Valesca Brasil Lemos

Holocene invertebrates from the Rocas Atoll: A contribution for the ecological history of South Atlantic islands

The South Atlantic Ocean is the youngest of the world’s oceans and one of the most important biodiversity hotspots; however, there is a lack of scientific knowledge about its ecological history. Here, we present the first results of a fossil invertebrate survey from the Rocas Atoll. By using radiometric dating (C) and a survey of fossilized benthic invertebrates on this atoll, we provide new paleobiogeographic and paleoceanographic information. The results suggest eight taxa (five mollusks, two corals, and one decapod). Dates ranged from 3449 ± 790 y BP to 3033 ± 620 y BP. The data represent new invertebrate records for the middle Holocene in this atoll, and evidence of sea-level changes in this period. Considering that the Rocas Atoll is one of the newest marine atolls in the world, these results suggest recent colonization by species from the Southwestern Atlantic Coast and Fernando de Noronha Archipelago.

Aspectos biogeomorfológicos do Atol das Rocas, Atlântico Sul Equatorial

Biogeomorphological aspects of Rocas Atoll, Equatorial South Atlantic. Biogeomorphological analysis and mapping of the reef units in the only Atoll from the Equatorial South Atlantic were held for understanding the dynamics and the relief of this oceanic reef. The zoning shows the presence of the following environmental compartments: reef front, adjacent bottom, reef margin, reef flat, reef ring, reef residues, lagoon, sand flat, reef pass, pools, puddles-of-tide and the sand cays. The results show that a variety of organisms in Atoll that act in processes groups such: control of erosion on sand cays, bioprotection, bioerosion, cementation of biogenic carbonate sand, production of biodetritic sediments and bioconstruction. Such biogeomorphological processes generate some of the unique characteristics of Rocas Atoll.

Primeira ocorrência dos gêneros Ellisonia, Gondolella e Ubinates (Conodonts) para a Formação Itaituba, Pensilvaniano da Bacia do Amazonas, Brasil

This paper analyzes and describes a fi rst occurrence of the conodonts Ellisonia, Gondolella and Ubinates in Amazonas Basin, North of Brazil. The recovered material comes from two outcrops along the Tapajos River and from a limestone quarry of Itaituba Formation, whose levels are included in the Itaituba Formation, with a Pennsylvanian age. Those conodonts are relevant paleoecological indicators of water depth, salinity and environmental energy and have implications in the Late Carboniferous to Triassic biostratigraphy. The fossil remains represent M and S conodont elements, associated to Pa elements of the Idiognathodus, Idiognathoides, Neognathodus, Adetognathus, Hindeodus and Diplognathodus genus . Key words: conodonts, Amazonas Basin, Itaituba Formation, Pennsylvanian.