Lancaster et al. (2002) provide some useful information on Quaternary eolian dune activity in western Mauritania. As outlined below, however, their publication could benefit from (1) a statement regarding the relevance of their research to the debate on the age of “Ogolien” dunes in western Mauritania, (2) a different interpretation of the timing and duration of episodes of Quaternary eolian dune activity in western Mauritania, and (3) an acknowledgment of previous work by certain French geologists.
The most significant aspect of the publication by Lancaster et al. (2002) is the dating of the dunes, particularly the “Ogolien” dunes. In the French literature, the term “Ogolien” is used to denote a period of eolian dune construction that is thought to have occurred ca. 20,000–13,000 14C yr B.P. (ca. 24,000–15,400 cal. yr B.P.) in the Mauritania/Senegal region (e.g., Beaudet et al., 1976; Elouard, 1976; Michel, 1980; Barbey, 1989). The dates provided by Lancaster et al. (2002) are the first dates obtained from these Ogolien dunes, but Lancaster et al. fail to point out the originality and significance of this work. Assuming different ages of these dunes leads to very different interpretations, especially regarding the sequence stratigraphy of eolian sediments (i.e., when are eolian sediments active and/or preserved in the stratigraphic record, relative to sea-level changes and glaciations?). Prior to the publication of Lancaster et al. (2002), the most accurate statement that one could make concerning the age of Ogolien dunes in the coastal region of western Mauritania was that the Ogolien dune sands at Site M8 (described in Barusseau et al., 1989; Swezey, 2001) are older than the oldest dated marine shells (ca. 7100 cal. yr B.P.) at that site. The new data published by Lancaster et al. (2002) suggest that Ogolien dunes in western Mauritania range in age from ca. 27,000 to 8,000 cal. yr B.P., and that Ogolien dune activity in western Mauritania spanned this entire range of ages.
Although Lancaster et al. (2002) report numerous dates from the dunes in western Mauritania, they may have misinterpreted their data in an attempt to correlate their dates with other dates from the rest of the Sahara. Lancaster et al. (2002) claim that their dates indicate that separate episodes of eolian dune activity occurred in western Mauritania at 25–15 ka, 13–10 ka, and <5 ka. However, when one considers ranges of uncertainty, the dates reported from the eolian dunes do not fall into three separate groups. Some of the ranges of uncertainty of the dates span the range between the 25–15 ka group and the 13–10 ka group proposed by Lancaster et al. (2002). Although there is evidence in other parts of the Sahara for multiple episodes of late Quaternary eolian activity (Swezey, 2001), three separate episodes of late Quaternary eolian dune activity cannot be recognized in western Mauritania on the basis of the dates that are currently available.
Finally, Lancaster et al. (2002) do not give appropriate credit to work published previously by various French geologists. For example, Lancaster et al. (2002) describe three different dune trends in western Mauritania (degraded dunes with a northeast trend, degraded dunes with a north-northeast trend, and nondegraded dunes with a north trend). These three dune trends have been identified and described in some detail by Hébrard (see Bureau de Recherches Géologiques et Minières, 1975; Hébrard et al., 1983), who postulated that the northeast-trending dunes were older than 30,000 14C yr B.P., the north-northeast–trending dunes were ca. 20,000 14C yr old, and the north-trending dunes were of recent age. Likewise, Lancaster et al. (2002) indicate that Kocurek et al. (1991) “identified a glacial-age period of dune construction (called the Ogolien in Mauritania).” Although it is true that Kocurek et al. (1991) published information on these dunes, it would be more appropriate to credit the identification of this period of dune construction to the original work by Elouard (1962, 1976), Beaudet et al. (1976), Michel (1980), and Hébrard et al. (1983).