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Utilizing Clinoform Architecture and Stratigraphic Forward Modeling to Understand the Drivers of Basin Margin Evolution


Clinoforms, the basic architectural form by which sediments are stored and eventually fed down depositional dip, exist in nature in diverse shapes and sizes. Extremely large clinoforms (giant clinoforms) are fairly common in modern and ancient continental margins. Understanding how they form and evolve is critical to the understanding of the transport mechanisms affecting the shelf margin region and sediment partitioning of a given basin. This study is concerned with the process of clinoform development and its implications for sediment distribution source-to-sink within a basin. The Taranaki Basin, New Zealand, is well known for a variety of clinoform architectures characterizing its Neogene margin. This basin was used as a natural laboratory to examine the manner by which clinoforms evolve along a tectonically active margin, under the influence of eustatic sea-level changes, tectonic- and isostatic-driven subsidence and dramatic changes in hinterland sediment supply. We combined seismic stratigraphic interpretations and paleontological studies to understand the Pliocene-Recent stratigraphic succession within the basin, and specifically the Giant Foresets Formation system. Nine different clinoform packages (SU1-SU9) were mapped on the basis of changes in their seismic stratigraphic characteristics. The units were grouped into three major stages of clinoform evolution based on their architectural parameters. Isochron maps were generated to identify correlations between stratigraphy and paleostructures. Seismic attributes were extracted to identify and characterize geological features and depositional elements. 2D stratigraphic forward modeling techniques were applied to determine in a quantitative manner the relative importance of the mechanisms acting in the basin. Our analysis showed, that during the early-late Pliocene, the activity of the Northern Graben, a back-arc rifting structure in the study area, played a key role in sediment redistribution and probably sediment partitioning; a global sea level drop, reflected in shelf edge trajectories and clinoform architectures, allowed sediment bypass to distal basin positions. Since the late Pliocene, changes in the Australian-Pacific subduction zone, including its faster southwest migration, allowed uplifting of the Southern Alps and associated increase in sediment supply. Model simulations suggest such changes in sediment supply and associated loading are likely the main controls on clinoform architectures.