Interplay between river discharge and topography of the basin floor in a hyperpycnal lacustrine delta |
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| Authors: | CORNEL OLARIU JANOK P. BHATTACHARYA MATTHEW I. LEYBOURNE STEPHEN K. BOSS ROBERT J. STERN |
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| Affiliation: | 1. Department of Geological Sciences, University of Texas at Austin, 1 University Station C1100, Austin, TX 78712‐0254, USA (E‐mail: cornelo@mail.utexas.edu);2. National Institute for Marine Geology and Geoecology – GeoEcoMar, 23‐25 Dimitrie Onciul Street, Bucharest 024053, Romania;3. Department of Geosciences, University of Houston, 312 Science & Research 1, 4800 Calhoun, Houston, TX 77204‐5007, USA;4. GNS Science, PO Box 30‐368, Lower Hutt, New Zealand;5. Department of Geosciences, University of Arkansas, 113 Ozark Hall, Fayetteville, AR 72701, USA;6. Geosciences Department, The University of Texas at Dallas, Box 830688, Richardson, TX 75083‐0688, USA
Associate Editors – Paul Carling and George Postma |
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| Abstract: | Basin‐floor topography influences the flow path of hyperpycnal plumes and delta morphology during progradation of the Red River delta in Lake Texoma, USA. The Red River discharge is typically a hyperpycnal plume due to elevated total dissolved solids. Because the river plume is a bottom‐hugging hyperpycnal flow, lake bathymetry and topography strongly influence deposition and subsequent delta morphology. In addition to elevated total dissolved solid concentrations compared with Lake Texoma water, the density contrast of the Red River outflow is increased by high suspended‐sediment concentrations during high‐discharge events. Steep lateral slopes in the Lake Texoma basin deflect hyperpycnal river plumes and, subsequently, change the delta progradation direction before the delta reaches the opposite bank of the lake. Analysis of multi‐temporal aerial and satellite images indicates that the hyperpycnal delta follows the steepest lake‐bottom gradients, corresponding to the pre‐impoundment river thalweg (i.e. bypassing shallow parts of the lake). An analytical model for the hyperpycnal‐plume trajectory indicates plume deflection during low‐discharge or high‐discharge events, towards the deepest part of the basin. The magnitude of plume deflection is a function of river discharge and basin‐margin gradients. Plume deflection can vary between 10° and 80° from the channel axis towards the old river thalweg. The high deflection appears in the case of maximum basin side gradients of 12·8° and in conditions of low river discharge. During low‐discharge periods, the Red River delta builds a lobate shape with multiple terminal distributary channels whereas, during high‐discharge periods the Red River delta builds an elongate shape with a single large distributary channel. The elongate morphology of the delta is formed through the development of a single distributary channel and abandonment of the other distributaries. Therefore, the lobate shaped delta is expected to be preserved in the rock record. |
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| Keywords: | Discharge hyperpycnal lacustrine delta Lake Texoma morphology Red River topography |
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