HR: 1400h
AN: OS23D-04    [Abstracts]
TI: The Amazon Mangrove Coast: The Role of Geological Factors in its Evolution During the Quaternary
AU: * Souza-Filho, P W
EM: walfir@ufpa.br
AF: Federal University of Para, Geoscience Center, Av. Augusto Correa 1., Belem, PA 66075- 110, Brazil
AU: Lara, R
EM: ruben.lara@uni-bremen.de
AF: Center for Tropical Marine Ecology, Fahrenheitstrasse 6, Bremen, 28359, Germany
AU: Silveira, O
EM: silveira@ufpa.br
AF: Federal University of Para, Geoscience Center, Av. Augusto Correa 1., Belem, PA 66075- 110, Brazil
AU: Miranda, F P
EM: fmiranda@petrobras.com.br
AF: Petrobras,CENPES, Ilha do Fundao, Q-7, RiodeJaneiro, RJ , Brazil
AB: The Amazon mangrove coast considered in this work includes the northeast Para and northwest Maranhao states. This coast is extremely irregular and jagged with numerous bays and estuaries. The main goal of the present work is to recognize the principal geological factors responsible for the development of the mangrove system. The integration of remote sensing data with other available studies indicates the existence of four main geomorphological sectors along the mangrove coast as described below. Sector 1 extends from Marajo to Pirabas Bay and is developed over the Para platform. The coastal plateau reaches the shoreline forming terraces and active cliffs. Sector 2 extends between the Pirabas and Gurupi bays and is structured over the Bragança- Viseu basin. In this sector, the coastal sedimentary environments widen considerably towards the east from Pirabas Bay and the coastal plateaus stretch out southward to constitute inactive cliffs. Mangroves developed seaward, reaching currently a width of 30 km. Sector 3 extends from Gurupi to Turiaçu Bay and is developed over the Gurupi horst. The latter represents a stratigraphic window where proterozoic rocks outcrop near the coast. Compared with the other sectors, mangrove deposits here reach their maximum extension with up to 40 km wide. Sector 4 extends between the Turiacu and Cuma bays and is structured in the Sao Luis basin. This coastal basin is also developed on land and represents a gravimetric low along a NE-SE direction.Mangroves are narrower, with a maximum width of 26 km. This analysis of the coastal geomorphology by considering neotectonic activity allows the identification of five sectors. Sector 1, with a positive gravimetric anomaly and poorly influenced by peripheral bulge. These characteristics suggest a relative tectonic stability of this sector, where the coastal plateau reaches the shoreline and mangroves are poorly developed. Sector 2 is marked by low gravimetric anomalies and normal faults reactived by peripheral bulge. In this sector, the location of these inactive cliffs is spatially coincident with the peripheral bulge. Hence, we suggest that the inactive cliffs are a result of the flexural reactivation of ancient normal faults, which is supported by studies of in the northeastern Brazilian coast. Sector 3 is also marked by normal faults and peripheral bulge influence, presenting geomorphological characteristics similar to Sector 2. In Sectors 2 and 3 the retreated coastal plateau and inundation deposits of the estuaries allowed the development of wide tidal flats where the largest mangrove belt is established. In Sector 4 there is a great mangrove development. This area is characterized by a gravimetric high, with little influenced by peripheral bulge and is structurally controlled by normal faults limited by the Cururupu arch. The interaction of regional framework and flexural deformation explains the reactivation of ancient faults responsible for the geomorphology of the North Brazilian mangrove coast. However, further structural and geodetic monitoring from interferometric SAR data are needed for a more detailed knowledge of the Quaternary tectonics of this region. This may provide elements for a better comprehension of wetland evolution in the moist tropics, particularly regarding their response to coastal subsidence and relative sea level changes in time of global changes.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 4217 Coastal processes
DE: 9360 South America
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly