Paleocene Dinoflagellate Cyst Biostratigraphy in Eastern New Zealand

Abstract

Although calcareous microfossils are the primary group that underpin the New Zealand Paleogene Time Scale, they often have a patchy distribution in Paleocene sediments due to poor preservation, sediments that have low levels of carbonate or are non-calcareous, and a lack of low-latitude calcareous biostratigraphic marker taxa. In contrast, diverse and abundant organic-walled dinoflagellate cyst (dinocyst) assemblages are found in almost all marine settings of Paleocene age throughout New Zealand. Until now, the Paleocene (Teurian Stage) has been encompassed by three formal dinocyst zones. Here we establish a more detailed Paleocene zonation and better correlate this scheme to the New Zealand and International Timescales. We have examined dinocyst assemblages from five sections in eastern New Zealand sedimentary basins. Calcareous nannofossil assemblages were also examined to assist with the age and correlation of dinocyst assemblages. Based on results from these sections, along with published earliest Paleocene records from Marlborough and the Canterbury Basin, we propose a revised Paleocene dinocyst zonation. The eight New Zealand Dinocyst Paleocene zones, NZDP1 to NZDP8, span the entire Paleocene, from the Cretaceous–Paleogene boundary (66.04 Ma) to the Paleocene–Eocene boundary (55.96 Ma). The NZDP zones are correlated with the 2012 International Geologic Timescale, utilising mainly calcareous nannofossil bioevents. We anticipate that the proposed zonation will be applicable throughout the New Zealand region, and perhaps wider afield in the southwest Pacific. Through the Paleocene, dinocyst assemblages record notable relative abundance variations in genera and in peridinioid and gonyaulacoid groups. Peridinioid dinocysts, thought to represent primarily heterotrophic dinoflagellates, dominate assemblages in two time intervals. A succession of peridinioid genera, such as Trithyrodinium, Palaeoperidinium and Vozzhennikovia, are abundant through the Early Paleocene. In the late Middle–early Late Paleocene peridinioid dinocysts, mainly Senegalinium species, are abundant in an interval that correlates with deposition of the Waipawa Formation, a distinctive organic-rich mudstone unit found throughout New Zealand sedimentary basins.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015