Da duna à rocha: distribuição e composição dos eolianitos da costa oeste cearense

Abstract

Eolianites are cemented dunes with a significant presence in the western sector of the coastal zone of the State of Ceará, serving as paleoclimatic records and acting in the defense of the coastline in this region. In this interim, the present study aims to analyze the spatial distribution and composition of eolianites located between Bitupitá Beach, in the municipality of Barroquinha (CE), and Pecém Beach, in São Gonçalo do Amarante. To this end, the adopted methodology included a literature review, the creation of a cartographic database, and detailed petrographic analysis. The analyses evidenced that the studied eolianites have a predominantly terrigenous composition, with quartz and feldspar as main components, in addition to a significant presence of heavy minerals in locations such as Moitas and Bitupitá. The presence of biogenic constituents was also identified, highlighting a compositional gradient influenced by the adjacent Continental Shelf, since samples collected in the eastern sector of the study area, near Pecém, showed low bioclast content, while the western sector, towards Barroquinha, stood out for the increase in biogenic fragments, mainly coralline algae, mollusks, and foraminifera. In addition to compositional variations between locations, the study also evidenced heterogeneity between fractions of the same location, as identified at Baleia Beach, located in the municipality of Itapipoca. The cementation, ranging from micritic to sparitic, suggests different conditions of carbonate precipitation. Thus, it is concluded that the formation of eolianites on the western coast of Ceará does not occur randomly, but is conditioned by factors such as the semi-arid climate, the presence of a shallow platform with low slope, and the presence of carbonate habitats in ultra-shallow waters, in addition to the coastal geomorphology of the region, which favors the existence of these eolian outcrops. It is under the influence of these variables that the dynamics of terrigenous and biogenic input acts, marking the composition of the eolianites and highlighting them as an essential geological feature for the Ceará coastal zone.