Three-dimensionality, longitudinal profile setting,and paleo-discharge capacity of incised valleys in recent stratigraphy of the Sunda Shelf, Indonesia

摘要

The Sunda Shelf of Indonesia is a key physiographic link between the South China Sea and the Indian Ocean. A high-quality, 3,154-km~2 3D seismic data volume was used to map ten architecturally complex, thick channelforms. A map of each valley base was exported to ArcGIS to determine its edges, thalweg, and planform centerline. Then along-valley width and thalweg depth were calculated. Global river longitudinal gradients were calculated from analysis of modern shelf bathymetric profiles to yield a median lowstand shelf and ancient channel gradient of 10-4. Width, depth, and gradient were input to the empirical Manning's Equation for Discharge to yield paleo-discharge capacities. These calculations yielded extremely high flood discharge calculations for these Sunda channelforms–discharges that frequently exceed the greatest flood discharge ever measured (274,400 m~3/s, Amazon River, 1989). This observation, coupled with observations of mean depth at thalweg (54 m), mean width-todepth ratio (21:1), and the absence of levees, lead to the interpretation that these channelforms are incised valleys rather than aggradational channels. ArcGIS methods developed here could be used to analyze channelform deposits and modern rivers alike in an along-stream framework, whether for reservoir characterization, water resource management, or ecological applications.