ABSTRACT: A Thermal and Structural Framework for the Otway Basin, S.E. Australia: An Integrated Kinetic Approach Using AFTA (Apatite Fission Track Analysis) and Vitrinite Reflectance

DUDDY, IAN R., and PAUL F. GREEN, Geotrack International Pty. Ltd., Melbourne University, Victoria, Australia

The thermal histories at a number of hydrocarbon exploration well and outcrop sites from the Otway basin and environs have been assessed using modern kinetic descriptions of Apatite Fission Track Analysis (AFTA) and vitrinite reflectance data, allowing fundamental constraints to be placed on the structural development of the basin. In particular, our approach permits the quantification of the timing and magnitude of major structuring at the cessation of rifting and initiation of the Southern Ocean at around 95 Ma, which was caused by reactivation of rift-phase extensional normal and transfer faults.

Paleotemperature profiles based on vitrinite reflectance data indicate that high paleogeothermal gradients (up to ~70 degrees C/km) in parts of the basin were present at the end of the rifting phase (up until ~95 Ma), but have subsequently declined to present levels of ~30 to 40 degrees C/km. While elevated paleogeothermal gradients are clearly indicated, caution must be exercised in interpreting these as a response to elevated basal heat-flow given the possibility of a number of "internal heat sources," including fluid flow, radioactive decay and exothermic diagenetic reactions, the influences of which are difficult to quantify.

Together, the thermal and structural framework established by this data-based approach allows more rigorous assessment of the hydrocarbon potential of the Otway basin than possible using thermal modeling based on unfettered manipulation of heat flow through time.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)