Facies and palaeosol analysis in a progradational distributive fluvial system from the Campanian–Maastrichtian Bauru Group, Brazil

Abstract

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.

The sedimentology of an ephemeral fluvial–aeolian succession

“…Miall, 1985). Some models depict an abundance of downstream accretion (Colombera et al, 2013;Batezelli et al, 2019) in addition to those features outlined above, and recent advancements have focused more on quantification of models at multiple scales (Colombera et al, 2013;Colombera & Mountney, 2019), rather than upon their sedimentology. In the study presented here, the sediments of laterally and vertically amalgamated, poorly channelized sheets and fluvial channels dominate the preserved deposits (36% and 26%, respectively) with corresponding element thickness to width ratios of 1 : 100 and 1 : 50.…”

“…The sediment deposited has a bimodal grain-size distribution, with a dominance of fine-grained mud/silt and coarser sediment that ranges from very coarse-grained sand to large pebbles (Dreyer, 1993;Billi, 2007). The conglomeratic sediment is typically poorly sorted, sub-angular to subrounded, contains both intra-formational and extra-formational clasts, and ranges from matrix to clast-supported (Dreyer, 1993;Batezelli et al, 2019).…”

Provenance and weathering index of the Upper Cretaceous São Carlos Formation and its tectonic significance in the eastern Bauru Basin, SE Brazil

“…The Bauru Basin is one of the most documented and studied sedimentary basins in Brazil, with available data including more than 500 outcrop descriptions (by Fernandes, 1998;Batezelli, 2003) and 1269 well-logs (180 presented by Paula e Silva et al, 2005;140 by Batezelli, 2003;135 by Batezelli, 2017; 814 by Batezelli and Ladeira, 2016;Batezelli et al, 2019) (Figure 1). This basin was developed during the Upper Cretaceous, in the central-south portion of the South American Platform, by thermomechanical subsidence (Riccomini, 1995(Riccomini, , 1997Fernandes and Coimbra, 1996;Fernandes, 1998).…”

“…aeolian processes in the Early Cretaceous (Batezelli, 2017). Sequence 2 (Bauru Group) is a record of the Late Cretaceous lacustrine system (Araçatuba and São Carlos formations), associated with a distributive fluvial system (Adamantina, Uberaba, and Marília formations) (Fernandes, 1998;Batezelli and Ladeira, 2016;Batezelli, 2017;Batezelli et al, 2019).…”

Tropical landscape evolution and its relationship with paleosurfaces, Ferralsols and ferruginous duricrusts in the Alto Paranaíba region (Central Plateau, Minas Gerais, Brazil)

“…Diamond-bearing kimberlites and alkaline intrusions from the Upper Cretaceous (e.g., Serra Negra, Salitre I and II and Tapira) related to the Alto Paranaíba Igneous Province crop out, following the NW-SE structural trend of the Az 125º Lineament (Moraes Rocha et al, 2019), forming an important province of mineral extraction (e.g., Riccomini et al, 2005). The APU acted as a source area supplying distributive fluvial sediments to the Sanfranciscana Basin to the northeast, and the Bauru Basin to the southwest (Sgarbi and Dardenne, 1996;Batezelli, 2017;Batezelli et al, 2019). These occur as sub-horizontal sedimentary deposits that overlie the Neoproterozoic and the volcanic units locally (Hasui and Haralyi, 1991;Riccomini, 1997).…”