BIOMARKER COMPOSITIONS IN TRANSKEI BASIN SEDIMENTS (IODP SITE U1581) SHOW CONTINUITY IN ALGAL COMMUNITIES FROM THE LATE CRETACEOUS THROUGH THE PALEOCENE AT HIGH SOUTHERN LATITUDES

The distributions and isotopic compositions of biomarkers in marine sediments serve as diagnostic indicators of sources of organic matter (OM). Hence, their stratigraphic profiles are employed extensively to elucidate temporal changes in paleoenvironments and paleoclimate. Similarly, consistencies in molecular compositions provide evidence that OM sources and processes governing biomarker preservation likely remained uniform over time. Investigation of a sequence of Campanian to Paleocene (~76-60 Ma) sediments recovered during IODP Expedition 392 from the Transkei Basin (Hole U1581B), offshore South Africa [1] reveals a temporal coherence in algal biomarker compositions from the Cretaceous to the Paleogene. The occurrence of suites of C₃₇-C₄₀ alkenones derived from haptophyte algae [2] expands their paleogeographic range during the late Cretaceous to southern high latitudes (~58°S). Similarities in alkenone profiles for Maastrichtian and Danian samples suggests temporal conformity in their haptophyte source(s). Moreover, the dominant series of steroidal hydrocarbons in Campanian through Paleocene sediments from the Transkei Basin are C₂₇ to C₂₉ Δ⁴- & Δ⁵-sterenes and Δ^4,22- & Δ^5,22-steradienes, accompanied by subordinate amounts of 5α- & 5β-steranes [3]. The relative abundance of C₂₇, C₂₈, and C₂₉ steroids can be represented on a ternary diagram [4], which reveals discrete differences among the three principal suites of steroidal hydrocarbons (i.e., sterenes, steradienes, steranes) but consistency in the distributions of individual series. In particular, the coherent dominance of C₂₈ steradienes, reflecting algal sources of OM, indicates temporal uniformity in phytoplankton producers, echoing the evidence of alkenones derived from haptophytes, and further substantiated by the distributions of tocopherols from photoautotrophs and 4-methylsteroids from dinoflagellates. Thus, biomarker compositions attest to a continuity in algal communities at high southern latitudes from the Cretaceous to the Paleogene.

References

[1] Uenzelmann-Neben et al., 2022. doi:10.14379/iodp.pr.392.2022

[2] Marlowe et al., 1984. doi:10.1080/00071618400650221

[3] Dumitrescu & Brassell, 2005. doi:10.1016/j.orggeochem.2005.03.001

[4] Huang & Meinschein, 1979. doi:10.1016/0016-7037(79)90257-6