Allostratigraphy of coastal south and east Otago: A stratigraphic framework for interpretation of the Great South Basin, New Zealand

Abstract

Sixteen unconformities, some with correlative conformities, are recognised within the Late Cretaceous‐Tertiary transgressive‐regressive sediments of coastal Otago. These provide the basis for stratigraphic division and correlation with seismic reflectors in the offshore age‐equivalent sediments of the Great South Basin. The ages of the unconformities/conformities are constrained mainly by dinoflagellate biostratigraphy, but foraminiferal biostrati‐graphy is important for the Oligocene—Miocene. In terms of current biozone‐stage correlation, the 16 unconformities comprise the following: two intra‐Haumurian (Late Cretaceous) unconformities, one at the K/T boundary, three intra‐Teurian (Paleocene) unconformities, two of early Waipawan age, two of late Mangaorapan — early Heretaungan age, a late Heretaungan unconformity, a late Porangan ‐ early Bortonian unconformity, a late Bortonian unconformity (a total of seven Eocene unconformities), a late Runangan ‐ early Whaingaroan unconformity, a late Whaingaroan unconformity (both Oligocene), and a mid‐Waitakian (Miocene) unconformity. Other, early—mid‐Cretaceous unconformities are inferred from offshore seismic profiles. Six unconformities/correlative conformities in onland Otago provide the basis for recognising four informal alloformations.