Stratigraphic Aspects of the Gargaresh Formation, Tripolitania, S.P.L.A.J.

Abstract

AbstractThe Gargaresh Formation, of Quaternary age, is shown to be comprised of six members each of which is made up from cross-bedded calcarenite dunes of aeolian origin resting on localised lenses of marine gravels and shallow-dipping, cross-bedded calcarenites of littoral type. The surfaces on which the marine deposits at the base of each member rest, are surfaces of discontinuity cut by wave action. Landwards, the surfaces are shaped by fluvial and aeolian erosion, soil formation and solution and delimit an equivalent number of members in quartzose silts of fluvio-aeolian origin making up the Jeffara Formation. Shorewards the Jeffara silts grade into, interdigitate with and, commonly, lap onto the marine deposits so that that within each depositional unit there is an overall sense of progradation reflecting advance of continental facies in response to falling sea level. A progressive seawards stacking of dune deposits with decreasing age suggests that progradation appears to have occurred at formational level also. However, while this may be true, the various elevations of the fossil beach deposits suggest that decreasing age of sea level high stands is not matched by decreasing altitudes, instead, high stands both higher and lower than present day sea level were involved in the overall drop. The possibility that variation in beach elevations may, however, reflect the influence of tectonic uplift and/or downwarp is also noted.