--> ABSTRACT: Basin-Floor Fans in the North Sea: Conceptual Sequence Stratigraphic Models vs. Conventional Core Data, by G. Shanmugam, R. B. Bloch, S. M. Mitchell, G. W. J. Beamish, R. J. Hodgkinson, J. E. Damuth, T. Straume, S. E. Syvertsen, K. E. Shields; #91020 (1995).

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Basin-Floor Fans in the North Sea: Conceptual Sequence Stratigraphic Models vs. Conventional Core Data

G. Shanmugam, R. B. Bloch, S. M. Mitchell, G. W. J. Beamish, R. J. Hodgkinson, J. E. Damuth, T. Straume, S. E. Syvertsen, K. E. Shields

The concept of basin-floor fans in a sequence stratigraphic framework is popular in hydrocarbon exploration because the conceptual model predicts that basin-floor fans are composed of sand-rich turbidites with laterally extensive, sheet-like geometries. However, our examination of nearly 12,000 feet (3658 m) of conventional core from these "basin-floor fans" (e.g., Faeroe, Frigg, Gryphon-Forth, and Agat areas), reveals that they are predominantly composed of slumps and debris flows (50-100% of the cored interval). Classic, laterally continuous turbidites are extremely rare and comprise less than 1% of the cored interval. Sedimentary features indicative of slump/debris flow origin include sand units with sharp upper contacts, slump folds, steeply dipping layers (up to 60&# 76;), glide planes, shear zones, brecciated clasts, clastic injections, floating mudstone clasts, a planar clast fabric, inverse size grading, and moderate to high matrix content (5-30%). Calibration of these facies in long cores (400^prime-700^prime) with seismic and wire-line log signatures suggests that seismic mounding and blocky log motifs are actually a manifestation of amalgamated sand units emplaced by slumps and debris flows. In some cases, sequence boundaries on seismic profiles correspond to primary glide planes (decollement) of slump sheets in cores examined. Unlike turbidites, slump and debris-flow emplaced sands are often laterally discontinuous; however, they still form important hydrocarbon-producing reservoirs (e.g., The Frigg Field). Because sands and muds deposited by lumps and debris flows in deep-marine environments mimic properties of basin-floor fans in seismic and log data, process sedimentological interpretation of conventional core is critical to establish the true origin and distribution of the deep-marine sands contained in such features.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995