--> Mass Transport Deposits (MTD) Seismic Facies Control on Topography Creation for Later Turbidite Deposition in Taranaki Basin, Offshore New Zealand

AAPG ACE 2018

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Mass Transport Deposits (MTD) Seismic Facies Control on Topography Creation for Later Turbidite Deposition in Taranaki Basin, Offshore New Zealand

Abstract

High quality 2D and 3D seismic data from Taranaki Basin offshore New Zealand reveal large mass transport deposits (MTDs). These MTDs are clearly identified on seismic sections as chaotic discontinuous reflections with low amplitudes. Key kinematic indicators, such as the orientation of lateral margins, the presence or absence of headwall scarps, the nature of the basal shear surfaces combined with probable causal mechanisms and features of slope instabilities peculiar to MTDs in the Taranaki region indicate that these are largely slope-attached MTDs. This study focuses on the role of these MTDs in creating topography which affected the deposition of later turbidite systems. Four (4) main seismic facies have been identified within the MTDs as: Extensional Blocky Facies (EBF), Low Amplitude Facies (LAF), Levee Channel Complex (LCC) and Folded Facies [(FF) – Crosscuts, Thrusted & Inclined]. These facies can indicate topographic relief and sediment accumulation due to irregularities on the surfaces of these MTDs. The relationship between ‘ponding’ of turbidites and the accommodation style on top of the MTDs is investigated, from the excavation point to the buckling stage. The results of this analysis show that MTD related topography directly affected sedimentation and the resultant turbidite system architecture. Two main types of topography were identified - Type I: Stress-Induced; and Type II: Depositional Topography. From the point of excavation and during emplacement, Type I is observed prominent in the headwall and Toe regions of MTDs, resulting in loosely connected and isolated ponds of sediments. Type II is observed in translational domain, where the effects of sediment loading are clearly recorded. The development of this topography type suggests that a continuous post differential compaction and lateral syn depositional remobilisation affects MTDs in this domain

This is significant to hydrocarbon reservoirs as our interpretation reveals how each stage of topography creation on the MTD surface can lead to reservoir development. Understanding ponding/accommodation relationships and reservoir quality distribution improves exploration and production planning.