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During the Cretaceous, the Brazilian Intracratonic Sanfranciscana Basin was characterised by fluvial and aeolian deposition, whose facies, palaeosols, and stratigraphic architecture indicate significant changes in tectonics and climate. This work proposes a low-frequency sequence stratigraphic model, using the facies and palaeosols distribution as the stratigraphic proxy for identifying variations in the accommodation space, sediment supply, and their relationship with the tectonic and climatic events. The Unconformity U-0 was generated by the extensional tectonic processes during the Gondwana breakup in the Early Cretaceous and marked the initial continental sedimentation. The Lower Cretaceous Sequence SF1 overlies this unconformity, constituted by fluvial and lacustrine deposits. From south to north, the unconformity U-1 truncates the top of the Lower Cretaceous Sequence SF1 and the Precambrian basement, respectively. Overlaying Unconformity U-1 are the Upper Cretaceous volcanic rocks, fluvial, and aeolian deposits of the Sequence SF2. Because of the vertical and lateral changes, Sequence SF2 is divided into two sequences, SF2A and SF2B, separated by the regional Unconformity U-2, representing climatic and tectonic changes in the basin. During the late stage of sedimentation of Sequence SF1, the ratio between accommodation (A) and sediment supply (S) was positive in the south and negative in the basin's north. The evolution of Sequence SF2A records a negative A/S ratio, followed by an abrupt change to a positive A/S ratio in Sequence SF2B, leading to the genesis of the regional erosive surface of Unconformity U-2. Sequence SF2B also records increased humidity from arid climatic conditions, marked by the 3D regional distribution of facies and palaeosols, linked to the climatic changes detected in South America for the Late Cretaceous. • Proposes low-frequency sequence stratigraphy analysis. • The 3D regional distribution of facies and palaeosols approach. • The Brazilian Intracratonic Sanfranciscana Basin. • Variations in the accommodation space, sediment supply, and their relationship with the tectonic events. • Late Cretaceous climatic changes. [ABSTRACT FROM AUTHOR]

Distributive Fluvial Systems (DFS) are fan-shaped landforms constituted by a radial system of channels that diverge downstream from an active apex, where the drainage emerges from the confinement valley. In such landforms, elevation, distance from fluvial channels, sedimentation rates, surface stability, and plant cover control weathering processes and soil development, but these features are obliterated within geological time. Thus, the micromorphological analysis of paleosols can be helpful for paleoenvironmental reconstruction of ancient DFS, improving the knowledge of soil genesis in these depositional landforms. Here, we describe macro and micromorphological features of twenty paleosols developed under arid to semiarid climates along the proximal to the medial zone of an Upper Cretaceous DFS in the Marília Formation, Bauru Basin, Brazil. Paleosols on the proximal zone typically showed features consistent with poor drainage, namely Bg, Btg and Bss horizons, and reddish Bt horizons in higher positions. Conversely, paleosols on the medial zone commonly showed reddish colours and pronounced secondary carbonate accumulation, consistent with a predominantly arid climate. Based on this distribution, we elaborated an evolution landscape model for the proximal and medial zone of the Bauru DFS, including allogenic and authigenic controls of soil development during the Campanian to the Maastrichtian epochs of southeastern Brazil. • Macro and micromorphological analysis of paleosols. • Identify the mainly paleosol-forming processes, such as palaeohydrology and palaeotopography conditions. • Soil Paleocatena. • Allogenic control in soil development and geomorphic relationships. • Conceptual framework for recognition criteria for paleosols and geomorphic evolution in distributive fluvial systems (DFS). [ABSTRACT FROM AUTHOR]

The Late Cretaceous Marília Formation located in the central-southern portion of Brazil is characterized by a succession of sandstones, conglomerates, and paleosols. The paleosols constitute more than 60% of this formation, providing significant information about pedogenetic processes as well as paleoenvironmental and paleoclimate implications. The paleosols of the Marília Formation have been studied principally from a stratigraphical, sedimentological and paleopedological point of view; however, there are no studies addressing in detail the geochemical behavior of the paleosols. Therefore, we used a robust geochemical dataset combined with stratigraphical and macromorphological interpretations as well as clay mineralogy to conduct a paleoenvironmental and paleoclimate analysis of the Marília Formation in the western portion of the state of Minas Gerais in Brazil. The results indicate that the paleosols of the Marília Formation can be divided into three pedotypes and pedochemical units based on their geochemical variations and are limited at the base and top by pedochemical markers. Moreover, X-ray diffraction identified quartz and calcite as primary minerals associated with montmorillonite, smectite, illite and palygorskite, indicating wet periods combined with dry stages associated principally with dry and arid environments. The paleosol distribution and weathering index allow us to interpret the paleoenvironmental evolution of the Late Cretaceous Marília Formation, suggesting an increase in humidity from east to west in the study area. • A new approach using pedochemistry analysis was used. • Three pedochemical units and geochemical markers were identified. • Seasonal variations based on weathering indexes were observed. • Paleoenvironmental and paleoclimate conditions indicate arid to semiarid climate. [ABSTRACT FROM AUTHOR]

The Upper Cretaceous Bauru Group in south‐east Brazil consists of alluvial strata whose characteristics and distribution indicate a fluvial system developed in a semi‐arid to arid climate. Sections exposed within a 90 000 km2 study area in Minas Gerais State (in south‐eastern Brazil) were evaluated using facies and palaeosol analysis to formulate depositional and pedogenic models that may account for geomorphic and climate features. From east to west, the study succession records a gradual decrease in grain size, an increase in the width/thickness ratio in channels, a decrease in the lateral and vertical connectivity of channel deposits, and an increase in overbank deposits. The fluvial architecture indicates a braided channel belt, ephemeral ribbon–channels, and an unconfined fluvial facies from east to west in the study area. The lateral and vertical distribution of facies, stratigraphic architecture and palaeocurrent data suggest proximal, medial and distal portions of a progradational distributive fluvial system. The sedimentary dynamics were marked by the building and abandonment of channels related to processes of aggradation, vegetation growth and palaeosol generation. Macromorphological and micromorphological analyses have identified pedological and mineralogical features that indicate an arid to semi‐arid climate with a provenance from the north‐eastern part of the basin (Alto Paranaiba Uplift). From the proximal to the distal portions of the distributive fluvial system, the palaeosol development is different. In the proximal portion, the palaeosols are absent or poorly developed, allowing a possible general comparison with the present soil order: Inceptisols and Aridisols. In the medial portion of the fluvial system, the palaeosols are well‐developed and characterized by Bt, Btk, C and Ck horizons (Alfisols, Aridisols, Inceptisols and Entisols). Poorly drained to well‐drained palaeosols from the base to the top in the distal plain (Aridisols and Inceptisols) are associated with geomorphic and hydromorphic changes in the fluvial system due to progradational evolution. The genetic relationship between the fluvial architecture and the palaeosols enhances the understanding that the sedimentation and pedogenesis that occurs in different portions of the distributive fluvial system are related to the tectonic and climatic evolution of the basin. [ABSTRACT FROM AUTHOR]

Abstract Rhizoliths are organosedimentary structures produced by plants and are an important proxy for paleoenvironmental reconstructions because the differences in the morphology of rhizoliths and their rooting depths can be used to interpret soil humidity regimes, overall biomass at the soil surface, and the behavior of the water table. With the objective of advancing knowledge on rhizoliths, a study was performed on the macromorphological and micromorphological characterizations of the rhizoliths preserved in the thirty-one paleosols of the Marília Formation in Minas Gerais, southeastern Brazil. Based on the topological and architectural attributes of rhizoliths, and on their possible functional adaptations, such as mycorrhizal associations, three different types of rhizoliths are described in this study and represent at least three different plants: rhizohaloes, root casts and rhizocretions. Well-developed paleosols with nodular horizons contain the higher density of long root casts, indicating a seasonally dry environment, because the root casts present two meters in length. These adaptations are associated with an exploitation of a lowered water table during most times of the year. The higher density of rhizoliths indicates an area with agglomerated arboreous arbustive vegetation cover. Paleosols with chalky horizons also show a high density of root casts, indicating a landscape with high plant density that is adapted to drained soils, but with a seasonally elevated water table or the influence of ephemeral flows, given the proximity to the flow channels. The poorly drained paleosols with redoximorphic features show the lowest density of rhizoliths, thus indicating an incipient vegetation in response to near-surface water table and waterlogged soils in a distal floodplain. The rhizogenic laminar horizons have developed near fluvial channels with frequent sedimentary input, resulting in a sequence of laminar horizons composed of rhizocretions that are separated by sandy deposits or poorly developed pedogenic horizons. The micromorphological analysis on the rhizogenic laminar calcretes showed biogenic features, such as alveolar septal structures, calcified filaments, microcodium, calcified cells and pisoliths. Despite the scarce paleobotanical findings in the Marília Formation, the results obtained indicate an ecosystem that was composed of plants varying from herbaceous to arboreous, with an environment similar to modern semiarid shrublands. Graphical abstract Unlabelled Image Highlights • The architecture and geometry of rhizoliths indicate different types of paleosols. • The preservation of rhizoliths are linked to the paleosols characteristics. • A link between the type of rhizolith and paleotopography was established. [ABSTRACT FROM AUTHOR]

Palaeosols can be used as stratigraphic proxies, palaeosurface indicators, and palaeorelief reconstitution tools, as they reflect a complex interrelationship between sedimentation, erosion, non-deposition, and pedogenesis. The objective of the article was to estimate the relative time of formation of palaeosols of the Marília Formation, to determine the periods of non-deposition and non-erosion, indicative of stabilities on the surfaces, and to interpret the profiles as markers of palaeosurfaces in distributive fluvial systems (DFS) of the Late Cretaceous of Brazil. Eleven sections of the Marília Formation (S1, S2, S3, S4, S5, S6, S7, S8, S9, S10, and S11) were described, comprising forty-three profiles. The pedotypes classification (polygenic, compound, and cumulative) and the determination of palaeosols' relative formation time and residence time were based on the specialized literature. The reconstitution of pedosedimentary cycles considered the dynamics of sedimentation, erosion, and pedogenesis. Eight sedimentary cycles and 45 pedosedimentary cycles were interpreted. All the Maastrichtian pedosedimentary cycles of the Bauru Basin corresponded to depositional cycles interspersed with erosive and pedogenic processes. Palaeosols with argillic (Btk, Bt, Bss) and calcic (Bkm) horizons, developed from fluvial sandstones, evolved in processes predominantly after the deposits, with later erosive processes. However, although most of the profiles developed in periods between deposits and erosion, pedogenic processes also occurred concomitantly with the sedimentary cycles, favouring the formation of polygenetic profiles, which presented the longest pedogenic cycles in chronological terms. Palaeosols with argillic horizons can be important stratigraphic landmarks. They represent stopping moments in erosion and sedimentation of up to 1.374 My, thus consisting of the closing of high-frequency depositional cycles. Although palaeosols can demonstrate relief inversion and pedotypes with Bt-horizons can indicate ancient regional surfaces, the complete reconstitution of the topography becomes more possible at the local level, in a palaeoslope approach, due to the variability of pedofacies. • Palaeosols represent moments of non-deposition and non-erosion, indicative of landscape stability. • Compound and polygenetic palaeosols with Bt and Btk horizons correspond to the largest intervals of non-erosion, non-deposition, of topographical and tectonic stability in the evolution of the Maastrichtian palaeolandscape of the Bauru Basin. • The palaeosols represent relief inversion and the pedotypes with Bt-horizons indicate ancient regional surfaces, providing the reconstitution of palaeoslopes. [ABSTRACT FROM AUTHOR]

This is the first report of trace fossils potentially associated with insect social behavior in sandy and well-drained paleosols of the Upper Cretaceous continental sequence of Brazil. The trace fossils consist of dozens of lobed and vertical structures cemented by CaCO 3 and preserved mainly in full relief in paleosols of the Marilia Formation (Bauru Basin) in the state of Minas Gerais. The described ichnofossils are predominantly vertical, up to 2 m long, and are composed of horizontal lobed structures connected by vertical tunnel-like structures that intersect in the center and at the edges. The lobed structures range from 3 to 15 cm long and 2–6 cm thick. Two different hypotheses are analyzed to explain the origin of the trace fossils; the less probable one is that the structures are laminar calcretes associated with rhizoliths and rhizoconcretions. The hypothesis involving social insects was considered because the trace fossils described herein partially resemble a modern ant nest and the ichnofossil Daimoniobarax. The micromorphological analysis of the lobed and tunnel-like structures indicates modifications of the walls, such as the presence of inorganic fluidized linings, dark linings and oriented grains, supporting the hypothesis that they are chambers and shafts. The architecture and size of the reported nests suggest the possibility that social insect colonies existed during the Maastrichtian and are direct evidence of the social behavior and reproductive strategies of the Cretaceous pedofauna. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Cretaceous climate was characterized by arid and semiarid conditions in different parts of the world. Climatic changes for the Early to Late Cretaceous had been reported by many authors in North America, East Asia, Africa, and South America due to the geological evolution of Laurasia and Gondwana. In South America, the Bauru Basin, located in Brazil, is one of the most critical places to develop paleoclimatic reconstructions due to the presence of well-preserved Cretaceous sedimentary sequences, as well as abundant fossil content and paleosol profiles. The transition between the Lower and Upper Cretaceous in the Bauru Basin is represented by the Santo Anastácio and Araçatuba formations, which are characterized by a succession of sandstones, claystones, and paleosols. The paleosols are well distributed in the basin, providing valuable information about the paleoenvironmental conditions and insights about the tectonic and climatic changes in the Cretaceous Period. Since the 1960's decade, the Cretaceous paleosols of the Bauru Basin have been used as stratigraphic and sedimentological proxies providing paleoenvironmental and paleoclimatic insights, principally for the Late Cretaceous Period. This study, based on macromorphological descriptions, clay mineralogy (X-ray diffraction and scanning electron microscopy - SEM), and geochemical of paleosols, identified environmental and climatic patterns from the Lower and Upper Cretaceous. Results allowed to elaborate maps of paleoclimatic evolution that indicate changes occurred from Lower to Upper Cretaceous sequences of the Bauru Basin. These changes were compared and correlated with other continental basins in West Gondwana and Laurasia around the world, contributing to the understanding of the Cretaceous paleoclimatic context of South America. • A first interpretation of the Early Cretaceous climate using geochemistry was made. • The Early Cretaceous Period displayed predominantly arid to semi-arid conditions. • The Late Cretaceous indicated some rainfalls intervals and an increase in humidity. [ABSTRACT FROM AUTHOR]

Paleosols are soils that were formed on an ancient landscape. They may be buried soils and/or soils incorporated into the sedimentary sequences, exhumed soils, or soils developed on ancient relief surfaces (relict soils). Exposed on the surface and influenced by later environmental changes, paleosols reveal ancient environments and contain records regarding the climate, vegetation, landforms, organisms, parent material, time, intensity of pedogenesis, and sedimentation rates in effect during their training. In the Marília Formation, the paleosols, exhumed and buried, developed on sandstones have argic (Btk, Bt and Bss), hydromorphic (Cg) and calcic (Bk) horizons with different degrees of cementation, forming mainly calcretes. The objective of this study was to characterize the genesis of the paleosols of the Marília Formation, addressing the dynamics of their formation factors and processes at local and regional levels in order to reconstitute the conditions of environmental evolution of the Maastrichtian of the Bauru Basin. Eleven sections (S1, S2, S3, S4, S5, S6, S7, S8, S9, S10 and S11) of the Marília Formation were described and collected on nine sample profiles. Micromorphological, mineralogical and geochemical analyses were performed according to the specialized literature. In the Marília Formation, sedimentation, erosion and pedogenesis are processes that occurred together, concomitantly or subsequently, in view of the fluvial paleoenvironmental dynamics. The paleosols indicate the end of depositional cycles, with differentiated rates, intensities and duration. The paleosols of the Marília Formation comprise well-drained (Bt-horizon) and poorly drained or hydromorphic (Cg-horizon) pedotypes, of drier conditions (Bkm-horizon) and pedotypes indicative of drier periods alternated with periods of higher humidity (Bss-horizon). The profiles were classified as Luvisols (Bt and Btk horizons), Calcisols (Bk and Ck horizons), Arenosols (C-horizons) and Vertisols (Bss-horizons). Paleosols developed on the flatter and lower portions of the slopes and floodplains and were commonly influenced by the oscillation of the groundwater and the seasonality of the climate. Sandstone with allochthonous and autochthonous carbonate cementation constituted the main parent material of the paleosols. The predominant climate during the Maastrichtian was semi-arid, with seasonality and variations in precipitation patterns and a precipitation-evapotranspiration relationship that provided conditions for the formation of paleosols with Bk, Btk, Bss, Bg and Bt horizons. The time of formation of these diagnostic horizons was dependent on climatic and edaphic factors. However, the time factor lasted until approximately 200,000 years, allowing paleosols to develop with Bt-horizons and prismatic and block structures. Calcification and argilluviation were the formation processes responsible for the genesis and evolution of paleosols during the Maastrichtian of the Bauru Basin. Weathering indexes have shown that paleosols with Bt-horizons are more weathered than are those with Btk and Bk horizons. The paleosols with Bk-horizons reflect periods with more arid conditions in the general context of the semi-arid paleoclimate of the Maastrichtian of the Bauru Basin. • The calcretes of the Marília Formation are of pedogenic origin. • The calcretes (paleosols) developed in situ by the weathering of sandstones. • These paleosols were formed in flatter slopes of relief, under semi-arid environment. • Calcification and argilluviation acted in the evolution of the paleosols. • Paleosols with Bt-horizon are more weathered than those with Btk and Bk horizons. [ABSTRACT FROM AUTHOR]

• Pedogenetic processes involved in the argillic horizon (Marília Formation) have been studied. • Argillic horizons show clay illuviation, accumulation of carbonates and gleyic properties. • Argillic horizons developed in a semi-arid environment. A study of paleosols with argillic horizons found in the Marília Formation associated with Maastrichtian in the Cretaceous is presented herein. This study aims to investigate the polygenetic processes involved in argillic horizon formation under paleoclimatic conditions from arid to semiarid in the Brazilian Cretaceous and considers morphological soil attributes, such as evidence of cementation, macromorphological data (horizons, matrix color, structure, clay coatings, nodules, and bioturbations), micromorphological data (coarse/fine patterns, b-fabric, clay coatings, infillings, and nodules), and water table oscillation. Seven representative profiles of paleosols were selected in the São Paulo state, Brazil, and soil samples of lithified paleosols were collected to determine their macromorphological–micromorphological and chemical properties. Clay illuviation, carbonate accumulation, and gleization were dominant processes in the paleosols. Clay illuviation was identified from clay coatings along grain and ped surfaces. Carbonates occurred as nodules and rhizoliths and as coatings on peds. Red mottles, gray rhizohaloes with red oxidation rims, oxidic nodules, an iron-depleted matrix, and iron oxide depletion hypocoatings confirmed gleization. The argillic horizon polygenesis in the Marília Formation is usually interpreted as evidence of high-moisture events under arid/semiarid climates or climate change toward moister conditions than arid/semiarid. Thus, argillic horizon paleosols in the sedimentary records of the Marília Formation are not necessarily reliquial characteristics of wet paleoenvironments but are associated with changes in dominant granulometry, types of macroaggregates–microaggregates, carbonate accumulation in horizons, and/or water table oscillation. Thus, the presence of Bt horizons does not necessarily imply wet conditions with changes in the depositional system, as proposed by some authors. [ABSTRACT FROM AUTHOR]