Análise digital de terreno do centro-leste brasileiro

Digital terrain analysis, or geomorphometry, is the practice of ground-surface quantification, through the application of techniques in Earth sciences, mathematics, engineering and computer science. 

The Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) is currently the only near-global data available to perform local to regional-scale landform analysis. The production of a DEM using a single technique, radar interferometry, means that there is consistency in quality, availability and scale. 

This work focuses upon the study of landforms in central-eastern Brazil by means of morphometric characterization of DEMs and integration between morphometric, thermochronologic and geophysical data, as well as an evaluation of the validity of use of flat surfaces in regional stratigraphic correlations.

Morphological profiles and aspect maps show a N-S trend of the major landforms of central-eastern Brazil, while smaller landforms have a NW-SE organization, better observed in the southeast region, but visible throughout the study area.

The spatial distribution of thermochronological data in Brazil is highly heterogeneous, with samples clustered in the south-southeast and northeast regions. Data from the southeast region does not show continental break-up as the main cooling event, which is identified by the large number of samples with fission-track ages (FT) between 60 and 80 Ma and that can be seen as a regional uplift event (followed by intense denudation), given the elevation range of the samples in this time span. There is a subtle trend of older FT ages from the coast towards the interior.

The trend of older FT ages as distance from the coast increases is better represented in data from the northeast region. Samples with ages around 100 Ma can be related to the continental break-up.

Morphometric analyses did not allowed the identification of vast erosional planation surfaces in the study area. Areas with a very smooth topography are related to alluvial plains (São Francisco, Araguaia and Tocantins rivers), Cretaceous sedimentary basins (Chapadão Ocidental da Bahia, Chapada do Araripe, Bauru Basin) and Paleozoic basins with Cretaceous cover (Parecis Basin) where the surface follows the subhorizontal bedding. In shield regions, several low-relief areas can be identified, although they are small in extent.

The large extent of low-lying surfaces associated with Cretaceous sedimentary basins has lead several authors to suggest that these -- presently isolated -- surfaces were continuous. This, added to inferences of ``summit levels'' based on the apparent levelling of hilltops in crystalline terrains, has also lead several authors to suggest that the planation surfaces extend close to the Atlantic shore.

The integration of morphometric, thermochronologic and geophysical data does not support the validity of use of flat surfaces in regional stratigraphic correlations. However, correlation between distinct morphological levels, at a local scale, is suitable.

The morphometric techniques used in this study are valid not only for the analysis of topographic surfaces, but also of buried surfaces and their palaeogeography. The availability of remote sensing generated elevation data allows the application of digital terrain analysis from local to global scales, with a range of applications, not only in the study of terrestrial landforms, but also of other planetary bodies.