Geomorphology and Sedimentary Facies of the Maricá Lagoon (State of Rio de Janeiro, Brazil)

Abstract

The present study focuses on the geomorphology and sedimentary facies of the Maricá Lagoon, Southeastern Brazil. Bathymetric data and 72 samples were collected from the margins and floor of the lagoon. Grain size and morphology, composition and organic matter content analyses were conducted. The results show that the floor of the Maricá Lagoon is mainly flat, reaching a maximum depth of 2 m in its central section. From the water line, depth gradually increases in different ways: the northern margin shows a flat gently inclined profile towards the bottom, whereas the southern margin is steeper. Five sedimentary facies were identified: sub-rounded sand facies that form the lagoon margins near the coastal barriers; angular sand facies found along the land-facing margins. Sand is composed by quartz, traces of feldspar, heavy minerals and shells. Silty sand facies occur along the transition between the coarser facies and the finer facies typical of the lagoon center. Sandy silt facies and silt/clayey silt facies cover most of the central lagoon floor, indicating areas of low hydrodynamic. Mud is rich in organic matter, with 13% on average. Fluvial input, strong winds and waves are the main processes responsible for the lagoon sedimentary dynamics.