Quantitative and geomorphologic parameterization of megaclasts within mass-transport complexes, offshore Taranaki Basin, New Zealand

Abstract

Mass-transport complexes (MTCs) in sedimentary basins reflect the gravitational transport of sediments from the shelf edge to the abyssal plain. Megaclasts, large sedimentary blocks of hundreds of meters long within MTCs, can record kinematic and sedimentary information deemed essential to understanding source-to-sink systems. Yet, deformation structures in such megaclasts remain poorly understood. This study uses high-quality, three-dimensional (3-D) seismic reflection data from the deep-water Taranaki Basin offshore New Zealand to analyze the morphological character of 123 megaclasts and propose a new classification scheme based on their morphometric properties. The megaclasts are up to 400 m tall, 1900 m long, and 1200 m wide. In the study area, they are high- to moderate-amplitude features owing to their different lithologies and continuous-to-contorted seismic facies. The megaclasts can be classified as undeformed, rotated, deformed, and highly deformed based on their internal deformational styles. Two different kinds of morphological depressions observed on their basal shear zones further indicate whether the megaclasts are transported or formed in situ. Our study demonstrates that quantitative parameterization of the megaclasts provides important information about their deformational processes and a more complete understanding of megaclast emplacement along continental margins.