--> The Nature of Connections Between Coastal Systems and Submarine Canyons - Implications for Sediment Transit to Deep Water

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The Nature of Connections Between Coastal Systems and Submarine Canyons - Implications for Sediment Transit to Deep Water

Abstract

The heads of submarine canyons represent a critical link in the transfer of sediment from terrestrial sediment sources to deep basin sinks. Data from modern canyons and submarine fans suggests the strength of this connection determines the proportion and caliber of sediment stored in shelfal environments relative to that which is transferred to deep-water. Data on grain size, bathymetry and geochronology from twenty-four modern submarine canyons demonstrate this link to be very sensitive to the distance between the canyon head and the shoreline, and, to a lesser extent, wave energy. These data show the width of this zone filters the caliber of sediment delivered into deep-water with significant implications for understanding sediment budgets and reservoir and seal distribution. A surprising observation from these data is how sensitive the transport of grains of sand-size and coarser clasts is to the distance between the river mouth or shoreline and the head of the submarine canyon. Data from these modern systems shows the river mouth or longshore drift system must come within ~500 m of the head of the canyon to deliver gravel-size material and within 1–5 km to deliver sand-size material to be transported down the canyon into deep water. Clay- and silt-size particles are transported greater distances across the shelf, up to a few 10's of kilometers, whereas beyond about 40 kilometers little sediment makes the connection to the heads of canyons and deposits are commonly dominated by carbonate-rich sediments. Many large, passive margins currently fall into this realm. The insights from this study can be translated and applied to conditions typical of other periods in Earth's history and have powerful implications for predictions of reservoir and seal. During Greenhouse times, with high but relatively stable sea level and/or narrow continental shelves, a longer-lived connection between fluvial to near-shore environments and deep water was more likely to occur. However, in relatively high-gradient systems, long-lived connections may prevent the deposition of laterally extensive mudstones that are effective top seals. In contrast to Greenhouse conditions, during Icehouse periods, high-amplitude sea level fluctuations and inherently wider continental shelves result in repeated landward and seaward transits of river mouths and shorelines, and shorter connection times between source and sink, especially for sand-size sediment.