Paleoclimatic interpretations from pedogenic calcretes in a Maastrichtian semi-arid eolian sand-sheet palaeoenvironment: Marيlia Formation (Bauru Basin, southeastern Brazil)

Stratigraphic and sedimentologic studies in continental successions do not always devote particular attention to the paleosols, in particular in arid 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 Marيlia 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. rيlia Formation, which crops out in the eastern portion of the Bauru Basin (Sمo 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. arbonate paleosol profiles with prominent calcic horizons (Bk and Ck) and secondary argillic horizons (Bt and Btk) have been studied in Marيlia 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. lar 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.