Lowstand Fan Model, Basal Complex, Barbados: Utility as a Predictor of Reservoir Geometry and Continuity

D. K Larue, R. M. Lindholm, A. R. G. Sprague, and C. R. Bissell

Lowstand fan deposits on Barbados were studied in outcrop to construct a conceptual reservoir model for prediction of fades assemblages. Lowstand fan and wedge deposits are found in terrigenous clastic strata of the Basal Complex of Barbados, and are of Eocene age. The Barbados Lowstand fan model consists of five parts, discussed below. 1. Residual lag facies with contrasting texture (conglomerate and coarse-grained sandstone beds interbedded with pebbly mudstone and mudstone) and depositional processes (debris flows, high- and low-density turbidity currents, suspended-load deposits) are interpreted to characterize an area largely of sediment bypass (bypass corridor 1) occurring updip of the lowstand fan. Channel-fill complexes, isolated channel-fills and interch nnel deposits are recognized by different types of upward-fining vertical successions and associations of lithologies and compose the lowstand fan proper. 2) Conglomerate, pebbly sandstone and high- and low-density turbiditic sandstone forming hierarchical upward-fining successions, characterize channel-fill complexes in the proximal fan, and are typically amalgamated with other channel-fill complexes. 3) High- and low-density sediment gravity-flow deposits in well-developed hierarchical upward-fining packages characterize amalgamated channel-fill deposits, and are interstratified with mud-rich facies strata representing abandoned channel deposits and interchannel deposits. Together, the amalgamated channel-fill deposits and. interchannel deposits characterize deposition in the EM>middle fan. 4) A residual lag facies, similar to that observed in bypass corridor 1, characterized by cross-bedded lenticular tractional deposits, interbedded with low- density sediment gravity flow deposits, defines bypass corridor 2: this occurs at the transition from the middle fan to the distal fan. 5) Low-density sediment gravity-flow deposits in tabular beds are observed in the distal fan. Distal fan channel deposits have high width to thickness ratios and are aggradational. High-frequency sequences can be recognized through analysis of stacking patterns of these fan facies.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California