Loess Records - Mineral Dust: A Key Player in the Earth System - page 417

The best-studied desert loess in northern Africa is located on the carbonate-rich
Matmata Plateau in southern Tunisia (Coudé-Gaussen 1987 ; Coudé-Gaussen et al.
1987 ; Coudé-Gaussen and Rognon 1988 ; Coudé-Gaussen 1990 ; White et al. 2002 ;
Dearing et al. 2001 ). The Tunisian loess covers an estimated area of 4,000 km 2 and

reaches thicknesses of up to 20 m. On the basis of radiocarbon ages, Coudé-Gaussen
et al. ( 1987 ) showed that the age of the Tunisian loess ranges from >43 to 10 ka,
whereas a chronology based on optically stimulated luminescence (OSL) (Dearing
et al. 2001 ) suggests that the lower part of this loess is much older (250-100 ka).
Loess deposits are also located on a carbonate-rich mountain range in northwestern
Libya, between the Jefera Plain to the north and the Tripolitanian Plateau to the
south. These deposits are considered to be a continuation of the Tunisian loess
(Coudé-Gaussen 1987 ).
The best-known loess in the Sahel of Africa is the informally named Zaria loess,
located on the Kano Plains in central-northern Nigeria (McTainsh 1984 , 1987 ). This
is probably one of the largest desert loess regions known in the world, covering
an area of 41,000 km 2 and located today in a tropical climate zone. Loess PSD is
mainly trimodal, with modes at 75 m, 44 m, and <2 m(McTainsh 1984 ). OSL
dating of the loess indicates an age of 37-10 ka (Stokes and Horrocks 1998 ). Scat-
tered reports from other Sahelian countries suggest the presence of a noncontinuous
loess belt, oriented west to east from southern Senegal through Guinea, Mali,
Burkina Faso, Niger, and Nigeria to northern Cameroon; loess-like deposits are also
found on the Canary Islands (Figs. 16.1 cand 16.6 ).
Loess in southern Africa is found mainly in northwestern Namibia, where it
is located on a vast area between the Great Escarpment to the coast, and it is
characterized by variable underlying lithologies (Eitel et al. 2001 , 2006 ; Brunotte
et al. 2009 ). On the basis of the carbonate content and the heavy-mineral assemblage
of the loess, Eitel et al. ( 2001 ) suggested that the source of the loess was a
combination of exposed calcretes from the east and silt from local metamorphic
and volcanic rocks. Crouvi et al. ( 2010 ) suggested that the main sources of quartz
silt in the loess are the nearby quartz-rich Kalahari Sands that lie only a few tens
to hundreds of kilometers to the east and southeast of the loess. Linear dunes in
these sands are oriented east-west to east-southeast-west-northwest, suggesting an
easterly wind regime when the dunes were formed; these easterly winds currently
prevail in the region (Fig. 16.6 ). Similar to the Sahelian loess, the Namibian loess
stretches westward into the Atlantic Ocean, as finer silt deposits from marine cores
are reported off the Namibian coast (e.g., Stuut et al. 2002 , see also Chap. 17 ) .
There is a good temporal correlation between the period of sand-dune activity, loess
accumulation, and silt deposition off the Namibian coast (Crouvi et al. 2010 ).
The most prominent loess in the Middle East is located in the Negev desert,
southern Israel, covering an area of 5,500 km 2 (Figs. 16.1 dand 16.6 ). It mantles

most of the exposed carbonate bedrock in the northern Negev and fills depressions
and valleys farther south in the central Negev highlands (Yaalon and Dan 1974 ).
The PSD of the loess is bimodal (50-60 m and 3-8 m), with a general
upward increase of the coarse mode versus the fine mode in all sequences that
have been studied (Crouvi et al. 2008 , 2009 ). Bulk mineralogy is quartz, calcite,