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- Title
River-plume sedimentation and Pb/Be seabed delivery on the Mississippi River delta front.
- Authors
Keller, Gregory; Bentley, Samuel; Georgiou, Ioannis; Maloney, Jillian; Miner, Michael; Xu, Kehui
- Abstract
To constrain the timing and processes of sediment delivery and submarine mass-wasting events spanning the last few decades on the Mississippi River delta front, multi-cores and gravity cores (0.5 and <3 m length respectively) were collected seaward of the Mississippi River Southwest Pass in 25-75 m water depth in 2014. The cores were analyzed for radionuclide activity (Be, Pb, Cs), grain size, bulk density, and fabric (X-radiography). Core sediments are faintly bedded, sparsely bioturbated, and composed mostly of clay and fine silt. Short-term sedimentation rates (from Be) are 0.25-1.5 mm/day during river flooding, while longer-term accumulation rates (from Pb) are 1.3-7.9 cm/year. In most cores, Pb activity displays undulatory profiles with overall declining activity versus depth. Undulations are not associated with grain size variations, and are interpreted to represent variations in oceanic Pb scavenging by river-plume sediments. The Pb profile of one gravity core from a mudflow gully displays uniform basal excess activity over a zone of low and uniform bulk density, interpreted to be a mass-failure event that occurred 9-18 years before core collection. Spatial trends in sediment deposition (from Be) and accumulation (from Pb) indicate that proximity to the river mouth has stronger influence than local facies (mudflow gully, depositional lobe, prodelta) over the timeframe and seabed depth represented by the cores (<40 years, <3 m length). This may be explained by rapid proximal sediment deposition from river plumes coupled with infrequent tropical cyclone activity near the delta in the last 7 years (2006-2013), and by the location of most sediment failure surfaces (from mass flows indicated by parallel geophysical studies) deeper than the core-sampling depths of the present study.
- Subjects
MISSISSIPPI River; RIVER sediments; OCEAN bottom; RADIOISOTOPES; MUDFLOWS
- Publication
Geo-Marine Letters, 2017, Vol 37, Issue 3, p259
- ISSN
0276-0460
- Publication type
Article
- DOI
10.1007/s00367-016-0476-0