Repeated cycles of submarine channel incision, infill and transition to sheet sandstone development in the Alpine Foreland Basin, SE France

Abstract

The Grès de Champsaur turbidite system, deposited in a distal setting in the Alpine Foreland Basin of south-eastern France, exhibits a repeated upsection alternation in sand body geometry between incised channels and sheet sands. The channels form symmetric lenticular erosional features, of width 900-1000 m (measured between the lateral limits of incision) and depth 65-115 m, and can be traced axially for up to 5 km. In each case, the channel fill is capped by a laterally persistent sandy sheet-form interval, which lies upon a finegrained substrate beyond the channel margins. No intrachannel elements have been traced into the substrate sequence, suggesting that, before infill, the channels acted as open sea-floor conduits of essentially the same dimensions as the preserved channel deposits. The channels are vertically stacked, although axial erosion juxtaposes younger channel axis deposits against the fill of older channels and their channel-capping sheet sandstones to produce an apparently well-connected composite sandstone body geometry. The predominant channel-fill facies comprises coarse-grained, amalgamated sandstones, which are commonly parallel-or cross-stratified. Subsidiary facies of finer grained sandstone-mudstone couplets and clast-bearing muddy debrites are commonly preserved as erosional remnants, suggesting a complex channel history of aggradation and erosion. The repeated cycles of channel incision, infill and transition to sheet sandstone development indicate repetitive incision and healing of the palaeo-sea floor. A model is proposed that links incision to the development of relatively steep axial gradients (parallel to the mean dispersal direction) and the return to sheet-form deposition to the re-establishment of lower axial gradients, with the repetitive switch between incisional channels and sheet sandstones driven by changes in sediment input rate against a background of ongoing sea-floor tilting.

Facies Anatomy of a Sand‐Rich Channelized Turbiditic System: The Eocene Kusuri Formation in the Sinop Basin, North‐Central Turkey

“…The vertical stacking of channels is attributed to the flow confinement by intrabasinal growth-fold synclines, probably related to blind thrusts (see later text). Similar nested channels, although not necessarily filled with similar facies, have been described by Cronin et al (2000b), Kolla et al (2001), McCaffrey et al (2002 and Grecula et al (2003b).…”

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“…Seismic evidence rules out this sequence being a channel complex, and there is also little seismic evidence for leveed channels in this area. Channel deposits are often stacked massive sandstone (Hartog Jager et al, 1993;McCaffrey et al, 2002), but Unit II does not show this type of sequence. Instead, it is characterized by common muddy interbeds between the sand beds that suggest the depositional character is more distal.…”

Nature of thrust zones in deep water sand-shale sequences: outcrop examples from the Champsaur sandstones of SE France

“…This large-scale layering is disrupted at several levels in the succession by erosional channels (e.g. Waibel, 1990;McCaffrey, Gupta, & Brunt, 2002) with significant amounts of sand body amalgamation. The channels do not form continuous layers but can be traced as sinuous ribbons (McCaffrey et al, 2002).…”

“…Waibel, 1990;McCaffrey, Gupta, & Brunt, 2002) with significant amounts of sand body amalgamation. The channels do not form continuous layers but can be traced as sinuous ribbons (McCaffrey et al, 2002). Interspersed between these sand-rich packages are turbidites with significantly lower sand content.…”

“…Our study builds on these foundations and utilises field observations together with oblique air photography coverage acquired during on-going investigations of the sedimentary architectures and facies (e.g. McCaffrey et al, 2002).…”