Paleocene–Eocene stratigraphy and paleoenvironment at Tora, Southeast Wairarapa, New Zealand

Abstract

The Upper Cretaceous and Lower Paleogene sedimentary rocks at Tora, southeast Wairarapa, are considered to form a transitional sedimentary succession within the East Coast Basin, containing elements of both the siliciclastic succession to the north in the eastern North Island and the pelagic succession to the south in eastern Marlborough. However, the Tora succession is complicated by rapid lateral facies changes, numerous unconformities and unusual occurrences of coarse-grained facies in what is more typically a rather monotonous fine-grained passive-margin sequence. We interpret the uppermost Cretaceous and Paleocene units (Manurewa, Awhea, Mungaroa and Awheaiti formations) as components within a middle to lower bathyal, submarine channel and fan complex that unconformably overlies the Upper Cretaceous Rakauroa Member of the Whangai Formation. The two overlying Lower–Upper Eocene units (Pukemuri Siltstone, Wanstead Formation) both consist of a basal debris-flow deposit grading into middle bathyal mudstone, deposited during progressive marine transgression and deepening to lower bathyal–abyssal depths.