Ferruginous Crust Research Articles

Firmgrounds and hardgrounds in the Coniacian carbonate platform of the Iberian basin: Origin and model for development of omission surfaces in tidal environments

Distinctive erosional and omission surfaces occur at several stratigraphic levels in the tidal carbonates of the 3rd-order Coniacian sequence (Iberian Basin). They are ancient analogs of omission surfaces developed on lithified carbonates in subaerial and coastal settings. Omission surfaces consist of (i) firmground Glossifungites ichnofacies (Balanoglossites-Thalassinoides); and (ii) hardground Trypanites ichnofacies (scalloped and planar surfaces and Gastrochaenolites-Entobia surfaces). Firmgrounds are also related to erosion or ferruginous crusts. Hardground surfaces are related to bioerosion, dissolution and physical erosion. Grain size and textural features in Balanoglossites and Thalassinoides firmground surfaces are essentially the same, suggesting that even bathymetry could be similar. Several stages in hardgrounds consist of different, scalloped or planar surfaces related to bioerosion, dissolution and physical erosion. Gastrochaenolites-Entobia borers represent a major change in the trace fossil associations and imply different processes in their origin, being originated at slightly different depths with Gastrochaenolites representing shallower environments. The studied field sections display a cyclicity on the scale of meters that tentatively reflects the presence of 4th-order parasequence sets. Two kinds of sedimentary discontinuities have been used for correlation: omission surfaces and ferruginous crusts representing regional sea level falls and rises. Part of the described surfaces does not appear to have been previously recognized in older carbonate deposits. Their common presence of similar surfaces along modern coasts and in karst terrains, as well as their abundance in the Coniacian sequence, suggests that they might also be abundant in the geologic record in other sedimentary basins for defining palaeoshorelines.

Enhancing iron biogeochemical cycling for canga ecosystem restoration: insights from microbial stimuli.

The microbial-induced restoration of ferruginous crusts (canga), which partially cover iron deposits and host unique ecosystems, is a promising alternative for reducing the environmental impacts of the iron mining industry. To investigate the potential of microbial action to accelerate the reduction and oxidation of iron in substrates rich in hematite and goethite, four different microbial treatments (water only as a control - W; culture medium only - MO; medium + microbial consortium - MI; medium + microbial consortium + soluble iron - MIC) were periodically applied to induce iron dissolution and subsequent precipitation. Except for W, all the treatments resulted in the formation of biocemented blocks. MO and MI treatments resulted in significant goethite dissolution, followed by precipitation of iron oxyhydroxides and an iron sulfate phase, due to iron oxidation, in addition to the preservation of microfossils. In the MIC treatment, biofilms were identified, but with few mineralogical changes in the iron-rich particles, indicating less iron cycling compared to the MO or MI treatment. Regarding microbial diversity, iron-reducing families, such as Enterobacteriaceae, were found in all microbially treated substrates. However, the presence of Bacillaceae indicates the importance of fermentative bacteria in accelerating the dissolution of iron minerals. The acceleration of iron cycling was also promoted by microorganisms that couple nitrate reduction with Fe(II) oxidation. These findings demonstrate a sustainable and streamlined opportunity for restoration in mining areas.

Ferralsols and plinthosols derived from the degradation of crusts of the Serra dos Martins formation in the brazilian semiarid region

In a landscape characterized by etchplanation under a semi-arid climate, with summits formed by mesetas and ferruginous crusts, found in the states of Paraíba and Rio Grande do Norte, Brazil, there is pedogenesis of Ferralsols (meseta cores) and Plinthosols (meseta edges). This research aims to characterize soils derived from the alteration of the ferruginous crust of the Serra dos Martins Formation. The studied soils were cataloged in the municipalities of Areia, Bananeiras, and Cuité, involving the examination of six soil profiles: Umbric Xanthic Ferralsol (P1), Petric Xanthic Ferralsol (P2), Petric Xanthic Ferralsol (P3), Haplic Petric Plinthosols (P4), Haplic Petric Plinthosols (P5), and Haplic Petric Plinthosols (P6). These were described and classified according to the WRB/FAO, with a focus on macromorphology. The Ferralsols vary from deep to moderately deep, are chemically poor, kaolinitic, and exhibit intense biological activity. The Plinthosols (P1, P2, and P3) feature A horizons with a granular structure and concretionary FA horizons (petric). These characteristics reflect the complexity and diversity of the soils of the Serra dos Martins Formation.

In situ assessment of terrestrial gamma radiation dose and associated radiological hazards in Katsina State, Nigeria

ABSTRACT Terrestrial gamma radiation dose (TGRD) rates were measured in situ from different locations in Katsina State, Nigeria, using a portable radiation survey metre based on geological formations and soil types. The measured TGRD rates ranged from 45 to 271 nGyh–1 with an average value of 116 ± 1 nGyh–1. Geological formation (silicified sheared rock) and soil type (lithosols and ferruginous crusts and ferruginous tropical soils) appeared to have the highest mean TGRD values of 163 and 134 nGyh–1 with sandstone geological formation and alluvial and hydromorphic soils having the lowest TGRD with values of 80 and 61 nGyh–1, respectively. One way ANOVA results shows that the tested null hypothesis was rejected. Thus, indicating that there exists a strong relationship between the various geological formations, soil types with the measured TGRD values based on the alternate hypothesis. Human health hazard indices like annual effective dose equivalent (AEDE), lifetime outdoor annual equivalent dose, and relative excess lifetime outdoor cancer risk associated with the mean TGRD of the study area were also calculated and found to be 0.711, 9.955 mSv, and 5.79 × 10–4, respectively. These values were higher than the world average values but favourable compared with the safety limits recommended by ICRP.

MINERALOGIA E ASPECTOS GEOQUÍMICOS DOS LATERITOS FOSFÁTICOS DA ILHA PEDRA GRANDE DO GURUPI (PA)

The Pedra Grande Island located at the mouth of the Gurupi River, is equivalent to a small plateau, which is currently partially drowned by the sea, where the impacts of the waves have already left longitudinal fractures and caves on the island. The island is entirely made up of lateritic rock, represented by the ferruginous lateritic crust, exhibiting a dominantly brownish red coloration. Texturally it consists of nodules, pisoliths and pseudo-fragments, which are surrounded by a whitish cream cement, giving the rock a general brechoid appearance, in addition to columnar and cavernous features. Two mineralogical associations are individualized in these laterites: a group formed by iron and calcium phosphates, widely developed in the ferruginous lateritic crust, together with iron oxy-hydroxides; and another formed by the aluminous phosphates, which constitute the whitish cream phosphate cement. The quantification of major, minor and trace elements revealed high contents of Fe2O3, P205 and A1203, and low of SiO2. In terms of traces, Mn and Zn display low contents, associated with ferruginous lateritic crust. On the other hand, rare earth elements are more concentrated in phosphate cement, mainly in Ce, Nd and La. The Ilha de Pedra Grande do Gurupi exhibits some mineralogical and chemical similarities with other occurrences of lateritic phosphates in the region, located on the continent. This correlation reveals that in the recent geological past, the ocean coastline presented a very different morphology from the current one. The geochemical and mineralogical analyzes of the Pedra Grande laterites allow us to suppose that this lateritic profile developed under a tropical climate and semi-flat topography, enriching itself in phosphorus from a phosfor-bearing parent rock, which could have the following characteristics: a clayey rock, with of shales, carbonates and phosphorites, or even a low-grade metamorphic rock, composed of schists and phyllonites containing phosphorite levels. Keywords: ferruginous crust; breccia like rocks; duphrenite; mitridatite; crandallite.

Zamites (Bennettitales) from the Minjur Formation (Norian) of Saudi Arabia – a unique record from the Late Triassic palaeotropics of Gondwana

ABSTRACT Late Triassic plant macro-remains are extremely rare in an equatorial belt stretching across the North of Gondwana from northern South America to Arabia. Located between the Laurussian floral province to the North and the Gondwana floral province to the South, this large area, is almost entirely lacking palaeobotanical data. Thus, this region is of special interest to our knowledge of Late Triassic floral provincialism and plant distribution. Based on impressions from ferruginous crusts, the first record of identifiable plant macro-remains from the Late Triassic (Norian-Rhaetian) Minjur Formation is described, as belonging to the bennettitalean taxon Zamites aff. persicus. This new finding at least tentatively supports palynological data, which indicated similarities between the Late Triassic (Norian) palynoflora of the Minjur Formation of the Arabian Peninsula on the southern shores of the Tethys and the Norian palynoflora of Iran, during this time located in the northern part of the Tethys.

Quaternary ironstones in the Xingu River, eastern Amazonia (Brazil)

AbstractUsing a multimethod approach, including polarized light microscopy (PLM), scanning electron microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS), SEM with mineral liberation analyzer (MLA), X-ray diffraction (XRD), and Raman spectroscopy, we examined sub-recent ferruginous crusts in the Xingu River in the Amazon Basin that have formed since the Early Pleistocene (<1.2 Ma), as indicated by (U-Th)/He dating of goethite. Although now preserved as goethite, the size and form of the smallest components of the ironstone (nanorods) and the nature of isomorphic substitution in the goethite point to very early transformation of the original precipitate, an unstable hydrous ferrous oxide (HFO) mineral, into goethite. The fine, multiply undulating laminae of the ironstone contain abundant filamentous microbial molds and casts that together support identification of the crusts as ferruginous microbialites and suggest a role of bioinduction/bioinfluence in ironstone precipitation, although inorganic precipitation is also evident. The Xingu Quaternary ironstones are the first evidence of ferruginous microbialite in a modern freshwater system in South America and may hold clues to the recent history of the Xingu River.

Microfacies and composition of ferruginous beds at the platform-foreland basin transition (Late Albian to Turonian Natih Formation, Oman Mountains): Forebulge dynamics and regional to global tectono-geochemical framework

Two forebulge successions exist in the Oman Mountains at the platform-foreland basin transition between the Late Albian to Turonian Natih Formation and the foreland basin shales of the Late Cretaceous Muti Formation. Forebulge creation is suggested by limestone microfacies analyses and analyses of ferruginous crusts and oolites, showing rapid changes in bathymetry and relative sedimentation rate. Each succession displays basal shallow subtidal limestone, passing upward directly to ferruginous crusts and then to Fe-rich oolites deposited in shallower and agitated water. Each succession is topped by clayey layers. Microfacies and lithological evolution of the two successions are alike, suggesting repetitively similar depositional and tectonic conditions. As both sequences occur at the same site, lateral forebulge migration possibly did not occur, suggesting an overall stationary vertical and stepwise forebulge development. The compositional evolution of the ferruginous crusts was complex and includes postdepositional diagenetic effects of the rocks. Both ferruginous crusts once consisted of iron sulfides, implying at least slightly reducing conditions during their formation, associated with water-deepening events. Both oolite levels contain chlorite, hematite, quartz, calcite and apatite. They also contain fragments of chlorite and hematite as nuclei, suggesting that these fragments derived from preexisting ferruginous crusts. Iron oxyhydroxides and clinochlore within the oolites reflects bathymetric changes to more oxidizing aqueous conditions, associated with water-shallowing events. Fe-rich anoxic to sub-oxic sea water of the marine foreland basin was the source for the crusts and oolites which coincided with a high rate of global Cretaceous ocean crust production and related hydrothermalism as well as the regional proximity of an active spreading axis. Fe was probably stabilized in ocean water as organic Fe complexes and Fe colloids.

Statistical analysis of terrestrial gamma radiation dose rates in relation to different geological formations and soil types of Katsina State, Nigeria

ABSTRACT Terrestrial gamma radiation is the major source of outdoor radiation exposure to human being. Because of the variation of underlying geological characteristics of surface soil, the terrestrial gamma radiation dose (TGRD) rates vary significantly with the soil type. This work performed in situ measurements of the TGRD rate for a range of geological formation and soils of Katsina State, Nigeria by using a portable hand-held radiation survey metre, RADOS. The TGRD rates ranged between 45 and 271 nGyh−1 with an overall mean value of 116 nGyh−1, which is two times higher than the world average value of 59 nGyh−1. Geological formation (Silicified sheared rock) was found to have the highest mean TGRD value of 163 nGyh−1. Likewise, soil type (lithosols, ferruginous crusts and ferruginous tropical soils) appeared to have the highest mean TGRD value of 134 nGyh−1. One-way ANOVA was used to investigate the variation of the significant difference between the geological formations and soil types with TGRD, which shows the influence of geological formation and soil types on the measured TGRD values of the study area. Measured data could further be used to evaluate the public radiation exposure and in formulating safety standards and radiological guidelines.

New data on geology of the Rybalsky Quarry, unique object of geological heritage of Global Significance


 
 
 Among the great variety of geological relics of Ukraine, one of the most attractive is the Rybalsky Quarry, located in the city of Dnipro, and well known outside Ukraine. First of all, it is famous for the Mandrykivski Layers exposed in one of the ridges of the Quarry back in the 1970s, although there are many other important peculiarities of the geological structure of the Quarry which attract scientists from Ukraine, Germany, France, Netherlands, Russia and other countries. There are full data on the history of discovery and survey of the Mandrykivski Layers from their discovery by Valerian Domger in 1882 to current studies that reveal various aspects of geological structure of the Quarry, the results of study of different groups of fossil fauna, compare them with the fauna of the Paris Upper Eocene basin and other well- known locations. Particularly in the Rybalsky Quarry, thanks to the author`s efforts, the Layers received the status of “layers with geographic name”, as confirmed by the decision of Cenozoic Commission of the National Stratigraphic Committee of Ukraine in 2001. New fragments of the section of subaerial and subaqueous deposits of the Quaternary deposits were found and their composition, structure and complete stratigraphic content were studied. The research allows us to consider it typical for the Middle Prydniprovia. Fluvioglacial and lake-glacial deposits of the Dnipro glaciations in the Quarry exposed for the second time in 25 years, but this is the first time when their genetic origin, position in the section and lithological-facies peculiarities were determined. Thick layer of sands embedded on the roof of the Mandrykivski Layers were identified to the fifth or Hadzhybeiska terrace of the Dnipro, in the upper part of which there were notable siliceous-clayey-ferruginous formations or lateral crust (ferruginous crusts). The studies of the layer of brown-green and red-brown clays in the roof of the Mandrykivski layers allows us to presume their marine origin. In this case, they are underwater weathering crust (terra rossa) developed in the process of halmyrolysis or are the product of dissolution of carbonate silt enriched with detritus of mollusks, corals and other inhabitants of the warm Mandrykivske Sea.
 
 

Early and Middle Jurassic tectonically controlled deposition in the High-Tatric succession (Tatricum), Tatra Mountains, southern Poland: a review

The High-Tatric succession of the Tatra Mountains represents the Tatricum domain of the Central Western Carpathians, which in the Jurassic was located on the southern margin of the incipient and expanding Vahic Ocean – a branch of Western Tethys. This paper describes the various depositional consequences of extensional tectonic activity as it impacted on sedimentation in the High-Tatric succession of the Tatra Mountains during the Early and Middle Jurassic. Evidence of such impacts on depositional style and facies development are present within the Dudziniec, Smolegowa and Krupianka formations, in all the High-Tatric tectonic units. These impacts also include erosional surfaces and sedimentary gaps separating particular formations, commonly associated with minor angular unconformities. The Lower Jurassic, pre-Bajocian, Dudziniec Formation of the Kominy Tylkowe (autochthonous) Unit is developed in mixed carbonate-clastic facies. The occurrence and proportion of sand-dominated and carbonate-dominated facies, as well as their thickness differences, were controlled by syndepositional tilt-block tectonics, taking place both in depositional and in neighbouring source areas. The Smolegowa and Krupianka formations (Bajocian–Bathonian) occur in all High-Tatric tectonic units, but in the Czerwone Wierchy and Giewont units they are represented mainly by laterally discontinuous bodies of crinoidal limestone of very limited thickness. The preservation of these deposits only in some areas, as well as their thickness reductions, are effects of differentiated subsidence and uplift of isolated blocks taking place in an extensional regime. Moreover, the Krupianka Formation abounds in condensed facies with ferruginous crusts and stromatolites – a feature characteristic of rapidly drowning ocean margins. Deposits of the Dudziniec, Smolegowa and Krupianka formations are also preserved as infills of extensive systems of neptunian dykes penetrating mainly the Triassic substrate, which is yet another classic symptom of synsedimentary extension. The dominant influence of tectonics on sedimentary development ceased with the onset of deposition of the Raptawicka Turnia Formation in the Callovian.

Mineralogy and geochemistry of a bauxite-bearing lateritic profile supporting the identification of its parent rocks in the domain of the huge Carajás iron deposits, Brazil

A bauxite-bearing lateritic profile, developed along a borehole within the supergenic Fe-deposits of the Carajás Mineral Province in Brazil, is investigated after its textural aspects, mineralogy, and geochemistry. Petrographic studies, XRD mineralogical analysis, SEM-EDS, and whole-rock chemistry were used to study selected samples. The 156 m depth borehole is composed of basaltic andesite at the substratum and an overlying lateritic profile well-structured in distinct horizons, from base to top composed of: a saprolite, with rock relicts within a clayey matrix of mainly vermiculite and kaolinite; a clayey horizon dominated by kaolinite; a bauxitic horizon with gibbsite as the main phase; a ferruginous crust mainly composed of hematite and goethite. XRD mineralogical quantifications indirectly confirmed the chemistry of Si, Al, Fe, and Ti, as the most abundant elements in the lateritic horizons. Statistical factor analysis of the whole chemistry and mass balance calculations showed groups of elements arranged according to their enrichment or depletion character in the distinct horizons. Si, Ca, Na, and K are leached out to the top of the profile following the destabilization of their carrier mineral phases feldspar, hornblende, and clinochlore, whereas Al, Fe, and Ti are enriched to the upper horizons, respectively in the structure of gibbsite, hematite/goethite, and anatase. The basaltic andesite at the substratum has its parental affinity confirmed after textural changes, REE normalized patterns, and Zr/Ti ratios throughout the profile, nevertheless, parent rock variations are expected. The studied lateritic profile is comparable to most of the bauxite-bearing laterites in the Amazon region, except for its unparalleled 22 m thick Fe-rich bauxitic horizon and absence of a truncating clay cover on the top of the profile. The lateritic sequence was probably formed during the Paleocene-Eocene bauxitization event that reached the Amazon region and survived as a complete unaltered fossil lateritic profile through the time.

Trace metals in Rio Doce sediments before and after the collapse of the Fundão iron ore tailing dam, Southeastern Brazil

The collapse of the Fundão Dam, in Southeastern Brazil, caused about 50 million m³ of iron ore tailings to sluice down the mountain to Rio Doce, in what is considered the greatest environmental disaster in Brazilian history. The fluvial system received an intense and sudden mudflow that was transported for more than 650 km, before reaching the Atlantic Ocean. Because the area was already impacted by the mineral activities in the region, it becomes essential to evaluate the environmental conditions before the disaster to correctly assess the disaster real damage. This study compares the concentration of trace metals in the sediments of the Rio Doce alluvial plain, before and after the dam collapse, as well as the newly deposited iron ore tailings that became part of the sedimentary framework. The data indicate that the fine particles deposited have since been incorporated into the sandy river sediments. The cadmium and arsenic contents in the sediments increased to levels above the National Environment Council thresholds. The comparison between the levels of trace metals in the situations before and after disaster shows that the mining mud is the source of cadmium while the arsenic was present before the environmental disaster, and its concentration increased due to sediment remobilization. The iron ore tailings deposited on the alluvial sediments also affected the physical parameters since the formed ferruginous crusts waterproofed the ground surface and may, gradually, release toxic metals when exposed to weathering and river reworking.

Geology and structural control of the Cutia Prospect, Serra Leste, Carajás Mineral Province, Pará, Brazil / Geologia e controle estrutural do Garimpo Cutia, Serra Leste, Província Mineral de Carajás, Pará, Brasil

The Cutia Prospect is an occurrence of gold located at the Serra Leste, Carajás Mineral Province. This occurrence is related to magnetite/hematite breccia zones, hosted by hydrothermally altered metavolcano-sedimentary rocks in contact wich felsic ignous rock. The contact has a structural control and hosts oxidized quartz veins and mineralized siliceous breccias. This structure has features of a shear zone with characteristics of a brittle-ductile environment, showing a high degree of maturity, represented by breccias and faults, anastomosed foliation and porphyroclast deformation with the formation of kinematic indicators. Structures such as ruptured and rotated layers, tension gashes, well developed foliation and high angle are evidence of a transcurrent shear zone. Exploration activities in the area allowed to verify that the gold was removed from a transition zone of a gossanic sequence where the oxidized zone of the gossan comprises a superficial ferruginous crust.

Geochemistry of canga (ferricrete) and evolution of the weathering profile developed on itabirite and iron ore in the Quadrilátero Ferrífero, Minas Gerais, Brazil

Mineralogical and whole rock geochemical analyses for 60 elements on 31 samples of hard ferruginous crust (canga) provide insights into the evolution of the lateritic profile developed on itabirite. Canga can form in two environments: in situ canga that typically caps itabirite and transported canga that covers country rock. Both have similar mineralogical and chemical compositions. Detrital haematite and rare quartz inherited from the itabirite and iron ore comprise the matrix of canga, cemented by goethite, minor gibbsite, and rare manganese oxides and secondary phosphates. Fe2O3 represents more than 91% of its chemical composition and the concentrations of trace elements are low, generally less than 50 ppm. A comparison of the chemical weathering of dolomitic itabirite against the quartz itabirite shows that, although weathering processes are less effective in the former, the geochemical trends of major and trace elements are similar. Negative Ce anomalies (Ce/Ce* = 0.8) and U/Th ratios lower than 1.5 suggest that saprolite formation occurred under slightly anoxic and mildly acidic conditions, allowing rare earth elements (REEs) to remain in the saprolite and also the formation of secondary Al phosphates, instead of Fe phosphates. These conditions became more aggressive during the canga formation process, resulting in further removal of trace elements from the system. The canga formation (pedogenesis) and the chemical weathering of the itabirite (saprolite formation) are independent, but interrelated processes that have been occurring since the Palaeocene.

Evidence of synsedimentary microbial activity and iron deposition in ferruginous crusts of the Late Cenomanian Utrillas Formation (Iberian Basin, central Spain)

Ferruginous sandstones and crusts are prominent sedimentary features throughout the continental (braided)-coastal siliciclastic (estuarine-tidal) wedges of the Late Cenomanian Utrillas Formation in the Iberian Basin. Crust types recognized are: Ferruginous sandy crusts (Fsc) with oxides-oxyhydroxides (hematite and goethite) concentrated on sandstone tops presenting a fibro-radial internal structure reminding organic structures that penetrate different mineral phases, suggesting the existence of bacterial activity in crust development; Ferruginous muddy crusts (Fmc) consisting of wavy, laminated, microbial mats, being composed mainly of hematite. On the other hand, a more dispersed and broader mineralization included as Ferruginous sandstones with iron oxides and oxyhydroxides (hematite and goethite) representing a limited cement phase on these sediments. The presence of microbial remains, ferruginous minerals, Microbially-induced sedimentary structures, microbial laminites and vertebrate tracks preserved due to the presence of biofilms suggest firstly a direct evidence of syn-depositional microbial activity in these sediments; and, secondly, that iron accumulation and ferruginous crusts development occurred immediately after deposition of the host, still soft sediments. Ferruginous crusts cap sedimentary cycles and they represent the gradual development of hard substrate conditions, and the development of a discontinuity surface at the top of the parasequence sets, related to very low sedimentary rates; the overlying sediments record subsequent flooding of underlying shallower environments; crusts are, consequently, interpreted as boundaries for these higher-order cycles in the Iberian Basin.

Geochemistry, mineralogy, and isotope composition of Pb, Zn, and Cu in primary ores, gossan and barren ferruginous crust from the Perkoa base metal deposit, Burkina Faso

Gossan at the Perkoa deposit of stratabound lead and zinc ores (Burkina Faso) is composed of hematite, goethite, clay minerals, minerals of the brucite group and sulfates (corkite, alunite, natroalunite, hinsdalite and hidalgonite). Residual quartz contains inclusions of chalcopyrite, sphalerite and cinnabar. Compared with the primary ores, the gossan is especially enriched with As, Ba, Pb, P, and Sb. On the other hand, the contents of Ag, Co, Cu, Hg, Mo, Ni, and particularly Zn are significantly lower. However, compared with the barren ferruginous crust in the same area, the gossan is significantly enriched in most of chemical elements, namely As, Pb, Sb, and Zn and to lesser extent also in Ag, Ba, Cd, Mo, S, and Sr.The isotopic composition of lead in massive primary ore and in gossan is practically identical. However, the isotopic composition of lead in disseminated ores, the bleached gossan envelope, and in mineralized soils in the Perkoa area is very variable and reflects mixing of ore and lithogenic lead. The 206/207Pb ratio in barren soils and ferruginous crusts is much higher compared with gossan and related altered rocks.Compared to massive ore (δ65Cu=+1.91 to +2.17‰ and δ66Zn=+0.30 to +0.36‰, respectively), the gossan is depleted in heavy isotopes of copper and zinc (δ65Cu=−0.02 to −0.58 and δ66Zn=−0.10 to −0.88‰, respectively). The chemical weathering of sulfide-rich rocks thus gives rise to considerable variations in Cu isotopes (median: −2.36‰, Δ65Cugossan–massive ore), and minor changes in Zn isotopes (median: −0.73‰, Δ66Zn gossan–massive ore). Isotopic composition of copper in gossan and lateritic soil sampled in the vicinity of gossan is similar but differs from barren laterite duricrust which is more depleted in the 65Cu isotope. In zinc, no differences were proved between the δ66Zn values in the gossan and those in the soil and ferruginous crust.

THE LATERITIC BAUXITE DEPOSIT OF RONDON DO PARÁ: A NEW GIANT DEPOSIT IN THE AMAZON REGION, NORTHERN BRAZIL

Detailed geologic surveys (including mapping, drillings, trenches, and mineralogical and chemical analyses) have delimited a new giant lateritic bauxite deposit with 642 million metric tons (Mt) of 42.7% Al2O3 (available) in the world-renowned Amazon Province, northern Brazil. The mineral resource is part of a mature laterite profile and consists of reddish to mottled clay at the base that narrows upward to massive bauxite, followed by ferruginous bauxite, and is capped by an iron horizon (nodular and columnar ferruginous crust) and nodular bauxite with a clayey matrix; a thick clay cover sealed the profile after abrupt contact. The bauxite ore is composed of gibbsite in addition to goethite, hematite, and kaolinite. In general, the ore has high concentrations of Al2O3 (avg 52.4% in massive bauxite and 39.9% in ferruginous bauxite) and Fe2O3 (avg 14.8% in massive bauxite and 35.1% in ferruginous bauxite) and low concentrations of SiO2 (avg 4.33% in massive bauxite and 3.21% in ferruginous bauxite) and is therefore of metallurgical grade. Geologic contact features together with REE distribution patterns indicate that the horizon successions were formed in situ via alteration of the basal sedimentary rocks through polyphasic bauxitization events. These features are comparable with those of other world-class bauxite deposits in this province, such as Trombetas, Juruti, and Paragominas. The Rondon do Para bauxite orebody consists of massive bauxite and ferruginous bauxite layers. The last layer is a differentiated horizon that is not always present in other deposit profiles; when it is present, however, it is not classified as ore. Correlation with other Amazonian bauxite deposits demonstrates that the Rondon do Para deposit is of lateritic origin, was formed during the Paleocene-Eocene, and was reworked in the Miocene.

A new Cenomanian vertebrate tracksite at Tamajón (Guadalajara, Spain): Palaeoichnology and palaeoenvironmental implications

A new Upper Cretaceous vertebrate tracksite has been discovered at Tamajón (Iberian Ranges, Guadalajara, Spain). The track level is a relatively smooth and slightly undulating sandy ferruginous crust, corresponding to an erosive surface at the base of a small meandering channel. It is incised into the underlying planar cross-bedded sandstones of coastal bars located at the middle-upper part of the Utrillas Formation (middle-upper Cenomanian). The site shows an extraordinary concentration of vertebrate tracks, among which numerous sets of two to five isolated digit impressions (“swim tracks”) and, at least, two trackways referred to crocodyliforms, and a single tridactyl footprint probably produced by a theropod dinosaur can be recognized. There are also several long traces (epichnial grooves) revealing sharp direction changes (up to 90°) which seem to be fish fin traces (Undichna unisulca), although crocodyliforms (tail marks) and/or fish invertebrates cannot be rejected as possible tracemakers. Some crocodyliform tracks reveal a thin raised rim, due to the displacement of the sediment by the pressure produced by the feet. Several impressions are moderately deformed by small sediment slides, only preserving their deepest part (claw marks). This is clearly indicative of a soft substrate with a high degree of plasticity and water content at the time of the track registration. Nevertheless, the sediment was hard enough to preserve manus and pes print morphologies and also possible crocodyliform tail and/or fish fin traces. Small rhizoliths can also be recognized and may belong to herbaceous wetland vegetation. The morphology of the palaeochannel, the sedimentary context and the track preservation seem to indicate that the tracks were impressed in a shallow channel located near the coast, under wet conditions and in different moments of time. This discovery represents the first occurrence of vertebrate ichnites in the Utrillas Formation, a stratigraphic unit where osteological and ichnological remains are relatively scarce, and it confirms that some crocodyliforms lived in near coast channels during the deposition of this unit.

Characterization and evolution of primary and secondary laterites in northwestern Bengal Basin, West Bengal, India

It is quite impossible to travel far in India without observing the remarkable ferruginous crust to which Buchanan in 1807 gave the name of laterite. In Indian peninsula, it is a post-Cretaceous stratigraphic succession with a polycyclic nature of evolution which marks the unconformity with recent Quaternary alluvium. There are perennial problems and research gaps in the investigation of laterites in India as well as in West Bengal: (1) defining, identifying and classifying lateritic materials, (2) mode of formation of laterite and its other horizons, (3) determining the ages of laterites, (4) reliability of laterites as palaeoclimatic indicators, (5) identifying topographic requirements and pedogeomorphic processes for laterite formation, and (6) reconstructions of former lateritized landscapes. The formation of north‒south lateritic hard crust (i.e. Rarh Bengal) on the Rajmahal Basalt Traps, Archean granite‒gneiss, Gondwana sediments, Paleogene gravels and older deltaic alluvium is analyzed here to resolve the aforesaid problems and to depict the variable characteristics of laterites with special reference to its tectono-climatic evolution in the northwestern marginal part of Bengal Basin. This paper reveals that the low-level secondary laterites (probably the Pliocene‒Early Pleistocene age) of Rarh Bengal are composed of heterogeneous Fe‒Al rich gravelly materials which were derived from the high-level primary laterites (probably the Eocene‒Miocene age) of plateau since the Paleogene Period by the peninsular river system, following the underlying structure of Bengal Basin. Alongside the roles of drifting of Indian Plate, establishment of monsoon climate, neo-tectonic uplifts and re-lateritization of ferruginous shelf deposits are determined here to unearth the palaeogenesis of primary and secondary laterites in West Bengal.