Publication Name: PESA Journal No. 26
Authors: N.F. Exon, G.R. Dickens, J-M. Auzende, Y. Lafoy, P.A. Symonds and S. Van de Beuque
Publication Volume: 26
Date Published: December 1998
Number of Pages: 12
Reference Type: Journal Article
Abstract:
Two recent reflection seismic surveys by AGSO's R.V. RigSeismic have revealed a bottom simulating reflector (BSR)
that extends over an area of at least 25,000 km2 of the Lord
Howe Rise and New Caledonia Basin in the Tasman Sea at
water depths of 1500-3600 m. Rift and post-rift sequences
in the area include Cretaceous, Palaeogene and Neogene
sediments, up to 3000 m thick. BSRs generally indicate an
interface between overlying sediment containing methane
hydrate (a frozen crystalline mixture of methane and water)
and underlying sediment containing free methane gas
bubbles. The depth of the BSR of 520-600 m below sea bed,
as inferred from seismic reflection profiles, is consistent
with this interpretation, given the expected thermal gradient
for the region. These seismic results constitute the first
compelling evidence for methane hydrate deposits in waters
off Australia. The deposit appears to be an immense
accumulation of natural gas in an unexpected location that
straddles the French-Australian international seabed
boundary. In the shorter term, indications of free gas,
including a flat spot within a horst, are probably of more
interest to the petroleum exploration industry. Forthcoming
research cruises will be devoted to mapping the overall
dimensions of the deposit and to understanding its origin. If
it proves to be largely thermogenic, the existence of
petroleum source rocks in the region will also be proven.