Geology and hydrocarbon potential of the Antarctic continental margin

Abstract

Seismic surveys have been conducted on most of the seasonally ice-free portions of the Antarctic continental margin, but drilling has been limited to only a few areas. These data, coupled with the results of geological studies of coastal outcrops and information from the conjugate Gondwana continents, are used to infer the subsurface geology of five different sectors of the Antarctic continental margin and to assess their hydrocarbon potential. Potential source rocks are believed to exist on most portions of the continental margin and are buried deep enough, or are subjected to high enough geothermal heat, for hydrocarbon maturation to have occurred in these deposits. Suitable reservoir rocks are also considered to be widespread on the margin, with the possible exception of that portion of the Pacific-Antarctic margin situated north of the Tula Fracture Zone and including the Bransfield Basin. Structural traps are generally confined to the older sequences on the margin that fill early rift basins. Stratigraphic traps are probably common. WILKES LAND SECTOR GeologyPrior to the breakup of Gondwana, the Australian and Antarctic continents were joined along what is now the Wilkes Land continental margin of Antarctica ( Figure 2). Initial studies of magnetic data from the Indian Ocean by Weissel and Hayes [1972] led to the conclusion that seafloor spreading between Australia and Antarctica began 55 million years ago. Later, Cande and Mutter [1982] reinterpreted these data and concluded that initial rifting between the two continents had actually begun between 110 and 90 Ma, and Veevers [1986] constrained the time of breakup to 95 _+ 5 Ma. Actual breakup was preceded by an extended period of extension and rifting, which Falvey [1974] refers to as the Rift Valley Phase. This phase probably began in the mid-Jurassic [Veevers, 1987]. During this time, rift basins formed in the vicinity of the incipient breakup axis. Initially, these basins were broad troughs which developed into narrow fault-bounded basins as rifting progressed [Falvey and Mutter, 1981]. Subsidence rates on Australia's southern margin were high (an average of 0.1 km/Ma) during the rifting phase and slowed appreciably (an average of 0.01 km/Ma) during the postbreakup phase [Falvey and Mutter, 1981]. During the rifting phase, a thick sequence of mostly continental deposits accumulated in the basins of southern Australia, with periodic marine invasions from the west result-

Antarctic Glacial History and Sea-Level Change

“…The peninsula interior is 2000 m high and is composed largely of Andean-type plutonic and volcanic rocks. Before ridge subduction, the Pacific margin was a welldeveloped forearc terrain on which the glacial regime has superposed an extensive prograded wedge (Larter and Barker, 1989Barker, , 1991bAnderson et al, 1990;Larter and Cunningham, 1993;Bart and Anderson, 1995;Larter et al, 1997). The topography and geology of the peninsula vary little along strike, which simplifies the models of erosional and depositional response to climate Leg 178 Preliminary Report Page 10 change.…”