Geomorphic Elements in Modern Continental Sedimentary Basins

Weissmann, Gary; Hartley, Adrian J.; Nichols, Gary; Scuderi, Louis

Modern analogs for continental sedimentary rocks (e.g., alluvial fans, fluvial successions, eolian deposits, and lacustrine deposits) should be developed from an understanding of geomorphology in modern sedimentary basins since these are locations on Earth where subsidence allows for long-term preservation of these deposits. Weissmann et al. (2010) compiled a compendium of 724 modern continental sedimentary basins around the world to evaluate fluvial form common in these basins. Here we assess satellite imagery of several sedimentary basins to quantify the aerial extent and form of different geomorphic elements that are present in the sedimentary basin.

Geomorphic elements identified in the basins include (1) Large DFS (DFS greater than 30 km in length; (2) Smaller DFS (DFS that are less than 30 km in length); (3) Incised valleys cut through the apex of DFS deposits; (4) Abandoned DFS surfaces if the DFS is incised; (5) Bajadas and Pediment surfaces (coalesced DFS that form large fluvial/alluvial plains where it is difficult to distinguish individual DFS from imagery); (6) Interfan tributary systems; (7) Axial tributary fluvial systems; (8) Eolian deposits; and (9) Permanent and ephemeral lake deposits. Wetlands are commonly present on distal portions of DFS and are included as part of the DFS elements.

In the large modern foreland basins of the Andes and the Himalayas, DFS deposits (e.g., elements 1-5) dominate the depositional area of the sedimentary basin. In the Himalayan Foreland, these elements comprise approximately 92% of the basin area while the tributary fluvial successions (e.g., elements 6 and 7) comprise only about 8% of the area. Similarly, the DFS elements form about 98% of the area in the Andean Foreland Basin while the axial fluvial system only comprises approximately 2% of the area. DFS comprise almost all of the depositional area in the Andean Foreland basin located west of the buried forebulge (approximately 250 km from the mountain front). Other sedimentary basins around the world show similar distributions of fluvial deposits, indicating that DFS dominate depositional areas in modern sedimentary basins. We expect the same to have been true in ancient sedimentary basins; therefore, DFS and axial river deposits should be more fully evaluated in the context of position in a sedimentary basin in order to understand the development and distribution of facies observed in the sedimentary rock record.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013