Calcareous duricrust, Al Qasim Province, Saudi Arabia: Occurrence and origin M.A. Khalifa a, b, * , Fujio Kumon b , Kokhi Yoshida b a Geology Department, Menoufia University, Shiben El Kom, Egypt b Geology Department, Shinshu University, Asahi 3-1-1, Matsumoto, 390-8621, Japan article info Article history: Available online 28 February 2009 abstract In Al Qasim Province, Saudi Arabia, calcareous pedogenic duricrust overlies the Upper Permian carbonates and clays of the Khuff Formation, and ranges in thickness from 60 cm to 2 m. It consists of white sandy duricrust capped by brown, nodular porous duricrust. Petrographic investigation led to recognition of three lithofacies that show spatial distribution: 1- structureless sandy calcareous mudstone, 2- brecciated-nodular calcareous mudstone, and 3- pisolitic calcareous mudstone. The diagenetic changes in duricrust are aggrading neomorphism and formation of calcite rims around quartz grains. Microprobe chemical analysis was performed on the diagenetically altered material. The devel- opment of the duricrust is controlled by four factors: the climate changes, the type of underlying rocks, source of carbonate and biological effects. The repeated changes from semi-arid climate with alternating wet and dry seasons are the main controlling factor, in generation of duricrust development. During humid periods, descending water carries the dissolved carbonates downward as bicarbonates, whereas dry and interpluvial period, the carbonate-rich solutions are carried upwards by capillary or evaporation. The claystone and sandstone interbeds possibly affect the development of calcareous duricrust, more than the sandstones and dolostones, because the former have the ability to attach calcium carbonate to form the duricrust. The development of calcareous duricrust is mainly attributed to the Pleistocene and Early Holocene alternating humid and arid periods that prevailed over the Arabian Peninsula during this time. Ó 2009 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction The name ‘‘duricrust’’ was used by Woolnough (1927) to describe indurated surface layers consisting of siliceous, aluminous, ferruginous and calcareous materials in the uppermost part of soil profile resting upon topographic surfaces formed during Miocene erosion in Australia. Duricrusts have been recorded in many parts of the world as the product of soil-forming processes, and represent the B-horizon of the soil profile (Chapman,1974). Other terms used include calcrete, caliche, croutes, calcaires, Nari, and Kaunkar (Wright and Tucker, 1991; Khadkikar et al., 2000). Calcihe or cal- cretes refer to near surface, terrestrial predominantly calcium carbonates within soil profiles, in the vadose zone or associated with shallow ground water, where waters are saturated with calcium carbonate (Wright and Tucker, 1991). Two main groups of calcrete occur in the natural environment and are broadly classified according to the processes by which they formed (Nash et al., 1994). Calcretes that developed in association with soil-forming processes are termed pedogenic forms and typically have considerable evidence of biological activity (Tandon and Friend, 1989; Wright and Tucker, 1991; Tandon and Gibling, 1997). The development of such calcrete is closely determined by climatic factors, which directly influence the nature of soil-forming processes. Non-pedogenic forms comprise a variety of other types of calcrete of varying origin (laminar crust, gravitational zone cal- crete, valley channel and deltaic calcrete and ground water cal- crete) (Carlisle, 1983) with little or no evidence of biological activity (Wright and Tucker, 1991; Spotl and Wright, 1992; Pimentel et al., 1996; Khadkikar et al., 1998). Development of such calcretes is less closely linked to climatic regime given their independence from pedogenic mechanisms of carbonate precipitation. In the present study, use of the term ‘‘duricrust’’ follows the former investigators on this area as applied to the adjacent locali- ties (Powers et al., 1966; Chapman, 1974). The calcareous duricrust is a resistant duricrust carapace that masks the underlying strati- graphic and structural details, over a rather extensive area in * Corresponding author. Geology Department, Menoufia University, Gamal Abdel Nasser, Shiben El Kom, Menoufia, Egypt. Tel.: þ2 26353592; fax: þ2 048 235689. E-mail address: kh_cycke@yahoo.co.uk (M.A. Khalifa). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint 1040-6182/$ – see front matter Ó 2009 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2009.02.014 Quaternary International 209 (2009) 163–174