Wednesday, 8 October 2008
George R. Brown Convention Center, Exhibit Hall E
Since meanderbelt deposits are typically sand dominated, they form important features in petroleum reservoirs and fresh-water aquifers. Facies models reasonably describe the internal structure of these units; however, the rivers typically used to formulate these facies models are not aggradational nor are they in active sedimentary basins (thus, they will not be preserved in the rock record!). A comprehensive review of over 690 modern continental basins shows that fluvial deposition in basins occurs on either distributary fluvial systems (DFS) or along axial streams, with the DFS dominating basin deposition. Though a braided pattern is typically cited as dominant on DFS, meandering rivers are also common. Meandering rivers form both compound meanderbelts and simple meanderbelts. In a compound meanderbelt, the channel is held in one location for a sufficiently long period of time to create a complex sandstone unit with coalesced vertically and laterally stacked point bar deposits. These are observed (1) within incised river reaches on the DFS, (2) along axial streams in the basin, and (3) in a distal position on some DFS. In the first two cases, the river is confined in a valley so that fine-grained sediment is winnowed out through reworking of the floodplain. Rivers in degradational settings produce similar meanderbelts. In the latter case, the compound meanderbelt stacking pattern may be more diffuse. ‘Simple' meanderbelts are formed where a channel develops a meandering pattern but avulses to a new position on the DFS prior to developing a compound meanderbelt. We present several examples of meanderbelts on DFS from modern sedimentary basins around the world. Through evaluating river form in modern continental sedimentary basins, we can begin to place fluvial facies models in a basin context, thus improving our ability to interpret and predict facies distributions in the rock record.