The rock varnish in the Messak Settafet (Fezzan, Libyan Sahara) Age, Archaeological context, and paleoenvironmental implication

The manganese-rich rock varnish from the Messak Settafet plateau is a relict feature that developed at the end of the Holocene humid cycle, before the onset of the present-day hyperarid conditions. The Messak Settafet varnish consists of three microlayers of different composition and micromorphological features. The innermost microlayer is composed of illuvial clay. The second, middle microlayer is the classic manganese-rich rock varnish. The outermost microlayer is composed of unaltered aeolian dust. Each microlayer formed under different climatic conditions, and the microstratigraphy records a climatic evolution from a wet environment towards progressive desertification. The relationship between desert varnish, rock engravings, and radiocarbon-dated archaeological evidence and the comparison with the Holocene climatic evolution as from cave deposits suggest that most of the varnish developed since the end of the VI millennium B.P. under a semiarid climate characterized by steppe-type vegetation, up to the onset of desert conditions, during the IV millennium B.P.