Registros botânicos preservados nos eolianitos de Camocim (Holoceno do Noroeste do Ceará)

Abstract

Coastal zone of Ceará state extends through 570 km, Rio Grande do Nortestate to the east and Piauí to the west, with parts that exhibit low plateaus supported by Barreiras Formation and above it, quaternary flatland that has fluvial, lacustrine and eolian deposits. Eolianites, rock deposited by wind action, are geomorphologic units that, in Brazil, occur in Northeast region only. Some outcrops may show lithified plant remains, firstly interpreted as roots, cutting through sandstone layers and exposed by erosion. The analyses and depth study of these past life forms from coastal zone, assisted by early geological, geochronological and sedimentological data, they serve as an aid for interpretation of paleoenvironmentaland paleohydrologic data, so as of edaphic information, allowing a better understanding of local environmental conditions. This research aimed to identify these ancient plants preserved as mineralized stems in eolianites from Camocim coastal zone. The research method was based on literature review, field data and direct observation of material, with chemical and morphological analyses of collected samples. The interpretation of biological and geological phenomena made use ofthe Biology, Ecology and Paleontology general principles. The chemical analyses in the mineralized plants were made by energy-dispersive X-ray spectroscopytechnique,revealing there were not significant variations between samples composition, being primarily made of calcium carbonate (CaCO3).Trace elements like Magnesium, Silicon, Aluminum, Chlorine, Bromine and Phosphorus were alsoidentified.The morphological investigationin these plantsoccurred in four specimens with different diameter measures (0.5, 1.2, 1.7 e 2.0 cm), noting external and internal anatomic features with electronic microscopy analyses. Only the fourth specimenshowed structures interpreted as vesselssolitary and/or multiple of two elements and homocellular rays with procumbent cells, features correlated to family Fabaceae. The specimens were interpreted as herbaceous and sub-shrub plants inhabiteda marine-influenced area.The chemical characterization of samples attests the compositional variety of sediments deposited at the coastland region, while the presence of cytological structures preserved with identification of a probable taxon add new information about the eolianites history and its plant mineralized content.