SOIL CRUSTS OF A TYPIC NATRARGID OF CHUBUT: FEATURES AND GENESIS.

Abstract

The objectives of this work were: (i) to document the micromorphological and physico-chemical properties of a vesicular layer of a Typic Natrargid; and Oi) to determine the factors controlling crust formation. The Av horizont studied showed characteristics like high silt, high exchangeable sodium percentage and low organic matter contents. The crust Iying below the desert pavement consisted of an upper zone (5 mm thick) of laminated sands, silts and clays, large vesicles (60 %) up to 3 mm in diameter. The very dense lower zone (15 mm thick) has few (20 %) and small vesicles up to 1mm in diameter. The vesicles have rough walls on the upper half and smooth walls at the bottom. The walls oflarger vesicles close to the surface area are subject to microerosion and microdeposition by a descending water front. The Av horizon seems formed on the Bt itself, with a differential development of pores and structure. The papules correspond to residual argillans strongly fragmented and deformed by stress. The observations show evidence of lateral rather than vertical transport of material. The major proceses responsible for crust formation are considered to be a combination of erosion by raindrop impact and redeposition by rainwash.