Murilo Rodolfo de Lima

The ultrastructure of fossil ephedroid pollen with gnetalean affinities from the Lower Cretaceous of Brazil

Abstract The micromorphology and fine structure of several dispersed polyplicate, “ephedroid” palynomorphs, originally assigned to Equisetosporites spp., are described from the Lower Cretaceous (Aptian-Albian) Santana Formation of northeastern Brazil. Pollen grains are elliptic in shape and have a variable number of longitudinally oriented plicae, but lack a distinct aperture. Plicae do not reach the grain tips and are psilate to faintly scabrate in surface ornamentation. The exine is distinctly two-parted with the sexine typically staining more lightly than the nexine. The sexine is on average 1.5 times thicker than the nexine, and has a tectate granular fine structure with the granular infrastructural layer having a graded organization. Small granules characterize the lower region of the infratectum and are directly contiguous with nexine; these gradually grade into larger granules that appear to fuse with a thick, homogeneous tectum. The nexine is thick and lamellate throughout. Both sexine and nexine sporoderm components are markedly thinner between the plicae (i.e. within the wall furrows), with the granular infratectum laterally thinning until completely absent. An additional wall layer, external to the tectum, is also present within sporoderm furrows; both the tectum and this layer typically occur in a folded, hinge-like fashion in the furrow. This unique feature as well as several other structural characters of the sporoderm are discussed with regard to their possible functional significance. Exine architecture is also compared with that of the only other three fossil polyplicate palynomorphs known at the ultrastructural level ( Ephedripites sp., Equisetosporites chinleana , and Cornetipollis reticulata ) as well as with that of the pollen of the extant Gnetales ( Ephedra, Welwitschia , and Gnetum ). By comparison, the Brazilian grains are most similar to Ephedripites using fine structural features.

DESCOBERTA DE MICROFLORA EM SEDIMENTOS DO GRUPO BAURU, CRETÁCEO DO ESTADO DE SÃO PAULO

The presence of fossil animals (invertebrates and vertebrates) in sediments of the Bauru Group is quite common. Despite this fact, lhe pronounced endemism of the faunas has not permitted, till now, the precise dating of the fossil-bearing levels. On the other hand, the occurrence of plants is much scarcer. In this context, the discovery of a very well preserved microflora, at the Fazenda Nossa Senhora do Carmo, Sao Carlos Municipality, Sao Paulo States, deserves attention. This assemblage represents, in fact, the first record of palynomorphs in the Cretaceous of the Parana Basin. Study of the very diversified material, including several stratigraphically important species, has allowed the attribution of a Coniacian age for the fossiliferous strata. It has also been possible to drawn important stratigraphic, paleoecological, paleoclimatological and tectonic conclusions regarding the studied outcrop

Palinologia dos carvões paleozóicos do Estado de São Paulo, Brasil: I - O carvão de Buri

Numerous stratigraphic problems persist regarding the ltarare Subgroup, the principal unit representative of Late Paleozoic glaciation in the Parana Basin, as the result of the great lithologic and faciologic variety and the relative rarity of fossils in this sequence. Thus, because of their potential biostratigraphic significance, special attention is due to the classic coal occurrences at Buri, Monte Mor and Cerquilho in the State of Sao Paulo. Palynological work presented here reveals that the Buri coal is the oldest of these three levels. Thirty-four taxa have been identified in the assemblage, with an absolute predominance of zonate spores. Various species allow correlation with Carboniferous sediments of the Paganzo Basin, Argentina (Malanzan Formation - Estratos Carbonosos Member), of probable Westphalian age, deposited in a deltaic environrnent.

Palinologia de sedimentos da Bacia de São Paulo, Terciário do Estado de São Paulo, Brasil

The Tertiary sediments of the Sao Paulo Basin, which include the Sao Paulo and Itaquaquecetuba Formations, have been recently interpreted as a Paleocene sedimentary ensemble comprising: a basal alluvial fan to braided-stream system; a partially contemporaneous lacustrine system; a meandering fluvial system at the top of the sequence. The origin of the Itaquaquecetuba Formation (braided-channel system) is controversial, and it has been considered by different authors as having been associated with the basal deposits of the basin and as due to tectonic reactivation and sediment reworking during the Neogene or Quaternary. This study comprises the palynological analysis of sediments from the alluvial fan, laustrine and braided-stream systems (this latter attributed to the Itaquaquecetuba Formation); the respective palynofloras are homogeneous and include several taxa of stratigraphic and paleoclimatic value, suggesting very close ages and climates. The dorninance of Oligocene taxa together with only a few others considered as Eocene or older suggest two hypothesis: 1) possible reworking of Eocene sediments in the Oligocene; 2) the taxa previously considered as Eocene in age may have, in fact, lived until Oligocene, and so should have their distribution interval suitably corrected. The relative abundance of taxa indicating colder climates (conifers) and the scarcity of others more typical of hot and wet climate suggests that sedimentation took place under cold conditions. However, it was not possible to establish precisely the influence of altitudinal floristic differentiations in the preserved palynological assemblage

Um invariante no controle da percepção e ação em tarefas de bissecção

Resumo: Diversos estudos empregando acoes visualmente dirigidas como indicadores da distância percebida demonstraram que as pessoas podem caminhar acuradamente para alvos distantes em ate 22m. Estes resultados, somados aos relacionados com medidas perceptuais de distância percebida, demonstram que estas respostas sao controladas por uma unica variavel interna, denominada de localizacao visualmente percebida. No presente estudo, comparamos os desempenhos em tarefas de bisseccao, realizadas por caminhada visualmente dirigida, ou por emparelhamento perceptual. Os observadores (N=20) caminharam ou ajustaram a posicao de uma ponteira ao ponto medio da distância egocentrica de um alvo (5, 10 or 15m), sob observacao binocular. Os resultados indicaram acuracia em ambas respostas, sem diferencas significativas entre elas, o que sustenta a hipotese de uma unica variavel interna controlando acao e percepcao. Este invariante pode ser determinado por um conjunto ponderado de fontes de informacao. Palavras-chave: Percepcao espacial, percepcao visual, sistemas de percepcao-acao, bisseccao, locomocao PERCEPTION-ACTION INTERACTION AND BISSECTION