4th International Conference of Palaeogeography

273 / 2019-07-06 19:21:04

Preliminary study of empirical source-to-sink scaling relationships in a rift basin: the late Pleistocene and recent Lake Malawi (Nyasa) Rift, East Africa

Lake Malawi; Source-to-sink; scaling relationship; climate variablity; Paleogeographic reconstruction

Geomorphological scaling relationships derived from world’s river systems within different tectonic settings have been well investigated to decipher source-to-sink (S2S) geomorphological changes. However, it is still very difficult to correlate between most geomorphological components throughout the lacustrine rift that is sensitive to tectonic and climatic variability. Lake Malawi (Nyasa) Rift, the southernmost rift basin of the East African Rift System (EARS), have experienced severe precession-forced droughts since 150 ka, recording at 200m, 350 m and 500 m below present lake level (BPLL). Several relationships of the catchment segment in the late Pleistocene and recent Lake Malawi Rift are fairly robust regardless of tectonic or climatic effect, except for the relationship between the maximum relief and the drainage area. The S2S scaling relationships, which are derived from the late Pleistocene S2S system along the axial or shoaling margin with a relatively lower tectonic subsidence, will be generally stronger between the long-term delta deposition rate, the areal extent of the millennial-scale delta package, and the drainage area, considering of climatic variability. There will also be stronger correlations between the long-term delta deposition rate and the delta area among several drought intervals. Besides, the delta width appears to scale to the delta length, and sometimes greater delta width than its length can be attributed to the multi-stage delta migration.
Validation of these first-order S2S scaling relationships in an archetypical lacustrine rift can help us reconstruct paleodrainage systems and quantify their geomorphological characteristics of pre-modern S2S systems in the Lake Malawi, especially when the lake dropped to a much lower lake-level and the paleodrainage systems were merged into a larger one during megadroughts. Also, the semi-quantitative geomorphological scaling approach will shed some lights on predicting dimensions of less constrained subsurface deltas from sedimentological and hydrocarbon exploration perspectives, and it could extend to investigate some genetically-related geomorphological components in some pre-Quaternary lacustrine rift basins around the world.