Seismic attributes and analogs to characterize a large fold in the Taranaki Basin

Abstract

The Taranaki Basin lies in the western portion of New Zealand, onshore and offshore. It is a Cretaceous rift basin that is filled with up to approximately 10 km thick deposits from marine to deepwater depositional environments from the Cretaceous (approximately 93 ma) to the Neogene (approximately 15 ma). This basin underwent important tectonic events that resulted in large-scale features such as faults and folds and the deposition of turbidites such as channels and channel belts. These features easily are recognizable in seismic data. When analyzing the offshore 3D Pipeline data set, we recognized a peculiar fault-like feature with large-scale dimensions (approximately 15 km long and approximately 1 km wide) within the sequence. The alignment was perpendicular to the direction of deposition in the basin (southeast–northwest) as identified by previous studies and subparallel to the main structures in the area (southwest–northeast). We interpreted the seismic character of the funny-looking thing (FLT) likely as (1) a fault, (2) a fold, or (3) a large channel belt within the basin. We use seismic attributes such as coherence (Sobel filter), dip, cosine of phase, and curvature to characterize this feature geomorphologically. The geologic background of the area and analog settings aided in understanding and distinguishing the nature of this large structure. Monocline examples in seismic data are rare to find, and we want to show how to avoid misinterpretations. Geological feature: Fault-bend fold or large-amplitude fold (possibly monocline) Seismic appearance: Large, discontinuous, high-variance feature Alternative interpretations: Fault, fold Features with a similar appearance: Fault, fold, wide straight channel belt (time or horizon slice) Formation: Rift sequence of the Taranaki Basin Age: Eocene Location: Taranaki Basin, Western offshore New Zealand Seismic data: Provided by New Zealand Petroleum and Minerals Contributors: Karelia La Marca, Heather Bedle, Jerson Tellez; School of Geosciences; University of Oklahoma, Norman, OK, USA Analysis tool: 3D reflection seismic, geometric seismic attributes