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Categorizing the morphologic variability of siliciclastic passive continental margins

¹ Institute of Arctic and Alpine Research, Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USA
² Department of Earth and Ocean Sciences, Duke University, Durham, North Carolina 27708, USA
³ Mobil Exploration and Producing Technical Center, Dallas, Texas 75247, USA

The basic morphology of the continental shelf, slope, and rise on passive continental margins has many variations in the modern ocean environment. Through using a satellite-derived bathymetric data set of the global ocean, we have developed a classification for the shape of modern, siliciclastic-dominated, passive margins. The classification subdivides 50 margins into five distinct shape categories based on each margin's pattern of sea-floor slopes as a function of depth. By comparing these shape categories with the underlying stratal architecture, sediment input, and present degree of canyon incision of the margins, we find apparent correlations between these factors and basic margin shape. In general, gently sloped margins tend to occur in regions with high sediment input, few modern canyons, and unstable substrates. Higher gradient margins tend to have lower sediment input, more modern canyons, and a variety of subsurface architectures. These results suggest two important conclusions: (1) morphology differences among modern siliciclastic passive margins can be objectively and systematically categorized, and (2) these shape differences seem to be related to aspects of the modern sedimentary environment despite the fact that the margins have evolved over geologic time.

Key Words: passive margins • morphology • sea-floor slopes • classification

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