Sequence stratigraphy of the Miocene, Pohokura field, Taranaki Basin, New Zealand

A sequence stratigraphic study of the Miocene age was conducted in the Pohokura field, that is located offshore from the northern coast of Taranaki Penisula, New Zealand. It is a low-relief, north-south elongated anticline approximately 16 km long and 5 km wide. The study was carried out with two objectives which are to identify the Miocene seismic facies and to identify the sequence stratigraphic parameters. One seismic line and Pohokura-2 well was use in the study. Various seismic facies were observed in the seismic section including parallel, subparallel, continuous, subcontinuous, wavy, free reflection, subchaotic, high amplitude-high frequency and high amplitude-low frequency reflection. The interpreted seismic line showed three chronostratigraphic units which is sequence boundary 1 (SB1) represent top Manganui, sequence boundary 2 (SB2) represent top Mount Messenger and sequence boundary 3 (SB3) represent top Urenui. SB1, was separated by two distinct seismic facies namely sub-parallel and sub-chaotic. Parallel and sub-parallel reflection was observed on top of the sequence boundary SB2 while sub-chaotic and wavy seismic facies is found below the sequence boundary. SB3 is characterize by erosional truncation as shown by the present of toplap and downlap terminations in the western part of the seismic section. It is also supported by the clear difference of very high amplitud-high frequency reflection on top of SB3 overlying low amplitud-low frequency reflection of Urenui Formation. A complete depositional system including highstand, lowstand and transgressive system tracts are observed in the incised valley within the Urenui Formation.