Single-grain OSL chronologies for Middle Palaeolithic deposits at El Mnasra and El Harhoura 2, Morocco: Implications for Late Pleistocene human-environment interactions along the Atlantic coast of northwest Africa
Optically stimulated luminescence (OSL) measurements were made on individual, sand-sized grains ofquartz from Middle Palaeolithic deposits at two cave sites (El Harhoura 2 and El Mnasra) on the Atlanticcoast of Morocco. We were able to calculate OSL ages for 32 of the 33 samples collected from the MiddlePalaeolithic deposits, including the earliest and latest Aterian levels at both sites. These ages revealperiods of occupation between about 110 and 95 ka (thousands of years ago), and at w75 ka. A lateMiddle Palaeolithic occupation of El Harhoura 2 is also recorded at w55 ka. Our single-grain OSLchronologies largely support previous age estimates from El Mnasra and other sites along the Atlanticcoast of Morocco, but are generally more precise, reproducible and stratigraphically more coherent (i.e.,fewer age reversals). We compare the single-grain ages for El Harhoura 2 and El Mnasra with thoseobtained from single- and multi-grain OSL dating of Middle Palaeolithic deposits in the nearby sites ofContrebandiers and Dar es-Soltan 1 and 2, and with records of past regional environments preserved insediment cores collected from off the coast of northwest Africa. A conspicuous feature of the newchronologies is the close correspondence between the three identified episodes of human occupationand periods of wetter climate and expanded grassland habitat. Owing to the precision of the single-grainOSL ages, we are able to discern gaps in occupation during Marine Isotope Stages 5 and 4, which mayrepresent drier periods with reduced vegetation cover. We propose that these climatic conditions can becorrelated with events in the North Atlantic Ocean that exert a major control on abrupt, millennial-scalefluctuations between wet and dry periods in northwest and central North Africa.