South Australia Offshore

Bight Geographic Basin (Denmark / Bremer Sub-Basin )

These geographic sub-basins corresponds to a series of half-grabens, developed over a Proterozoic substratum, and filled by Jurassic to Lower Cretaceous sediments. They were initiated by a Late Jurassic lengthening, which was followed by a Berriasian-Hauterivian thermal subsidence to breakup from Antarctica in the Santonian and into Maastrichtian following the breakup of the Pangea. During the breakup, many of the rifting faults were reactivated and some new faults were formed. Major uplift and erosion was restrict, mainly, to the western Bremer geographic sub-basin, where uplift of the rift-flanks produced a major tectonically enhanced unconformity (angular unconformity). The predominant carbonate Atlantic-type divergent margin, particularly, in the overlying Eucla geographic basin, seems to be associated with a pronounced Middle Eocene and younger submarine canyon incision.

Taking into account the seismic pitfall induced by the abrupt changes in water depth, on this Canvas autotrace the pre-rifting unconformity is Late Jurassic and the breakup unconformity, which separates the rift-type basins from the Atlantic-type divergent margin, is Lower Cretaceous, probably, Aptian. The majority of the normal faults responsible by the lengthening die at the breakup unconformity, what means there is a change in the realm of subsidence. The rift-type basins are, easily, recognized not only by their geometry in half-graben, but the associated growth faults as well. The Atlantic-type divergent margin, which is quite thin, comprise, mainly, Cretaceous sediments covered by a narrow Cenozoic interval.

This tentative interpretation corroborates the conjectures proposed on the previous autotrace, particularly, on the onset of the rifting, which seems to start in the Late Jurassic, and on the age of the breakup unconformity (Lower Cretaceous, probably, in Barremian/Aptian). In addition, this autotrace, clearly, illustrates the reactivation of some old normal faults during the Atlantic-type divergent margin development.

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Copyright © 2001 CCramez
Last update: 2022