THE CRETACEOUS/PALEOGENE TRANSITION AT OCEAN DRILLING PROGRAM SITE 1172 (EAST TASMAN PLATEAU, SOUTHWESTERN PACIFIC)

Ocean Drilling Program Leg 189 recovered a potentially complete siliciclastic-dominated shallow-marine record of the Cretaceous-Paleogene boundary (KPB) at Site 1172D on the East Tasman Plateau (~70° S paleolatitude). However, our post-cruise high-resolution (cm-scale) data from micropaleontology, geochemistry, sedimentology, and paleomagnetism provide no evidence for a stratigraphically complete KPB, but instead suggest a boundary-spanning hiatus of at least 0.8 Ma based on biomagnetochronology and the absence of any bulk sediment iridium enrichment. We interpret this major hiatus as the sequence boundary between the uppermost Maastrichtian Ta1.1 and lowermost Danian Da-1 sequence stratigraphic cycles (sensu Haq et al., 1988 and Hardenbol et al., 1998), and an underlying siderite-rich horizon may reflect mixed phreatic and marine porewaters associated with subaerial exposure. The hiatus surface is distinctly burrowed, likely while a firmground or hardground. Abundant palynomorphs (particularly dinocyst) and extensively pyritized diatom assemblages indicate increasingly shallow paleodepths, restricted circulation, and eutrophic conditions through the latest Maastrichtian, while more oceanic and warmer conditions characterize the earliest Danian. Glauconite content also increases markedly in the Danian, consistent with the onset of low sedimentation rates within deeper waters (i.e., transgressive systems track). The Site 1172D KPB section is broadly comparable to other southern high-latitude KPB sections in Antarctica and New Zealand, but appears to record a more shallow and restricted environment that was susceptible to a eustatic-driven hiatus that precluded recording of the Cretaceous-Paleogene mass extinction event.