Revisão sistemática e paleoecologia da paleoictiofauna da Formação Morro do Chaves (Cretáceo Inferior), Bacia de Sergipe-Alagoas

Abstract

The Sergipe-Alagoas Basin presents the most complete stratigraphic record directly related to all phases of the Gondwana breakup and consequent opening of the South Atlantic. On the other hand, the Morro do Chaves Formation is related to the rift and post-rift supersequences of the basin, deposited during the Eocretaceous (Barremian-Aptian). It is characterized by the intercalation of coquinas and shales, presenting a continuous stratification. However, there is still some debate about the depositional origin of these sediments. Furthermore, the paleoictiofauna of the Morro do Chaves Formation is often referred to in the literature as diverse, abundant and well preserved. However, most of the taxa referred to the locality have been the subject of many debates and phylogenetic proposals over the years, which need revision. Although there have been studies on the fauna and flora of the Morro do Chaves Formation since 1870, few studies have been dedicated to the paleoecology of this locality. Thus, the aim of this thesis is to conduct a taxonomic review of the paleoecology of the Morro do Chaves Formation, which, together with organic geochemical data on the shales, will allow a new paleoecological view of the locality. Furthermore, the relative abundance of type II kerogen at the site is indicative of a reductor, marine-influenced paleoenvironment. The hypothesis is supported by the positive correlation between Hydrogen Index (HI) and TOC. Furthermore, the samples of the F01 and F08 pelitic levels are representative of warmer, more reductor paleoenvironments, while pelitic level F05 represents a calmer and more oxygenated scenario. Similar conditions are observed in the Cretaceous of New Mexico, Iran, and Egypt. In addition, the paleoictiofauna of the Morro do Chaves Formation is composed of Aulopiformes, Clupeiformes, Coelacanthiformes, Ellmmichthyiformes and Lepisosteiformes. Furthermore, the probable life history and feeding habits of the São Miguel dos Campos Unit fish paleocommunity can be defined as piscivorous active predators, benthic, and planktonic. Aulopiformes would probably act as top-down influence in the paleocommunity, controlling the local fish populations. In turn, Mawsonia and "Lepidotes" are commonly found associated in the outcrops and would probably share behavioral patterns and food preferences, which is interpreted as potential competition between the taxa.z