Estudo geoquímico-mineralógico de litologias aflorantes na orla litorânea de Icapuí – Ceará

Abstract

This dissertation presents the geochemical and mineralogical characteristics of the outcropping lithologies on the coast of Icapuí – Ceará from X - rays diffraction data, chemical analysis of fundamental oxides and Loss On Ignition and description of thin sections. These lithologies comprise rocks of the Jandaíra, Barreiras and Potengi Formations, belonging to the Potiguar Basin. These rocks were deposited in paleoenvironments and paleoclimates distinct from each other, in particular, in the Barreiras Formation, different paleoclimates from more arid tropical to more umid, with special condition of development of facies in the more umid tropical paleoclimate that allowed the development of laterite. In this case, degrees of alteration were defined to which the rocks of the Barreiras Formation were submitted. The limestone of the Jandaíra Formation was deposited in distal carbonaceous platform with little terrigenous influence, in semiarid paleoclimate, and presents anomaly in Cd, whose origin is attributed to the development of oceanic magmatism since the break-up of Gondwana, still active in the Upper Cretaceous. The sandstones of the Barreiras Formation showed evidence of having been submitted to a strong hydrolysis, provoking absence or subordinate presence of potassic feldspars (average of 0,9% in total rock). The laterite has a strong presence of iron minerals (goethite) reaching 36,47% of Fe2O3 content besides anomalous values in Cr and Ni, indicating the existence of basic-ultrabasic rocks in the domains of source-areas, not yet characterized. Differently, the sandstone of the Potengi Formation preserved some more significant presence of potassic feldspar (7,2% in total rock) indicating a tendency to semiarid paleoclimate