New petrified forest in Maranhão,Permian (Cisuralian) of the Parnaíba Basin,Brazil

This work presents a new fossil plant-bearing area located in the municipalities of Duque Bacelar and Coelho Neto, Maranhão State, Brazil, recovered from lower Permian (Cisuralian) strata of the Pedra de Fogo Formation, northeastern portion of the Parnaíba Basin. The area comprises more than five exposures with assemblages formed mostly of large gymnosperm woods, a number of them in life-position (reaching up to ∼2.30 m in height and 1.15 m in diameter) and, in lesser degree, of horizontal tree-fern stems (up to 5 m in length), some of them being referable to Psaronius sp. The fossils are recorded in sedimentary beds of continental origin that accumulated in shallow, nearshore areas of large lakes, which eventually were affected by rapid burial episodes generated by non-channelized, high energy fluvial systems. The new fossil assemblages are included within lacustrine rocks placed at the base of the Pedra de Fogo Formation, i.e., Sílex Basal Member, near the contact with the underlying Piauí Formation (Pennsylvanian). This observation contrasts with previous studies at the southwestern portion of the basin, where the stratigraphic position of plant fossils is referred to the upper Pedra de Fogo Formation (Trisidela Member) or even to the overlying Motuca Formation. The new sites currently suffer damage from human activities and require urgent actions in order to protect them. Based on the current laws, some measures of protection for these sites are discussed and proposed herein.     

Palynological and sedimentary analysis of the Igarapé Ipiranga and Querru 1 outcrops of the Itapecuru Formation (Lower Cretaceous,Parnaíba Basin), Brazil

The siliciclastic sediments of the Itapecuru Formation occur in a large area of the Parnaíba Basin and its deposits crop out along the Itapecuru River, in Maranhão State, northern Brazil. The palynological analysis of the Igarapé Ipiranga and Querru 1 outcrops strata yields a rich and diversified data. The presence of index-palynofloras in assemblages allows the identification of the Complicatisaccus cearensis Zone, of Late Aptian-Early Albian age. Terrestrial palynomorphs are abundant in the assemblages, being represented by bryophytes and pteridophytes, especially perisporate trilete spores (Crybelosporites and Perotrilites), and gymnosperms and angiosperms (Afropollis and Elaterosporites). The composition of palynological assemblages suggests the presence of moist soils for both outcrops. Acritarchs were recovered in the Querru 1 outcrop, which suggest a marine setting supporting a tidal flat environment indicated by facies associations. Furthermore, reworked Paleozoic palynomorphs were observed in the Querru 1 outcrop. The microflora from Igarapé Ipiranga outcrop suggests terrestrial environment corroborating with floodplain environment indicated by facies association.     

Carbon- and Oxygen-Isotopic Behavior of Carbonate Rocks of the Phosphatic Gramame Formation,Pernambuco-Paraíba Coastal Basin,Northeastern Brazil

In the basal section of the carbonates of the Maastrichtian Gramame Formation in the Pernambuco-Paraiba coastal basin of northeastern Brazil, major phosphate concentrations (P₂O₅ > 10%) were deposited in shallow-marine environments (inner shelf). In contrast, dolomite-associated phosphates are characterized by low P₂O₅ concentrations (<10%) and were deposited in the relatively deep water of a platform ramp, under conditions of limited oxygen availability. Calcite is the main carbonate phase remaining after the diagenesis that affected the phosphorite. A positive δ¹³C (up to +2%_PDB), coupled with a positive MgO-δ¹⁸0 correlation in the phosphate-enriched carbonates, suggests that upwelling currents were the early phosphogenic vectors during marine transgression, in contrast to warm superficial seawater that prevailed during the Maastrichtian elsewhere. The major phosphate concentrations are related to reworking and diagenesis in a shallow shelf environment during a regression pulse of sea level, followed by a dramatic drop of δ¹³C to negative values (down to ?6%_PDB). This study suggests that carbon and oxygen isotopes can be used as potential tools for phosphorite prospecting elsewhere.     

Discovery of 2Obaichthyidae gars (Holostei,Ginglymodi, Lepisosteiformes) in the Aptian Codó Formation of the Parnaíba Basin: Remarks on paleobiogeographical and temporal range

Here we report the first 2obaichthyid gar from the Lower Cretaceous (Aptian) Codó Formation of the Parnaíba Basin, Northeastern Brazil. It shows the following obaichthyid characters: numerous odontods firmly attached to the outer surface of the dermal bones, free and mobile maxilla, presence of interopercle, lack of contact between the metapterygoid and ectopterygoid, absence of lacrimomaxillary bones, and a prominent spine at the posterior margin of the scales. Due to the presence of scales bearing a prominent ventral posterior spine and a number of additional posterior marginal spines, the fish from the Codó Formation is noticeably the same species found in the Albian Santana Formation of the Araripe Basin, Dentilepisosteus laevis. Although probably restricted to fresh or brackish water, the new discovery adds one more taxon to the assemblages found in the Parnaíba and the Araripe basins. The new record extends the temporal range of this species down into the Aptian (about ∼10 myr older than the previous occurrence).     

The definition of potential infiltration areas in Guaratinguetá watershed, Paraíba do Sul Basin, Southeastern Brazil: an integrated approach using physical and land-use elements

This work describes the methodological approach used for mapping the potential infiltration areas of the Guaratinguetá watershed (160?km²), situated in Southeastern Brazil. The method is considered a qualitative approach, which takes into account thematic maps (geology, pedology, geomorphology, and land use/land cover) and the precipitation spatial distribution. A group of experts in Earth Sciences and Geotechnical Engineering has applied an infiltration potential scale factor that ranges from 5 (highest influence) to 1 (lowest influence). The final infiltration map was produced using several ArcGIS^? tools. The results showed that the most suitable (very high) infiltration areas represent only around 7% of the watershed area, which are associated with smooth and gentle hills, fluvial Tertiary sediments and yellow oxisols. However, growing impacts caused by land farming and urban developments require urgent planning for this region. Areas with high to moderate capacity of infiltration represent around 56% of the watershed and are found in the domain of igneous-metamorphic rocks associated with steep hill-slopes and relatively well-preserved forest fragments. This region requires a land-use strategy, such as reforestation programs, in order to increase the infiltration capacity of the watershed.     

Seasonal variation of particulate heavy metals in the Lower Paraíba do Sul River, R.J., Brazil

 Temporal and spatial variability of particulate metal concentrations (Cu, Cr, Zn, Mn and Fe) were investigated in the lower drainage basin of the Paraíba do Sul River. The results showed that the spatial variability was not important for all the studied metals, however, temporal variations seems to be considerable. In general, two distinct behaviors were observed for particulate heavy metals: (1) metal concentration increase together with water flow (Fe and Cu) and (2) concentration decrease with increasing water flux (Zn, Cr and Mn). The Fe and Cu behavior is probably due to the strong association of these metals with surface runoff, although their sources seem to be distinct. Iron probably originates from the regional soils rich in iron oxides, and Cu is possibly associated to the large-scale use of copper fungicides in the sugar cane plantations. The opposite trend observed for Zn, Cr and Mn probably reflects the importance of the industrial and urban effluents as a secondary source of these elements for the system. Their behavior is probably associated with the dilution effect caused by the input of a suspended matter poor in these metals originated from the surface runoff during the rainy season. Received: 4 March 1998 · Accepted: 30 June 1998     

Correction to: Spatial distribution and estimation of rainfall trends and erosivity in the Epitácio Pessoa reservoir catchment,Paraíba,Brazil

Natural Hazards - The article “Spatial distribution and estimation of rainfall trends and erosivity in the Epitácio Pessoa reservoir catchment, Paraíba, Brazil”, written by da...     

Open carbonate ramp facies,microfacies and paleoenvironments of the Gramame Formation (Maastrichtian), Pernambuco–Paraı́ba Basin,Northeastern Brazil

The monotonous carbonates of the Maastrichtian Gramame Formation can be divided into 11 microfacies, but these do not correspond with the five major facies distinguished in the field. The microfacies were grouped into six composite microfacies which were used to construct a depositional model. In this model, tectonic disturbances of a relatively steeply sloping carbonate ramp caused apparently random occurrences of coarser and sandier bioclastics and influx of clastic material into generally mid-outer-ramp environments. Only the central section of the carbonate ramp is exposed in a strike section. Shallower and deeper facies must be inferred from the transgressive nature of the sequence. Dolomitization is ubiquitous but apparently random. The closest modern analogy of the Gramame Formation is the relatively steep West Florida ramp. However this does not have fault-bounded shallows, for which analogies can be found on the shelf of the Arabian Gulf. Combining features from both of these allows a plausible reconstruction to be made of Gramame Formation environments. We envisage a steeply sloping ramp cut by horsts and grabens related to the opening of the south Atlantic ocean.     

Spatial distribution and estimation of rainfall trends and erosivity in the Epitácio Pessoa reservoir catchment,Paraíba,Brazil

Natural Hazards - The main goals of this study are to better understand the spatial and temporal variabilities in rainfall and to identify rainfall trends and erosivity for the period from 1963 to...     

Age and correlations of the Siluro‐Devonian strata in the Yass Basin,New South Wales

An early Ludlovian (early eβ1) to early Gedinnian (early eγ) age is assigned to the Cliftonwood Limestone—Elmside Formation strata of the Yass Basin, New South Wales. Several Australian sequences are correlated with the Yass Basin succession.     

High-Pressure Metamorphosed Fe-Ti Ore-Hosting Island-Arc Tholeiites at Itatuba (Paraíba) as an Indication of a Proterozoic Suture in the Pajeú-Paraíba Fold Belt,Borborema Province,Northeastern Brazil

Petrological investigations on metamafic rocks and three associated Ti-Fe occurrences from Itatuba in the state of Paraíba are reported. The rocks analyzed here are part of a Proterozoic gneissic-migmatitic complex that includes some marble intercalations.

Microtextural relations support a complex metamorphic evolution of three stages. A first stage, reflecting eclogitic conditions, is indicated by the lack of primary plagioclase in relics of garnet pyroxenite, with symplectitic intergrowths of pyroxenes and/or amphibole and secondary piagioclase replacing garnets and primary pyroxene, ostensibly omphacite. A second event at granulitic conditions is represented by the paragenesis of garnet-clinopyroxene-plagioclase. Equilibrium textures between hornblende-plagioclase are typical for the third stage under amphibolite-facies conditions. Mineral chemistry of the clinopyroxene-garnet pairs suggests equilibrium conditions in the range of 726° to 1185°C and 4.8 to 8.2 kb, established during the granulitic and amphibolitic stages of the metamorphic evolution. The chemical composition of the metamafic rocks reveals a tholeiitic basaltic composition.

Discriminant diagrams and spiderdiagrams based on rare-earth and trace elements (K, Rb, Ba, Sr, Ti, Zr, U, Th, Ta, V, Co, and Ni) suggest an island-arc tholeiitic character. The differentiation and fractionation of this tholeiitic melt generated the mafic protoliths, culminating with the formation of the Fe-Ti ore. This magma supposedly was generated from mantle below a subduction zone.     

Spatiotemporal variability of vegetation due to drought dynamics (2012–2017): a case study of the Upper Paraíba River basin,Brazil

Natural Hazards - Vegetation indices have been widely used for monitoring the spatiotemporal variables of vegetation and characterizing droughts, primarily in semiarid regions. Drought is a...     

Palynostratigraphy of two Neogene boreholes from the northwestern portion of the Solimões Basin,Brazil

Palynological studies in large basins yield the most significant results for understanding basinal and continental evolution. We selected the Solimões Basin in the upper reaches of the Amazon River as our study site due to the availability of drill cores in this jungle-covered terrain. The purpose of this paper is contribute to the palynological knowledge and to evaluate the palynostratigraphic schemes of Venezuelan (LM sheme) and Colombia (Jea sheme) applied for large basin situated in the Amazon jungle. Taxonomic studies of the analysed samples indicate a significant presence of Grimsdalea magnaclavata, suggesting both cores represent the Mio-Pleistocene Solimões and Iça Formations. These results are integrated and correlated with previously collected data for the entire basin, Venezuelan and Colombia. The ages attributed to the Miocene intervals of the boreholes studied vary according to the palynostratigraphic scheme. According to the biostratigraphy based on data from Venezuelan (LM sheme), the borehole 1AS-51-AM presents range in Early Miocene–Early Pliocene and from Middle Miocene–Early Pliocene in 1AS-52-AM. When the data from Colombia (Jea sheme) is used, the ages range from the Middle Miocene–Late Miocene in both boreholes. The differences between the results of two biostratigraphic schemes indicate the existence of distinct stratigraphic arrangements recorded in palynoflora of the Brazilian Amazon.     

Stratigraphic correlation of the Devonian sequence in the Blantyre Sub-basin,Darling Basin,western New South Wales∗

Seismic sections and the analysis of lithostratigraphic units from well-log data were used to develop a new stratigraphic correlation of the Winduck, Snake Cave and Ravendale Intervals for the Blantyre Sub-basin. The stratigraphic boundaries of the intervals were defined at marked changes in well-log characteristics, and depth estimates of the boundaries were derived from the well-log data in Mt Emu 1, Blantyre 1 and Kewell East 1. Six seismic-stratigraphic boundaries have been identified in the seismic sections to show the continuity of the latest Silurian to Holocene sediments throughout the Blantyre Sub-basin; from bottom to top they are: H-1, base of the Winduck Interval; H-2, base of the Snake Cave Interval; H-3, base of the Ravendale Interval; H-4/5 base of the undifferentiated Upper Carboniferous/Permian sediments; and H-6 base of the undifferentiated Cenozoic sediments. All stratigraphic boundaries are based on good continuous markers, with strong amplitudes throughout the whole sub-basin. A three-dimensional geological model was developed from the seismic data to map out the geometry of the key reflectors, and hence the structure and stratigraphy of the Winduck, Snake Cave and Ravendale Intervals in the areas where these intervals have been preserved. This model has better defined the Wilcannia High and two smaller highs around the Mt Emu 1 and Snake Flat 1 wells, and further defines the relationships between the stratigraphy, sub-basin geometry and development of complex structures in the Blantyre Sub-basin.     

The role of gravitational collapse in controlling the evolution of crestal fault systems (Espírito Santo Basin,SE Brazil)

A high-quality 3D seismic volume from offshore Espírito Santo Basin (SE Brazil) is used to assess the importance of gravitational collapse to the formation of crestal faults above salt structures. A crestal fault system is imaged in detail using seismic attributes such as curvature and variance, which are later complemented by analyses of throw vs. distance (T-D) and throw vs. depth (T-Z). In the study area, crestal faults comprise closely spaced arrays and are bounded by large listric faults, herein called border faults. Two episodes of growth are identified in two opposite-dipping fault families separated by a transverse accommodation zone. Statistical analyses for eighty-four (84) faults show that fault spacing is < 250 m, with border faults showing the larger throw values. Fault throw varies between 8 ms and 80 ms two-way time for crestal faults, and 60–80 ms two-way time for border faults. Fault length varies between ∼410 m and 1750 m, with border faults ranging from 1250 m to 1750 m. This work shows that border faults accommodated most of the strain associated with salt growth and collapse. The growth history of crestal faults favours an isolated fault propagation model with fault segment linkage being associated with the lateral propagation of discrete fault segments. Importantly, two episodes of fault growth are identified as synchronous to two phases of seafloor erosion, rendering local unconformities as competent markers of fault reactivation at a local scale. This paper has crucial implications for the understanding of fault growth as a means to assess drilling risk and oil and gas migration on continental margins. As a corollary, this work demonstrates that: 1) a certain degree of spatial organisation occurs in crestal fault systems; 2) transverse accommodation zones can form regions in which fault propagation is enhanced and regional dips of faults change in 4D.     

Correction to: Spatiotemporal variability of vegetation due to drought dynamics (2012–2017): a case study of the Upper Paraíba River basin,Brazil

Natural Hazards - This correction stands to support the updating of the original article for changing the name Glauciene Justino Ferreira to Glauciene Justino Ferreira da Silva. The author group...     

Tectono-stratigraphic evolution of the Upper Jurassic–Neocomian rift succession,Araripe Basin,Northeast Brazil

The rift succession of the Araripe Basin can be subdivided into four depositional sequences, bounded by regional unconformities, which record different palaeogeographic and palaeoenvironmental contexts. Sequence I, equivalent to the Brejo Santo Formation, is composed of fluvial sheetflood and floodplain facies association, while Sequence II, correspondent to the lower portion of the Missão Velha Formation, is characterised by braided fluvial channel belt deposits. The fluvial deposits of Sequences I and II show palaeocurrents toward SE. The Sequence III, correspondent to the upper portion of Missão Velha Formation, is composed of fluvial sheetflood deposits, which are overlain by braided fluvial channel deposits displaying a palaeocurrent pattern predominantly toward SW to NW. Sequence IV, equivalent to the Abaiara Formation, is composed of fluvio–deltaic–lacustrine strata with polimodal paleocurrent pattern. The type of depositional systems, the palaeocurrent pattern and the comparison with general tectono-stratigraphic rift models led to the identification of different evolutionary stages of the Araripe Basin. Sequences I, II and III represent the record of a larger basin associated to an early rift stage. However, the difference of the fluvial palaeocurrent between sequences II and III marks a regional rearrangement of the drainage system related to tectonic activity that compartmentalised the large endorheic basin, defining more localised drainage basins separated by internal highs. Sequence IV is associated with the renewal of the landscape and implantation of half-graben systems. The high dispersion of palaeocurrents trends indicate that sedimentary influx occurs from different sectors of the half-grabens.     

Conodont biostratigraphy and paleoecology of the marine sequence of the Tapajós Group,Early-Middle Pennsylvanian of Amazonas Basin,Brazil

This study was undertaken in the south and western regions of the Amazonas Basin to describe the conodont biostratigraphy and paleoecology of Pennsylvanian carbonate rocks of the marine portion of the Tapajós Group comprising the upper Monte Alegre, Itaituba, and lower Nova Olinda formations.The analyzed area includes one outcrop along the Tapajós river (TAP), two carbonate quarries (QI, QII), and 18 wells (dots 1–18). The conodont fauna is dominated by Idiognathoides sinuatus and Neognathodus symmetricus in the Monte Alegre Formation, followed by Idiognathodus incurvus, Diplognathodus coloradoensis and Neognathodus bassleri in the Itaituba and Nova Olinda formations. The conodont association suggests an Early to Middle Pennsylvanian age to the analyzed section. Relative ages attributed to the three lithostratigraphic units using conodonts, palynomorphs, and foraminifers are consistent.Herein are proposed one local taxon-range zone of Idiognathodus incurvus in the Itaituba and lower part of the Nova Olinda Formation and one local taxon-range subzone of Diplognathodus coloradoensis in the Itaituba Formation, suggesting a late Bashkirian – Moscovian (Atokan – early Desmoinesian) age to these strata.The Itaituba Formation marks the establishment of large Pennsylvanian marine conditions in the Amazonas Basin and is composed primarily of marine carbonates of abundant fossil content, tidal flat evaporites and siliciclastic thin intervals. Its lower limit, with the Monte Alegre Formation, is characterized by the predominant occurrence of fluvial-deltaic sandstones superimposed on an extensive sequence of aeolian sandstones, siltstones and shales intercalated with the interdune and lakes. From the upper strata of Itaituba Formation the faunal and lithological characteristics indicate the occurrence of a regressive phase culminating in a restricted environment, arid which indicates the Nova Olinda Formation. This is characterized by the occurrence of evaporites increasingly abundant to the top of carbonates, also shales and siltstones intercalated with the sabkha plain. The carbonate strata have similar marine fossils to those of Itaituba Formation, however, the fauna becomes impoverished in abundance and diversity. The conodont fauna of Early-Middle Pennsylvanian of Amazonas Basin suggests similarities of species with the North American Midcontinent region and the Illinois Basin indicating their probable cosmopolitism; however in a slightly different paleogeographic context, probably due to latitudinal differences, coal deposits are present in North America, whereas widespread evaporitic deposits are registered to the Tapajós Group, Amazonas Basin.     

The chemical composition of specular hematite from Tilkerode, Harz, Germany: implications for the genesis of hydrothermal hematite and comparison with the Quadrilátero Ferrífero of Minas Gerais, Brazil

The black shale-hosted selenide vein-type deposit at Tilkerode, eastern Harz, Germany, has specular hematite enclosed in clausthalite (PbSe). The specular hematite has Ti and V in amounts of up to ～1 wt.% TiO₂ and ～3 wt.% V₂O₅, and subordinate, but important, contents of Mo (22–372 ppm) and B (up to 68 ppm). The Tilkerode hematite serves as a reference for hydrothermal hematite formed at relatively low temperatures (<150 °C). The composition of the Tilkerode hematite is compared with that of two generations of specular hematite from itabirite-hosted iron-ore deposits in the Quadrilátero Ferrífero of Minas Gerais, Brazil. The first generation of specular hematite represents an early tectonic hematitisation of dolomitic itabirite at Águas Claras and occurs as fine-grained crystals. Reconnaissance data indicate that the Águas Claras hematite is poorer in Ti and V, relative to the Tilkerode hematite, but has ～5–10 ppm B and ～7–11 ppm Li. The second generation of specular hematite defines the pervasive tectonic foliation of the Gongo Soco iron ore. This hematite has Ti contents of up to ～2 wt.% TiO₂ and subordinate amounts of V (62–367 ppm); its B and Li concentrations are mostly below <2 ppm B and <1 ppm Li. The presence of Ti and B in the Tilkerode hematite can be explained by highly saline, B-bearing fluids that were capable of mobilising otherwise immobile Ti. The Mo signature of the Tilkerode hematite suggests that Mo was derived from the host black shale. In Minas Gerais, B and Li were incorporated into the early tectonic hematite from saline fluids at relatively low temperatures (Águas Claras) and then released during metamorphic hematite growth at higher temperatures, as suggested by the foliation-defining hematite without B–Li signature (Gongo Soco).     

Absolute Dating of Permian Ash-Fall in the Rio Bonito Formation,Paraná Basin,Brazil

The Rio Bonito Formation in southern Paraná basin contains a set of tonsteins interbedded with coal-seams. These tonsteins are composed mainly of kaolinite with zircon, apatite and beta-quartz paramorphs as accessory minerals, and were interpreted as volcanic ashes deposited by ash falls over pits protected by barrier islands in a barrier-lagoon system. A U-Pb dating of zircons in the tonstein A, which furnished an age of 267.1 ± 3.4 Ma (Early Permian) confirming previous age-dates based on palynology and correlating them with one of the main periods of volcanic activity in the Gondwana.The source of the pyroclastic material was attributed to the early Permian Choiyoi magmatic arc in Argentina, developed during the Sanrafaelic orogeny, and with a main peak of volcanic activity between 260 and 272 Ma.