Estudo paleoambiental em enclaves úmidos e subúmidos do Cariri Paraibano

Abstract

Paleoenvironmental reconstruction studies contribute to understanding the trajectory of scenarios related to the evolution of vegetation, soil and other elements that make up the landscape. The techniques for understanding paleoenvironments are diverse, the most used being 14C and Optically Stimulated Luminescence - LOE dating, isotopic analyzes (δ13C and δ15N), palynological and silica biomineralizations (phytoliths, diatoms, sponges) preserved in sediments and soils. They help to understand the evolution of the landscape, pedogenetic and archaeological processes at different temporal and spatial scales. The Caatinga is a biome that has countless mosaics of landscapes and is home to rich biodiversity, of great geoenvironmental, ecotouristic, economic and cultural importance. Furthermore, it presents crystalline masses known as slabs and mountains that form humid enclaves in the middle of the typical Caatinga. Despite recent advances, knowledge about this biome is still incipient, especially in relation to the soils and vegetation of the Borborema region. This work aims to investigate environmental evolution in the humid and sub-humid enclaves of Cariri Paraibano. For this purpose, a bibliographical survey was carried out on paleoenvironmental reconstruction studies in Brazil, which highlighted the scarcity of this type of research in the Northeast region. Field work was carried out to collect soil, in the area of influence of the Province of Borborema, in Cariri Oriental and in the Central-Western portion for the purpose of soil characterization and paleoenvironmental reconstitution. Routine soil analyzes and isotopic analyzes (δ13C and δ15N), 14C dating and phytolith analysis were carried out to reconstruct Holocene paleoenvironmental conditions. The results obtained demonstrate that the presence/absence of other silica biomineralizations, such as diatoms, sponge spicules and gemosclera contributed to explaining environmental moments, including to infer moments of greater/lower humidity in the Holocene; the occurrence of phytoliths with amber taphonomy, burned, subjected to high temperatures, associated with taxa used as a food source and the presence of cave paintings, archaeological sites indicate ancient human occupation in Lajedo Salambaia and Serra da Paula, in the Early Holocene (8,199 years BP) and in the Middle H. (3,498 years BP), respectively; Furthermore, the pedobioindicators analyzed revealed periods of drying and moistening in all profiles from the Early Holocene to the present day. Given this information, it was possible to apply the hypothesis of biotic exchange corridors between different floras in the areas of P2, P3, P4 and P7, located on the slope and foot of the crystalline, with P2 and P4 classified based on the WRB/FAO as Umbrisols , rich in organic carbon, it is believed that wetter and colder climates than the current one caused the formation of these soils. Regarding Vertisols, although they have a pH between 6 – 9, they were efficient for preserving phytoliths. The signs of breakage and corrosion in the phytoliths of these soils reflect the position in the landscape at the bottom of the valley and the seasonality of humidity, which ends up, in a certain way, minimizing the chemical attack on the morphotypes, preserving the phytoliths, since the sodium will not be dissolved. and available for corrosion to occur. The results obtained in this research indicate that phytoliths are good bioindicators and are well preserved in the soils studied and can be applied in new paleoenvironmental studies in the semiarid northeastern region for a better understanding of the dynamics and evolution of the local landscape, since different physical factors influence the configuration of the Caatinga Ecosystem, being a vegetation mosaic of socioeconomic and historical importance.