Abstract
ABSTRACT: Soils and paleosols reflect the complex interplay between sedimentation, erosion and non-deposition. An analysis of the mineralogical components of paleosols is critical for the reconstitution of the factors, processes and environments in which they were formed. The recognition of mineralogical assemblages can reveal the environmental conditions during pedogenesis and through quantitative analysis it is possible to identify a vertical variation in mineral concentration or leaching over the paleosol profiles, indirectly pointing to environmental processes that dominated during the pedogenetic evolution. The objective of this study is to discuss the significance of mineral phases and to quantify the environmental evolution and degree of development of paleosols of the Marília Formation, Maastrichtian of Bauru Basin. Three sections have been described (A1, A2, A3) in the Marília Formation. The mineralogy was determined by x-ray diffraction, and mineral quantification was obtained through the Rietveld refinement method. The calcretes of the Marília Formation are pedogenic, mostly authigenic minerals. The variation of quartz, calcite, palygorskite and smectite, the micromorphology, and the diversity of subsurface horizons (Bkm, Btkm, Bt) indicate that the studied paleosols did develop in semi-arid conditions, with episodes of higher rainfall rates, humidity, leaching and desilication.
Highlights
Progress in identification and mineralogical quantification techniques has contributed to the study of paleosols
Plenty of calcretes in the Marília Formation records are environments with a semi-arid paleoclimate, because they are rare in arid or humid climates and develop completely in semi-arid climates (Fedoroff & Courty 1989). Another factor that endorses this thesis is the lack of gley horizons associated with calcretes
Calcretes from humid climates are associated with horizons of reducing environments, because their position is in relief
Summary
Progress in identification and mineralogical quantification techniques has contributed to the study of paleosols. It is possible to define the factors’ conditions and the formation processes from the analysis of paleosols. Paleosols, defined as soil formed in an ancient landscape (Wright 1986), reveal the environmental conditions and characteristics that identify parental material, estimate formation time, and reconstitute paleosurfaces, paleoclimate and paleobiote. The use of paleosols enables the identification of the relationship between deposition, non-deposition and erosion. They have taken an increasingly prominent role in the study of paleoenvironmental and stratigraphic reconstructions (Andreis 1981, Kraus & Brown 1988, Birkeland 1999, Kraus 1999, Retallack 2001)
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