Paranaíba P

The Alto Paranaíba Uplift (APU), an Upper Cretaceous tectonic feature associated with the opening of the Atlantic Ocean, is embedded within the Brasília Orogenic Belt. The APU is between two Proterozoic cratons (the São Francisco and Paranapanema) and lies on the highlands of the Central Plateau, dividing two of the largest Brazilian catchments (the São Francisco and Paraná).

The Quebra-Anzol (QA) catchment is the largest (~10,600 km2) complete catchment in the APU and a large tributary of the Araguari River on the left side of the Paranaíba River. The bedrock of the QA region is complex and spatially variable, with ferruginous duricrusts mantling low-relief uplands located near the QA's interfluves.
We performed a quantitative study of the topography of the study area in order to investigate the spatial patterns in topography and their relationship with variations in bedrock lithology, including ferruginous duricrusts. The post-orogenic history of such landscape that last experienced active tectonics ~80 Ma show a dynamic evolution with at least two regional, transient topographic disequilibrium events. We showed that ferruginous duricrusts slow the propagation of the transient base level lowering signal (Marques et al., 2021).
Samples from three thick Fe-duricrust profiles were collected. One profile (see below) at ~ 1,100 m developed over pyroclastic and epiclastic rocks was investigated in detail, due to be potentially suitable for weathering geochronology investigations.
We explored the geochemical and mineralogical composition of different samples through ICP- OES + IPC-MS, conventional XRD, SEM-EDS and µXRD on synchrotron. In addition, goethite and hematite samples were dated by (U-Th)/He method in collaboration with the GEOPS (Université Paris-Saclay), IMPMC (Sorbonne Université) and ETH Zürich. We showed that undisturbed grains can be used to analyze the mineralogy of ferruginous duricrusts by rotating anode-XRD with a short exposure, and the same grains can subsequently be dated by (U-Th)/He method. We also revealed two evolution phases of the ferruginous duricrust, indicating their exposure over a long period.
Marques K. P.P., dos Santos M., Peifer D., Lima da Silva C., Vidal-Torrado P. (2021). Transient and relict landforms in a lithologically heterogeneous post-orogenic landscape in the intertropical belt (Alto Paranaíba region, Brazil). Geomorphology. 391. 107892