Pronounced Climatic and Environmental Changes in the South West Pacific Ocean Following the End-Cretaceous Extinction Event

Abstract:

Dinoflagellate cyst assemblages from Cretaceous/Paleogene (K/Pg) boundary sections in eastern New Zealand record an alternating succession of pronounced abundance changes in two peridinioid (primarily heterotrophic) genera following the K/Pg boundary event. In Canterbury and East Coast Basin sections, two phases of abundant Trithyrodinium evittii, the first immediately following the K/Pg boundary, are interposed by two acme intervals of Palaeoperidinium pyrophorum. While several lines of evidence suggest T. evittii was a warm-water species and P. pyrophorum flourished in cooler oceanic conditions, robust temperature records have not been available from these K/Pg boundary sections. We have completed sea surface temperature (SST) reconstructions, based on glycerol dialkyl glycerol tetraether (GDGT) distributions, at mid-Waipara River, North Canterbury, from ~1 m below to 20 m above the K/Pg boundary. Changes in GDGT distribution across the K/Pg boundary indicates warming of 2–3°C, regardless of which TEX₈₆-based proxy is used, coincident with the interval of abundant T. evittii. Detailed climatic records at the K/Pg boundary layer are hampered by intense bioturbation. Above an unconformity (at 23 cm) notable shifts in GDGT distribution indicates pronounced cooling, yielding SST estimates that are 7°C lower than the uppermost Cretaceous. The acme of P. pyrophorum corresponds with these cooler SSTs, and an unusual increase in the proportion of GDGT-2 in this interval can be attributed to cool water upwelling. The P. pyrophorum acme is also documented in distal diatom-rich siliceous sediments in Marlborough, where siliceous microfossils and element geochemistry indicate cool-water upwelling in the basal Paleocene. The second phase of abundant T. evittii, at ~2 m in Waipara, coincides with an interval of more stable SSTs that are comparable to the uppermost Cretaceous. Further discussion of the TEX₈₆-based SST proxy and GDGT distributions will be provided in the presentation.