Lithostratigraphy and depositional episodes of the Oligocene carbonate‐rich Tikorangi Formation, Taranaki Basin, New Zealand

Abstract

The subsurface Oligocene Tikorangi Formation is a unique and important oil producer in the onshore Waihapa-Ngaere Field, Taranaki Basin, being the only carbonate and fracture-producing reservoir within the basin. Core sample data from seven onshore wells (foredeep megafacies) and a single offshore well (basinal megafacies) are correlated with a suite of sonic and gamma-ray geophysical well log data to derive interpretative carbonate facies for the Tikorangi Formation. Four mixed siliciclasticcarbonate to carbonate facies have been defined: facies Acalcareous siliciclastite (<25% carbonate); facies B-very calcareous siliciclastite (25-50% carbonate); facies Cmuddy limestone (50-75% carbonate); and facies D-coarse limestone (>75% carbonate). Single or interbedded combinations of these facies form the basis for identifying nine major lithostratigraphic units in the Tikorangi Formation that are correlatable between the eight wells in this study.The Tikorangi Formation accumulated across a shelfslope-basin margin within a tectonically diversified basin setting, notably involving considerable off-shelf redeposition of sediment into a bounding foredeep. Analysis of gamma, sonic, and resistivity well logs identifies five major episodes of sedimentary evolution. Episode I comprises retrogradational siliciclastic-dominated redeposited units associated with foredeep subsidence. Episode II is a continuation of episode I retrogradation, but with increased mass-redeposited carbonate influx during accelerated foredeep subsidence and relative sea-level rise, the top marking the maximum flooding surface. Episode III involves a progradational sequence comprising relatively pure redeposited carbonate units associated with declining subsidence rates and minimal siliciclastic input, with movement of facies belts basinward. Episode IV consists of prograding aggradation involving essentially static facies belts dominated by often thick, periodically mass-emplaced, carbonate-rich units separated by thin background siliciclastic shale-like units. Episode V is a retrogradational sequence marking the reintroduction of siliciclastic material into the basin following uplift of Mesozoic basement associated with accelerated compressional tectonics along the AustraliaPacific plate boundary, initially diluting and ultimately extinguishing carbonate production factories and terminating deposition of the Tikorangi Formation.

Discriminating cool‐water from warm‐water carbonates and their diagenetic environments using element geochemistry: The Oligocene Tikorangi Formation (Taranaki Basin) and the dolomite effect

“…4,10), particularly so in the dolomiterich samples (Table 2). The source of this Fe enrichment was probably from compaction in interbedded siliciclastic shale-like sequences (Hood et al 2003a). Elevated Mn levels in the Tikorangi Formation in relation to the New Zealand database are similarly attributable to dolomite formation at considerable depths and elevated temperatures (Hood 2000).…”

Tectonic controls on Miocene sedimentation in the Southern Taranaki Basin and implications for New Zealand plate boundary deformation

“…25–21 Ma (King & Thrasher, ; Strogen et al, ). The resulting low clastic sediment supply lead to widespread deposition of condensed carbonate‐rich facies in distal parts of the basin (Hood, Nelson, & Kamp, ; King & Thrasher, ).…”

Petrogenesis of diachronous mixed siliciclastic‐carbonate megafacies in the cool‐water Oligocene Tikorangi formation, Taranaki Basin, New Zealand

“…Petrographic variability over short vertical intervals within the foredeep megafacies resulted from the complex interplay of a number of controlling factors: (1) the rapidly evolving tectonic setting which provided a range of coexisting shelfal, active foredeep, and tectonically quiescent distal basinal settings; (2) deposition during a number of relative sea-level changes within an overall transgressive or submergence regime (Hood et al 2003); (3) the proximity to, and availability of, different siliciclastic sources, including from the east (Patea-Tongaporutu-Herangi High), south (South Island), and possibly even west (Australia) (Stein & Robert 1986); and (4) the variability of composition, timing, and spatial distribution of mass redepositional events supplying sediment into the Taranaki foredeep basin.…”

“…The potential of highstand shedding as a mechanism for supplying shelfal material basinward in the cool-water Taranaki foredeep setting is possible given the broad scale transgressive event (King & Thrasher 1996) which was reaching its culmination (highstand) during and following Tikorangi deposition (Hood et al 2003). The occurrence and importance of carbonate mass redeposition events in the cool-water setting, whether solely or truly highstand or not, is certainly worthy of specific mention alone.…”

“…Initial deepening-upward sequences show foredeep subsidence outpaced sedimentation. Shallowingupward sequences developed in the upper part of Tikorangi Formation (Hood et al 2003) when sedimentation exceeded subsidence/sea-level rise, so that the foredeep was gradually filled with Tikorangi carbonate and siliciclastics associated with uplift and subaerial exposure of eastern Taranaki and South Island basement rocks. Renewed clastic input to the basin began in the earliest Miocene as a result of tectonic uplift and erosion, and by the end of the early Miocene rates of clastic supply surpassed rates of subsidence.…”