Observations on the composition and mineralogy of an algerian duricrust complex

Abstract

Duricrusts from the northern margin of the Plateau du Tademait are examined using a variety of techniques including: optical and scanning electron microscopy, X-ray diffraction, differential thermal analysis and infra-red spectroscopy. The escarpment edge is capped by a dolomitic limestone containing fibrous palygorskite. Two “older” duricrusts are recognised, a relatively pure limestone found only as isolated blocks on the plateau surface and a banded silcrete on top of and within the dolomatic limestone. The latter resembles silcretes described from elsewhere in western Algeria and ascribed to a period of Villafranchien silicification. Finally, two superficial duricrusts are described: a vesicular calcrete which occurs in pockets on the plateau surface and a friable gypcrete on the escarpment. Both contain quartz and feldspar grains which exhibit evidence of limited aeolian abrasion and chemical weathering, it is suggested that they are Holocene in age.