Hyperpycnal flow variability and slope organization of an Eocene shelf margin, Central Basin, Spitsbergen

Petter, Andrew Lucas, 1980-
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Identification of bypass at the shelf margin is critical to deepwater exploration. The shelf margin of an early Eocene fourth-order sequence with an attached basin-floor fan in the Central Spitsbergen Basin was examined in this study. Turbidity currents were fed mainly by hyperpycnal flow emerging from shelf-edge deltas. The lifespan of any turbidity current was determined primarily by the sediment concentration of the flow and the duration of the river flood. High-density hyperpycnal flows created sand-filled slope-channel complexes 10-15 meters (33-49 feet) thick and 100-200 meters (328-656 feet) wide that served as conduits for bypass to the basin floor. Low-density hyperpycnal flows were unconfined and deposited heterolithic lobes on the slope. Shelf-margin accretion of ~1.5 kilometers (0.9 miles) during the falling stage gave way abruptly to bypass in the early lowstand. Most of the basin-floor fan growth was achieved after shelf-edge incision and before relative sea level rise. Coastal-plain aggradation in the late lowstand sequestered sediment from the shelf-edge distributaries, effectively diminishing high-density hyperpycnal output. The late lowstand was therefore marked by a second pulse of shelf-margin accretion with only limited bypass to the basin floor, and a heterolithic, prograding complex downlapped the early lowstand channels. Transgression ultimately led to abandonment of the shelf-edge delta complex and accumulation of mainly mudstone on the margin. The shelf-margin architecture exhibited in this sequence should serve as a type example of a deepwater feeder system in which hyperpycnal flow is the primary initiator of turbidity currents for sand accumulation on the slope and basin floor