干旱区生态环境知识资源中心

Episodic desert loess and paleosol sequences in South Yemen provide a late Pleistocene to Holocene record of climatic change and soil development. At Sana, one paleosol based on its thickness and development formed during mid or early Holocene time in approximately four thousand years. The 2Akb horizon sample of this paleosol has a C-14 age of 7750 +/- 300 years. At Ibb the 2ABtb horizon of another paleosol has a C-14 age of > 33,100 years. Deposition (silt + very fine sand + clay) for the Sana site calculates to average 110 g m(-2) yr(-1) and includes 3.3 g or less of CaCO3 m(-2) yr(-1). This rate of desert loess and carbonate deposition is probably 2 to 5 times greater than that in the Lahontan Basin of the United States during the last 13 kyr, and about 2 to 5 times higher than that in the southwestern United States today. It is about the same as the 12 cm kyr(-1) (170 g m(-2) yr(-1)) estimated for central North Iran and the 10 cm kyr(-1) (0.1 mm yr(-1)) estimated for the Netivot section of the Negev of Israel but some 7 to 9 times less than the rate estimated for Wisconsinan loess in Iowa. Thickness of desert loess examined and the calculated rate of deposition indicate that the crater has been receiving desert loess for at least 15 kyr, and that the crater is pre Holocene. Pedogenic development of the Camborthids and Haplargids in the ground soils and that of the argillic horizons in the Sana paleosols suggest that these soils formed in a somewhat more humid phase than the present warm-tropical, semi-arid environment. The occurrence of mollic epipedons in the Sana paleosols, but not in the ground soils is evidence of a more humid past climate (mid or early Holocene). The Ibb paleosol, which formed at least partly during a more humid part of the late Pleistocene, is even more strongly developed than the mid or early Holocene Sana paleosols.