Sabrina van De Beuque5
(1) Australian Geological Survey Organisation, Canberra, Australia
(2) IFREMER, DRO/GM, Nouvelle-Calédonie, France
(3) University of Texas Institute for Geophysics, Austin, TX
(4) James Cook University, Townsville, Australia
(5) IFREMER, Canberra, Australia
The Lord Howe Rise is a rifted continental fragment about 1600 km long, 250-600 km wide and 700-1500 m deep that extends NNW from the South Island of New Zealand. The rise separated from Australia during the 85-52 Ma episode of seafloor spreading that formed the Tasman Basin.
Recent reflection seismic surveys revealed bottom simulating reflectors (BSRs) over the northeastern and western flanks of the rise that may indicate the presence of gas hydrate (a frozen crystalline mixture of methane and water) within the upper 600 m of sediment. These observations constitute the first compelling evidence for methane hydrate deposits in waters off Australia.
Coincidence of some BSRs with the margins of sedimentary basins may indicate a deep thermogenic component to the gas hydrates, rather than forming solely from shallow biogenic gas. Associated evidence for low-level oil slicks and films on satellite synthetic aperture radar (SAR) imagery, combined with seismic evidence for fluid migration through the sedimentary section, provide further indications of hydrocarbon generation and active migration to the seafloor.
Complementary ongoing investigations incorporate geophysical characterisation of the BSR seismic signal; multibeam swath mapping of the seafloor and continuous analysis of surface water for traces of oil using a fluorimeter; and analyses of gas and pore water samples from cores.
These integrated studies provide new insights into the nature of the BSRs and the possibility of unconventional gas resources beneath Lord Howe Rise, as well as an improved understanding of the conventional hydrocarbon resource potential of this frontier region.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana