Pollen and spore biostratigraphy of the mid-Cretaceous Tupuangi Formation, Chatham Islands, New Zealand

Abstract

The Tupuangi Formation, a mid-Cretaceous terrestrial stratigraphic succession from the Chatham Islands (New Zealand), provides a unique perspective into high polar latitudinal (75–80°S) conditions that have no modern analogues. Detailed investigations of the biostratigraphy of these sediments have constrained the age of crucial tectonic, climatic and ecologic events of this time. This study examined two sedimentary successions of the Tupuangi Formation on Pitt Island (Chatham Islands), and 41 palynomorph samples were retrieved and processed for biostratigraphic analysis. By comparing the stratigraphy and palynological assemblages of the two examined outcrop successions, this study produced the first island-wide biostratigraphic correlation of the Tupuangi Formation, and four allostratigraphic units (one alloformation subdivided into three allomembers) were identified; the unconformities that define the boundaries of these were verified by pollen and spore index species. Two of these unconformities have correlatives on mainland New Zealand. 18 spore/pollen taxa were used for these correlations, including two new spore taxa (Biretisporites labruplenus sp. nov. and Klukisporites sphaerogoufus sp. nov.), one newly validated spore taxon (Gleicheniidites ancorus sp. nov.), and two new pollen taxa (Liliacidites exquisitus sp. nov. and Trichotomosulcites hemisphaerius sp. nov.). The examined Tupuangi Formation outcrop successions correspond to the Ngaterian to Mangaotanean New Zealand chronostratigraphic stages (Cenomanian to Turonian; 99–89Ma). The timing of deposition for the Tupuangi Formation yields supporting evidence for the notion of a failed-rift basin in eastern Zealandia prior to sea-floor spreading between Zealandia and Marie Byrd Land, Antarctica. Previous studies suggested a negligible time-gap between the Tupuangi Formation, and the overlying Kahuitara Tuff; however, supported by evidence of reworking, this study suggests a temporal hiatus of >4Ma. This time-gap was most likely caused by thermal uplift prior to the onset of sea-floor spreading between Zealandia and Antarctica.