Stratigraphic hierarchy and three-dimensional evolution of an exhumed submarine slope channel system |
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Authors: | Daniel Bell David M Hodgson Anna S M Pontén Larissa A S Hansen Stephen S Flint Ian A Kane |
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Institution: | 1. School of Earth and Environmental Sciences, University of Manchester, Oxford Road, Manchester, M139PL UK;2. Stratigraphy Group, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT UK;3. Research Centre Rotvoll, Equinor ASA, NO-7005 Trondheim, Norway |
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Abstract: | Submarine slope channel systems have complicated three-dimensional geometries and facies distributions, which are challenging to resolve using subsurface data. Outcrop analogues can provide sub-seismic-scale detail, although most exhumed systems only afford two-dimensional constraints on the depositional architecture. A rare example of an accessible fine-grained slope channel complex set situated in a tectonically quiescent basin that offers seismic-scale, down-dip and across-strike exposures is the Klein Hangklip area, Tanqua-Karoo Basin, South Africa. This study investigates the three-dimensional architecture of this channel complex set to characterise the stratigraphic evolution of a submarine channel-fill and the implications this has for both sediment transport to the deep-oceans and reservoir quality distribution. Correlated sedimentary logs and mapping of key surfaces across a 3 km2 area reveal that: (i) the oldest channel elements in channel complexes infill relatively deep channel cuts and have low aspect-ratios. Later channel elements are bound by comparatively flat erosion surfaces and have high aspect-ratios; (ii) facies changes across depositional strike are consistent and predictable; conversely, facies change in successive down depositional dip positions indicating longitudinal variability in depositional processes; (iii) stratigraphic architecture is consistent and predictable at seismic-scale both down-dip and across-strike in three-dimensions; (iv) channel-base-deposits exhibit spatial heterogeneity on one to hundreds of metres length-scales, which can inhibit accurate recognition and interpretations drawn from one-dimensional or limited two-dimensional datasets; and (v) channel-base-deposit character is linked to sediment bypass magnitude and longevity, which suggests that time-partitioning is biased towards conduit excavation and maintenance rather than the fill-phase. The data provide insights into the stratigraphic evolution and architecture of slope channel-fills on fine-grained continental margins and can be utilised to improve predictions derived from lower resolution and one-dimensional well data. |
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Keywords: | Channel architecture channel base drape channel hierarchy Karoo Basin sediment bypass submarine channel |
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