Paper No. 7
Presentation Time: 10:10 AM


OWEN, Sarah, Department of Geology, University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom and TANSEY, Kevin, Department of Geography, University of Leicester, University Road, Leicester, LE17RH, United Kingdom,

Brazilian Sugarloaf mountains are steep-sided dome-shaped landforms whose geological origins and geomorphological development are poorly understood. Along the eastern Brazilian margin, preferential tropical weathering and the subsequent fragmentation of the rift shoulder plateau form a dense arrangement of these mountains creating an excellent setting for the study of sugarloaf geomorphology. This research aims to determine the stages of sugarloaf landscape evolution through the recognition of new geomorphological surface features, and to address problems in the retrieval of sugarloaf landscape classes within established automated topographic mapping programs.

The main outcomes of this research concern the identification of four new types of morphometric classes to define the sugarloaf landscape (Summit, Slope, Collar, and Valley Floor). The quantification of these classes by height, slope, minimum curvature and topographic profile index (TPI) enabled the development of an automated geospatial mapping program to retrieve these unique morphometric features in a Shuttle Radar Topography Mission (SRTM) dataset. This new program addresses the difficulties in depicting the extreme nature of these morphometric classes using established topographic mapping programs through the application of a multi-faceted dataset. The spatial analysis of the geomorphological feature class map, combined with geological field data, enables the first landscape evolution model for Brazilian sugarloaves to be presented. This model illustrates how the sugarloaf mountains develop from initial exhumation to mature peaks, and how the geomorphological evolution of the landscape is dominantly controlled by Neoproterozoic ductile shear fabrics and late brittle dykes.

The implications of these results in depicting the spatial relationship of the previously undocumented morphometric landscape classes provides a powerful tool, not only in understanding the geomorphological evolution of sugarloaf mountains but in determining dynamic landscape interactions. This is particularly pertinent along the east coast of Brazil where these geomorphological sugarloaf landscape features also form bio-geographical niches for the threatened eastern Mata Atlantica rainforest.