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Stratigraphic and sedimentologic studies in continental successions do not always devote particular attention to the paleosols, in particular in and or semi-arid paleoenvironments. The aim of this paper is to: (1) describe in detail the macro- and microscopic pedogenic features of four types of paleosol profiles with calcic horizons of the Marilia Formation (Maastrichtian), and (2) elaborate paleoclimatic considerations based on the depth of the nodular calcic horizon and on the molecular weathering ratios of the main oxides.

The Marilia Formation, which crops out in the eastern portion of the Bauru Basin (Sao Paulo State, southeastern Brazil), usually contains profiles of calcic paleosols developed over sandstone deposits which formed in a eolian sand sheet paleoenvironment. The type of calcium carbonate accumulation in paleosol horizons varies from thin discontinuous coatings on ped surfaces trough faint filaments in soil matrix to massive accumulations between coalesced nodules, which are associated respectively to the stages I, II, and III of calcic soil development morphology classification.

Four carbonate paleosol profiles with prominent calcic horizons (Bk and Ck) and secondary argillic horizons (Bt and Btk) have been studied in Marilia Formation: two near the homonymous city and other two around the Monte Alto plateau. Field data and petrographic, geochemical, and clay mineralogy analyses allowed to classify these four paleosol profiles as Aridisols and define some paleoclimate considerations on their development.

Molecular weathering ratios relative to calcification, hydrolysis, clay formation, salinization, and hydration of the paleosol profiles has been calculated to define the characteristic of the paleosols and the paleoclimatic proxies. Paleoprecipitations have been estimated by the application of an empirical equation that related this value to the depth of the Bk horizon. (C) 2008 Elsevier Ltd. All rights reserved.