Characteristics of Some Submarine Fan Channels, Permian Ecca Group, South Africa

Abstract

The vary well exposed submarine fan complex in the southwestern part of the Karoo basin permits close examination of channel-fills and in places their associated overbank deposits. The complex comprises five arenaceous fan systems some of which attain 60 m in thickness. The fans are vertically stacked and separated by basinal shale deposits; each system with its own direction of growth. The association of channelized sandstone bodies and thin-bedded sandstone and shale packages in an updip position from predominantly stacked lobe deposits suggest preservation of middle fan settings. A 500 m wide, 20 m thick channel-fill consisting massive amalgamated sandstone beds occupying the channel thalweg occurs in a setting dominated by thin-bedded, ripple-laminated sandstone and shale. Gradual thinning of the channel-fill beds toward the channel edges, lack of internal lateral accretion, and a high width to depth ratio suggests a low sinuous to straight channel. The channel-fill is capped by an abandonment facies characterized by ripple-laminated sandstone and shale. Stacked, laterally offset channel-fill deposits with highly erosional contacts and typical well-bedded overbank deposits form channel-overbank complexes and characterize the mid-fan region of the uppermost fan system. Palaeocurrent directions and gradual diminishing of bed-thickness away from the generally massively bedded, amalgamatedmore » channel-fill sandstones confirm a simultaneous channel/overbank origin for these deposits. Levee morphology has not been recognized. Both examples of channel-fills cited reveal part of the complexity of the channelized portions of submarine fans and hence the implications thereof in exploring for hydrocarbon reservoirs.« less