Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a "green Sahara" to the present hyperarid desert.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/climate-driven-ecosystem-succession-sahara-past-6000-years
[2] http://admin.indiaenvironmentportal.org.in/category/author/s-krpelin
[3] http://admin.indiaenvironmentportal.org.in/category/author/d-verschuren
[4] http://admin.indiaenvironmentportal.org.in/category/author/m-lzine-et-al
[5] http://admin.indiaenvironmentportal.org.in/category/journal/science
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/ecosystems
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/deserts
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/sahara
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/lakes
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/sedimentation
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/monsoons
[12] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-change
[13] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-science
[14] http://admin.indiaenvironmentportal.org.in/category/thesaurus/flora
[15] http://admin.indiaenvironmentportal.org.in/category/thesaurus/hydrology
[16] http://admin.indiaenvironmentportal.org.in/category/thesaurus/chad