Micromorphology of colluvium-aluvium in paleogully filling in the Pinhão/Guarapuava and Palmas/Caçador summit surface- South of Brazil

Abstract

The objective of this work was to determine the micromorphological properties of the colluvium-alluvium deposits that filled paleogullies established on the Pinhão/Guarapuava and Palmas/Caçador summit surfaces, inserted in the Paraná Basin Volcanic Plateau, aiming to deepen the understanding of the genetic processes involved in the establishment of colluvium-alluvial deposits, as well as to recognize characteristics of source area materials, depositional processes and post-depositional transformations. Two stratigraphic records containing filled paleogullies macroscopically described previously were selected, one on the Pinhão/Guarapuava surface and the other on the Palmas/Caçador surface. A total of five undisturbed samples of the paleogullies clogging sediments were collected for micromorphological analysis, which had a descriptive nomenclature from Stoops (2003). As a result, it was found that the the c/f-Related Distributionis integrated, being enaulic for sandy facies and porphyric for the muddy facies. The first consists of pedogenic intrusive aggregates (pedorelicts), whose aggregate morphology reflects the transport conditions along the slope by laminar and/or channel flows. The second has a massive microstructure, indicating mudflow. The coarse-matrix consists of quartz, ilmenite, magnetite, litho- and pedomorphic nodules, which indicate that the source area underwent a high stage of weathering. Coatings, hypocoating and quasicoating of depletion and impregnation, as well as loose infilling features consisting of fine fraction as well as the b-fabric indicate migration of Fe and Mn from the micromass, result from water circulation in the syndepositional and post-depositional processes. The low amount of channels voids signals the inexpressive biological activity in the sediments of both stratigraphic records, indicating that post-depositional transformations are at an early stage and not sufficient to rearrange the materials by pedogenesis. From the micromorphological analysis of the materials, it was possible to verify changes in the overlandflow viscosity when being channeled, generating sandy and muddy facies, suggesting that in the paleogullies clogging there were flows with different sediment concentrations in the depositional process.