Print this pagePalaeogeography of a Mid-Miocene Turbidite Complex, Moki Formation, Southern Taranaki Basin, New Zealand
The Moki Formation, Taranaki Basin, New Zealand, is a Mid Miocene sand-rich turbidite complex bounded above by the massive marine mudstone of the Manganui Formation. The Moki Formation is more than 300 m thick with amalgamated sandstone packages of up to 100 m. Good hydrocarbon shows in the Moki Formation have been documented in numerous wells and the formation provides the reservoir for the Maari field.
Previous regional studies have used well data alone and resulted in strongly contrasting palaeogeographic interpretations. Since the last regional interpretation was presented in 1996, several more wells have been drilled. This study combines well data with seismic interpretation to identify key stratal geometries between and away from wells, therefore better constraining the palaeogeography of the Moki Formation.
Nearly 30,000 km of 2D seismic and two 3D surveys, along with data from 18 key wells and three cores were available for interpretation. The Mid Miocene interval was mapped throughout the study area, and regional seismic lines, wireline log correlations and two-way travel-time (TWTT) structure maps are presented. Important stratal geometries have been identified which provide key constraints for the development of the Moki Formation. These include: marked eastern extent of the fan system, fan lobe switching as seen through amplitude variations, thinning and fining of the distal turbidite complex onto the basin floor, spectacular meandering channel systems incised into the formation at seismic scales and the coeval palaeoshelf-slope break in the southeast of the study area showing lensoid geometries and channelisation.
The Moki Formation was deposited when most of the basin was at bathyal water depths, and hinterland uplift permited a large supply of sediment to the basin-floor. During the Late Altonian (Burdigalian-Langhian), sandstone deposition was localised to a small fan body. By Clifdenian times (Langhian)the fan system was well-developed but localised in the south. With continued sediment supply during the Early Lillburnian (Early Serravallian), the fan system prograded substantially to the north and spilled onto the Western Stable Platform. Complex fan switching and spectacular meandering channel systems are well imaged in sediment of this age. As a result of seismic facies interpretation, the palaeogeography of the Late Altonian to Early Lillburnian in the southern Taranaki Basin has been better constrained.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil