heterohelix globulosa, H. rajagopalani, Globigerinella aspera, and Globotruncana arca manage to survive through E-2 and were present in high abundance (~10%). Our long-term study suggests an overall stress built up in the background that must have aided in the K-Pg boundary mass extinction.