Allogenic vs. Autogenic Controls on Megaflute Formation

Submarine slope processes in rift-margin basins, Miocene Suez Rift, Egypt

“…Several processes result in scoured seafl oor depressions, including: (1) allogenic megafl ute and fl ute formation (e.g., Elliott, 2000;Kane et al, 2009), (2) slump scar formation (Locat and Lee, 2002), and (3) erosional turbidite channel formation (e.g., Kneller, 2003;Pyles et al, 2010). Lenticular beds <10 m across were formed by localized scouring, perhaps linked to megafl ute formation.…”

“…(2) the lenticular geometry of the beds represents typical channel-form cross-sectional shapes (e.g., Pyles et al, 2010) and implies full containment of fl ows; (3) depositional sedimentary structures onlap basal surfaces, indicating infi lling of topography via aggradation rather than draping of preexisting relief; (4) the lateral scale of the scouring, up to 250 m, is wider than other outcrop examples of megafl utes (1-45 m; Elliott, 2000;Kane et al, 2009);and (5) there is little evidence of slumps or slides infi lling scours, as would be expected if they were mass movement scars. Flat-lying conformably based tabular beds are interpreted as deposits from extensive unconfi ned, depositional turbidity currents that were able to deposit across the studied area.…”

Development and flow structures of sand injectites: The Hind Sandstone Member injectite complex, Carboniferous, UK

“…Kane et al (2009) documented the occurrence of sand-filled scours, or megaflutes, within the HSM. In fact much of the HSM is comprised of lenticular sandstones (Aitkenhead et al, 1992).…”

“…The recognition of injected sandstones within the HSM has led to a re-appraisal of the 'bedding' geometries and sedimentary features within the unit. The megaflute fill described by Kane et al (2009) is interpreted to have been deposited within an erosional scour cut into the top of a sandstone bed, draped by mud prior to infill by sand. The megaflute fill was recognised as being of primary sedimentary origin due to its graded bedding, and gradual increase in mud content towards the top of the bed, which includes an increasing abundance of mud-flakes.…”

“…happens relatively rapidly, i.e., at a greater rate than the encased porous sediment can dewater, overpressure may develop rapidly. The HSM was firstly overlain by hemipelagic and gravity flow mudstones, forming a thick seal (original thickness of w30 m), but would have undergone relatively rapid loading with the emplacement of the Pendle Grit turbidite fan system (Sims, 1988;Martinsen, 1993;Kane et al, 2009Kane et al, , 2010. The Pendle Grit onlaps the pre-existing structure of the Sykes Anticline in this area (Moseley, 1962;Sims, 1988); this could potentially lead to the development of a differential pressure gradient by disequilibrium compaction of sediment deposited over the anticline (Fig.…”