Palynofacies analyses of Santana Group, upper Aptian of the Araripe Basin, northeast Brazil: Paleoenvironmental reconstruction

Abstract

We present the paleoenvironmental analysis based on sedimentary organic matter (SOM) of alluvial-lacustrine-transitional deposits that crop out in the east portion of the Araripe Basin, Ceará State, Brazil. Samples were collected from the Barbalha, Crato, Ipubi and Romualdo formations, Santana Group. For the palynofacies analyses, the kerogen categories were counted and grouped. The described SOM were subdivided into six groups: Structureless, which consists of resin and amorphous organic matter (AOM); Terrigenous, which consists of non-opaque biostructured-phytoclast; Opaque, which consists of equidimensional, lath and corroded of black color; Sporomorphs, which consist of spores and pollen grains; Freshwater, constituted by Botryococcus and Pediastrum microplankton and Marine elements, represented by dinoflagellate cysts and foraminiferal lining. The stratigraphic distribution of the seven palynofacies reflects a change from fluvial system to a lacustrine environment, as well as the first marine incursion on Serra da Mãozinha section (Crato Formation). In the top of the Santana Group recorded a transition from a lacustrine environment close to a fluvio-deltaic source to an estuarine system, marked by the presence of Subtilisphaera, during the late Aptian. The palynological data presented indicates that the entire Santana Group is of Aptian age considering the conspicuous presence of Sergipea variverrucata in the sections.