A support for the existence of paleolakes and paleorivers buried under Saharan sand by means of "gravitational signal" from EIGEN 6C4

Abstract

The goal of this study is to demonstrate that and how the recent gravitational and topographic data support the findings made by geologists and others as for the existence of the paleolakes and paleoriver systems, now buried under the sands of Sahara. It is always important and useful to have such an independent analysis supporting certain results, and this paper is such a case. We make use of the gravity disturbances (or anomalies), the Marussi tensor of the second derivatives of the disturbing geopotential, the gravitational invariants and their certain ratio, the strike angle and the virtual deformations. The geopotential is represented by the global combined (from satellite and terrestrial data) high-resolution gravity field model EIGEN 6C4 (till degree and order 2160 in spherical harmonic expansion). The topography is derived from the ASTER GDEM and ETOPO 1 models (both are used). With all these data, we confirm the existence of huge paleolakes or paleoriver systems under the Saharan sands known or anticipated in an independent way by geologists for the lakes MegaChad, Fazzan and Chotts; for Tamanrasset river valley; and Kufrah Basin, presumptive previous flow of the Nile River. Moreover, we suggest a part of the Grand Egyptian Sand Sea as another "candidate" for a paleolake and hence for a follow-up survey.