The K-T boundary in Brazilian marginal sedimentary basins and related spherules.

Abstract

During the last 10 years some important results have been reached after extensive research performed on some Brazilian basins relating to the Cretaceous-Tertiary Boundary (KTB) matter. This paper presents some of these results mainly focused on the spherule content of the sediments. The preliminary analysis carried out without strong constraints have not revealed any distinguishing and typical characteristics known for the KTB. These geochemical analysis were performed on ditch samples, from subsurface data, submitted to statistical tests such as factor and discriminant analysis. The result of the factor analysis indicated general trends in the concentration of chemical elements while the discriminant analysis showed a very clear discontinuity of the chemical data between the Cretaceous and Tertiary periods. The first occurrence of spherules was found in sediments from the KTB of Pernambuco-Paraíba Basin (PE-PB). Despite other impact-derived characteristics present in this sedimentary section these spherules do not show any direct evidence of an impact origin. On the other hand, the study of microspherules recovered from a drilling core of Campos Basin has probably revealed the first documented occurrence of tektites in South America.