Depositional and organofacies influences on the petroleum potential of an unusual marine source rock: Waipawa Formation (Paleocene) in southern East Coast Basin, New Zealand

The Paleocene Waipawa Formation is a widespread, ∼2–80 m-thick marine mudstone that occurs in several New Zealand basins. It is relatively enriched in organic matter (OM) and is the inferred source of a sub-commercial oil discovery and several correlated oil seeps. To determine the organofacies and depositional influences on the petroleum potential of the formation, we have undertaken a high-resolution, multidisciplinary study of the Taylor White section in the central East Coast Basin. This section is the thickest stratigraphically coherent surface exposure of the formation and includes contacts with the bounding Whangai and Wanstead formations. Bathymetric indicators within the foraminiferal assemblages indicate a slope setting for the section, deepening from middle to lower bathyal through the Waipawa–Wanstead succession. Significantly, the Whangai Formation in this section is barren of foraminifera. Dinoflagellate and calcareous nannofossil biostratigraphy provides somewhat conflicting age control but a resulting age model indicates a tenfold increase in compacted sediment accumulation rate during Waipawa deposition (from ∼1 to ∼10 cm/ky).