ABSTRACT: Classification of Turbidite Systems: A Suggestion for an Old Problem

NELSON, C. H., U.S. Geological Survey, Menlo Park, CA, S. O'CONNELL, Wesleyan University, Middletown, CT, A. MALDONADO, Instituto de Ciencias del Mar, Barcelona, Spain, D. C. TWICHELL, U.S. Geological Survey, Woods Hole, MA, and A. PULHAM, BP America, Houston, TX

Different types of turbidite systems (sediment bodies derived from multiple sediment gravity flows) make up basin fill sequences. Primary descriptors for turbidite systems are size utilizing long-axis dimension (small, <10 km; medium, 10-100 km; large, 100-1000 km; and very large, >1000 km) and type of system (i.e., fan, apron, or connecting valley). If data are insufficient to define the type of system, "undefined turbidite system" is preferred rather than naming parts of systems as separate fan types (e.g., channel-levee complex-slope fan). We propose a tripartite system of identification for the type of system; this utilizes (1) morphology for present-day systems, (2) seismic sequence criteria for reflection profiling data, and (3) facies associations for outcrop and well-log information. Fans are defined by (1) morphologic evidence of proximal fan valleys and attached distal lobes, (2) seismic reflection criteria of proximal channel-levee complexes with high-amplitude floor and associated overbank reflections changing to distal lobes with bidirectional downlap, and (3) channel floor (A, B) and overbank (E) evolving to distal lobe (C, D) facies. Aprons are characterized by (1) base of slope cones without significant channel development, (2) wedging to continuously bedded sequences, and (3) progressive proximal to distal change from A-B-C-D sandy facies. Connecting valleys are differentiated by (1) morphologic evidence of depositional canyons, channel-levee complexes not attached to lobes, or axial valleys draining rift and trench basin floors; these valleys e hibit the same general (2) seismic reflection and (3) facies characteristics as proximal channel-levee complexes.

Each type and size of turbidite system may be followed by second-order descriptors of morphology (e.g., radial, elongate), reflector character (e.g., chaotic, parallel) or facies (e.g., sand-rich, mud-rich).

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)