Paleoenvironmental indicators for evaluation of stream captures in wet tropical

Author(s)

Natália Nunes Patucci

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Letras e Ciências Humanas (FFLCH/SBD)
• Defense date: 2019-09-27

Examining board members

Déborah de Oliveira; Antonio Carlos Colangelo; Carlos Roberto Espindola; João Osvaldo Rodrigues Nunes

• Advisor: Déborah de Oliveira

Abstract

The research aimed to evaluate the capture of the Guaratuba River, located on the reverse side of the Serra do Mar in tropical humid environment. Morphometric aspects, the sedimentary and organic materials of the dry valley superficial cover were used as paleoenvironmental indicators to explain the capture. Samples were collected in the basin division between the upper Guaratuba and river Claro, for the integrated evaluation of macromorphological, granulometric, morphological, mineralogical, geochronological and palynological data. Samples of sandy material were subjected to absolute dating by the method of Optically Stimulated Luminescence (OSL), while those of organic material were submitted to absolute dating of 14C via Mass Spectrometry by Accelerators (MSA). The superficial cover materials were classified in macromorphological analysis as Gleisols, Spodosols and Cambisols which contained gravels up to 75 cm layer thick. The Spodosol represents a paleosol and the ortstein horizon as a lithostratigraphic indicator. In the granulometric analysis the predominance of the sandy fraction occurred in all the horizons described, as well as quartz and mica in the mineralogical analysis. In the morphoscopic analysis of the sand fraction there was a wide rounding of the gravels and quartz grains in all the horizons, indicating that these sediments suffered in the past mechanical erosion by current flow or torrent deposition indicating paleoclimate and water conditions different from the current. The morphometric characteristics of the basins attest to rejuvenation of the Guaratuba basin in response to capture. The dates indicate specific periods of the Holocene, Pleistocene and Late Glacial Maximum, mostly linked to precipitation conditions in the Southeast region. The surface cover materials of the dry valley as well as the hydrodynamics of the river channels are being worked by the humidity cycles in the system for at least 36,500 years. It is possible to link the change of the base level between the rivers and the consequent capture of the Guaratuba to the Last Glacial Maximum, to approximately 25,000 years A.P. The taxon assembly formed by Podocarpus sp, Ilex sp, Symplocus sp, Weinmannia sp, Myrsine sp, Alchornea sp, Mytenyus sp, Hedyosmum sp, Myrtaceae, Poaceae and Asteraceae families respond as indicators of wet and / or flooded paleoflorests and cold and humid paleoclimates. The taxon found, mostly adapted to cold and humid and constantly or seasonally flooded forest environments indicate an ancient marshy region in the present dry valley. In a scenario with elevation of precipitation, would be resume the increase erosion in areas near the back of the escarpment would be resumed, which would promote the retraction of the dividers, escarpment and new captures. The captures are essential for the evolution of the Serra do Mar and the coastal plain in the Southeast of Brazil, with a moist regional climatic condition as the driving force. The responses suggest that in the Quaternary the wetter phases were marked by the increase of erosion rates, emptying of bottoms of valleys by the increase of fluvial incision and lowering of the base level. The use of the systemic approach for the study of captures, based on multidisciplinary techniques, becomes essential to elucidate in its results the positive response of paleoenvironmental indicators at regional and local level. (AU)

• FAPESP's process: 16/06654-0 - GEOCHRONOLOGY FOR EVALUATION OF STREAM PIRACY PROCESSES: APPLICATION IN SEDIMENTS OF DRY VALLEYS OF GUARATUBA(SP).
• Grantee: Natália Nunes Patucci
• Support Opportunities: Scholarships in Brazil - Doctorate