Key Indicators of Epeirogenic Uplift of the Canterbury Basin, South Island, New Zealand

Abstract:

The Canterbury Basin (South Island, New Zealand) is a passive margin that formed after rifting of Zealandia from Gondwana at ~83Ma. IODP expedition 317 cores from Sites U1351, U1353, and 1U352 have been resampled and analyzed with emphasis on benthic foraminifera and trace fossils from the Late Eocene to the Present. Using revised water depth and age data from these sites and from the Clipper-1 well, a new basin subsidence model has been generated for the Canterbury Basin. One-dimensional backstripping of the upper shelf wells is interpreted to have been influenced by significant downslope contamination, erosional/non-depositional events and low accommodation space. However, slope sites U1352 and Clipper-1 indicate possible uplift coupled with an erosional/non-depositional event that began at ~5.7 Ma and reached a minimum water depth by ∼3.7 Ma. During this time interval 2 sequences and 3 sequence boundaries are identified.

A possible explanation is epeirogenic uplift resulting from the migration of the South Island over a slab graveyard. In this model, water released from these slabs generated a Rayleigh-Taylor instability in the mantle lithosphere, causing the lithospheric mantle to drip or delaminate. This hypothesis explains the rapid uplift while preserving the passive margin geometry of the Canterbury Basin.