Abstract:
This study examines the final emergence of the southeastern Wairarapa within a
sequence stratigraphic framework. New exposures of the Pleistocene marginalmarine
Hautotara Formation, and non-marine Te Muna Formation allow facies to be
detailed and sequence architecture to be analysed.
Cyclicity observed within the facies successions of the Hautotara and Te Muna
formations are placed in a series of four motifs. These motifs record 40 kyr glacioeustatic
cyclicity superimposed upon the basinward to landward progression of the
environments, showing the region shallowing through time.
The positions of the top of the Pukenui Limestone and the base of the Hautotara
Formation are revised, and are now at the top of the “Pukenui C” - a widespread
marker bed, which also removes a historical nomenclatural gap. The recognition of
the significance of the coccolith Gephyrocapsa sinuosa within the underlying
Pukenui Limestone allows this contact to be dated at 1.73 Ma.
The ~1.6 Ma age limit provided by a number of tephra within the lower sediments of
the Te Muna Formation allow the ages of the examined formations to be constrained
further. The eight 40 ka cycles identified within the Hautotara Formation suggests
deposition between 1.73 and 1.42 Ma.
The Hautotara - Te Muna Formation is revealed to be diachronous, with the base of
the Te Muna Formation type section shown to be much younger, 1.12 Ma, than the
1.58 Ma age of the lower contact observed elsewhere in the region. A series of
palaeogeographic reconstructions at 1.73, 1.58 and 1.57 Ma demonstrate how closely
related sedimentation patterns are to structural growth, with marginal-marine
Hautotara Formation sedimentation persisting in the centre of the study area well
after the initiation of Te Muna Formation terrestrial deposition to the north and south
of this site.
