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MORPHOTECTONICS OF THE CURITIBA SEDIMENTARY BASIN The morphostructural framework differentiation in the Precambrian/Eo-Paleozoic basement and Cenozoic sedimentary cover of the Metropolitan Area of Curitiba is due to extensional and transtensional neotectonic movements, with the concurrence of climatic changes. Drainage morphometric analysis indicates tectonic influence in the morphogenetic processes. Structural alignments control the sub-rectangular and sub-parallel patterns of the drainage system, the asymmetry of the second-order drainage sub-basins of the Iguaçu basin river, the main local base level, and the geometry of the Cenozoic sediments, including the alluvial deposits, which present asymmetric spatial distribution and narrowing segments in areas of crossed-alignments. The main second order tributaries of the Iguaçu river, like the Pequeno and Barigüi rivers, present tectonically controlled channels, as indicated by the coincidence of anomalies with older structures reactivated since the Lower Tertiary, as well as scarps that may be clearly observed in digital elevation models, even not so accentuated. The higher northnorthwestern margin inclination of the Iguaçu River in relation to its south-southeastern margin is a salient morphostructural characteristic related with the Upper Iguaçu Fault, which deformed the Curitiba sedimentary basin and to which part of the upper Iguaçu valley is adjusted. The fault was active during and after the Pleistocene, reflecting the more recent neotectonic activity, and may be recognized through the faulted colluvial-alluvial deposits and the weak seismic activities in the Serra do Mar.

Several types of structures are observed in the Precambrian, Mesozoic and Cenozoic rocks of theAmazon region, which represent the major features of the neotectonic framework developed since theMiocene. They controlled the sediment deposition of the Upper Tertiary and Quaternary, as well as haveinfluenced the development of the present landform patterns and drainage systems. Transpressive andtranstensive areas are recognized based on their nature and geometry, and related to two main episodes oftranscurrent displacement of Miocene/Pliocene and Upper Pleistocene /Recent ages. Sets of E-W, ENEWSWand NE-SW right-hand strike-slip faults are present in most of these areas. These sets are linked bynormal faults trending NW-SE and NNW-SSE, or by thrust faults trendig NE-SW and ENE-WSW,depending upon their geometry. Large areas with N-S trending younger normal faults are also observed.Earthquakes, the phenomenon of “fallen lands”, fluvial channels migration, hot springs, etc., are related toareas where some of these faults remain active. All these structures are related to an intraplate E-W righthandshear system induced by the rotation of South American Plate towards west.

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