Post‐Depositional Alteration and Preservation of Sedimentary Strata

Abstract

All sediment that is delivered to the seabed is subject to post-depositional alteration before it becomes part of the preserved stratigraphic record. Physical and biological processes occurring in the upper few decimetres of the seabed alter newly deposited sediment, thereby creating the fine-scale sedimentary record. The geographical region of focus is the Eel margin of northern California, where a combination of high precipitation, frequent winter storms and intense benthic biological processes exert fundamental controls on the fine-scale stratigraphy. Major findings are that:1 although the wave conditions on the Eel shelf are highly energetic, only a few millimetres to one or two centimetres of bed material are typically put in suspension during storms; 2 despite a high initial porosity (i.e. low strength), flood beds quickly become resistant to erosion; 3 shelf macrofauna show considerable resilience to deposition of flood sediment; 4 storm deposits have a low preservation potential on open continental margins; 5 episodic sedimentation is key to preservation of strata and signals produced by flood and storm events.Future insight into post-depositional alteration will benefit from focused observations and theoretical modelling that explicitly couple physical and biological processes on multiple time-scales.

Wave-enhanced sediment-gravity flows and mud dispersal across continental shelves: Reappraising sediment transport processes operating in ancient mudstone successions

“…Preservation of beds within these shelf mud belts is enhanced by high rates of sediment burial (diminishing the infl uence of bioturbation on preserved fabric) and by self-weight consolidation that rapidly strengthens sediment to limit erosion by currents (Wheatcroft et al, 2007). Primary depositional fabrics are most clearly preserved where beds are thickest in the crossshelf center of the deposit (Addington et al, 2007;Wheatcroft et al, 2007), and recurrence frequency of fl ows is high enough to minimize overprinting by bioturbation.…”

“…Primary depositional fabrics are most clearly preserved where beds are thickest in the crossshelf center of the deposit (Addington et al, 2007;Wheatcroft et al, 2007), and recurrence frequency of fl ows is high enough to minimize overprinting by bioturbation.…”

“…This total maximum thickness is less than both the fl uid mud and wave boundary layer thicknesses (<~0.2 m) . Moreover, as initial porosities for these on June 5, 2015 geology.gsapubs.org Downloaded from event layers (particularly unit C) are very high (to ~0.9) (Wheatcroft et al, 2007), and because mud compacts by as much as 90% of its original thickness during burial, bed thicknesses of the active fl ow (units B and C) will nearly always be <20 mm when encountered in ancient strata.…”

Effects of a major typhoon on sediment accumulation in Fangliao Submarine Canyon, SW Taiwan

“…Deposits resulting from wave-supported gravity flows have also been shown to exhibit an increase in clay content, which may be coincident with increased sediment supply that occurs during river floods (Sommerfield et al, 1999;Mullenbach and Nittrouer, 2000). The combination of finegrained sediment and rapid deposition results in decreased bulk density within a flood layer, relative to underlying pre-existing material (Wheatcroft et al, 2007). This transition should appear in x-radiographs obtained soon after gravity-flow deposition.…”

Comparison of Present Day and Historical Dispersal Patterns in the Western Adriatic

“…The cross-shelf location of a flood deposit is sensitive to wave energy, but the volume of the flood deposit depends critically on partitioning of sediment into aggregated particles and disaggregated single grains . Related to this study, I have contributed towards two chapters of a volume on continental-margin sedimentation Wheatcroft et al, 2005b].…”