The antiquity of the Sahara Desert: New evidence from the mineralogy and geochemistry of Pliocene paleosols on the Canary Islands, Spain

Abstract

The Sahara is the largest warm desert in the world, but its age has been controversial, with estimates ranging from Miocene to Holocene. Mineralogical and geochemical data show that paleosols of Pliocene to mid-Pleistocene age on Fuerteventura and Gran Canaria in the Canary Islands have developed in part from inputs of dust from Africa. These paleosols contain quartz and mica, minerals that are abundant in African dust but are rare in the basaltic rocks that dominate the Canary Islands. Trace elements with minimal mobility, Sc, Cr, Hf, Th, and Ta as well as the rare earth elements, show that paleosols have compositions that are intermediate between those of local rocks and African-derived dust. Thus, results reported here and in a recently published study by others indicate that 9 paleosols record delivery of African dust to the Canary Islands between~4.8-2.8 Ma, 3.0-2.9 Ma,~2.3-1.46 Ma, and~0.4 Ma. A long-term paleosol record of African dust input agrees with deepsea records off the coast of western Africa that imply increased dust fluxes to the eastern Atlantic Ocean at 4.6 Ma. It is concluded that the Sahara Desert has been in existence as an arid-region dust source, at least intermittently, for much of the Pliocene and continuing into the Pleistocene.

Climate-driven vicariance and long-distance dispersal explain the Rand Flora pattern in the liverwortExormotheca pustulosa(Marchantiophyta)

“…While dispersal events from mainland regions explain the current distribution of E. pustulosa on the different oceanic archipelagos, the major split events might have resulted from the fragmentation of a once continuous and widespread E. pustulosa population (vicariance). For example, the separation of northern Macaronesian and western Mediterranean populations from South Africa and Saint Helena populations occurs in the Pliocene, and this coincides with recent estimates for the formation of the Sahara Desert (~4.8 -0.4 Ma; Muhs et al, 2019). Prior to the formation of Sahara, a significant portion of north Africa was covered by lowland rainforest, which was gradually replaced by woodland savannah (Plana, 2004;Senut et al, 2009) allowing the connection between the Macaronesian and Mediterranean regions with eastern Africa.…”

“…The climatic changes that occurred during the Miocene (23.0 -5.3 Ma) and Pliocene (5.3 -2.6 Ma) are thought to be consequential in shaping the biogeography of African plant lineages (Pokorny et al, 2015). During these periods, increasing aridification of Africa and the formation of the Sahara Desert (~4.8 -0.4 Ma; Muhs et al, 2019) caused the fragmentation of a large number of African plant lineage distributions, with the subsequent restriction of persisting geographically disjunct sister clades to these peripheral African regions (Sanmartín et al, 2010;Mairal & Sanchez-Meseguer, 2012;Pokorny et al, 2015). Most of these Rand flora lineages are adapted to temperate or (sub)tropical montane humid climates and the tropical lowlands of Central Africa, the Sahara and Sino-Arabic Deserts in the north and the Kalahari Desert in the south, are major environmental barriers to dispersal (Mairal et al, 2017).…”

Late Miocene and Early Pliocene coastal deposits from the Canary Islands: New records and paleoclimatic significance

“…The first appearance of these egg pods in the Canary Islands was in the Orzola aeolian calcarenite, in the north of Lanzarote. They have been dated in the range 4.3 ± 0.7 and 3.78 ± 0.71 Ma (Lomoschitz et al, 2016) and their presence coincides roughly in time with the first arrival of African dust on these islands (Muhs et al, 2019). These marine deposits of Lanzarote and Fuerteventura, therefore, must be older than ca.…”

“…We infer this in part from the layers of (Haq et al, 1987), the early cold CC (Canary Current) (Meco et al, 2015), the gradual closure of the CAS (Central American Seaway) (Schmidt, 2007) and the Arctic ice shelf installation (Lisiecki and Raymo, 2005;Petit et al, 1999). (B) North Africa drying and increasing presence of desert dust in paleosols of the Canaries (Muhs et al, 2019). (C) The Canary record of ages from dated lava flows (Meco et al, 2007(Meco et al, , 2015Lomoschitz et al, 2016) and fossil species (Meco et al, 1997(Meco et al, , 2011 permit to establishment of time intervals for littoral marine deposits and aeolianites, revealing the most pronounced climatic events.…”

“…The authors pointed out the warm nature of the fossil fauna of the marine deposits and the temperate climate of the associated aeolianite. Moreover, the arrival of the first desert-origin dust from Africa occurred in the Pliocene and after the Canary Pliocene marine deposits (Muhs et al, 2019).…”