Shallow sedimentation of Natal shelf and coastal erosion implications, NE Brazil

Abstract

High-resolution seismic stratigraphic analysis to reconstruct the depositional history of the inner shelf Holocene successions was performed on the northeastern Brazilian, adjacent to Natal City. Boomer seismic data was collected between the coastline up to ~ 15-m water depth. Three seismic units and three seismic surfaces were observed with regional significance and low lateral variability. They represent the transgressive to highstand deposits lying on the Pleistocene/Holocene boundary surface S1—older, regional, and the irregular unconformity at ~ 35 m, forming a semi-enclosed environment near the coast. The basal unit (U1) is related to a moderate/high-energy environment and grade upward to units (U2 and U3) of lower energy conditions and thin thickness that decrease seaward with large through near coast on the west. Above this surface, chaotic and parallel internal configurations represent unit U1 that limited at the top by S2. The ravinement surface S2 at ~ 18 m reveals wave-tide influence in a very shallow inner shelf, which controlled the accommodation space and sediment transport. Unit U2 fills the scours with onlapping terminations over S2. The shallowest surface (S3) occurs at ~ 12 m below modern sea level probably associated with the maximum flooding surface underlying the U3 with dominant aggradation character in parallel/wavy configuration. U1 represents a shallow marine environment with a greater sediment supply controlled mainly by the water depth during the initial transgressive shelf inundation. The lower sediment accumulation of U2 and U3 indicates a decreasing of sediment supply, higher sediment transport or higher rates of erosion in shallow marine environments.