HR: 1400h
AN: OS23D-03    [Abstracts]
TI: High-Resolution Subsurface Imaging and Stratigraphy of Quaternary Deposits, Marapanim Estuary, Northern Brazil
AU: Silva, C A
EM: clea@museu-goeldi.br
AF: Universidade Federal do Para, Programa de Pos-Graduacao em Geologia e Geoquimica, Campus Universitario do Guama CP1611, Belem, Pa 66075110, Brazil
AU: * Souza Filho, P M
EM: walfir@ufpa.br
AF: Universidade Federal do Para, Programa de Pos-Graduacao em Geologia e Geoquimica, Campus Universitario do Guama CP1611, Belem, Pa 66075110, Brazil
AU: Gouvea Luiz, J
EM: gouvea@ufpa.br
AF: Universidade Federal do Para, Programa de Pos-Graduacao em Geofisica, Campus do Guama,
AB: The Marapanim estuary is situated in the Para Coastal Plain, North Brazil. It is characterized by an embayed coastline developed on Neogene and Quaternary sediments of the Barreiras and Pos-Barreiras Group. This system is strongly influenced by macrotidal regimes with semidiurnal tides and by humid tropical climate conditions. The interpretation of GPR-reflections presented in this paper is based on correlation of the GPR signal with stratigraphic data acquired on the coastal plain through five cores that were taken along GPR survey lines from the recent deposits and outcrops observed along to the coastal area. The profiles were obtained using a Geophysical Survey Systems Inc., Model YR-2 GPR, with monostatic 700 MHz antenna that permitted to get records of subsurface deposits at 20m depth. Were collected 54 radar sections completing a total of 4.360m. The field data were analyzed using a RADAN software and applying different filters. The interpretation of radar facies following the principles of seismic stratigraphy that permitted analyze the sedimentary facies and facies architecture in order to understand the lithology, depositional environments and stratigraphic evolution of this sedimentary succession as well as to leading to a more precise stratigraphic framework for the Neogene to Quaternary deposits at Marapanim coastal plain. Facies characteristics and sedimentologic analysis (i.e., texture, composition and structure aspects) were investigated from five cores collected through a Rammkernsonde system. The locations were determined using a Global Positioning System. Remote sensing images (Landsat-7 ETM+ and RADARSAT-1 Wide) and SRTM elevation data were used to identify and define the distribution of the different morphologic units. The Coastal Plain extends west-east of the mouth of the Marapanim River, where were identified six morphologic units: paleodune, strand plain, recent coastal dune, macrotidal sandy beach, mangrove and salt marsh. The integration of GPR profiles and stratigraphy data allowed for the recognition of paleochannel geometry, with width of 150m and depth of 20m, developed on Barreiras Group, two discontinuity surfaces and three facies associations organized into sedimentary facies: (i) Tidal channel with mottled sand, Conglomerate with clay pebble and Ophiomorpha/linear Skolithos, channel-fill and tabular cross-bedding sand and sand/mud interlayer facies. (ii) Dune/interdune with wavy bedding and cross-bedding sand and planar bedding and tabular cross-bedding sand facies. (iii) infilled tidal channel with mottled sand, planar/flaser bedding sand, lenticular bedding clay and sand/mud interlayer facies. The present study demonstrates that some facies associations occur restricts to tidal paleochannels and shows features well preserved that are very important to reconstruction of the relative sea-level history in the Marapanim Estuary.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1641 Sea level change (1222, 1225, 4556)
DE: 4217 Coastal processes
DE: 4235 Estuarine processes (0442)
DE: 9360 South America
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly