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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 52 (2002), Pages 59-64

Geological Reservoir Characteristics of Fine-Grained Turbidite Systems

Bouma, Arnold H., Sprague, Ronald A., Khan, Arfan M.

ABSTRACT

Coarse-grained and fine-grained turbidite systems are the two end members of the majority of deepwater sand deposits. Their internal characteristics differ considerably, requiring different analytical approaches. Coarse-grained systems are sand-rich, prograde gradually into the basin and become thinner and finer in the downdip direction. Fine-grained systems bypass more than 75% of their sand to the outer fan area.

Characteristics of fine-grained systems are: (1) upper fan (basin slope) with erosional canyon, feeding sediments into the basin. It is the last part filled, composed of mud-rich deposits; (2) middle fan with leveed channels and leveed parts of distributaries. Net accumulation is slow because of frequent erosion, which removes mud drape and part of the underlying sands. Massive amalgamated sands may locally show preserved muds at bed contacts. Levee deposits often show parallel lamination, crossbedding, and climbing ripples; (3) lower fan with nonleveed distributaries and oblong, sinuous sheet sands, commonly in mutual contact. Individual layers show turbidite sequence characteristics. Several layers can be stacked with sand-on-sand contact in the axis, becoming laterally thickening mudstone at the margins. Stacking is followed by lateral switching and occasional forward progradation. Muds are found between these packages. Individual sand sheets split into narrow, sinuous fingers in the fan fringe area. Mud deposition in the depressions between sheet sands and their fingers presents a morphology that mimics a progradational, bifurcating channel system. Major deposition takes place during the initial transgressive systems tract period.


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