Upward‐thickening patterns and lateral continuity of Permian sand‐rich turbidite channel fills, Laingsburg Karoo, South Africa

摘要: Analysis of extensive exposures the Permian Laingsburg Formation, Karoo basin, South Africa, have enabled a detailed reconstruction base slope stratigraphy and palaeoenvironments in deep-water system characterized by very narrow grain-size range (fine sandstone). The deposits include an ≈ 4 km wide 80 m thick channel complex, fringed sandy sheet that extend laterally for at least 6 km across depositional strike. Within individual fills are marked shallow basal erosion surfaces draped thin, parallel-stratified beds fine sandstone siltstone, interpreted as flow tails to largely bypassing flows. These thin overlain 0·4 5 m structureless, fine-grained represent majority fills. packages may be partially completely removed localized scour axial zone complex but can mapped into overbank areas where they thicken dominated rippled sandstones with intercalated siltstones. Axial confinement resulted from subtle topography on basin floor, whereby lower, dense parts initially erosive flows were confined lows more dilute, slower moving upper deposited sheet-like successions slightly elevated areas. distribution prohibited formation ofcoarse-grained residual bypass during initial phases formation. With decreasing magnitude, later became depositional, filling remaining depressions thick-bedded structureless sandstone. smaller volumes late-stage sediment axially focused, producing local scour-and-fill features starvation Resulting vertical profiles complex. tail overlying massive form thickening coarsening-upward trend show thinning- fining-upward profile result less plus sand. Application traditional facies models could therefore potentially lead erroneous interpretations prograding lobe sheets channel-fills.