HR: 1400h
AN: OS23D-01    [Abstracts]
TI: The Morphologic Evolution of the Amazon Coastal Plain, Cabo Norte, Amapa, Brazil: The Need for Integrated Investigation on the Internal Continental Shelf.
AU: * Silveira, O
EM: silveira@ufpa.br
AF: Universidade Federal do Para, Av. Augusto Correa, 01 Bairro Guama, Belem, PA 66075-110, Brazil
AU: Santos, V F
EM: valdeniraferreira@yahoo.com
AF: Instituto de Pesquisas Cientificas e Tecnologicas do Estado do Amapa, Rodovia JK, Km 10 Fazendinha, Amapa, AP 66903-000, Brazil
AU: Takiyama, L R
EM: luis.takiyama@iepa.ap.gov.br
AF: Instituto de Pesquisas Cientificas e Tecnologicas do Estado do Amapa, Rodovia JK, Km 10 Fazendinha, Amapa, AP 66903-000, Brazil
AB: The north brazilian coastal region is submitted to the conjunction of three major forcing: 1) Atmospheric, related to the wind and precipitation regimen and controlling the climatic seasonality and the local rivers hydrology; 2) Oceanic, result of the general oceanic circulation (North Equatorial Current-NEC) and it modulation with the atmospheric forcing (North Brazilian Coastal Current reflection), and 3) Amazonic, which is a result of the sedimentary transport from Amazon river, being itself under the influence of the atmospheric and oceanic forcing. Their main characteristic are the proper periodicities and also variabilities expressed according multiples and differentiated scales of time and space, determining the structure and functioning of the coastal space, giving to the Amazon coast line a considerable environmental instability. The Amapa Coastal Plain shows important part of this environmental instability. Semidiurnal macro tides, strong currents and tidal bores acts over a low gradient coastal plain which evolutionary process are intrinsically related with tectonic and geological settings. Two main areas can be distinguished in this scenario. The first one is the Amapa Lakes Region, developed over meanders of ancient drainages building a mosaic of low relief forms, with varied shapes, linked throughout communication channels. Two lacustrine belts showing alignments with the main tectonic traces were recognized beginning at the internal limit of the coastal plain, flowing southeast through the Tabaco Creek until reach the Araguari River. In it way it conform the Occidental and Meridional Belts represented by shallow lakes, totally dependent of Tartarugal River discharge and surrounded by enormous areas of peat highly sensitive to fire during the regional low discharge. Light blue clays, peat and a package of tidal deposits with fluidization structures were recognized close to Araguari River, suggesting deposition during high sea level. The second area refers to the coastal zone between the Amapa Grande River and Araguari River, including Maraca Island and the Oriental lacustrine Belt. Westward the island, at least three paleolevels of clays with roots in life position suggests regressive/transgressive events. Extraordinaty paleodrainage network beginnig at the continent and recognized at the insular portion suggests links with the paleochannels found at the continental shelf. The Oriental Belt of lakes is located close to the coastline, at Cabo Norte. It main feature is a mud lump approximately 10 Km ratio, well recognized at the remote sensing. It shows similar evolutionary processes with Araguari River, dating from XIX century, when this river had two mouths defined by the Carpori Island. The reasons of the deactivation are still unknowed, but, this rapid morphological evolution indicates short time colmatation processes that can be linked to tectonic regional processes. On the other hand, the Cabo Norte feature consolidation may impose changes in the sedimentation processes yielding space reduction over the coastal plain accumulation, diminishing of the solid and liquid fluvial discharge and promoting the availability of the local sediment transport over the littoral. The investigation of these processes requires an integrated coastal plain-continental shelf morphological study applying adequate techniques for modification studies and dating ages over short geological time frame, in century scale level.
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