--> Abstract: Sequence Stratigraphy Of Deltaic Sands And Shales, Upper Miocene And Pliocene, Offshore Brunei Darussalam, by A. H. Saller, G. Blake, S. Smith, J. Baines, C. Morgan, and P. Wagenhofer; #90928 (1999).

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SALLER, ARTHUR H., GREG BLAKE, SHERMAN SMITH, JOHN BAINES, CHIP MORGAN, and PAUL WAGENHOFER
Unocal Corporation, Sugar Land, Texas

Abstract: Sequence Stratigraphy of Deltaic Sands and Shales, Upper Miocene and Pliocene, Offshore Brunei Darussalam

A depositional trough formed offshore Brunei during the Middle to Late Miocene due to progradation of shelf margins in adjacent areas of offshore Sabah and Sarawak. Progradation associated with two different deltaic systems, Champion and Baram, filled in much of the Brunei shelf during the Late Miocene and Pliocene. The Champion delta (to the northeast) prograded more than 40 km during the Late Miocene. The Baram delta (to the southwest) prograded approximately 40 km during the Pliocene when the Champion area prograded only 10 km. Deltaic sequences, approximately 50-100 m thick, could be identified in both seismic data and wells logs. Each sequence is estimated to represent 100,000 to 400,000 years. Deltaic sequences consist of a lower shaley transgressive systems tract , and an upper, sandy progradational highstand systems tract. Lowstand reflectors onlap shelf margins at sequence boundaries. Shales are dominant on the upper slope. Shales and siltstones with only minor sandstone dominate at seismic inflection points (shelf margins). Sandstones become more abundant landward of the shelf margin with good reservoir quality sands beginning 1-2 km landward of the shelf margin. Broad, not lobate, shelf margin geometries and the widespread occurrence of sand along depositional strike suggest deposition by wave-dominated deltas. Syndepositional tectonics greatly affected deposition. Toe-thrusts are common on the outer slope while counter-regional growth faults are common on the shelf during early progradation, and listric normal growth faults are common during later stages of progradation.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas