LECKIE, DALE A., Geological Survey of Canada, Calgary, Canada; HUGH MORGANS, GRAEME WILSON, HUNTLY CUTTEN, and CHRIS URUSKI, Institute of Geological and Nuclear Sciences Ltd., Lower Hutt, New Zealand; and DAVID FRANCIS, Lower Hutt, New Zealand

ABSTRACT: Late Cretaceous-Paleogene Shale of the East coast Basin, North Island, New Zealand: Regional Context and Hydrocarbon Potential

East coast Basin, New Zealand, contains thick source rocks, multiple reservoir systems and several large structures but is poorly explored. Gas and oil seeps are common. Late Cretaceous to Paleogene strata include (approx.) 1 km of dominantly marine siltstone with lesser sandstone. Siliceous siltstone of the Whangai Formation has low TOC content and HI except for the Calcareous Member. The Uri Member, at the top of Whangai, consists of glauconitic sandstone, mudstone and poorly-sorted conglomerate. The mid- to late Paleocene Waipawa Formation, up to 50 m thick, represents a marine condensed section. TOC contents are up to 5.3%, with Type II organic matter, and HI to 550. TOC content and HI increase above a pebbly mudstone interpreted as glacial dropstones representing a correlative co formity. All Waipawa Formation outcrop is immature but eastwards, sedimentary cover places the shale in the oil window. The volume of source rock present in the offshore may be at least 500 cu km. The Wanstead Formation downlaps onto the Waipawa and represents highstand marine shale with Type III organic matter and low HI. Potential reservoirs include the Tertiary to Quaternary fractured

calcareous and siliceous mudrock, turbidites, and shallow-marine sandstone and conglomerate, coquina limestone and fractured limestone. The late Cretaceous-Paleocene strata have been uplifted and exposed by Neogene movement on the Hikurangi subduction margin, active since the late oligocene/early Miocene. East Coast occupies an accretionary prism on the eastern flank of the Australian Plate above the westward, obliquely-subducting Pacific Plate.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.