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ABSTRACT: Late Pleistocene Aligning Basins at a Subduction to Transform Plate Boundary: Evolution of Cook Strait, New Zealand

LEWIS, KEITH B., and LIONEL CARTER, New Zealand Oceanographic Institute, Wellington, New Zealand

Seismic stratigraphy and a variety of other data sets are used to show how five basins on an oblique subduction to intercontinental transpressional margin have linked to form a central gap in the rising axial ranges of New Zealand. Until late Pleistocene times, rotating, mud-filled, forearc to transform, southeastern basins were separated from muddy, northwestern, foreland basins by a land barrier. The barrier was gradually submerged as the foreland Wanganui basin migrated southward and an interconnecting Narrows basin developed in response to divergent branching of a major transcurrent fault.

The barrier was breached for the first time during a post-glacial transgression about 450 ka. Fierce tides then scoured the muddy basin sediments on either side of the barrier. A landbridge re-emerged 3 times during subsequent glacio-eustatic falls of sea level and was breached at the next post-glacial rise. High sea level erosion and low sea level deposition (the opposite to normal shelf processes) are recorded by three highly irregular unconformities and three seismic sequences in basins adjacent to the barrier. During the last such fall, tidal scour and subsidence had lowered the barrier sufficiently that it did not reemerge. Despite building of spit barrier in the western approaches to Cook Strait at maximum lowering of sea level, the gravel-lag lined Narrows seaway and its powerf l tides was able to survive at all stages of the glacio-eustatic cycle.

 

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