The Bertioga Coastal Plain: An Example of Morphotectonic Evolution

Abstract

The Bertioga coastal plain, located in the metropolitan region of Baixada Santista (central coast of São Paulo state), contains nearly all of the types of depositional systems that are found on the rest of the Brazilian coast, in spite of its highly restricted area that is less than 6 km wide. Similar to other coastal plains, Bertioga’s evolution was associated with variations in climate and the relative sea level (SL) during the Quaternary period. However, the evolution was also influenced by tectonic pulses that produced the following features: (a) a seismic signature indicating a normal fault in the central part of the coastal plain, which depressed block faces the Serra do Mar mountain range, suggesting the presence of a hemigraben (“Bertioga Graben”); (b) a sedimentary column thicker than 100 m in the central part of the coastal plain; (c) the presence of morphotectonic features on the coastal plain (anomalous arrangement and spatial distribution of some Quaternary units (QUs), drainage anomalies, and sets of systemic fractures in marine terraces) and on the Serra do Mar (fluvial capture of the Guaratuba River and triangular facets); (d) the preservation of marine terraces and fluvial deposits that are older than the Cananéia Formation (Marine Isotope Stage—MIS 5e, 100–140 ka); (e) differential control of Holocene marine and alluvial sediments throughout the coastal plain; and (f) the presence of guide layers in Pleistocene and Holocene deposits with throws up to 7.5 m. Thus, the evolutionary model of this coastal plain can in some ways be compared with those proposed for most Brazilian coastal plains, but with the peculiarity that it shows rare features of the transgressive–regressive event that is correlated with MIS 7 (240–260 ka) and has been affected by at least two tectonic pulses at the end of the Pleistocene and one pulse during the Middle to Upper Holocene. The recent creation of the Restinga of Bertioga State Park, embracing nearly half of the coastal plain, will enable the conservation of much of the rich plain’s biodiversity and protect its important geological–geomorphological heritage, strengthening proposals for future geosites for geoconservation according to the principles set forth by UNESCO.