RECOGNITION AND MAPPING OF SEISMIC FACIES IN THE SANDY SPITS OF THE PATOS LAGOON, RS, BRAZIL

Abstract

The main objective of this work is to recognize and map the seismic architectural elements of the sandy spits occurring in the Patos lagoon, a lagoonal body located in the coastal plain of the State of Rio Grande do Sul, Brazil. The study is based on data from a high frequency (3.5 kHz) and resolution seismic survey performed in the Patos lagoon, aboard of the research vessel Larus of the Fundação Universidade Federal do Rio Grande. About 400 km of seismic profiles were collected in various sections. It was considered the seismic profiles recorded near the sandy spits of the lagoon margin. The analyses of the seismic records allowed the recognition and mapping of the seismic facies that built up the sandy spits of the Patos lagoon. The progradation of the sandy spits is well marked by oblique-tangential reflectors dipping to the lagoon interior. The package composed of these progradation reflectors overlies a package of subparallel reflectors or, sometimes, an erosional unconformity. Throughout the records a seismic facies composed of parallel, regular, and gentle dipping reflectors occurs in the top of the sequence. It was related to the lagoonal sedimentation.