The late Quaternary seismic, sedimentary and palynological stratigraphy beneath Evans Bay, Wellington Harbour

Abstract

Boreholes and offshore seismic profile surveys in southern Evans Bay, WelIington Harbour, indicate that a drowned river valley has been partly infilled with sediments during two glacial interglacial cycles. The original valley was probably eroded along the shatter zone of a late Pliocene fault situated on the eastern side of the bay. The infilling sediments include two assemblages: (I) interglacial age (including Holocene) shelly marine sands and muds, which have a palynoflora from flourishing rimu-podocarp forest, and (2) g1acial age gravelly and carbonaceous terrestrial deposits, wh ich have a palynoflora dominated by grasses or, in slightly milder times, by beech and manuka. Postdepositional deformation of early Holocene sediments may indicate either further faulting along the shatter zone of the Pliocene fault or an effect of sediment compaction during earthquake stress. Deformation of late Holocene sediments is interpreted as differential compaction and slumping being a secondary effect of earthquake shaking.