Utilising clinoform architecture to understand the drivers of basin margin evolution: a case study in the Taranaki Basin, New Zealand

Abstract

Morphological variations within continental-margin clinoforms can help improve our understanding of sediment dispersal on, the composition of, and the sediment transport mechanisms occurring along shelf margins. In this study, we combine 2D and 3D seismic reflection and well data to document variations in clinoform morphologies within the Pliocene-Recent Giant Foresets Formation of the northern Taranaki Basin, offshore western New Zealand. Quantitative analysis of slope geometries, shelf-edge trajectories and geomorphological patterns allowed for the identification of three major stages of clinoform evolution. These results were combined with the analysis of isochron maps and seismic attribute extractions to determine the temporal and spatial relationship between depositional patterns and tectonic activity. Stage 1 clinoforms (early Pliocene) have gentle and smooth architectures, low-angle foresets and rising rollover trajectories. During stage 1, the shelf-edge region was stable and a few slope fans developed. Stage 2 clinoforms (early–late Pliocene) are characterised by concave profiles, increased foreset steepness, mostly flat rollover trajectories and dissected shelf-edge regions. Slope steepening during Stage 2, which coincided with a relative sea-level fall, is reflected in an increase in canyon incision and sediment bypass towards the basin. The onset of back-arc rifting and formation of the Northern Graben during stage 2 caused local changes in basin physiography and focusing of sediment dispersal along the axis of the structure; deep-water deposits are thus expected in more distal parts of the basin. Stage 3 (late Pliocene-Recent) clinoforms are characterised by sigmoidal, higher and steeper architectures, rising rollover trajectories and dissected slopes that lack a clear connection to the shelf edge area. Stage 3 conditions were dominated by an increase in sediment supply and accommodation, and the progradation of the system resulted in gradually steeper slope gradients that triggered slope mass-wasting. This study demonstrates that the systematic description of clinoform architectures can be coupled with process-oriented interpretations associated with paleoenvironmental and tectonic conditions at the time of deposition to reconstruct basin evolution through time, to predict sediment character in distal portions of the system and to understand the influence of underlying structures on the overall stratigraphic evolution of the system.