Etiene Fabbrin Pires

Sommerxylon spiralosus from Upper Triassic in southernmost Paraná Basin (Brazil): a new taxon with taxacean affinity

The anatomical description of silicified Gymnospermae woods from Upper Triassic sequences of southernmost Parana Basin (Brazil) has allowed the identification of a new taxon: Sommerxylon spiralosus n.gen. et n.sp. Diagnostic parameters, such as heterocellular medulla composed of parenchymatous and sclerenchymatous cells, primary xylem endarch, secondary xylem with dominant uniseriate bordered pits, spiral thickenings in the radial walls of tracheids, medullar rays homocellular, absence of resiniferous canals and axial parenchyma, indicate its relationship with the family Taxaceae, reporting on the first recognition of this group in the Triassic on Southern Pangea. This evidence supports the hypothesis that the Taxaceae at the Mesozoic were not confined to the Northern Hemisphere.

Palaeoclimatic inferences based on dendrological patterns of permineralized wood from the Permian of the Northern Tocantins Petrified Forest, Parnaíba Basin, Brazil

The Northern Tocantins Petrified Forest is classified in the scientific literature as one of the most important Permian assemblages of permineralized plant remains from the warm temperate palaeobiome of the Southern Hemi-sphere. Part of this forest is located in the Tocantins Fossil Trees Natural Monument, which is a Full Protection Conservation Unit in the northeastern part of the Brazilian state of Tocantins. Geologically, the Petrified Forest is part of the Parnaíba Basin, and the studied stems originate from the Permian Motuca Formation. The aim of the present work is to reconstruct aspects of the regional climate during the Permian by using proxy data obtained from the analysis of gymnospermous fossil stems preserved in the Northern Tocantins Petrified Forest. The material analysed comes from 32 gymnospermous fossil wood fragments derived from nine sampling points located inside and outside the park area. In order to determine climatic influence on wood growth, a total number of 682 growth increments were investigated using mean sensibility and annual sensibility analysis. Moreover, thin sections were made and the anatomical details of the growth patterns of the stems were investigated. The results obtained from these analyses allowed the establishment of the presence of growth zones in the gymnospermous fossil stems. Detailed analysis of these growth zones led to the reconstruction of a seasonal climate with periods of high precipitation alternating with periods of more or less severe dryness, probably in a semi-arid palaeoenvironment. This result is in agreement with previous reconstructions for the Northern Tocantins Petrified Forest area, which postulated a kind of monsoonal climate, characterised by marked seasonality, with strong rains and distinct dry periods.

Growth ring analysis of fossil coniferous woods from early cretaceous of Araripe Basin (Brazil)

Growth ring analysis on silicified coniferous woods from the Missão Velha Formation (Araripe Basin - Brazil) has yielded important information about periodicity of wood production during the Early Cretaceous in the equatorial belt. Despite warm temperatures, dendrological data indicate that the climate was characterized by cyclical alternation of dry and rainy periods influenced by cyclical precipitations, typical of tropical wet and dry or savanna climate. The abundance of false growth rings can be attributed to both occasional droughts and arthropod damage. The present climate data agree with palaeoclimatic models that inferred summer-wet biomes for the Late Jurassic/Early Cretaceous boundary in the southern equatorial belt.

Relation between the sedimentary organic record and the climatic oscilations in the Holocene attested by palynofacies and organic geochemical analyses from a pond of altitude in southern Brazil

This paper presents the quantitative and qualitative results obtained from palynofacies and geochemistry analyses carried out on a core covering approximately 8000 years of sedimentation of a pond of altitude located at the mining district of Ametista do Sul, southernmost Brazil. The main objective of this paper is to consider the paleoclimatic and paleoenvironmental significance of these analyses. The hydrological isolation renders this pond climatically sensitive to variations in pluviometric regime and this enabled infer rainfall events during the early Holocene, which was responsible for the beginning of the processes of water accumulation in the gossan and the sedimentation of the pond. Changes in the pattern of moisture over the time become the drier environment, resulting in the intermittent pattern of water depth that currently exists at the site. The fluctuations in water depth are inferred from the frequency of Botryococcus and other algae, which tend to decrease progressively toward the top where the autochthonous elements are replaced by parautochthonous and allochthonous elements. Pseudoschizaea, in turn, appears to act as a biological marker of these transitional intervals. The present results are of great importance for understanding the extent of climate change and its environmental impacts at regional and global levels.

Incêndios vegetacionais Indo-Brasileiros no Neopaleozoico: uma revisão dos registros de carvão vegetal macroscópico

Sedimentary charcoal is widely accepted as a direct indicator for the occurrence of paleo-wildfires and, in Upper Paleozoic sediments of Euramerica and Cathaysia, reports on such remains are relatively common and (regionally and stratigraphically) more or less homogeneously distributed. On the contrary, just a few reliable records have been published for the Late Paleozoic of Gondwana and only recently it has been demonstrated that macroscopic charcoals (and thus fires) were also common in the southern continent during this period. The most important Gondwanan records are predominantly charred gymnosperm woods mainly related to coal bearing strata. Late Paleozoic macro-charcoal occurs in both, the Damodar Basin (India) and the Paraná Basin (Brazil), demonstrating that paleo-wildfires were spread out in different sequences and distinct stratigraphic intervals during this period in Gondwana. Based on the so far published records as well as new samples from the Seam-VI coalfield, Raniganj Formation (Damodar Basin – Lopingian of India), an overview of the Late Paleozoic Indo-Brazilian macro-charcoal remains is presented. The hitherto unpublished samples were anatomically analyzed under Scanning Electron Microscope and a gymnosperm affinity could be established. The data presented here reinforce the relevance of paleo-wildfire as a source of environmental disturbance over large areas of Gondwana during the Late Paleozoic.

Vegetational changes during the last millennium inferred from a palynological record from the Bananal Island, Tocantins, Brazil

The Bananal Island is regarded the largest fluvial island in the world, bounded by Araguaia and Javaes rivers, being located in southwest of Tocantins. The objectives of this work were to provide information about the vegetational changes that occurred at the Bananal Island, in order to contribute to the understanding the dynamics of past and current savanna and areas of ecotones with forests. Thus, a sedimentary core collected from a small lake at the Bananal Island plain was submitted to pollen and radiocarbon dating analyses. The results showed that the last millennium was dominated by forest reflecting a wet climate. At the beginning of the record (920-770 yr cal BP) the wet climate and high rainfall produced flooding during long rainy seasons that maintained the Javaes River connected to the studied lake, and hence, this environment was marked by the presence of a homogenous forest rich in Moraceae/Urticaceae, due to flooded soils occurrence. During the following period (770-304 yr cal BP) the reduced rainfall and shortening of the rainy seasons isolated the lake from the Javaes River for long periods, which caused a diversification of the forest and gave rise to the appearance of the components of floodplain forest and marsh vegetation adapted to waterlogged soils. Since 304 years cal BP to the present day this environment remained dominated by this diverse forest and the lacustrine conditions were also similar to previous phase, with a slight increase of moisture in the last 84 years that caused the increase of Piranhea.

Registro palinológico de depósitos sedimentares neopleistocênicos do Rio Madeira, Rondônia, Amazônia brasileira

The present paper presents a study of identification of palynological assemblages from a layer of sediment taken from a modern forested area situated in the upper course of the Madeira River, within the region of influence of the AHE Jirau, Rondonia, Brazilian Amazon. Radiometric carbon dating using 14C (AMS method) furnished ages between 41,350 and 43,500 years Before Present (B.P.), or Late Pleistocene, for the studied layer. The results reveal a set of palynomorphs marked by low diversity of pollen families with predominantly tropical forest types showing an upward increase in pollen grains typical of wet environments, probably suggesting the installation of a swamp. No other vegetational change was observed during the period recorded in this study, and in general the data are in agreement to palynological records obtained from other areas of the Amazon forest region that indicate a steady forested environment for the same period.