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ABSTRACT: Petroleum Potential of the West Southland Sedimentary Basins

URUSKI, CHRIS, DSIR Geology and Geophysics, Lower Hutt, New Zealand

Seismic mapping of the West Southland basins as part of the Cretaceous and Cenozoic Project has elucidated the stratigraphic and structural history of the region. At the same time a range of potential hydrocarbon traps have been mapped, many for the first time.

Onshore, the Te Anau ana Waiau basins developed initially as tensional rifts and potential traps were formed by rollover against listric faults. In the late Oligocene, uplift and erosion is locally important near the basin axes. This unconformity, marks the onset of regional compression which continues to the present day. Neogene compression and syn-tectonic sedimentation produced a variety of possible traps by tightening earlier tensional rollover and by rollover on the back of thrusts and reverse faults.

Offshore, from east to west, the Solander, Waitutu and Balleny basins shared a similar history to that of the onshore basins. North-easterly-trending normal faults controlled sedimentation during the Cretaceous and Paleogene. The effects of Neogene compression are more intense in the northeast and die away to the south and west such that the Baileny Basin appears to have been relatively undeformed by compression. Several closures were formed during the compressive episode as sedimentary basin fill was driven back up fault ramps to form large anticlines against basement blocks.

With coal measures buried to depths which should ensure maturity and abundant marine mudstones in the Miocene section it is likely that hydrocarbons have been generated and trapped in the region. The number of closures both onshore and offshore suggests that the legion is a target-rich environment.

 

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