Western Otway Crayfish Group Troughs

Abstract

Commercial volumes of hydrocarbons have been discovered in Early Cretaceous synrift sediments of the Crayfish Group of the Penola Trough, western Otway Basin. Four other such depocentres are recognised using available seismic and drilling data. A standard nomenclature is proposed for the major structural elements observed in this part of the Otway Basin.Various tectonic models proposed for the Early Cretaceous rift history of the Otway Basin are reviewed and tested using true dip analysis of seismic events and sandbox modelling experiments. Results support a generally north-south direction for rift extension in the Tithonian-Barremian. This implies that the ENE trending Robe Trough is the headwall rift compartment (although with 20°obliquity), whereas the NW trending Penola Trough is a more oblique or transtensional rift compartment.

Site U1512

“…The Eumeralla Supersequence is up to 2300m thick in well intersections and estimated to reach up to 4500m in the Shipwreck Trough (based on calculated seismic velocities; this study) The Aptian-Albian was also a period of prolific volcanic eruptions to the east and input of volcaniclastic sediments into the eastern basins (Mortimer et al, 2005) Observations of active fault movement appear to cluster in the eastern Otway Basin (Palmowski et al, 2004;Krassay et al, 2004; this study), Torquay Sub-basin (Cooper and Hill, 1997;this study), possibly the western Bass Basin (Blevin et al, 2005; this study), and in the western Gippsland Basin (Power et al, 2001). Other workers (e.g., Cockshell et al, 1995;Morton et al, 1995;O'Brien et al, 1994) describe deposition of the Eumeralla Formation in the Otway Basin as an uppermost syn-rift sequence deposited during a slower, second rifting phase where fault activity was reduced in the onshore basin, but continued offshore. To the east, the New Zealand margin entered an extensional phase around 120 Ma (mid-Aptian) following the end of subduction and Rangitata metamorphism (Norvick and Smith, 2001).…”

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

“…BerriasianBarremian (141-115 Ma) deposition of the Crayfish Group is evident in a series of half-graben rift segments in the onshore and some offshore parts of the basin. Hill et al (1995) and Cockshell et al (1995) indicated that the pattern of structural development is consistent with a general north-south extensional regime during the Early Cretaceous.…”

Remote sensing of subsurface fractures in the Otway Basin, South Australia

“…Changes in far‐field plate boundary forces during the mid‐Eocene resulted in a change in the nature of the basin, with a compressional stress regime dominating [ Perincek and Cockshell , ; Holford et al ., ]. The onset of compression led to the reactivation of existing extensional faults and possibly the formation of antiforms; however, no large‐scale inversion is seen within the Penola Trough [ Cockshell et al ., ].…”