Origin and morphology of natural tanks of northeastern Brazil

Abstract

Natural tanks of Northeastern Brazil have been widely analyzed in paleontological terms. However, studies related to the origin and morphology of these natural depressions are stagnated since the 1990s. This work aims to present new interpretations about the origin of these tanks, as well as to establish an internationally correlated nomenclature and to propose a morphological classification of these features. Academic works elaborated from the beginning of the 19th century until more recent articles, including theses and dissertations, have been consulted on the application of the term, the paleontological importance and origin of the natural tanks in northeastern Brazil. We propose the use of the term natural tank (shallow and steeped) to depressions of non-fluvial origins on the bedrock, and maintain the term caldrons to those of fluvial origin. The previous models for the formation of natural tanks were based on three situations in subaerial environment. In this work, we associate the chemical corrosion and migration and concentration of charges in subsurface as important processes for the genesis of natural tanks. Instead of the necessity of the surface be exposed to start the formation of the cavity, the tank may have its origin and development associated with subedaphic environment.