SISMOESTRATIGRAFÍA DE SECUENCIAS DELTÁICAS PLEISTOCENAS, ESTUARIO DE BAHÍA BLANCA, ARGENTINA.

SALVADOR ALIOTTA; SILVIA SUSANA GINSBERG; DARÍO A. GIAGANTE; LAURA G. VECCHI

Congreso; Congresso Brasileiro de Oceanografia - CBO´2012; 2012

Marine dynamics as well as geomorphological and sedimentological conditions play a key role in determining the environmental systems which, at present, constitute coastal regions and their adjacent marine areas. Bahía Blanca estuary, which is located in the south of the province of Buenos Aires, Argentina, has a morphological configuration resulting from hydrological and sedimentary processes related to Late Quaternary changes at the sea level. This estuarine system occupies a large coastal area that is characterized by a dense net of tidal channels of different dimensions and depths, numerous low altitude islands and large sandy clayey silt intertidal flats. Little is known from the stratigraphic point of view of the subbottom sedimentary cover. In this study we performed a seismic analysis of sedimentary sequences of the bottom and marine sub-bottom that characterizes the northern coast of Bahía Blanca estuary. The seismic stratigraphic analysis by means of high resolution seismic (3.5 kHz profiler) was therefore carried out in order to: i) define Quaternary sequences, ii) describe sedimentary structures, and iii) infer the paleoenvironmental conditions of sedimentation. In addition, the sedimentological and morphological features were analyzed by means of side scan sonar, echo sounder and bottom sampling. The seismostratigraphic analysis conducted together with drilling lithological correlation shows that the acoustic basement is represented by five seismic sequences. Thus S1-S2 are associated with a continental-fluvial paleoenvironment (silty clay and clayey sandy silt sediments) of Miocene-Pleistocene age. On these materials were defined the S3 and S4 seismic sequences. Their lithology and seismic facies (paleochannel structures and prograding reflection configurations) demonstrate the development of an ancient deltaic environment, which was part of an extensive Pleistocene drainage system. The S5 sequence (sand with shells and y silt clay sediments) were formed during Holocene transgressive-regressive processes and complete the seismostratigraphic column defined in this study.. Thus S1-S2 are associated with a continental-fluvial paleoenvironment (silty clay and clayey sandy silt sediments) of Miocene-Pleistocene age. On these materials were defined the S3 and S4 seismic sequences. Their lithology and seismic facies (paleochannel structures and prograding reflection configurations) demonstrate the development of an ancient deltaic environment, which was part of an extensive Pleistocene drainage system. The S5 sequence (sand with shells and y silt clay sediments) were formed during Holocene transgressive-regressive processes and complete the seismostratigraphic column defined in this study.