Cretaceous–Paleogene palynodebris from two offshore cores in Cape Basin, South Atlantic Ocean and their paleoenvironmental implications

Abstract

Palynodebris in two cores from the western South African margin provides an opportunity for investigating stratigraphical changes across the Cretaceous/Paleogene (K/Pg) boundary and the depositional environments during this interval. Changing palynodebris trends of more than 200 sidewall cores and cuttings, sampled from two offshore ocean borehole sites ca. 243 km apart and situated in the Cape Basin, reflect the regional environmental processes during the Cretaceous and early Cenozoic. Thirteen categories of microscopic structures of palynomorphs and palynodebris (phytoclasts) are identified and recorded. These categories include amorphous organic matter, marine palynomorphs, fresh-water algae, resins, black debris (charcoal), yellow-brown fragments, black-brown fragments (including microscopic charcoal), cuticles, plant tissues, woody material, sporomorphs, and fungal material such as fungal spores, fruit bodies, tubes and filaments. The relative abundances of these organic components from each site were analyzed and compared. Palynodebris compositions and patterns differ between borehole sites over time but also show some similar regional trends, e.g., growing indications of burning from the Late Cretaceous to early Paleocene. The woody component suggests that both offshore sites received similar land-derived Cretaceous and Cenozoic sediments via fluvial transport. Palynodebris was compared to previously published palynological data from the cores, showing shifts in vegetation and climate. Around and shortly after the K/Pg boundary, black debris and yellow-brown debris components fluctuate strongly and could possibly be related more to the transition from the Maastrichtian regressive events than a terminal K/Pg boundary event. Stronger marine influence, as indicated by an increase of marine palynomorphs together with geological evidence of glauconitic sandstone, Inoceramus, other bivalves, and shelly material during the Late Cretaceous and Paleogene, reflects the flooding of the basin. The stratigraphy and depositional environments contribute to a better understanding of conditions associated with the opening of the South Atlantic Ocean.