The Oligocene-Neogene deep-sea Columbia Channel system in the South Brazilian Basin: Seismic stratigraphy and environmental changes

The Columbia Channel (CCS) system is a depositional system located in the South Brazilian Basin, south of the Vitoria-Trindade volcanic chain. It lies in a WNW-ESE direction on the continental rise and abyssal plain, at a depth of between 4200 and 5200 m. It is formed by two depocenters elongated respectively south and north of the channel that show different sediment patterns. The area is swept by a deep western boundary current formed by AABW. The system has been previously interpreted has a mixed turbidite-contourite system. More detailed study of seismic data permits a more precise definition of the modern channel morphology, the system stratigraphy as well as the sedimentary processes and control. The modern CCS presents active erosion and/or transport along the channel. The ancient Oligo-Neogene system overlies a ""upper Cretaceous-Paleogene"" sedimentary substratum (Unit U1) bounded at the top by a major erosive ""late Eocene-early Oligocene"" discordance (D2). This ancient system is subdivided into 2 seismic units (U2 and U3). The thick basal U2 unit constitutes the larger part of the system. It consists of three subunits bounded by unconformities: D3 (""Oligocene-Miocene boundary""), D4 (""late Miocene"") and D5 (""late Pliocene""). The subunits have a fairly tabular geometry in the shallow NW depocenter associated with predominant turbidite deposits. They present a mounded shape in the deep NE depocenter, and are interpreted as forming a contourite drift. South of the channel, the deposits are interpreted as a contourite sheet drift. The surficial U3 unit forms a thin carpet of deposits. The beginning of the channel occurs at the end of U1 and during the formation of D2. Its location seems to have been determined by active faults. The channel has been active throughout the late Oligocene and Neogene and its depth increased continuously as a consequence of erosion of the channel floor and deposit aggradation along its margins. Such a mixed turbidite-contourite system (or fan drift) is characterized by frequent, rapid lateral facies variations and by unconformities that cross the whole system and are associated with increased AABW circulation. (C) 2009 Elsevier B.V. All rights reserved.

Microfacies and sequence stratigraphy of the Amapa Formation, Late Paleocene to Early Eocene, Foz do Amazonas Basin, Brazil

On the basis of thin-section studies of cuttings and a core from two wells in the Amapa Formation of the Foz do Amazonas Basin, five main microfacies have been recognized within three stratigraphic sequences deposited during the Late Paleocene to Early Eocene. The facies are: 1) Ranikothalia grainstone to packstone facies; 2) ooidal grainstone to packstone facies; 3) larger foraminiferal and red algal grainstone to packstone facies; 4) Amphistegina and Helicostegina packstone facies; and 5) green algal and small benthic foraminiferal grainstone to packstone facies, divisible locally into a green algal and the miliolid foraminiferal subfacies and a green algal and small rotaliine foraminiferal subfacies. The lowermost sequence (Si) was deposited in the Late Paleocene-Early Eocene (biozone LF1, equivalent to P3-P6?) and includes rudaceous grainstones and packstones with large specimens of Ranikothalia bermudezi representative of the mid- and inner ramp. The intermediate and uppermost sequences (S2 and S3) display well-developed lowstand deposits formed at the end of the Late Paleocene (upper biozone LF1) and beginning of the Early Eocene (biozone LF2) on the inner ramp (larger foraminiferal and red algal grainstone to packstone facies), in lagoons (green algal and small benthic foraminiferal facies) and as shoals (ooidal facies) or banks (Amphistegina and Helicostegina facies). Depth and oceanic influence were the main controls on the distribution of these microfacies. Stratal stacking patterns evident within these sequences may well have been related to sea level changes postulated for the Late Paleocene and Early Eocene. During this time, the Amapa Formation was dominated by cyclic sedimentation on a gently sloping ramp. Environmental and ecological stress brought about by sea level change at the end of the biozone LF1 led to the extinction of the larger foraminifera (Ranikothalia bermudezi). (c) 2009 Elsevier B.V. All rights reserved.

A new species of Hemigrammus from the upper Rio Tapajos basin in Brazil (Teleostei : Characiformes : Characidae)

Hemigrommus silimoni is described from the Rio Juruena, upper Rio Tapajos basin, Mato Grosso State, Brazil. The new species is distinguished from all congeners, and in fact from the remaining Characidae, by the autapomorphic presence of an ocellus-like blotch on the caudal-fin dorsal lobe. The high level of fish endemicity In the Rio Juruena (upper Rio Tapajos basin) is discussed.

A new, brightly colored species of Pseudoboa Schneider, 1801 from the Amazon Basin (Serpentes, Xenodontinae)

A new species of Pseudoboa, P. martinsi, is described from the Amazon basin of Brazil, with records from the states of Para, Amazonas, Roraima and Rondonia. The new species is distinguished from the other five species of the genus by a combination of scalation and coloration characters. Individuals of the new species were found in both primary and disturbed forested areas. The species seems to be predominantly nocturnal and secretive because specimens were found foraging in the litter during night.

Knodus dorsomaculatus (Characiformes: Characidae), a new species from Teles Pires River, Tapajos River basin, Brazil

Knodus dorsomaculatus, a new species, is described from Teles Pires River, a tributary of the Tapajos River, Brazil. It can be distinguished from its congeners by the presence of a conspicuous dark blotch on the base of the first five branched dorsal fin rays and the presence of ii,9 dorsal fin rays. Additional comparisons between K. dorsomaculatus and its congeners are presented.

New Species of the Thorny Catfish Genus Leptodoras (Siluriformes: Doradidae) from Rio Fresco, Xingu Basin, Brazil

A new species of the thorny catfish genus Leptodoras (family Doradidae) is described. The new species shares three characters with its congeners, the modified oral hood with distinct upper labial extensions, the first gill arch with enlarged accessory lamellae extending well onto medial face of gill filaments, and the pelvic fin inserted in anterior half of body. The new species is distinguished from congeners by having a large dark submarginal blotch on distal half of dorsal-fin spine and anteriormost dorsal-fin branched rays, lower labial extension of modified oral hood extending more posteriorly than upper labial extension, relatively few midlateral scutes, gas bladder moderately sized (not reduced), paired bony capsules on anteriormost vertebrae reduced to paired cup-like laminar ossifications separated by a triangular septum, pair of small, swelling-like diverticula on each side of the anterior chamber of gas bladder, a well-developed anterior nuchal plate, and nuchal foramina present. The new species was discovered from a single specimen collected in the rio Fresco, a tributary of the rio Xingu, and is described based on this and on additional material recently collected in the same area. A discussion of its placement within Leptodoras is also presented.

A new genus and species of inseminating characid fish from the rio Xingu basin (Characiformes: Characidae)

Phallobrycon adenacanthus, is described as a new genus and species belonging to Clade A characids of Malabarba & Weitzman (2003). The new taxon is the only characid possessing two developed spines on unbranched portions of fifth, sixth and seventh anal-fin rays associated with intumescent glandular tissue on the anterior portion of the anal fin of sexually mature males. Other non-exclusive diagnostic features of the new genus (observed in male specimens) are: urogenital papilla modified into a copulatory organ, absence of pelvic-fin hooks and glandular tissue not organized into an organ. The presence of these features in members of Clade A and other characids is discussed in order to hypothesize the relationships of Phallobrycon.

Review of the genus Microphilypnus Myers, 1927 (Teleostei: Gobioidei: Eleotridae) from the lower Amazon basin, with description of one new species

Microphilypnus Myers, 1927 is a genus with three nominal species (M. amazonicus and M. macrostoma from the lower Amazon basin, and M. ternetzi from Orinoco), and is among the most poorly studied groups of Neotropical fishes. In this paper, M. ternetzi and M. macrostoma are redescribed and validated and M. amazonicus is regarded as synonym of M. ternetzi. Also, a new species, M. acangaquara, is described from the lower Amazon.

Whole-rock geochemistry and Sr-Nd isotopic composition of the pre-rift sequence of the Camamu Basin, northeastern Brazil

Whole-rock geochemistry, combined with Sr-Nd isotopic composition of pelitic sedimentary rocks, have been considered to be useful parameters to estimate not only their provenance but also to make inferences about their depositional environment as well as the weathering processes they have been through. The basal sedimentary units of the basins of the northeastern Brazilian continental margin, particularly those of the pre-rift sequence, have been subject of interest of studies based on chemical and isotopic data, since they lack fossil content to establish their age and, therefore, stratigraphic correlations are difficult. The major and trace element contents as well as Sr-Nd isotopic compositions of whole-rock shale samples from five outcrops attributed to the pre-rift supersequence of the Camamu Basin were analyzed with the purpose of characterizing and obtaining further information that would allow a better correlation between the sites studied. The geochemical data suggest that the rocks exposed in the studied outcrops are part of the same sedimentary unit and that they might be correlated to the Capianga Member of the Alianca Formation of the Reconcavo Basin, exposed to the north of the Camamu Basin. The chemical index of alteration (CIA) suggests conditions associated with a humid tropical/subtropical climate at the time of deposition. Nd isotopic compositions indicate provenance from the Paleoproterozoic rocks of the Sao Francisco craton. The results presented here, therefore, show that the combined use of chemical and isotopic analyses may be of great interest to characterize and correlate lithologically homogeneous clastic sedimentary sequences. (C) 2012 Elsevier Ltd. All rights reserved.

An Early Permian Glossopteris flora from the Umrer Coalfield, Wardha Basin, Maharashtra, India

A rich and well-preserved Glossopteris-dominated plant fossil assemblage is described from the Barakar Formation of the Makardhokra and Umrer open-cast projects, Umrer Coalfield, Nagpur District, Wardha Basin, Maharashtra, India. The assemblage includes equisetalean axes, cordaitalean leaves (Noeggerathiopsis hislopii), Gangamopteris clarkeana and diverse Glossopteris leaves and a fertile organ assigned to Scutum sp. cf. S. leslii. The flora, although similar to that of the Barakar Formation of the Damodar Basin complex (the reference basin system with respect to the qualitative and quantitative distribution of Indian Permian plant taxa), exhibits unique characteristics and is Artinskian to Kungurian in age. Besides supplementing knowledge of the broader Wardha Basin flora, this is the first systematic documentation of the Glossopteris flora from the Barakar Formation of this basin.