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This study was carried out to determine the sedimentary provenance of Upper Cretaceous turbidites of Tanjero Formation. The sandstone portion of the unit has been examined based on field and laboratory studies. Seven sections were measured and described in detail on the perfectly cropped out part of the unit at the southern limb of the Sulaimaniyah Syncline. The thickness of the measured sections varies from 120 m to 192 m. The measured sections start from the top of the underlying Shiranish Formation to the syncline axis in the Tanjero Formation. For petrographic analysis sixty- nine representative rock samples were collected. Modal analysis and ternary diagrams point out that, the sandstones are calclithite (litharenite), very fine to medium grained in size consisting of chert, siltstone, mudstone, radiolarian chert and radiolarian mudstone fragments, angular to subangular in shape, very poorly to moderately sorted, transported over short distances and represent submature stage. Grain contact types and high contact index (4.7) indicate moderate to tightly packing, moderate compaction. Transported broken neritic fossil shells, moderately rounded glauconite grains, and undefinable fossils in the altered carbonate rock fragments indicate that the tectonic provenance, lithic recycle category, composed of not only the clastics as interpreted in previous studies derived from Lower Cretaceous Qulqula (radiolarian) Formation which represents deep marine, but also it revealed that a sedimentary formation must also exist in the source area, which is the Lower Cretaceous Balambo Formation. more...

The cross-border correlations of the Miocene lithostratigraphic units (Slovakia, Austria) remain poorly constrained, owing to the various sources of clastic material transported into the basin and the low stratigraphic resolution of conglomerates. Therefore, this study is focused on the Lower and Middle Miocene conglomerates in the deltaic systems of the northern Vienna Basin and assesses their implications for cross-border correlations, as well as for the evolution of the Eastern Alpine - Western Carpathians junction area. Revision of lithostratigraphy is based on analyses of the Zohor-1 and Lozorno-1 wells, including the reassessment of published data to account for any refined geochronology and paleogeography. The Lower Miocene Jablonica deltaic system is formed by deposits originating in the alluvial, deltaic, and littoral environments in the basin's northernmost tip. The conglomerates of exclusively Western Carpathian provenance pass into the deep-water marine mudstones of the Ottnangian Lužice and Karpatian Lakšáry fms. The Karpatian conglomerates at the base of the Zohor-1 well can be correlated both with the conglomerates of the Jablonica deltaic system in the north, as well as with the conglomerates of the Gänserndorf Mb. in the south. The overlying heterolithic flood plain of the deltaic sediments from the Závod Fm. most likely form the facies continuation of the alluvial to flood plain deposits of the Schönkirchen Mb. (upper part of the Aderklaa Fm.). The Middle Miocene deposition starts with terrestrial sediments along the slopes of the Malé Karpaty Mts. dated to 15.2 Ma. Later, along with the Devínska Nová Ves fan-delta, the presence of Orbulina suturalis developed in the marginal parts of the Vienna Basin during the Early Badenian. Despite having the same structural position, it is younger than the Rothneusiedl Formation in the southern part of the Vienna Basin. The provenance of clastics reflects the source in the Central Western Carpathian units and documents the Miocene uplift of the horst structure of the Malé Karpaty Mts. [ABSTRACT FROM AUTHOR] more...

Petrographic analyses are presented for the Rivera, Tacuarembó and Cuchilla Ombú formations, which constitute the outcropping Guaraní Aquifer System in the Rivera and Tacuarembó departments, Uruguay. Sedimentary petrography studies were carried out with the objective of qualitatively and quantitatively evaluate the porosity of sedimentary rocks. To determine the porosity in sandstones, the method of impregnation of petrographic thin sections followed by point-counting of total pore area and interconnected pore area was used. Clast and matrix composition was determined using both optical microscope and scanning electron microscope (SEM), with an energy dispersive X-ray analyzer (EDS) The study shows average values of total porosity of 17% and effective porosity of 14% for the Rivera and Cuchilla Ombú aquifer units and average value of total porosity of 15% and effective porosity of 9% for the Tacuarembó unit. There are compositional differences between sandstones of the Rivera and Tacuarembó formations, the former being essentially quartz-arenites and the latter predominantly subarkoses and sublithic arenites. more...

The Late Permian succession of the Upper Indus Basin in northeastern Pakistan is represented by the carbonate‐dominated Zaluch Group, which consists of the Amb, Wargal and Chhidru formations, which accumulated on the southwestern shelf of the Paleo‐Tethys Ocean, north of the hydrocarbon‐producing Permian strata of the Arabian Peninsula. The reservoir properties of the mixed clastic‐carbonate Chhidru Formation (CFm) are evaluated based on petrography, using scanning electron microscopy (SEM), energy dispersive x‐ray spectroscopy (EDX) and x‐ray diffraction (XRD) techniques. The diagenetic features are recognized, ranging from marine (isopachous fibrous calcite, micrite), through meteoric (blocky calcite‐I, neomorphism and dissolution) to burial (poikilotopic cement, blocky calcite‐II‐III, fractures, fracture‐filling, and stylolites). Major porosity types include fracture and moldic, while inter‐ and intra‐particle porosities also exist. Observed visual porosity ranges from 1.5%–7.14% with an average of 5.15%. The sandstone facies (CMF‐4) has the highest average porosity of 10.7%, whereas the siliciclastic grainstone microfacies (CMF‐3) shows an average porosity of 5.3%. The siliciclastic mudstone microfacies (CMF‐1) and siliciclastic wacke‐packestone microfacies (CMF‐2) show the lowest porosities of 4.8% and 5.0%, respectively. Diagenetic processes like cementation, neomorphism, stylolitization and compaction have reduced the primary porosities; however, processes of dissolution and fracturing have produced secondary porosity. On average, the CFm in the Nammal Gorge, Salt Range shows promise and at Gula Khel Gorge, Trans‐Indus, the lowest porosity. [ABSTRACT FROM AUTHOR] more...

The Mesozoic syn-rift sediments of the Bredasdorp Sub-basin were deposited during the structural inversion of the orogenic Cape Fold Belt (CFB), a crucial time during the break-up of Gondwana. The Late Jurassic to Early Cretaceous non-marine to marine sediments of the Bredasdorp Sub-basin were studied to infer their composition, parent-rock lithologies, tectonic settings and their dynamic response to tectonic perturbations. The knowledge on the provenance terrains in the Bredasdorp Sub-basin is poorly understood and therefore this research shed light on these provenance terrains. Petrographic quantitative analysis revealed that the mineralogical composition of the sediments comprises mainly of litho-quartzose and feldspatho-litho-quartzose sediments. Modal petrographic data indicates a recycled orogen provenance on QFL plots suggesting the occurrence of a collisional provenance terrain. This setting can be interpreted as the reactivation of the CFB structures eroding the Bokkeveld Group (and younger Karoo Supergroup) and the Table Mountain Group metasediments (and Pre-Cape sediments). The shedding of these sediments in the Bredasdorp Sub-basin were coeval with the deposition of the D-V, V-BUSM and BUSM-1AT1 'informal' sequences. Furthermore, an evolving recycled provenance from sedimentaclastic (un-dissected) to basementaclastic (dissected) sediments are proposed and could be a defining characteristic to the enigmatic offshore Jurassic-Cretaceous stratigraphic nomenclature. During the deposition of the D-V Sequence, a spatial variation in provenance due to intrabasinal uplifted fault blocks (possibly reactivated shear zones) occurred between the erosion of the Bokkeveld Group (and Karoo Supergroup) and the Table Mountain Group (TMG) metasediments. The deposition of the V-BUSM Sequence showed a similar compositional trend within their provenance terrain but showed a stronger correlation to an increased quartz and feldspar content. This is possibly due to the erosion of the dominant TMG, which was further supported by the occurrence of distinct type 3 polycrystalline quartz. The deposition of the BUSM-1AT1 sequence saw an increase in plutonic lithic fragments and feldspar content, indicative of an igneous source, which was attributed to the erosion of the proximal Cape Granite Suite. This distinction is crucial in creating a unifying stratigraphic nomenclature for the Jurassic-Cretaceous sequences of South Africa. A dynamic recycled orogen is envisaged for the Bredasdorp Sub-basin and therefore the use of these type of dynamic models should be incorporated in provenance models especially if there is a well-documented geological setting. • Syn-rift deposits in the Bredasdorp sub-basin were deposited during structural inversion of the Cape Fold Belt (CFB). • Sediments were classified as litho-Quartzose and feldspatho-litho-Quartzose sandstones. • An evolving recycled provenance from sedimentaclastic (undissected) to basementaclastic (dissected) sediments is proposed for the Bredasdorp Sub-basin, offshore South Africa. • Recycled provenance models and terrains can still be evaluated through petrographic data. [ABSTRACT FROM AUTHOR] more...

This study was carried out to determine the sedimentary provenance of Upper Cretaceous turbidites of Tanjero Formation. The sandstone portion of the unit has been examined based on field and laboratory studies. Seven sections were measured and described in detail on the perfectly cropped out part of the unit at the southern limb of the Sulaimaniyah Syncline. The thickness of the measured sections varies from 120 m to 192 m. The measured sections start from the top of the underlying Shiranish Formation to the syncline axis in the Tanjero Formation. For petrographic analysis sixtynine representative rock samples were collected. Modal analysis and ternary diagrams point out that, the sandstones are calclithite (litharenite), very fine to medium grained in size consisting of chert, siltstone, mudstone, radiolarian chert and radiolarian mudstone fragments, angular to subangular in shape, very poorly to moderately sorted, transported over short distances and represent submature stage. Grain contact types and high contact index (4.7) indicate moderate to tightly packing, moderate compaction. Transported broken neritic fossil shells, moderately rounded glauconite grains, and undefinable fossils in the altered carbonate rock fragments indicate that the tectonic provenance, lithic recycle category, composed of not only the clastics as interpreted in previous studies derived from Lower Cretaceous Qulqula (radiolarian) Formation which represents deep marine, but also it revealed that a sedimentary formation must also exist in the source area, which is the Lower Cretaceous Balambo Formation. [ABSTRACT FROM AUTHOR] more...

Abstract The Middle to Late Triassic El Tranquilo Group (El Tranquilo anticline, Deseado Massif, Patagonia) is a key area between coeval West Argentinean and North Patagonian outcrops and of the area of Southwestern Gondwana. The El Tranquilo Group's continental sequence is part of an extensional setting related to the accretion of Patagonia. Petrographic (qualitative and modal) analyses and geochemical analyses (major, trace elements, and rare earth elements (REEs)) of 90 samples were carried out. The sediments of the El Tranquilo anticline are arkoses and lithic arenites containing lithic fragments from felsic volcanic rocks. Polycrystalline quartz, sub-euhedral K-feldspar, and biotite are abundant and corroborate an acidic plutonic source. Major element ratios, trace element ratios (Ti/Nb, Th/Sc, Eu/Eu*), and REE distribution patterns indicate direct derivation from igneous felsic rocks. Paleogeographic constructions locate the El Tranquilo anticline near a Permo-Triassic volcanic arc. Although the input of acidic igneous material to the El Tranquilo sag is clear, the composition of the sandstones could not be confirmed as predominantly volcaniclastic. Thus, petrography could not confirm the extension of Permo-Triassic Choiyoi volcanism to Southern Patagonia, Karoo basin, and Antarctic Peninsula. Low recycling rates indicate short transport distances; considering the time between cooling and exhumation, the most probable dominant source areas are the Late Ordovician Dos Hermanos granitoids, Silurian El Sacrificio granitoids, Devonian Bahía Laura granitoids, or Carboniferous Mina La Leona granitoids. Graphical abstract Image 1 Highlights • Link between the North Patagonian Massif and the Antarctic Peninsula and Karoo Basin. • Volcanic activity of the Permotriassic Arc (Choiyoi) in the Deseado Massif doubtful. • Triassic sediments of Deseado Massif derived from Paleozoic granitoids. • New approaches to the interpretation of geochemical analyses of clastic sediments. • Providing a most complete geochemical dataset for El Tranquilo Group. [ABSTRACT FROM AUTHOR] more...

Located in NW Switzerland, the Mont Terri rock laboratory is a research facility primarily investigating the Opalinus Clay as potential host rock for deep geological disposal of radioactive waste. In the Mont Terri area, this Jurassic shale formation is characterized by three distinctive lithofacies: a shaly facies, a carbonate-rich sandy facies and a sandy facies. However, the lithological variability at dm- to cm-scale is not yet fully understood and a detailed lithofacies characterization is currently lacking. Within the present study, petrographic descriptions at micro- and macro-scale, geophysical core logging (P-wave velocity and gamma-ray density), geochemical core logging (X-ray fluorescence) and organic matter quantification (Rock-Eval pyrolysis) were combined on a 27.6 m long Opalinus Clay drillcore comprising the three major lithofacies. The high-resolution investigation of the core resulted into a refinement of the three-fold lithofacies classification, and revealed high intra-facies heterogeneity. Five subfacies were defined and linked to distinctive depositional regimes. The studied succession is interpreted as a shallowing-upward trend within a storm-wave-dominated epicontinental sea characterized by relative shallow water depths. [ABSTRACT FROM AUTHOR] more...

The occurrence of a Lower Cretaceous flysch group, cropping out from the Gibraltar Arc to the Balkans with a very similar structural setting and sedimentary provenance always linked to the dismantling of internal areas, suggests the existence of only one sedimentary basin (Alpine Tethys s.s.), subdivided into many other minor oceanic areas. The Maghrebian Basin, mainly developed on thinned continental crust, was probably located in the westernmost sector of the Alpine Tethys. Cretaceous re-organization of the plates triggered one (or more) tectonic phases, well recorded in almost all the sectors of the Alpine Tethys. However, the Maghrebian Basin seems to have been deformed by Late- or post-Cretaceous tectonics, connected with a “meso-Alpine” phase (pre-Oligocene), already hypothesized since the beginning of the nineties. Field geological evidence and recent biostratigraphic data also support this important meso- Alpine tectonic phase in the Sicilian segment of the Maghrebian Chain, indicated by the deformations of a Lower Cretaceous flysch sealed by Lower Oligocene turbidite deposits. This tectonic development is emphasized here because it was probably connected with the onset of rifting in the southern paleomargin of the European plate, the detaching of the so-called AlKaPeCa block (Auct.; i.e. Alboran + Kabylian + Calabria and Peloritani terranes) and its fragmentation into several microplates. The subsequent early Oligocene drifting of these microplates led to the progressive closure of the Maghrebian Basin and the opening of new back-arc oceanic basins, strongly controlled by extensional processes, in the western Mediterranean (i.e. Gulf of Lion, Valencia Trough, Provençal Basin and Alboran Sea). more...

Banded iron formations (BIFs) are marine chemical sedimentary rocks that were widely deposited before the start of the Great Oxidation Event (2.45–2.32 Ga). They represent an important archive into the chemistry of the Precambrian oceans and atmosphere, and the evolution of the marine biosphere. It is believed that BIFs were derived from ferric oxides/hydroxides that were deposited by iron-oxidizing bacteria or by reaction with oxygen released by Cyanobacteria. Hematite is traditionally interpreted to represent the dehydrated product of the ferric oxide/hydroxide precipitate, whereas magnetite is thought to have formed from ferric oxides/hydroxides via bacterial iron reduction and oxidation of microbial biomass. However, studies are equivocal about when and how magnetite formed in BIFs. We present the results of a detailed petrographic study of magnetite in BIFs of the Hamersley Group, Western Australia. We find no evidence that magnetite was precipitated from seawater or was a product of bacterial iron reduction. Instead, most of the magnetite formed by replacement of siderite and other ferrous-rich minerals after burial. Our observations suggest that magnetite growth was linked to the breakdown of siderite during metamorphism. Published experimental data indicate that in the presence of water and under the metamorphic conditions experienced in the southern Pilbara Craton (200–350 °C), the thermal decomposition of siderite could account for much of the magnetite in the Hamersley BIFs (3FeCO 3  + H 2 O → Fe 3 O 4  + 3CO 2  + H 2 ). The relationship between magnetite and the primary precipitates, which are preserved as greenalite nanoparticles and microgranules in chert bands, suggests that much of the magnetite formed in siderite-rich, iron-silicate bands that developed by compaction of non-silicified iron-silicate muds. These bands acted as reactive pathways for fluid flow and the formation of magnetite. If most of the magnetite formed after burial then it is necessary to reassess assumptions about the chemistry of the original precipitates and the role of microbial life in the redox cycling of iron. Our results are consistent with models for the deposition of BIFs that center around a precursor sediment comprising greenalite precipitates and diagenetic siderite that was partially replaced by magnetite and hematite after burial. [ABSTRACT FROM AUTHOR] more...

We critically evaluate the potential and limitations of an alternative way to calculate erosion rates based on petrographic and mineralogical fingerprints of fluvial sediments coupled with gauged sediment fluxes. Our approach allows us to apportion sediment loads to different lithological units, and consequently to discriminate erosion rates in different tectonic domains within each catchment. Our provenance data on modern Taiwanese sands indicate focused erosion in the Backbone Range and Tananao Complex of the retrowedge. Lower rates are inferred for the northern part of the island characterized by tectonic extension and for the western foothills in the prowedge. The principal factor of uncertainty affecting our estimates is the inevitably inaccurate evaluation of total sediment load, because only the suspended flux was measured. Another is the assumption that suspended load and bed load are derived from the same sources in fixed proportions. Additional errors are caused by the insufficiently precise definition of lithologically similar compositional end-members and by the temporal variability of sediment composition at the outlet of each catchment related to the spatial variability of erosional processes and triggering agents such as earthquakes, typhoons, and landslides. To evaluate the robustness of our findings, we applied a morphometric technique based on the stream-power model. The results obtained are broadly consistent, with local discrepancies ascribed to poorly constrained assumptions and choices of scaling parameters. Our local erosion estimates are consistent with GPS uplift rates measured on a decadal timescale and generally higher than basin-wide results inferred from cosmogenic-nuclide and thermochronology data. [ABSTRACT FROM AUTHOR] more...

Contention surrounds the Ediacaran–Cambrian geodynamic evolution of the palaeo-Pacific margin of Gondwana as it underwent a transition from passive to active margin tectonics. In Australia, disagreement stems from conflicting geodynamic models for the Delamerian Orogen, which differ in the polarity of subduction and the state of the subduction hinge (i.e., stationary or retreating). This study tests competing models of the Delamerian Orogen through reconstructing Ediacaran–Cambrian basin evolution in the Koonenberry Belt, Australia. This was done through characterising the mineral and U–Pb detrital zircon age provenance of sediments deposited during postulated passive and active margin stages. Based on these data, we present a new basin evolution model for the Koonenberry Belt, which also impacts palaeogeographic models of Australia and East Gondwana. Our basin evolution and palaeogeographic model is composed of four main stages, namely: (i) Ediacaran passive margin stage with sediments derived from the Musgrave Province; (ii) Middle Cambrian (517–500 Ma) convergent margin stage with sediments derived from collisional orogens in central Gondwana (i.e., the Maud Belt of East Antarctica) and deposited in a backarc setting; (iii) crustal shortening during the c. 500 Ma Delamerian Orogeny, and; (iv) Middle to Late Cambrian–Ordovician stage with sediments sourced from the local basement and 520–490 Ma igneous rocks and deposited into post-orogenic pull-apart basins. Based on this new basin evolution model we propose a new geodynamic model for the Cambrian evolution of the Koonenberry Belt where: (i) the initiation of a west-dipping subduction zone at c. 517 Ma was associated with incipient calc-alkaline magmatism (Mount Wright Volcanics) and deposition of the Teltawongee and Ponto groups; (ii) immediate east-directed retreat of the subduction zone positioned the Koonenberry Belt in a backarc basin setting (517 to 500 Ma), which became a depocentre for continued deposition of the Teltawongee and Ponto groups; (iii) inversion of the backarc basin during the c. 500 Delamerian Orogeny was driven by increased upper and low plate coupling caused by the arrival of a lower plate asperity to the subduction hinge, and; (iv) subduction of the asperity resulted in renewed rollback and upper plate extension, leading to the development of small, post-orogenic pull-apart basins that received locally derived detritus. [ABSTRACT FROM AUTHOR] more...

In carbonate reservoirs, the relationship between porosity Ø, a measure of the combined volumes of several kinds of pore space (e.g. interparticle and separate-vug), and permeability K are neither linear nor logarithmic, hence only weakly correlatable. Approaches to an estimation of permeability that employ both petrographical and petrophysical parameters, the so-called rock-typing techniques, have proven to be the most nearly precise. However in many studies simple K/Ø cross-plots are used for each rock-type to provide trendlines from which K values are derived as a function of Ø values; this is common practice even though the coefficient of correlation r2 departs significantly from 1.This paper describes and provides examples of an improved technique of rock-type classification in which each rock-type is characterized by a discrete and unique Gaussian distribution of log K. It facilitates upscaling for it suggests the use of a single geometric mean value for permeability and a corresponding standard deviation (variance, or coefficient of variation) for each rock-type.This new technique can be used in uncored wells by extrapolating these determinations into wireline logs as documented below in a case study of layer-cake reservoirs in a field of the Abu Dhabi offshore (U.A.E.). more...

The northern Austral basin from Patagonia is characterized by an Early Cretaceous (Barremian–Albian) coarse-grained regressive sequence. These littoral to continental deposits conform a 150 km long basin cropping out along the Southern Patagonian Andes between 47 and 48°S. The basin fill consist of basal deltaic sandstones with interbedded shales and limestones from the Río Belgrano Formation, topped by up to 350 m of fluvial conglomerates and reworked tuffs of the Río Tarde and Kachaike formations. This continental depocenter represent a major geodynamic and paleoenviromental change from the underling marine Río Mayer Formation. In this study we analyze the tectonic setting and provenance during deposition of the coarse-grained sequence using sedimentary petrography of 37 thin sections in four stratigraphic profiles covering the northern basin. Our dataset indicates mainly a recycled orogenic sandstones provenance, in agreement with potential surrounding basement sources. [ABSTRACT FROM AUTHOR] more...

Abundant early diagenetic siderites occur as spherulites and rhombohedral microcrystalline and macrocrystalline crystals in the cores of the 2-MU-1-RJ well, drilled in the Paraíba do Sul Deltaic Complex, Rio de Janeiro (Brazil). The host sediments of the siderites are siliciclastic, hybrid, and carbonate deposits. Intense pedogenetic processes affected the siliciclastic sediments immediately after deposition, comprising clay illuviation, plants bioturbation, feldspar dissolution, and iron oxide/hydroxide precipitation. Siderite and pyrite are the main diagenetic constituents. The other diagenetic products are kaolinite, smectite, argillaceous and carbonate pseudomatrix, quartz overgrowths, diagenetic titanium minerals, jarosite, and iron oxides/hydroxides. Early diagenetic siderites were separated into four groups based on their elemental and stable isotopic composition, as well as on their paragenetic relationships with the other constituents and with the host sediments. Spherulitic to macrocrystalline siderites from group 1 are almost pure (average: 94.7 mol% FeCO 3 ; 1.2 mol% MgCO 3 ; 2.3 mol% CaCO 3 ; 1.8 mol% MnCO 3 ) and precipitated from meteoric porewaters in continental siliciclastic rocks under suboxic conditions (δ 18 O vpdb values range in − 10.28 to − 5.57‰ and the δ 13 C vpdb values in − 12.68 to − 4.33‰). Microcrystalline rhombohedral siderites from group 2 have zonation due to substantial Ca and Mg substitution (core average: 78.5 mol% FeCO 3 ; 4.2 mol% MgCO 3 ; 15.7 mol% CaCO 3 ; 1.6 mol% MnCO 3 ; edge average: 74.0 mol% FeCO 3 ; 9.2 mol% MgCO 3 ; 15.6 mol% CaCO 3 ; 1.1 mol% MnCO 3 ), and δ 13 C vpdb and δ 18 O vpdb values of + 0.17‰ and − 1.96‰, precipitated from marine porewaters in packstones/wackestones under methanogenic conditions. The group 3 is represented by irregular spherulitic siderites with moderate Ca and Mg substitutions (average: 80.2 mol% FeCO 3 ; 7.9 mol% MgCO 3 ; 11.3 mol% CaCO 3 ; 0.6 mol% MnCO 3 ), with δ 18 O vpdb values ranging from − 5.96 to − 7.61‰ and δ 13 C vpdb values ranging from − 5.15 to − 10.41‰. The group 4 microcrystalline siderites are magnesium-rich (average: 57.3 mol% FeCO 3 ; 31.4 mol% MgCO 3 ; 9.6 mol% CaCO 3 ; 1.7 mol% MnCO 3 ; δ 13 C vpdb + 1.43‰ and δ 18 O vpdb − 14.09‰). The group 3 and 4 siderites were formed from brackish porewater under suboxic conditions in hybrid and siliciclastic rocks. These variations in siderites are probably related to the Paraíba do Sul River dynamics, to sea level changes and to climatic variations that took place during the Quaternary. [ABSTRACT FROM AUTHOR] more...

This paper challenges the classical idea that the Val Marecchia Nappe, the highest of the north-eastern Apennines, is a nappe that originated from the External Ligurian Domain and consisting of Upper Cretaceous-Middle Eocene rocks, accreted to the Palaeo-Apenninic Chain in the Middle-Late Eocene due to the Ligurian tectonic phase. Its succession comprises a Middle-Late Jurassic ophiolitic substratum and its sedimentary cover of Late Jurassic to Early Miocene age. This succession is quite similar to those of the North-Calabrian and Parasicilide Units of the Southern Apennines and of many Maghrebian and Betic Flysch Domain Units, all originating from the Western Tethys and deformed since the Early Miocene. The Val Marecchia Nappe succession was likely deposited in an oceanic realm that differs from that of the Ligurian Domain and was located in a more external palaeogeographic position with respect to that of the Ligurian Domain. The oceanic realm of the Val Marecchia Nappe constituted the northwards extension of the Maghrebian Flysch Basin-Lucanian Ocean system. [ABSTRACT FROM AUTHOR] more...

In their recent paper entitled "Early Archean biogeochemical iron cycling and nutrient availability: New insights from a 3.5 Ga land-sea transition", Johnson et al. (2022) use the Fe isotope and trace-element compositions of ~3.5 Ga jaspilites from the North Pole Dome area of the Pilbara Craton, northwestern Australia, to investigate links between the ancient Fe biogeochemical cycle, continental exposure and nutrient (P) availability. The geochemical arguments are based on the underlying assumption that the jaspilites contain primary hematite that was initially deposited as Si-ferrihydrite precipitates following Fe(II)(aq) oxidation by photoferrotrophs. In support of a primary origin for the iron oxide, the authors present observations from standard light petrography showing the presence of fine-grained hematite dispersed amongst the chert. Here, we question whether the fine-grained hematite is the sole iron precipitate, and indeed, whether it is primary. These concerns arise from work on nearby and slightly younger jaspilites (3.46 Ga Marble Bar Chert Member), in which SEM and TEM studies revealed the presence of fine-grained particles (typically <1 µm) of greenalite and siderite, as well as evidence for pervasive secondary oxidation. Although fine-grained hematite is readily identified using light microscopy, tiny Fe(II)-rich particles can easily be overlooked. For this reason, we believe that the Dresser jaspilites, which closely resemble the nearby Marble Bar jaspilites, may also contain Fe(II)-rich precipitates. In addition, given the widespread evidence for secondary oxidation in the Marble Bar jaspilites, there remains a distinct possibility that the fine-grained hematite in the Dresser jaspilites is not primary. The precipitation of Fe(II)-rich phases, rather than ferrihydrite, would undermine interpretations for Fe biogeochemical cycling centred on photoferrotrophy. We suggest that the conclusions of Johnson et al. (2022) should be treated with caution until the jaspilites have been examined by high-spatial resolution electron imaging and analysis. [ABSTRACT FROM AUTHOR] more...

Six cores, up to 2 m thick, were drilled during a multibeam and high-resolution seismic survey guided in the Vlora Bay with multidisciplinary objectives. In this work the results of grain size and mineralogical analyses of 29 samples are presented. The samples were collected from each core at the top and bottom, further at different depths where any textural changes were evident. Results from grain size analyses allow the comparison of the sediments both in the time (stratigraphic sense) and in the space among different cores. The samples show a good homogeneity: clayey silts in most parts of the core. Only one core presents some intervals with 70% sand and gravel. These samples have mainly a biogenic component, which suggest reworking and mechanical concentrations. The greatest amounts of bioclasts in the core closer to the eastern coast is significant. Results from mineralogical analyses show some differences only in the composition of sands , whereas the clays and silts are mainly composed of clay minerals and secondarily of quartz, feldspar, calcite, and dolomite.The sandy fractions are composed of quartz, muscovite, monazite, and particularly of bioclasts (locally covered with pyrite coatings), clay aggregates, coal, and anthropic material. The results indicate a basin supplied by a mainly terrigenous source, represented by many rivers of the eastern side. Coarse-grained sediments are lacking and are only documented by bioclastic concentrations. The pyrite coatings may indicate only a low rate of anoxic conditions. [ABSTRACT FROM AUTHOR] more...

Abstract: The Upper Cretaceous John Henry Member of the Straight Cliffs Formation preserves regressive shoreface and channel facies, and transgressive lagoonal tidal inlet facies that suggest distinct modal sandstone compositions. Detrital modes from six sandstone facies (upper shoreface, lower shoreface, deflected mouth bars, fluvial channels, tidal inlets and washover fans), and their spatial and temporal variations, provide additional data regarding the depositional environments and setting of the John Henry Member. Three statistical methods were utilized: univariate standard deviation and confidence interval and multivariate logratio transformations to assess the compositional difference between facies using estimation of means. Both univariate statistical methods have some inherent problems. Standard deviation does not account for sample size, while the confidence interval method incorporates a t-test to account for only some of the uncertainty of small sample size. The results of the univariate methods differ slightly and both indicate statistically distinct sandstone compositions based on facies. Multivariate statistics are much more robust and suggest similar trends, yet display different compositional means and have inconclusive confidence fields as they incorporate all of the uncertainty associated with small sampling sizes. In general, sandstone compositions become more quartz-rich and compositionally mature as sediment is transported from proximal fluvial environments to distal upper shoreface environments. This trend reflects the degree of preferential reworking or winnowing of unstable grains prior to lithification. More complicated relationships are observed as facies distributions shift through space and time. Sandstone compositions support a deflected wave-dominated deltaic interpretation for the John Henry Member in this area. Sandstone compositions become more lithic-rich from north to south, corresponding to the facies distribution of upper shoreface and deflected mouth bars, respectively. Mouth bars occur at the intersection of the fluvial channel and the coastline where sand is deflected via longshore drift to the southern portion of the field area. Upper shoreface facies located further away from mouth bar facies are heavily reworked by wave processes and contain more mature quartz-rich modal compositions. Additionally, high feldspathic and lithic concentrations in tidal inlet facies suggest that this facies was sourced closer to mouth bars rather than updrift upper shoreface sediments. A shift in sandstone composition occurs at the end of the second transgressive–regressive cycle of the John Henry Member throughout the Rogers Canyon area. This compositional change is concurrent with a relatively large basinward shift in facies, which suggests that it reflects the transition from regressive to transgressive facies associated with the relative sea level fall rather than a change in the main sediment source area. [Copyright &y& Elsevier] more...

Abstract: The paper presents a practical study of expertise in sedimentary petrography and its incorporation into a knowledge-based computing system, PetroGrapher. The study identifies features of expert geologists'' essentially visual knowledge that limit the usefulness of traditional logic-oriented symbolic methods for developing relevant knowledge-based systems. In particular, the experts'' expressions of knowledge differ significantly from what is taught through the literature about their subject. Also, the means (ontology) of describing the explicit objects of geological data are not well-suited to describe how experts combine such objects and make inferences about them. The paper indicates how to deal with those two different levels of ontology, proposes “knowledge graphs” as an effective medium for linking them and explains their place in a general descriptive model of how experts solve problems in interpretation based on visual evidence. The model is being validated through the use of PetroGrapher, for management of data and knowledge about reservoir rocks, in a petroleum company. [Copyright &y& Elsevier] more...

Abstract: The Late Cretaceous–Eocene clastic deposits of the Western Cordillera of Ecuador record significant changes in the source areas, grain size, and location of the depocenters, related to the accretion of oceanic terranes that constitute the present-day Western Cordillera and Coast. Major changes in the source areas occurred in the ?late Maastrichtian and ?late middle Eocene. They are interpreted as corresponding to the accretion of the Guaranda and Macuchi oceanic terranes, respectively. Major increases in the grain sizes occurred in the ?late Maastrichtian, late Paleocene(?), and ?late middle Eocene, and seem to coincide with the accretion of the Guaranda, Piñón, and Macuchi terranes, respectively. The increasing occurrence of plutonic or metamorphic fragments and the westward shift of the depositional areas through the Paleocene–upper Eocene interval indicate an increasing uplift and erosion of the Cordillera Real. Continuous, although jerky, uplift of the latter during the Maastrichtian–Eocene period, supports the idea that the accreted oceanic material contributed to the crustal thickening and relief creation of the Ecuadorian Andes. [Copyright &y& Elsevier] more...

The Eocene La Meseta Formation is the youngest exposed unit of the back-arc James Ross Basin, Antarctic Peninsula, cropping out in Seymour (Marambio) Island. The formation comprises 720 m of clastic sedimentary rocks of deltaic, estuarine and shallow marine origin. It was subdivided into six unconformity-based units (Valle de Las Focas, Acantilados, Campamento, Cucullaea I, Cucullaea II and Submeseta Allomembers) grouped into three main facies associations. Facies association I represents valley-confined deposition in a progradational/aggradational tide-dominated and wave-influenced delta front/delta plain environment. Facies association II includes tidal channels, mixed tidal flats, tidal inlets and deltas, washover and beach environments. Facies association III represents nonconfined tide- and storm-influenced nearshore environments. La Meseta Formation sandstones are quartzofeldspathic with some hybrid arenites (glauconite and carbonate bioclasts-rich). Sandstone detrital modes are subdivided into two distinctive petrofacies: the low quartz petrofacies (petrofacies I, Q<55% and L>12%), interpreted to retain the original provenance signal, and the high quartz petrofacies (petrofacies II, Q>55% and L<12%), representing the reworking product of the former after selective elimination of the more labile components. Petrofacies I sandstone framework grains were mainly derived from a dissected magmatic arc and an associated metamorphic belt. Textural evidence for recycling of some grains (e.g. garnet) from older sedimentary units during valley incision is not conclusive. Changes in the relative participation of source areas during the evolution of the incised-valley system are evaluated from the relative proportions of lithic fragments and monomineralic clasts derived from each rock type. Two lithic assemblages were recognized. The mixed lithic assemblage (Rv/Rm+Rp<1.4) shows participation of all rock types; it represented valley-confined environments, either during the initial stage of valley development, or after main episodes of incision. The volcanic lithic assemblage (Rv/Rm+Rp>1.4) is clearly dominated by volcanic-derived clasts; it developed at times of high sea level and/or during later stages of the valley fill, when an “energy fence” at the shoreline prevented delivery of sediment from the Antarctic Peninsula, thus enhancing the relative participation of local volcanic sources. [Copyright &y& Elsevier] more...

• Clay minerals have been widely used as proxies for paleoenvironmental reconstructions. • Most clay minerals are highly reactive and prone to post-depositional alterations. • New quantitative petrographic approach developed to differentiate detrital vs diagenetic phases. • Clay abundance rose from the Early to Mid Ediacaran records of Adelaide Geosyncline. • Clay abundance shift is consistent with appearance of biologically active soil. The detrital clay mineral assemblage contained within sedimentary archives has long been used as a proxy for palaeo-tectonic, -climate, and -environmental reconstructions as well as provenance analysis of sediments. However, many clay minerals such as smectite are highly reactive and thus prone to post-depositional alteration, or commonly form diagenetic replacement phases, which can fundamentally change clay abundance and composition within sedimentary successions. Although a critical requirement for making robust palaeo-environmental reconstructions, there are difficulties in distinguishing and quantifying clay minerals of detrital versus diagenetic origin in fine-grained sediments and in sedimentary rocks using bulk analytical techniques. A new generation of electron imaging and mineral mapping tools, optimized for analyzing fine-grained geo-materials, has the potential to resolve this long-standing challenge, if diagnostic criteria to systematically differentiate (clay) minerals of varying origin can be established. Here we define the petrographic criteria required to differentiate various classes of detrital and diagenetic illite, chlorite and kaolinite/dickite, based on a case study of continental palaeo-weathering recorded in late Neoproterozoic sequences of the Adelaide Geosyncline, South Australia. Comparison to quantitative XRD data demonstrates the accuracy of SEM-based mineral identification and quantification. After correcting for the effects of diagenesis, the original sediments are shown to have an immature mineralogy (e.g., high abundance of feldspar: 23–33% and detrital mica/2M 1 illite: 7–26%, no pedogenic clays), indicative of limited chemical weathering in the late Cryogenian Enorama Shale and the early Ediacaran Brachina Formation. The mid-Ediacaran Bunyeroo Formation, by contrast, is characterized by a substantially higher content (~20–23%) of pedogenic 1M and 1M d illite coupled with trace amounts of readily weathered phases such as feldspar (~1–4%). This is indicative of enhanced chemical weathering, consistent with previous studies arguing for a growing influence of biologically-mediated pedogenic weathering in the Ediacaran. [ABSTRACT FROM AUTHOR] more...

We studied the northern tip of the Austral-Magallanes basin in the Southern Patagonian Andes, between the Buenos Aires Lake and the Mayer River at 46°35′ SL and 48°35′ SL, respectively. Proposed objectives were: i) to differentiate Mesozoic-Cenozoic tectonostratigraphic units and, ii) to characterize the different deformational events that took place in the area linked to a variable regional geodynamic context. Sandstones provenance analysis was performed on the Aptian - Albian compressive retroarc deposits and Cenozoic foreland deposits. Studied samples were classified using tectonic discrimination diagrams which show: i) for Cretaceous rocks a dominant sediment source from a recycled orogen and, to a lesser extent, a dissected to transitional arc whereas ii) the Cenozoic rocks show a magmatic arc provenance. According to the performed analyses, the evolution of the northern sector of the Austral-Magallanes basin is proposed to include four tectonostratigraphic units related to: i) a Late Jurassic rift stage; ii) a Berriasian – Barremian thermal subsidence stage; iii) an Aptian – Albian compressive retroarc stage; and iv) a Miocene foreland stage s.s. The Late Cretaceous-Paleocene was a time for compression and uplift, represented in the study zone by a paraconcordance/angular unconformity with an extended hiatus between Albian/Cenomanian rocks and the Eocene. • An integrate study allow us to unravel the different deformational events that took place in the area linked to variable regional geodynamic contexts. • We propose an evolution model for the northern sector of the Southern Patagonian Andes and define four tectonostratigraphic stages. • A major change in the provenance pattern is detected between Cretaceous and Cenozoic rocks. [ABSTRACT FROM AUTHOR] more...