Abstract

Fluvio-eolian successions are generally characterized by a high degree of complexity and internal heterogeneity. Quantifying the rapid facies changes in time and space is a major challenge to characterization of hydrocarbon reservoirs.

We present a method for facies discrimination in fluvio-eolian successions. The method presented here is developed on the modern fluvio-eolian sediments from the Skeleton Coast dune field, Namibia. The examined sediments comprise eight different facies types: eolian dune sands, interdune fluvial channel sands, intraerg mass-flow deposits, intraerg hyperconcentrated-flow deposits, fluvial channel sands, fluvial mud, lacustrine heterolithic sand, and lacustrine heterolithic mud. The contrasting provenance of the fluvial and eolian sediments results in a distinct source fingerprint which can be discriminated using elemental whole-rock geochemistry. A multivariate statistical technique performed on the geochemical data has enabled discrimination of seven of the eight facies types. Furthermore, the facies discrimination method allowed a quantitative estimate of the degree of fluvial reworking of eolian sand.

The Skeleton Coast dune field was chosen as a test area for geochemical facies discrimination, because of its remarkable difference between the immature fluvial source and the mature quartz-rich eolian source. We hope that the method presented here can be applied to subsurface data from geological settings with the same difference in fluvial and eolian sources. It is furthermore hoped that the method can be used in more complex sedimentological settings.

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