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AAPG Bulletin

Abstract

AAPG Bulletin, V. 90, No. 10 (October 2006), P. 1451-1472.

Copyright copy2006. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/04240605144

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

Andrew L. Petter,1 Ronald J. Steel2

1Department of Geological Sciences, University of Texas at Austin, 1 University Station, C-1100, Austin, Texas 78712; [email protected]
2Department of Geological Sciences, University of Texas at Austin, 1 University Station, C-1100, Austin, Texas, 78712

ABSTRACT

Identification of bypass at the shelf margin is critical to deep-water exploration. We examine the shelf margin of an early Eocene fourth-order sequence with an attached basin-floor fan in the Spitsbergen Central Basin. Turbidity currents were fed mainly by hyperpycnal flow emerging from shelf-edge deltas. The life span 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 m (33–49 ft) thick and 100–200 m (328–656 ft) 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 about 1.5 km (0.9 mi) 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 flow output. The late lowstand was therefore marked by a second phase 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 the abandonment of the shelf-edge delta complex and the accumulation of mainly mudstone on the margin. The shelf-margin architecture exhibited by this sequence should serve as a type example of a deep-water feeder system in which hyperpycnal flow is the primary initiator of turbidity currents for sand accumulation on the slope and basin floor.

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