Holocene coastal evolution of the transition from transgressive to regressive barrier in southern Brazil

Abstract

In this study the evolution of a Holocene coastal barrier was determined based on a basal transgressive unit followed by a regressive unit. Standard penetrating test, vibrocore and ground-penetrating radar profiles were used to acquire stratigraphic data. Sedimentological, paleontological and geochronological analyses were performed to describe and interpret the sedimentary facies. The base of the Holocene record indicates the existence of pre-transgression continental and coastal environments (basal peat), which resulted from the initial flooding of the antecedent topography (Pleistocene substrate) due to rising sea levels. During this period, the continental environments were flooded by lagoon environments that occupied the landward displacement of the transgressive barrier, which had channels that connected the lagoon and the ocean. At this time, the coastal barrier had a transgressive configuration indicated by its morphology and characterized by washover fans. As the backbarrier accommodation space decreased due to the displacement of the barrier (transgressive maximum), the transition of the transgressive/regressive record began at approximately 7.200 years BP, restricting the overwash events and the dynamics of the inlets. However, before the highest level (eustatic maximum) of the Postglacial Marine Transgression (PMT) was reached, this transgressive barrier stopped its migration toward the continent, causing an inversion of the depositional record, which became a normal regression. Later, at the end of the PMT, sea levels began to fall, causing a forced regression that persists to the present day.