Vandré, Claudius¹, Christian Brandes¹, Imke Struß¹, Jutta Winsemann¹ 
(1) Universität Hannover, Hannover, Germany

ABSTRACT: Deep-Water Upper- and Mid-Fan Channel-Fills from the Sandino Forearc-Basin: Depositional Processes and Facies Architecture

Deep-water channel-levee complexes are important potential hydrocarbon reservoirs. The reservoir architecture is largely controlled by depositional processes. Distinguishing sedimentary deposits resulting from mass-flow processes, such as debris flows, from those deposited by turbidity currents have important implications for predicting reservoir geometry and economic potential. The Mid to Late Eocene deep-water sediments of the Sandino Forearc-Basin, consist of thick channel-levee complexes, well exposed along the Pacific coast of southwest Nicaragua and northwest Costa Rica. These channel-levee complexes have been deposited in mid- and upper-fan environments, characterized by U-shaped deep feeder channels and shallow lens-shaped distributary channels. Within the channel complexes 22 lithofacies types can be distinguished on the basis of texture, sedimentary structures and bed thickness. Thick-bedded conglomeratic channel-fills have mainly been deposited by cohesive debris flows and, to a minor part by high-density turbidity currents. Thick-bedded pebbly sandstones and sandstones are interpreted to have been deposited by sandy debris flows or high-density turbidity currents respectively. Upper-fan channel-fills are dominated by both cohesive and sandy debris flow deposits. In contrast, channel-fills in more distal mid-fan settings are characterized by deposits of high-density turbidity currents, probably indicating water entrainment and flow transformation during down-slope movement. Therefore mid-fan channel-complexes probably are better reservoirs than upper-fan channel-complexes, because turbidity currents deposit more laterally continuous and interconnected sedimentary bodies than debris flows.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.