The effect of volcanism on cool-water carbonate facies during maximum inundation of Zealandia in the Waitaki–Oamaru region

Abstract

The paleogeography of the Waitaki-Oamaru region during the Oligocene-Miocene maximum inundation was defined by a volcanic paleohigh producing a rimmed cool-water carbonate shelf geometry. Basaltic surtseyan style cones became the setting for a productive cool-water carbonate factory isolated from terrigenous input. To the west, impure wackestones and calcareous siltstones contain terrigenous material derived from low relief landmasses farther to the west. A lowstand following the cessation of volcanism caused the paleohigh to become subaerially exposed, forming an extensive dissolution surface in the east correlative with submarine firmgrounds to the west. Stronger currents from the south and significant storm events sweeping over the high reworked carbonate and glauconitic sediment and deposited it in channels to the north. Carbonate deposition west of the paleohigh filled in the deeper part of the basin eventually resulting in a wider, shallower and more regular shelf environment. Depositional environments of the Waitaki-Oamaru region during the Waitakian (Late Oligocene-Early Miocene) were overall shallower than during the earlier Whaingaroan (Early Oligocene) Stage when a more complex paleotopography existed. This is unlike elsewhere in New Zealand where maximum depth was reached during the Waitakian Stage. Thus, the existence of an isolated, submerged paleohigh in a cool-water carbonate basin can have a significant effect on the evolution of that basin, stimulating carbonate factories to develop where they might otherwise not.

Sedimentary architecture of a Late Cretaceous under‐filled rift basin, Canterbury Basin, New Zealand

“…With time these facies transgressed progressively westward, associated with an overall deepening of the basin (Figure 2; Andrews et al, 1987;Browne & Field, 1985;Field & Browne, 1986, 1989Sahoo et al, 2015Sahoo et al, , 2017. By the end of the Eocene to Early Oligocene, the coastline had migrated to its most westerly extent and fine-grained carbonate sedimentation predominated throughout the basin, with localised shallow and cold-water bryozoan-molluscan-brachiopod dominated carbonate build-ups developed over paleo-topographic highs (Barrier et al, 2019;Field & Browne, 1989;Lever, 2007;Thompson et al, 2014).…”

A review of the genus Pelodiaetus Jeannel (Coleoptera, Carabidae, Anillini) of New Zealand, with re-description of the genus, description of a new species, and notes on the evolutionary history

“…Given that the lands of the Northland Allochthon were completely submerged during the late Oligocene and became subaerial only around the late-to mid-Miocene after subduction of the Pacific Plate under the Australian one (Bradshaw 2004), the later arrival of the members of Pelodiaetodes to the North Island can be assumed. The Oamaru region remained submerged from the Late Cretaceous to the early Oligocene, but some lands of this region were likely exposed during the Oligocene "drowning" from the late Oligocene to the early Miocene (Thompson et al 2014), which is supportive of the idea of the late arrival of the members of Pelodiaetodes to the Oamaru region as well. The absence of Pelodiaetodes-like forms in Australia but their presence as two morphologically distinct taxa in New Zealand suggests that the genus Pelodiaetodes arose after the East Gondwana breakup, but before New Zealand acquired its modern contour, i.e., somewhere on the Zealandia continent.…”

Oligocene paleogeography of New Zealand: maximum marine transgression

“…Thompson et al (2014) look at the effects of this volcanism in the Waitaki-Oamaru region of South Island. They suggest that the presence of a Kaiatan to early Whaingaroan volcanic paleo-high, where water depths were much shallower than in other parts of Zealandia, encouraged the deposition of cool-water carbonates.…”