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Quantitative analysis of submarine-flow deposit shape in the Marnoso-Arenacea Formation: what is the signature of hindered settling from dense near-bed layers?

Quantitative analysis of submarine-flow deposit shape in the Marnoso-Arenacea Formation: what is the signature of hindered settling from dense near-bed layers?
Quantitative analysis of submarine-flow deposit shape in the Marnoso-Arenacea Formation: what is the signature of hindered settling from dense near-bed layers?
Submarine sediment density flows are one of the volumetrically most important processes for sediment transport across Earth. The sediment concentration of flows that reach the deep ocean has never been measured directly, and understanding these long-runout flows remains a major challenge. The Miocene Marnoso-Arenacea Formation in the Italian Apennines is the only ancient sequence where individual submarine sediment-density-flow deposits (single beds) have been mapped out for more than 100 km down-flow. Here we document the external shape and internal architecture of thirty-two individual beds that record flow evolution and can be compared to deposit shapes in mathematical or experimental models. The large number of beds allows modes of flow behavior to be identified. Larger-volume turbidites are typically dominated by massive (TA) or planar-laminated (TB) sandstone intervals that have a broad thickness maximum. This shape is important because it suggests that massive and planar laminated sandstones record hindered settling from dense near-bed layers, which have high (>?10% by volume) sediment concentrations. Previously, some authors have inferred that planar-laminated sandstones (TB) are deposited mainly by dilute flows. The position of the broad thickness maximum moves basinward as the volume of sand in the flow increases. This is consistent with mathematical modeling that suggests the position of the thickness maximum depends on flow thickness, flow speed, and sediment settling velocity, as well as sediment concentration, variations in seawater entrainment rate, and local changes in seafloor gradient. Smaller-volume turbidite sandstone intervals are finer grained and dominated by ripple cross-lamination (TC) and have a near exponential decay in thickness that is consistent with deposition from a dilute sediment suspension. The rate of near exponential thinning is controlled by sandstone volume. In contrast, turbidite mudstone intervals show an approximately linear increase in thickness with distance. Flows that entered the basin in opposite directions produced turbidite mudstone intervals that thicken towards the same location, indicating that muddy turbidity currents can drain back over long distances to basinal lows.
1527-1404
170-191
Malgesini, G.
238aba28-0fb4-4731-ac1f-c9b4ea0723c3
Talling, P.J.
1cbac5ec-a9f8-4868-94fe-6203f30b47cf
Hogg, A.J.
2362a377-6a70-4520-ab24-fb7e18ed60e9
Armitage, D.
90d3278f-fe6f-443a-93cc-f05cbd8b23f6
Goater, A.
456d143f-f209-46eb-9db3-5e6a694015cc
Felletti, F.
98280c55-e59b-4f2f-9cc6-bea52377b01f
Malgesini, G.
238aba28-0fb4-4731-ac1f-c9b4ea0723c3
Talling, P.J.
1cbac5ec-a9f8-4868-94fe-6203f30b47cf
Hogg, A.J.
2362a377-6a70-4520-ab24-fb7e18ed60e9
Armitage, D.
90d3278f-fe6f-443a-93cc-f05cbd8b23f6
Goater, A.
456d143f-f209-46eb-9db3-5e6a694015cc
Felletti, F.
98280c55-e59b-4f2f-9cc6-bea52377b01f

Malgesini, G., Talling, P.J., Hogg, A.J., Armitage, D., Goater, A. and Felletti, F. (2015) Quantitative analysis of submarine-flow deposit shape in the Marnoso-Arenacea Formation: what is the signature of hindered settling from dense near-bed layers? Journal of Sedimentary Research, 85 (2), 170-191. (doi:10.2110/jsr.2015.15).

Record type: Article

Abstract

Submarine sediment density flows are one of the volumetrically most important processes for sediment transport across Earth. The sediment concentration of flows that reach the deep ocean has never been measured directly, and understanding these long-runout flows remains a major challenge. The Miocene Marnoso-Arenacea Formation in the Italian Apennines is the only ancient sequence where individual submarine sediment-density-flow deposits (single beds) have been mapped out for more than 100 km down-flow. Here we document the external shape and internal architecture of thirty-two individual beds that record flow evolution and can be compared to deposit shapes in mathematical or experimental models. The large number of beds allows modes of flow behavior to be identified. Larger-volume turbidites are typically dominated by massive (TA) or planar-laminated (TB) sandstone intervals that have a broad thickness maximum. This shape is important because it suggests that massive and planar laminated sandstones record hindered settling from dense near-bed layers, which have high (>?10% by volume) sediment concentrations. Previously, some authors have inferred that planar-laminated sandstones (TB) are deposited mainly by dilute flows. The position of the broad thickness maximum moves basinward as the volume of sand in the flow increases. This is consistent with mathematical modeling that suggests the position of the thickness maximum depends on flow thickness, flow speed, and sediment settling velocity, as well as sediment concentration, variations in seawater entrainment rate, and local changes in seafloor gradient. Smaller-volume turbidite sandstone intervals are finer grained and dominated by ripple cross-lamination (TC) and have a near exponential decay in thickness that is consistent with deposition from a dilute sediment suspension. The rate of near exponential thinning is controlled by sandstone volume. In contrast, turbidite mudstone intervals show an approximately linear increase in thickness with distance. Flows that entered the basin in opposite directions produced turbidite mudstone intervals that thicken towards the same location, indicating that muddy turbidity currents can drain back over long distances to basinal lows.

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Published date: February 2015
Organisations: Ocean and Earth Science, Marine Geoscience

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Local EPrints ID: 375477
URI: http://eprints.soton.ac.uk/id/eprint/375477
ISSN: 1527-1404
PURE UUID: cac1e09f-e654-4be4-b21f-f61084989c5b

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Date deposited: 25 Mar 2015 14:27
Last modified: 26 Apr 2022 20:37

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Contributors

Author: G. Malgesini
Author: P.J. Talling
Author: A.J. Hogg
Author: D. Armitage
Author: A. Goater
Author: F. Felletti

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