Deciphering shorelines of the Holocene Mega-Chad lake: role of the isostatic rebound
Abstract
Megalake-Chad (MLC) was a vast inland sea covering up to 350 000 km2 in the central part of Africa during the Holocene climatic optimum (around 11-5 ka BP). The littoral structures that follow its paleoshorelines have been highlighted thanks to remote sensing images and digital elevation models (DEM). The megalake regression due to the climate aridification at the end of the African humid period led to an isostatic uplift of the area that has modified the current altitude of the paleoshorelines. We investigate the impact of the isostatic uplift on the elevation of the paleoshorelines in order to better understand the MLC evolution.
We model for the first time, using several Earth models, the vertical deflection and pattern of the hydro-isostatic readjustment caused by the flooding (i.e., loading) and then drying-out (i.e., unloading) of this large paleo-lake, provided that the lithosphere deflection reached the isostatic equilibrium before the drying-out of the lake. Our model suggests that up to 16 m of vertical displacement may have occurred during the upper Holocene in the Chad Basin, with potential deflection of the MLC shorelines in the 2-12 m range from north to south. Finally, assessing the general morphology of the area using SRTM and GMTED 2010 data and comparing topographic features of the megalake's paleoshoreline before (-6ka) and after the rebound (today), we found that accounting for hydro-isostasy is crucial when deciphering former shoreline elevations and interpreting the late Quaternary MLC evolution.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.G53B0618M
- Keywords:
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- 1211 Non-tectonic deformation;
- GEODESY AND GRAVITY;
- 1217 Time variable gravity;
- GEODESY AND GRAVITY;
- 1218 Mass balance;
- GEODESY AND GRAVITY;
- 1236 Rheology of the lithosphere and mantle;
- GEODESY AND GRAVITY