Matrix-rich and associated matrix-poor sandstones: Avulsion splays in slope and basin-floor strata

摘要: A common facies observed in deep-water slope and especially basin-floor rocks of the Neoproterozoic Windermere Supergroup (British Columbia, Canada) is structureless, coarse-tail graded, medium-grained to coarse-grained sandstone with from 30% >50% mud matrix content (i.e. matrix-rich). Bed contacts are commonly sharp, flat loaded. Matrix-rich beds typically form laterally continuous units that up several metres thick tens hundreds wide, adjacent comparatively matrix-poor, scour-based large tabular mudstone clasts. proximal (Upper Kaza Group) deposits, but occur also more distal (Middle (Isaac Formation) deposits. Regardless stratigraphic setting, matrix-rich directly abruptly overlain by architectural elements comprising matrix-poor coarse channels splays). Despite a number similarities previously described literature, for example slurry beds, linked debrites co-genetic turbidites, important differences exist, including stratal make-up individual (for example, lack clean turbidite base) their occurrence (present throughout base strata, most lobe deposits) accordingly suggest different mode emplacement. The matrix-rich, poorly sorted nature abundance size clasts equivalent sandstones imply intense upstream scouring, probably related significant erosion an energetic plane-wall jet or within submerged hydraulic jump. Rapid energy loss coupled rapid charging flow fine-grained sediment changed rheology promoted deposition along margins jet. Moreover, these distinctive strata interpreted represent initiation local sedimentary system, caused upflow avulsion.