MORFOLOGIA, PROCESSOS DE SEDIMENTAÇÃO E LITOFÁCIES DOS AMBIENTES MORFO-SEDIMENTARES DA PLANÍCIE COSTEIRA BRAGANTINA, NORDESTE DO PARÁ, BRASIL

Résumé

The Bragança Coastal Plain is located in the Northeastern of Pará, in the Bragança-Viseu CoaxialBasin (Cretaceous), with an approximate surface area of 1,570 Km2. The geometry of the basin and itspaleotopography, associated with recent tectonic movements have controlled the distribution and thethickness of the tertiary and quaternary deposits. This coastal plain constitutes a macrotidal (6 m) depositionalsystem, developed in a hot and humid equatorial climate, with a dry and wet well defined seasons and anannual precipitation averaging 3,000 mm.The geomorphology of the area is subdivided into three main morphologic realms: (1) alluvial plain,with fluvial channel, levees and flood plain; (2) estuarine plain, with an estuarine channel subdivided intoestuarine funnel segment, straight segment, meandering segment and upstream channel, tidal creek and,floodplain and; (3) coastal plain, with salt marsh (inner and outer), tidal plain (supratidal mangroves,intertidal mangroves and sand flats with tidal shoals), chenier, coastal dunes and beach environments.The recent morpho-sedimentary units are separated from highland by a line of inactive cliffs that issituated 25 km from the coastline. This cliffs mark the higher Holocene sea level, very well knowed inbrazilian east coast as Holocenic Transgression (5,100 years B.P.). During this event was deposited a basaltransgressive sequence (S1), constituted by estuarine sand and mud and marine sand. Afterwards, underregressive or stillstand sea level the mangrove deposits prograde over the transgressive sand sheet buildinga prograding sequence (S2). Nowadays, this sequence are being overlain by a recent transgressive sequence(S3).The sedimentary model, based on lithostratigraphy and sedimentary processes, proposed to BragançaCoastal Plain show a complex coastal depositional system, constituted by different sedimentaryenvironments with singular sedimentary, stratigraphic and morphologic characteristics in relation to itsgeometry and spacial distribution of the environments.The morpho-sedimentary unit show that the environments studied from the alluvial plain to coastalplain represent a dynamic area dominated by macrotides and influenced by waves along the shoreline.Therefore, the depositional model proposed is composed by a coastal plain depositional system withfluvial-estuarine-tidal flat environments with dune-beach ridge associated.