Fast or slow melting of the Marinoan snowball Earth? The cap dolostone record

The end of the Neoproterozoic era is punctuated by two global glacial events marked by the presence of glacial deposits overlaid by cap carbonates. Duration of glacial intervals is now consistently constrained to 3-12 million years but the duration of the post-glacial transition is more controversial due to the uncertainty in cap dolostone sedimentation rates. Indeed, the presence of several stratabound magnetic reversals in Brazilian cap dolostones recently questioned the short sedimentation duration (a few thousand years at most) that was initially suggested for these rocks. Here, we present new detailed magnetostratigraphic data of the Mirassol d`Oeste cap dolostones (Mato Grosso, Brazil) and ""bomb-spike"" calibrated AMS (14)C data of microbial mats from the Lagoa Vermelha (Rio de Janeiro, Brazil). We also compile sedimentary, isotopic and microbiological data from post-Marinoan outcrops and/or recent depositional analogues in order to discuss the deposition rate of Marinoan cap dolostones and to infer an estimation of the deglaciation duration in the snowball Earth aftermath. Taken together, the various data point to a sedimentation duration in the range of a few 10(5) years. (C) 2010 Elsevier B.V. All rights reserved.

Pleistovultur nevesi gen. et sp nov (Aves: Vulturidae) and the diversity of condors and vultures in the South American Pleistocene

Pleistovultur nevesi, a new genus and species of a large Vulturidae is described from the Upper Pleistocene or beginning of the Holocene, based on a complete and well preserved right tibiotarsus from the Cuvieri cave deposits, one of the hundreds of caves of the Lagoa Santa region in Minas Gerais state, Brazil. Also described here is a distal half of a left tibiotarsus from Gruta dos Brejoes, a cave in Morro do Chapeu, Bahia state, Brazil, which probably belongs to another not-yet-known genus and species of the Vulturidae. The described material, added to prior literature, is proof of the appreciable diversity of the Vulturidae during the Pleistocene in South America.

Cladistic analysis of the suborder Conulariina Miller and Gurley, 1896 (Cnidaria, Scyphozoa; Vendian-Triassic)

Results of a cladistic analysis of the suborder Conulariina Miller and Gurley, 1896, a major extinct (Vendian-Triassic) group of scyphozoan cnidarians, are presented. The analysis sought to test whether the three conulariid subfamilies (Conulariinae Walcott, 1886, Paraconulariinae Sinclair, 1952 and Ctenoconulariinae Sinclair, 1952) recognized in the Treatise on Invertebrate Paleontology ( TIP) are monophyletic. A total of 17 morphological characters were scored for 16 ingroup taxa, namely the genera Archaeoconularia, Baccaconularia, Climacoconus, Conularia, Conulariella, Conularina, Ctenoconularia, Eoconularia, Glyptoconularia, Metaconularia, Notoconularia, Paraconularia, Pseudoconularia, Reticulaconularia, Teresconularia and Vendoconularia. The extant medusozoan taxa Cubozoa, Stauromedusae, Coronatae and Semaeostomeae served as outgroups. Unweighted analysisof the data matrix yielded 1057 trees, and successive weighting analysis resulted in one of the 1057 original trees. The ingroup is monophyletic with two autapomorphies: (1) the quadrate geometry of the oral region; and (2) the presence of a mineralized (phosphatic) periderm. Within the ingroup, the clade (Vendoconularia, Teresconularia, Conularina, Eoconularia) is supported by the sinusoidal longitudinal geometry of the transverse ridges, and the much larger clade (Baccaconularia, Glyptoconularia, Metaconularia, Pseudoconularia, Conularia, Ctenoconularia, Archaeoconularia, Notoconularia, Climacoconus, Paraconularia, Reticulaconularia) is supported by the presence of external tubercles, which, however, were lost in the clade (Notoconularia, Climacoconus, Paraconularia, Reticulaconularia). As proposed by Van Iten et al. (2000), the clade (Notoconularia, Climacoconus, Paraconularia, Reticulaconularia) is supported by the termination and alternation of the transverse ribs in the corner sulcus. The previously recognized subfamilies Conulariinae, Paraconulariinae and Ctenoconulariinae were not recovered from this analysis. The diagnostic features of Conulariinae (continuation of the transverse ornament across the corner sulcus and lack of carinae) and Ctenoconulariinae ( presence of carinae) are symplesiomorphic or homoplastic, and Paraconulariinae is polyphyletic. The families Conulariellidae Kiderlen, 1937 and Conulariopsidae Sugiyama, 1942, also recognized in the TIP, are monogeneric, and since they provide no additional phylogenetic information, should be abandoned.

Araucaria forest dynamics in relation to fire frequency in southern Brazil based on fossil and modern pollen dataf

To elucidate the relationship between forest dynamics and fire frequency pollen percentages and charcoal amounts from a 120 cm long peat core and from samples of modern pollen rain were collected along a transect. The study site in southern Brazil is characterized by a species-rich mosaic of grassland-Araucaria forest. It is of crucial importance for management strategies for conservation to understand the development and maintenance of these vegetation mosaics including their sharp forest-grassland boundaries. During the late Holocene, considerable changes occurred in the area. From Anno Domini (AD) 1360 to 1410, the area was dominated by Campos (grassland) vegetation and fire was very common. From AD 1410 to 1500, Araucaria forest expanded and fire was less frequent. From AD 1500 to 1580, Campos grassland spread and the Araucaria forest ceased its development, apparently due to the increase of fire. From AD 1580 to 1935, after a decrease in fire frequency, Araucaria forest expanded again. From AD 1935 to the present, the Araucaria forest expanded while the Campos area decreased. Fire was very rare in this period. The results indicate a strong interaction of forest expansion, forming a mosaic of Campos and Araucaria forest, and the frequency of fire during the past 600 years. A possible collapse of the indigenous population following the post-Colombian colonization in southern Brazil after about AD 1550 may have caused a great reduction of fire frequency. The introduction of cattle (probably after AD 1780) and the resulting decrease of fire frequency might be the reason for forest expansion. Fire is probably the most important factor controlling the dynamics of the forest-grassland mosaics and the formation of sharp borders between these two vegetation types. (C) 2010 Elsevier B.V. All rights reserved.

Late Quaternary sedimentation in the Paraiba Basin, Northeastern Brazil: Landform, sea level and tectonics in Eastern South America passive margin

Late Quaternary deposits in the northeastern Brazil have been scarcely investigated, despite their relevance to the discussion of the post-rift evolution of the South American passive margin within the context of landform, sea level and tectonic deformation. Sedimentological, stratigraphic and morphological characterization of these deposits, referred as Post-Barreiras Sediments, led to their distinction from underlying Early/Middle Miocene strata. Based on optically stimulated luminescence (OSL) dating, two sedimentary units (PB1 and PB2) were recognized and related to the time intervals between 74.8 +/- 9.3 and 30.8 +/- 6.9 ka, and 8.8 +/- 0.9 and 1.8 +/- 0.2 ka, respectively. Unit PB1 consists of indurated sandstones and breccias either with massive bedding or complex types of soft sediment deformation structures generated by contemporaneous seismic activity. Unit PB2 is composed of massive sands or sands related to structures developed by dissipation of dunes. The present work, focusing on the Post-Barreiras Sediments, discusses landform, sea level and tectonics of the eastern South American passive margin during the latest Quaternary. Non-deposition and sub-aerial exposure related to the Tortonian worldwide low sea level combined with tectonic quiescence followed the Miocene transgression. Tectonic deformation in the latest Pleistocene created space to accommodate unit PB1 in downthrown faulted blocks and, perhaps, also synclines produced by strike-slip deformation. Although deposition of this unit was simultaneous with the progressive fall in sea level that followed the Last Interglacial Maximum, punctuated rises combined with land subsidence led to marine deposition close to the modern coastline. Renewed subsidence in the Holocene gave rise to accommodation of the Post-Barreiras Sediments. Most of unit PB2 was deposited during the Holocene Transgression, but it is not composed of marine sediments, which suggests either an insignificant rise in relative sea level or aeolian reworking of thin transgressive sands. The data presented here lead to a review of the evolution of the South American passive margin based on assumptions of uniform sedimentation and undeformed planation surfaces over a wide coastal area of the northeastern Brazil. (C) 2011 Elsevier B.V. All rights reserved.

Petrogenesis of Upper Paleozoic post-collisional peraluminous leucogranites, Sierra de Ancasti, northwest Argentina

The Santa Rosa and Sauce Guacho plutons are two post-collisional peraluminous Late Devonian to Early Carboniferous leucogranites that intruded the banded schists of the Ancasti Formation. The leucogranites are composed of microcline phenocrysts along with quartz, plagioclase, muscovite, biotite, ilmenite, tourmaline, apatite, monazite and zircon. Their geochemical composition is consistent with S-type granites and mineralogically they belong to MPG granites (muscovite-peraluminous granites). It is proposed that granite magma generation was related to shear zones that concentrated fluids in the metasedimentary crust during a collision or transcurrent tectonics. U-Pb analyses on monazite gave an age of 369.8 +/- 5.3 Ma, while Sm/Nd isotopic data yield epsilon(Nd(t)) values of -5.3 for Sauce Guacho and -5.7 for Santa Rosa indicating crustal provenance. Nd model ages between 1,544 and 1,571 Ma are within the range of magmatic rocks from the Lower Ordovician Famatinian Arc in the Central Sierras Pampeanas.

Related changes in biodiversity, insolation and climate in the Atlantic rainforest since the last interglacial

The long-term Colonia record is located in the Atlantic rainforest domain in Brazil (23 degrees 52`S 46 degrees 42`20 `` W 900 m a.s.l.). The 780 cm long core CO3 provides a coverage of a complete interglacial/glacial cycle for the first time in a neotropical rainforest. Information on the behavior of tropical climates compared to global changes in temperatures indicates specific climate responses in terms of precipitation at these latitudes. Winter extratropical circulation was very active during the last interglacial and most of the glacial. Floristic composition of the rainforest changed several times in each phase of expansion, twice during the interglacial, and three times during glacial episodes. Araucaria was well developed in the area of Sao Paulo until the beginning of the first dry phase of the glacial at ca. 50,000 yr B.P. Changes in insolation controlled the expansion of the rainforest and the tropical hydrological cycle as evidenced by a strong precession signal. However precession had no impact on regional climatic features. The two interglacials (MIS 5e and Holocene) showed completely different patterns attesting to the continuous evolution of the forest. The biodiversity index (Shannon-Wiener Index) remained high during both the interglacial and glacial attesting to the permanence of small patches of rainforest refugia during drier phases. The lowest Shannon-Wiener Indexes were recorded between 23,000 and 12,000 yr B.P. and 40,000 and 30,000 yr B.P. and characterize two marked phases of stress for the rainforest. (C) 2008 Elsevier B.V. All rights reserved.

Lycopodiopsis derbyi Renault from the Corumbatai Formation in the state of Sao Paulo (Guadalupian of Parana Basin, Southern Brazil): New data from compressed silicified stems

Lycopodiopsis derbyi Renault was analyzed on the basis of compressed silicified stems from four Guadalupian outcrops of the Parana Basin (Corumbatai Formation) in the State of Sao Paulo, Southern Brazil. Dichotomous stems have been recorded, and three different branch regions related to apoxogenesis are described. The most proximal region has larger, clearly rhomboidal leaf cushions, with protruding upper edges; the intermediate transitional region also has rhombic leaf cushions, but they are smaller and less elongated than the lower in the same axis; finally, the most distal region reveals only incipient cushions, with inconspicuous infrafoliar bladders; interspersed microphylls were still attached. A well preserved branch representative of this most distal region was sectioned; it has a siphonostelic cylinder similar to that previously described for L derbyi. The cortex, however, shows new traits, such as a short portion of elongated cells between the periderm and the external cortex (or leaf cushion tissue). The stems were apparently silicified prior to their final burial but were probably not transported for long distances. Their final burial may have taken place during storm events, which were common during the deposition of the Corumbatai Formation. These stems are commonly deformed due to compression, mainly because the internal cortical portions rapidly decayed prior to silicification due to their thin-walled tissue, and are therefore not preserved. The common alkalinity of a shallow marine environment such as that in which the Corumbatai Formation was deposited, should mobilize the silica and favors petrifaction. Based on the new data, an emended diagnosis is proposed and a modification of the identification key published by Thomas and Meyen in 1984 for Upper Paleozoic Lycopsida is suggested. (C) 2009 Elsevier B.V. All rights reserved.

Quaternary tectonics in a passive margin: Marajo Island, northern Brazil

Marajo Island is located in a passive continental margin that evolved from rifting associated with the opening of the Equatorial South Atlantic Ocean in the Late Jurassic/Early Cretaceous period. This study, based on remote sensing integrated with sedimentology, as well as subsurface and seismographic data available from the literature, allows discussion of the significance of tectonics during the Quaternary history of marginal basins. Results show that eastern Marajo Island contains channels with evidence of tectonic control. Mapping of straight channels defined four main groups of lineaments (i.e. NNE-SSW, NE-SW, NW-SE and E-W) that parallel main normal and strike-slip fault zones recorded for the Amazon region. Additionally, sedimentological studies of late Quaternary and Holocene deposits indicate numerous ductile and brittle structures within stratigraphic horizons bounded by undeformed strata, related to seismogenic deformation during or shortly after sediment deposition. This conclusion is consistent with subsurface Bouguer mapping suggestive of eastern Marajo Island being still part of the Marajo graben system, where important fault reactivation is recorded up to the Quaternary. Together with the recognition of several phases of fault reactivation, these data suggest that faults developed in association with rift basins might remain active in passive margins, imposing important control on development of depositional systems. Copyright (C) 2007 John Wiley & Sons, Ltd.

A putative gnetalean gymnosperm Cariria orbiculiconiformis gen. nov et spec. nov from the Early Cretaceous of northern Gondwana

Cariria orbiculiconiformis gen. nov. et spec. nov., a gymnosperm with gnetoid characters is described from the upper Aptian Crato Formation of the Araripe Basin in northeastern Brazil. Gross-morphology and anatomical details have been studied and characters have been discussed in respect to various seed plants. Several of these characters fit best with those of Gnetales and their putative fossil allies. However, the fossil plant cannot be assigned to any known extinct or extant group of seed plants in their current circumscription. Stem gross-morphology, xylotomical characters and epidermal features indicate a gnetophytic relationship, whereas characters of the reproductive organs are rather distinct from those found in extant taxa. The reproductive unit of the new taxon represents a triple organ consisting of two dichasial ovulate structures and one median pollen-producing structure containing smooth, monosulcate, boat-shaped pollen in-situ. Each ovulate structure consists of two distinct pairs of bracts, a sterile one at the base and a fertile one forming a terminal orbicular capsule. Stiff processes found in the apex of the ovulate structure may represent micropylar tubes of seeds, as seen in the Bennettitales-Erdtmanithecales-Gnetales group. C orbiculiconiformis gen. nov. et spec. nov. was ans herbaceous or semi-shrub-like plant that may have been adapted to the r-strategy in a stressful environment. (C) 2011 Elsevier B.V. All rights reserved.

Cearania heterophylla gen. nov et sp nov., a fossil gymnosperm with affinities to the Gnetales from the Early Cretaceous of northern Gondwana

Vegetative and fertile shoots of a shrub-like seed plant from the late Aptian Crato Formation of Brazil are described as Cearania heterophylla Kunzmann, Mohr and Bernardes-de-Oliveira, gen. nov. et sp. nov. Anatomical details of the axes, epidermal features and separate ovulate and pollen producing organs indicate the gymnospermous nature of this plant. The vascular tissue of the axes includes tracheids with bordered pits and fiber tracheids. Vegetative shoots comprising at least three branching orders bear opposite-decussately arranged ovate to lanceolate, dorsiventrally flattened, parallelodromous, rather thick leaves that vary tremendously in size. The amphistomatic leaves bear (brachy-)paracytic stomatal complexes arranged in simple longitudinal files. The ovulate structure is interpreted as a terminally attached single globular ovule/seed surrounded by at least five to six lanceolate bracts. A terminally attached pollen-cone like structure grows on a lateral leafy shoot. The unusual character combination may indicate that the fossils belong to a hitherto unknown group with affinities to ephedroid Gnetales. Sterile shoots formerly often described as Podozamites, Nageiopsis or Lilites that are at least partly congeneric with C. heterophylla Kunzmann, Mohr and Bernardes-de-Oliveira, gen. nov. et sp. nov. had a wide geographic distribution during the Early Cretaceous. (C) 2009 Elsevier B.V. All rights reserved.