Geological origins of sugarloaf mountains in eastern Brazil and their environmental significance as refugia for the Mata Atlantica rainforest
thesisposted on 2014-07-04, 08:51 authored by Sarah Caroline Owen
Sugarloaf mountains (inselbergs) are steep-sided, dome-shaped mountains often standing in isolation from the surrounding plains. Although principally recognised in Africa and Australia, the geological and geomorphological development of Brazilian sugarloaf mountains along the eastern Atlantic margin is poorly understood. The contemporaneous relationship of these landforms with the highly threatened Mata Atlantica rainforest, reduced to ~11% of its original distribution due to deforestation, provides a unique setting for multi-scale dynamic landscape research. This thesis determines the geological controls on sugarloaf mountain evolution, standardises geomorphometric inselberg landscape descriptors to improve the understanding of landform evolution through automated mapping retrieval, and assesses the environmental significance of these landscapes as refugia through measures of allometric biomass (AGB) across rainforest fragments in Pancas, eastern Brazil. Geological structural analyses reveal a five stage deformational history, with the granite gneiss sugarloaf basement encompassing both Neoproterozoic ductile shear and Cenozoic brittle extension. These structures, exploited during exhumation through the Eocene and Miocene, exert a strong control on the fragmentation of the plateau and morphology of the mountains revealing a “multi-stage etched” evolution of the current passive margin landscape. Geomorphological landscape analyses identify four novel types of sugarloaf morphometric classes: Summit, Slope, Collar, and Valley Floor. These features, defined by height, slope, minimum curvature and Topographic Profile Index in a Shuttle Radar Topography Mission dataset are used to develop an automated mapping program addressing issues in landscape feature extraction of extreme terrains, standardising descriptions of inselberg morphology and enabling evolutionary stages of inselberg landforms to be recognised. Measures of AGB across remnant forest fragments and analysis of their spatial distribution using Advanced Spaceborne Thermal Emission Reflectance (ASTER) imagery reveal that sugarloaf landscapes concentrate biomass in lowland topographic regions threatened by anthropogenic destruction. Therefore the environmental understanding of sugarloaves as refugia must be readdressed to inform future conservation efforts.
Supervisor(s)Tansey, Kevin; Berrio, Juan
Date of award2014-06-01
Author affiliationDepartment of Geology
Awarding institutionUniversity of Leicester