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Abstract: High Resolution Sequence Stratigraphy of Miocene Deep-Water Clastic Outcrops, Taranaki Coast, New Zealand

Peter R. King, Greg H. Browne, Roger M. Slatt, Julia L. Diridoni

Approximately 700 m of deep water clastic deposits of Mt. Messenger Formation are superbly exposed along the Taranaki coast of North Island, New Zealand. Biostratigraphy indicates the interval was deposited during the time span 10.5-9.2 m.y. in water depths grading upward from lower bathyal to middle-upper bathyal. This interval is considered part of a 3rd order depositional sequence deposited under conditions of fluctuating relative sea-level, concomitant with high sedimentation rates.

Several 4th order depositional sequences, reflecting successive sea-level falls, are recognized within the interval. Sequence boundaries display a range of erosive morphologies from metre-wide canyons to scours several hundred metres across. All components of a generic lowstand systems tract--basin floor fan, channel-levee complex and prograding complex-are present in logical and temporal order. They are repetitive through the interval, with the relatively shallower-water components becoming more prevalent upward.

Basin floor fan lithologies are mainly m-thick, massive and convolute-bedded sandstones that alternate with cm- and dm-thick massive, horizontally-stratified and ripple-laminated sandstones and bioturbated mudstones. Channel-levee deposits consist of interleaving packages of thin-bedded, climbing-rippled and parallel-laminated sandstones and siltstones; infrequent channels are filled with sandstones and mudstones, and sometimes lined with conglomerate. Thin beds of parallel to convoluted mudstone comprise prograding complex deposits.

Similar lowstand systems tracts can be recognized and correlated on subsurface seismic reflection profiles and wireline logs. Such correlation has been aided by a continuous outcrop gamma-ray log obtained over most of the measured interval. In the adjacent Taranaki peninsula, basin floor fan and channel-levee deposits comprise hydrocarbon reservoir intervals. Outcrop and subsurface reservoir sandstones exhibit similar permeabilities.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France