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 CretaceousTertiary transgressive-regressive sediments of coastal Otago. These provide the basis for stratigraphic division and correlation with seismic reflectors in the offshore ageequivalent sediments of the Great South Basin. The ages of the unconformities/conformities are constrained mainly by dinoflagellate biostratigraphy, but foraminiferal biostratigraphy 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 midWaitakian (Miocene) unconformity. Other, early-midCretaceous unconformities are inferred from offshore seismic profiles. Six unconformities/correlative conformities in onland Otago provide the basis for recognising four informal alloformations.

The Cretaceous/Tertiary boundary event in New Zealand: Profiling mass extinction

“…When related to the Clarence valley records, these inferred climate cycles are shown to be linked to sea-level changes (Hollis et al 2003a). When linked to evidence for significant relative sea-level changes (Moore 1989;McMillan & Wilson 1997;Laird et al 2003) and cool climatic conditions (Vajda et al 2001;Kennedy 2003;Vajda & Raine 2003) during the early Paleocene throughout New Zealand, a case can be made along the lines proposed by D 'Hondt et al (1996a). Namely, mass extinction of calcareous plankton, resulting in greatly reduced CO 2 drawdown, coupled with injection into the atmosphere of massive quantities of CO 2 following vaporisation of carbonate target rock (O'Keefe & Ahrens 1989;Pope et al 1997), caused long-term disruption to the biogeochemical feedback systems that influence climate.…”

“…In the majority of siliciclastic, shallow to deep marine sections in New Zealand, such indicators are lacking and the K/T boundary is an erosional surface (Moore 1989 1993; Field et al 1997;McMillan & Wilson 1997;. In the eastern basins, fine-grained Cretaceous sediments typically are overlain unconformably by coarser grained, glauconitic sediments (Table 1).…”

Paleoenvironmental changes across the Cretaceous/Tertiary boundary in the northern Clarence valley, southeastern Marlborough, New Zealand

“…However, the discontinuities, erosion, and interdigitation of proximal and distal facies evident in the units B-D1 at Branch Stream are similar to shelf sections throughout eastern New Zealand. Most commonly, the K/T boundary is marked by a significant disconformity and an increase in grain size consistent with a significant sea-level fall, perhaps by as much as 50 m (Moore 1989;McMillan & Wilson 1997;Laird et al 2003). Further disconformities within lower Paleocene strata in Otago indicate a succession of sea-level changes (McMillan & Wilson 1997).…”

“…Most commonly, the K/T boundary is marked by a significant disconformity and an increase in grain size consistent with a significant sea-level fall, perhaps by as much as 50 m (Moore 1989;McMillan & Wilson 1997;Laird et al 2003). Further disconformities within lower Paleocene strata in Otago indicate a succession of sea-level changes (McMillan & Wilson 1997). A eustatic origin for some of these events is possible as similar regressive pulses are recorded in lower Paleocene sections in the Tethyan region (Brinkhuis & Zachariasse 1988;MacLeod & Keller 1991;Adatte et al 2002;Keller et al 2002) and in eastern North America (Olsson et al 2002).…”

High-level stratigraphic scheme for New Zealand rocks

“…Moreover, the Marshall Unconformity is not recognised everywhere, has different ages and potentially different origins and occurs variably within or beneath the overall Oligocene carbonate-dominated succession (King et al 1999;Lever 2007). All things considered, our preference in this paper is not to use the Marshall Unconformity sensu stricto as a defining boundary between supergroups, as it is only one of many local unconformities developed in this period (see also McMillan & Wilson 1997). Latest Eocene-Early Oligocene carbonate units that underlie the Marshall Unconformity in its type area (e.g.…”