Association of Post-Barreiras and Barreiras Formation strata and influence on soil genesis, Southern Bahia – Brazil

Abstract

The term Post-Barreiras is a definition for sediments above the deposits of the Barreiras Formation, and the genesis of soils in these environments must be related to sedimentary deposition. Our objective was to apply multi-technique analyses to characterize the sediments and soils to understand pedogenesis in these environments. We analysed sedimentological parameters and the geochronology of sediments. Morphological, chemical, and mineralogical analyses allowed the characterization of the soil. Also, these data supported the analysis of lithological discontinuity. We considered the contents of Ti and Zr, uniformity value, the fraction of organic material, morphology, and palynological analysis. The age of Post-Barreiras sediments is from the Pleistocene, and they have a more significant variation of sedimentological parameters concerning Barreiras Formation layers. In general, the soils are sandy, acidic, have a low level of exchangeable cations. Mineralogy has a predominance of quartz and kaolinite minerals. In the region, there are soils with low morphological variation, classified as Quartzipsamments. In other cases, there are soils with apparent spodic morphology, which is conditioned by four aspects: (i) Podzolization in Post-Barreiras sandy sediments without evidence of lithological discontinuity, forming Bs horizon (Spodosols); (ii) contact zones (Post-Barreiras/Barreiras Formation) with physical, chemical, and morphological evidence of discontinuity, forming Quartzipsamments or Ultisols; (iii) layers of the Barreiras Formation buried by Post-Barreiras sediments and the subsequent podzolization process, forming Bhm horizon (Spodosols); and (iv) destruction of Ultisols clay, forming Bs horizon (Spodosols). The sedimentary association (Post-Barreiras/Barreiras Formation) favors the development of different soils. The contact zones generate a morphological aspect similar to the Spodosols, associated or not with podzolization processes.

Reply to the comments on Souza et al. (2022) “Recent geomorphological changes in the Paraiba do Sul delta, South America East Coast”

“…In Figure 5 of the comments, not to scale and representing the constant progradation of the PSRD, the commenters with a line arbitrarily relate our OSL dated shorelines (PS01 and PS02) with the two 14 C dating samples (PS41 and (PS42) of Martin et al (1993). In Figure 6 from our original article, which shows the distribution of surface sedimentary facies, they attribute the same samples of our trenches (PS01 and PS02) located in the river plain to the pre-LIA period, not to the LIA period: considering the ages, the stratigraphic sequence teaches us that from the base to the top there are generally Barreiras Fm.→post-Barreiras→pre-LIA→LIA→post-LIA→river plain deposits (Souza et al, 2020), even if some heteropic facies, erosion-deposition processes, and sediment reworking are commonly in transitional environments, locally modifying the original sequence.…”

A Compartimentalização Sedimentar de um Estuário do Nordeste Amazônico A Sedimentology Compartmentalization of a northeast Amazon Estu

“…The Barreiras formation is composed of sedimentary siliciclastic rocks that extend along the Brazilian coastline, from the State of Rio de Janeiro to Amapá (Araújo et al, 2006). The Pós-Barreiras formation defines the sediments deposited above de Barreiras formation, and its characteristic depends on the sedimentary deposition (Rossetti et al, 2013;Souza et al, 2020).…”