Mesozoic Tectonics of the Otway Basin Region: The Legacy of Gondwana and the Actve Pacific Margin—a Review and Ongoing Research

Abstract

Mesozoic extension along Australia's southern margin and the evolution and architecture of the Otway Basin were probably controlled by three factors: 1) changes in global plate movements driven by mantle processes; 2) the structural grain of Palaeozoic basement; and, 3) changes in subduction along Gondwana's Pacific margin. Major plate realignments controlled the Jurassic onset of rifting, the mid-Cretaceous break-up and the Eocene onset of rapid spreading in the Southern Ocean.The initial southern margin rift site was influenced by the northern limit of Pacific margin (extensional) Jurassic dolerites and the rifting may have terminated dolerite emplacement. Changed conditions of Pacific margin subduction (e.g. ridge subduction) in the Aptian may have placed the Australia-Antarctic plates into minor compression, abating Neocomian southern margin rifting. It also produced vast amounts of volcanolithic sediment from the Pacific margin arc that was funnelled down the rift graben, causing additional regional subsidence due to loading. Albian orogenic collapse of the Pacific margin, related to collision with the Phoenix Plate, influenced mid-Cretaceous breakup propagating south of Tasmania and into the Tasman Sea.Major offsets of the spreading axis during breakup, at the Tasman and Spencer Fracture zones, were most likely controlled by the location of Palaeozoic terrane boundaries. The Tasman Fracture System was reactivated during break-up, with considerable uplift and denudation of the Bass failed rift to the east, which controlled Otway Basin facies distribution. Palaeozoic structures also had a significant effect in determining the half graben orientations within a general N-S extensional regime during early Cretaceous rifting. The late Cretaceous second stage of rifting, seaward of the Tartwaup, Timboon and Sorell fault zones, left a stable failed rift margin to the north, but the attenuated lithosphere of the Otway-Sorell microplate to the south records repeated extension that led to continental separation and may be part of an Antarctic upper plate.

Structure and development of the west Tasmanian offshore sedimentary basins: Results of recent marine and aeromagnetic surveys

“…Uplift and erosion in the Cenomanian (Hill et al 1995a) coincided with Australia-Antarctica breakup farther to the west (Veevers 1986) and the onset of Tasman Basin rifting (Symonds et al 1996), prior to breakup at ca 80 Ma. In the eastern Otway and northern Sorell Basins, resumption of sedimentation in the CenomanianMaastrichtian (Sherbrook Group) took place in shallow marine to fluvial environments (Sarma 1995).…”

Otway Continental Margin Transect: Crustal architecture from wide‐angle seismic profiling across Australia's southern margin

“…In the eastern Otway Basin area the significant thicknesses of Sherbrook Group sequences are largely confined to the Port Campbell Embayment (Figure 3) and in the western/central parts of the basin there are significant thicknesses seaward of the Tartwaup Fault Zone in the Voluta Trough (Figure 4). The Otway Basin Tertiary sequences comprise the Wangerrip, Nirranda and Heytesbury Groups formed during a series of transgressiveregressive episodes and blanket most of the basin with notable exceptions across the Otway Ranges and Merino High (see Hill et al 1995).…”

“…Extensive onshore seismic reflection profiling by the oil exploration industry and the Australian Geological Survey Organisation (AGSO) defined the half-graben geometry of early basin rift segments along the basin's northern margins where there are outcropping Palaeozoic rocks of the Delamerian and Lachlan Fold Belts. Also highlighted was the two-stage extension/rifting process in the Otway Basin during the separation of Australia and Antarctica (Williamson et al 1990), with the landward limits of the second-stage extension being along what Hill et al (1995) termed the Tartwaup-Tyrendarra-Timboon fault system. It was recognised that much of the Otway Basin lay offshore and that defining the structures and crustal architecture of the offshore area was necessary to gain a full understanding of the basin's development and evolution.…”

Soil Gas Baseline Characterisation Study - Methodology and Summary.

“…The Early Cretaceous faults do not persist through to the Late Cretaceous but major northwest-southeast trending faults were activated as a consequence of high sediment loading and thermal relaxation (Morton, 1995). Late Cretaceous slow drift and regional subsidence in the western Otway Basin was replaced by rapid seafloor spreading in the Eocene (Hill et al, 1995).…”