Paleoecology and paleoenvironmental inferences based on palynomorphs from the Romualdo Formation (Lower Cretaceous) of the Araripe Basin, Serrolândia Mine, Pernambuco, northeastern Brazil

Abstract

The present study is based on a paleoecological and paleoclimatic analysis of the palynological associations found in the section of the Serrolândia Mine in Ouricuri, Pernambuco, which contributes to the reconstruction of the paleoenvironment of the Lower Cretaceous Romualdo Formation of the Araripe Basin, in northeastern Brazil. A total of 19 samples were collected from this section, which has a total height of 17 m. Only seven of these samples contained palynomorphs, which were analyzed by counting 200 palynomorphs per sample, permitting the identification of a total of 64 taxa, most of which were continental in origin. These continental palynomorph taxa included 34 pollen grains of gymnosperms and four of angiosperms, as well as the 14 spores of ferns and lycophytes, two freshwater microalgae, and fungal spores. The marine palynomorphs were represented by eight dinoflagellate cysts taxa and foraminiferal linings. The most abundant taxa overall were Classopollis spp., Afropollis jardinus, Cycadopites spp., and Gnetaceaepollenites jansonii, whose presence indicates a warm (semiarid to arid) paleoclimate. A distribution and cluster analysis identified two groups, G1, representing the lower layers (3.5–4.2 m), and G2, at a higher level (4.4–6.0 m). The palynomorphs of G1 were 92% continental and 8% marine, being represented by the dinocysts Batiacasphaera sp. A, Cometodinium ? sp., and Odontochitina ? sp. This group represents a proximal marine paleoenvironment with a strong terrestrial influence, whereas in G2, there is a decrease in the influence of continental palynomorphs (79%) and a significant increase in the contribution of marine palynomorphs (21%), including foraminiferal linings and the dinocysts of Subtilisphaera sp., Spiniferites sp., Odontochitina ? sp., and Atopodinium sp., etc. These characteristics are consistent with the conclusion that G2 represents a distal marine paleoenvironment. These findings provide important insights into the paleoenvironment of the Romualdo Formation in the Araripe Basin of northeastern Brazil during the Early Cretaceous.