Shelf-indenting canyons are fairly common constituents of Quaternary shelves, but they have been rarely reported from older successions. As a consequence, facies models for these conduits are noticeably lacking and far from complete. In this respect, the lower Pliocene Súa Member, northwest Ecuador, is of particular interest in that it gives unprecedented documentation for the stratigraphic organization of a backstepping nearshore clastic wedge that is dissected by shelf-indenting channels and overlain by their turbiditic infill. A comprehensive facies characterization combined with application of sequence stratigraphic concepts has led to definition of the following physical surfaces and stratal units in ascending order. (i) A polygenetic, regionally extensive erosional surface resulting from the superposition of the wave ravinement surface onto the previous subaerial sequence boundary (SB/wRS). (ii) A nearshore, sand-prone lithofacies succession comprising a condensed basal shellbed deepening upwards through lower-shoreface bioturbated silty sandstones, into inner-shelf sandy mudstones. (iii) Two steep, U-shaped erosional features (turbidite shelf-entrenchment surfaces), interpreted as shelf channels, deeply incised into the subjacent nearshore sediments and marking an abrupt deepening of facies. (iv) A thick, fining-upward sedimentary succession laid down within the confines of the channels by turbidity currents. Shelf-entrenchment surfaces are carved by bypassing turbidite currents in shelfal settings during transgression and headward erosion of shore-connected shelf channels is proposed as the most viable mechanism for their development. In order to address for sediment bypass across the shelf and deepwater sedimentation during transgression, exhisting sequence stratigraphic models need to be extended and the turbidite shelf-entrenchment surface adequately included. this study contributes to extend the existing sequence-stratigraphic schemes, further attesting that shelf-sediment bypass and deep-water sedimentation can take place at sea levels other than lowstand.

transgressive change from shoreface to shelf-indenting channel depositional systems in the Pliocene Sua Member, Ecuador

DI CELMA, Claudio Nicola;CANTALAMESSA, Gino
2012-01-01

Abstract

Shelf-indenting canyons are fairly common constituents of Quaternary shelves, but they have been rarely reported from older successions. As a consequence, facies models for these conduits are noticeably lacking and far from complete. In this respect, the lower Pliocene Súa Member, northwest Ecuador, is of particular interest in that it gives unprecedented documentation for the stratigraphic organization of a backstepping nearshore clastic wedge that is dissected by shelf-indenting channels and overlain by their turbiditic infill. A comprehensive facies characterization combined with application of sequence stratigraphic concepts has led to definition of the following physical surfaces and stratal units in ascending order. (i) A polygenetic, regionally extensive erosional surface resulting from the superposition of the wave ravinement surface onto the previous subaerial sequence boundary (SB/wRS). (ii) A nearshore, sand-prone lithofacies succession comprising a condensed basal shellbed deepening upwards through lower-shoreface bioturbated silty sandstones, into inner-shelf sandy mudstones. (iii) Two steep, U-shaped erosional features (turbidite shelf-entrenchment surfaces), interpreted as shelf channels, deeply incised into the subjacent nearshore sediments and marking an abrupt deepening of facies. (iv) A thick, fining-upward sedimentary succession laid down within the confines of the channels by turbidity currents. Shelf-entrenchment surfaces are carved by bypassing turbidite currents in shelfal settings during transgression and headward erosion of shore-connected shelf channels is proposed as the most viable mechanism for their development. In order to address for sediment bypass across the shelf and deepwater sedimentation during transgression, exhisting sequence stratigraphic models need to be extended and the turbidite shelf-entrenchment surface adequately included. this study contributes to extend the existing sequence-stratigraphic schemes, further attesting that shelf-sediment bypass and deep-water sedimentation can take place at sea levels other than lowstand.
2012
9788890736308
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11581/367394
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