Anatomia e Morfologia de Macrofósseis Vegetais Quaternários da Formação Boa Vista da Bacia do Tacutu-RR

Abstract

The Takutu Basinis located in the central region of the Guiana Shield, north of the Amazonian Craton. Its origin is related to the opening of the North and Central Atlantic Ocean (late Jurassic – early Cretaceous). Boa Vista Formation, stratigraphic unit of this research, almost completely covers the Takutu Graben region and has its age attributed to the interval Late Pleistocene-Holocene. The plant macrofossils (leaves) which are preserved as impressions/compressions were collected along the deposits of this formation, wrapped in clay “pellets”. The material was “rolled”, outside their original strata, making it necessary, therefore, to carry out analyzes that allowed inferring its stratigraphic positioning. Thus, the present study aimed to (i) describe, morphologically and anatomically, and taxonomically identify plant macrofossils, in addition to (ii) create a database on fossils and (iii) try to stratigraphically position the macrofossils studied. Morphological analysis was performed using leaf architecture and anatomical analysis by using stomatal architecture and cuticular description for possible identification, in addition to chemical and mineralogical analysis to determine the stratigraphic positioning of fossils. Representatives of the following genera were identified: Byrsonima Rich. ex Kunth, Psidium L. and Zanthoxylum L. and from the family Dilleniaceae Salisb. Unidentified specimens were grouped into five morphotypes. The determined taxa represent typical elements of the savanna formation of Roraima, called “lavrado”. The results obtained in Libs and in the DRX indicated that the analyzed samples are compatible with samples from Boa Vista Formation, which can be inferred that they are part of the same stratigraphic unit. Finally, the anatomical-cuticular characters of the leaves indicated the dominance of xeromorphic plants, similar to what is currently seen in the species in the “lavrado”, suggesting that the same climatic-environmental conditions existed in Roraima during the Quaternary.