The Carboniferous was a period of intense environmental perturbations, climate changes between greenhouse and icehouse, eustatic sea level change, and accumulation of organic carbon-rich sediments. ...At this time, the Tyler Formation was deposited in the midcontinent USA. A detailed palynological analysis of the Tyler Formation revealed a highly diverse assemblage of spores with minor pollen content, represented by 100 species belonging to 51 genera. Stratigraphically constrained spores and pollen grains were used to construct three interval zones of middle-late Chesterian (late Viséan-Serpukhovian) to early Morrowan (middle Bashkirian) ages. The stratigraphic position of the Mississippian-Pennsylvanian boundary was determined in the lower Tyler Formation based on the last appearance of typical forms of the late Chesterian, including Tripartites vetustus, Knoxisporites triradiatus, Knoxisporites stephanephorus, Densosporites diatretus, and Schopfipollenites acadiensis, compared to the first appearance of early Morrowan Crassispora kosankei, Cirratriradites saturnii, Radiizonates aligerens, and Raistrickia saetosa. Palynofacies analysis and statistical clustering of the Tyler Formation showed three palynofacies assemblages. PFA-1 showed moderate relative abundances of phytoclasts and AOM, suggesting deposition close to fluvio-deltaic and shallow marine environments, while PFA-2 exhibited high abundances of phytoclasts, mostly of opaque wood, reflecting deposition in active river-dominated delta plains. PFA-3 showed the highest abundances of AOM, suggesting deposition in a shallow marine environment. Organic petrography and geochemistry data indicate that the Tyler Formation is one of the best source rock intervals throughout the midcontinent USA. Based on organic matter richness, the Tyler Formation is subdivided into three groups. The first group has TOC contents higher than 10 wt% of kerogen Types III, mixed II/III, and II with excellent hydrocarbon generation potential. The second group has TOC content in the range of 2–10 wt% of kerogen Types III, mixed II/III, and II, and fair to excellent hydrocarbon generation potential. The third group shows organic matter richness with TOC content below 2 wt% with good organic matter richness and kerogen Types III to IV, and poor to fair hydrocarbon generation potential. The organic matter thermal maturity is evaluated based on Tmax and VRo% values, suggesting that all samples of Tyler Formation are in the early to late stages of the oil window. However, care should be considered when assessing a mature source rock because the kerogen typing and generation is based on present-day TOC, S2, and HI rather than their original values.
•The Mississippian-Pennsylvanian boundary is detected in the lower Tyler Formation.•Spores typical of late Chesterian were replaced by forms of early Morrowan.•Fluvio-deltaic, river-dominated delta plains, and shallow marine environments were predominant.•The Tyler Formation contains high quality, mature source rocks with excellent hydrocarbon generation.
Petrographic classifications of sand and sandstone proposed more than half a century ago are still in use, although they were formulated at a time when depositional and post-depositional sedimentary ...processes were poorly understood, and before the relationships between tectonics and sedimentation could be interpreted in modern plate-tectonic terms. As a consequence, too many scientific articles and technical reports are still encumbered with obsolete concepts, graphical tools, and ambiguous terminology that make sediment descriptions awkward and misleading. A renovation that treasures the legacy of the pioneers is required.
The descriptive petrographic classification of sand and sandstone proposed in this paper is based on the quasi-universally used Gazzi-Dickinson point-counting method, and simply translates into words ternary compositions of quartz, feldspar, and lithic fragments without introducing any new names. The classic QFL plot is subdivided into 15 fields - labelled by adjectives introduced long ago by K.A.W. Crook and endorsed by W.R. Dickinson and more recently by G.J. Weltje - which reflect relative abundances of the three main framework components (provided they exceed 10%QFL). According to standard use, the less abundant component goes first, the more abundant last (e.g., litho-feldspatho-quartzose composition translates into Q > F > L > 10%QFL). For lithic-rich sand and sandstone, information on the prevailing rock fragment type can be added by an additional free adjective (e.g., metamorphiclastic, carbonaticlastic), as proposed long ago by R.V. Ingersoll. For lithic-poor feldspatho-quartzose and quartzose sand and sandstone, further formal subdivisions are proposed based on the Q/F ratio, thus reaching a total of 18 compositional fields overall. Modern sand known to be derived from different source rocks and found in major world's rivers, deserts, and deep-sea fans fits in the pigeonholes defined by the relative abundance of quartz, feldspar, and lithic fragments.
The aim of this classification is to restore directness in sandstone petrology, and to avoid ambiguities generated in the past by making reference to badly defined archetypes, such as greywacke or arkose, thus confusing petrographic composition with subjective considerations about plate-tectonic setting, texture, hydraulic behaviour, mechanical durability, or chemical durability in the illusion that a classification could be genetic at the same time as descriptive.
Abstract
Magma decompression rate is one of the most important parameters in controlling eruption dynamics. One way to determine decompression rate is by fitting a volatile elements diffusion profile ...to a concentration gradient in crystal‐hosted embayments. Previous studies have used a variety of diffusion models, limiting the possibility for inter‐study comparison. Here, we introduce EMBayment‐Estimated Rates (EMBER), a standalone versatile tool that models diffusion of volatile elements along melt embayments. Our model relies on the
pdepe
function of MATLAB to calculate diffusion profiles of H
2
O, CO
2
, and S through the finite difference method. EMBER uses a grid search seeking out the best fits for decompression rates, initial dissolved concentration of each studied volatile and initial exsolved gas content, while setting three constants: temperature along the ascent and pressure at the beginning and end of the ascent. Our model can compute the rate for basaltic, intermediate, and rhyolitic compositions. We applied EMBER to previous studies to evaluate and validate our model. We then reprocessed “homogeneously” the raw data from the literature for a comparison. In other words, the same protocol was used for each diffusion profiles removing the literature‐specific strategies used to constrain unknown parameters. With this comparison, we found a statistically significant positive correlation between maximum magma decompression rates and explosivity of the related eruption. EMBER is expected to help increase the number of volatile diffusion in embayments studies aiming at constraining magma decompression and ascent rates and to facilitate inter‐study comparisons.
Key Points
EMBayment‐Estimated Rates (EMBER) is a new, freely available, Graphical User Interface software that models magma ascent rates for basalt to rhyolite with H
2
O, CO
2
, and S diffusion profiles
EMBER was validated by reproducing previous published literature data
For mafic eruptions, we found a notable correlation between maximum recalculated decompression rates and eruption magnitude or plume height
This study presents a detailed investigation into the microfacies, geochemistry, and depositional environments of carbonate rocks from the southern Benue Trough and eastern Dahomey Basin. This ...analysis involved a combination of techniques, including X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy-dispersive X-ray spectroscopy and thin-section petrographic examination. Samples from the Igumale Formation of the southern Benue Trough and samples from Ewekoro Formation of the eastern Dahomey Basin were analyzed, offering insights into their mineral compositions, elemental distributions, and depositional environments. In each basin, two carbonate microfacies were identified. The two microfacies found in the Igumale Formation were recognized as micritic bioclastic packstone and sandy bioclastic wackestone. In the Ewekoro Formation, the two microfacies recognized were bioclastic packstone and sparitic peloidal wackestone. The X-ray diffraction analysis of samples from both basins revealed a dominance of calcite. X-ray fluorescence analysis showcased calcium oxide and calcium as the predominant oxide and elements in both basins with varying concentrations. Scanning electron microscopy-energy-dispersive X-ray spectroscopy results unveiled the elemental composition with calcium and silicon emerging as major constituents. The photomicrographs suggest distinct depositional conditions for both samples with those from the Igumale Formation showing evidence of shallow marine and that of the Ewekoro Formation suggesting calm marine environments comprised of fined grained carbonate rocks containing fossils. This study has provided detailed understanding on the nature, microfacies types, mineralogical composition, depositional environment and diagenetic processes of Cretaceous-Paleocene carbonate rocks within the studied basins.
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•Carbonate microfacies characterization was performed in selected sedimentary basins in Nigeria.•Integration of carbonate microfacies and a sedimentological approach was used to establish paleodepositional conditions.•The use of petrographic study was used to investigate sedimentology, microfacies association and the paleoenvironment of the carbonate facies.•The use of geochemical index was used to reveal the original sources of the carbonate sediments in the basin.•Integration of SEM and XRD data for understanding the carbonate mineral formation processes, crystal growth and its morphology.•Integration of sedimentological, petrological and geochemical data is key in highlighting poor to fair reservoirs, bioclastic packestone to sandy bioclastic wackestone deposited in shallow marine carbonate environment.
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•Burn out level and unburnt carbon amount influenced by rank and inertinite content.•Organo-petrographic constituents in char is controlled by coal microlithotype.•The intrinsic ...reactivity of inertinite is low with respect to other macerals.•High-density char may be mainly derived from inertinite dominated microlithotypes.•A new type of char named vitrosphere is reported.
The inability to yield heat up to the expected and desired level by a few of the coal fired thermal power plants can primarily be attributed to the ineffectual combustion of coal. In an intensive endeavour to understand the role of petrographic characteristics in combustion behavior, the authors have collected inertinite rich feed coal and fly ash from six different power plants in India. The technological characteristics, petrographic make up (maceral – and microlithotype composition) and vitrinite reflectance of the feed coals were studied in details. The variation in char types were identified in the various fly ashes. The chars from different feed coals were prepared under controlled laboratory conditions. The burn out level and the unburnt carbon amount in fly ash appear to be controlled by rank and inertinite content. The good correlation between the high-density chars and inertinite dominated microlithotype suggests that high-density chars are mainly derived from these related microlithotypes. The presence of a new type of char, named vitrosphere is reported. The fly ash with little unburnt carbon is predominantly comprised of plerospheres.
Resumen: El presente trabajo aporta una investigación arqueométrica sobre piezas cerámicas de los siglos III-I a. C. halladas en contextos alfareros de la ciudad de Sevilla (Palacio Arzobispal) y ...Carmona (zona del Arrabal), pertenecientes en su mayoría a ánforas de tradición púnica y turdetana, o bien ya romanizadas. Entre los principales objetivos se ha pretendido su caracterización tecnológica y composicional, la comparación de las características de cada tradición productiva y la confirmación de la posible procedencia local de estas producciones.En total, han sido 13 las muestras estudiadas con análisis petrográfico de láminas delgadas, análisis químico mediante fluorescencia de rayos X y análisis mineralógico por difracción de rayos X. Los resultados químicos muestran su carácter sílico-aluminoso y cálcico, con contenidos variables de óxido de hierro, así como otros elementos minoritarios y trazas. El tratamiento estadístico ha diferenciado 3 conglomerados y una muestra que se distingue del resto. El análisis mineralógico ha identificado 8 fases cristalinas, unas ya presentes en las materias primas y otras formadas por tratamiento térmico. Destacan la illita, identificada como fase deshidroxilada, anortita, diópsido y gehlenita. En cuanto al análisis petrográfico, se han identificado tres grupos petrográficos que se corresponden composicionalmente con el contexto de origen de las muestras, diferenciando entre las piezas procedentes de Sevilla, las formas romanizadas de Carmona y la cerámica común y formas de imitación de este mismo enclave.Se realiza una estimación de las temperaturas de cocción, entre unos 820 °C y 850 °C en atmósfera oxidante. Por último, se ha discutido la procedencia de las materias primas empleadas, proponiéndose materias primas illítico-calcáreas con un origen localizado en el valle del Guadalquivir. Los resultados permiten corroborar la procedencia local de estas piezas, probablemente relacionadas con los hornos donde aparecieron, y aportan nuevas perspectivas para el estudio de la tradición alfarera local y los cambios que se operan con la implantación productiva romana. Abstract: The present work consists of an archaeometric investigation concerning ceramic samples, mostly unpublished, of the III-I centuries b.C. They were found in connection with kilns of the city of Sevilla (Archbishop's Palace) and the countryside (Arrabal zone, Carmona). They are identified with evolved variations of Iron Age amphorae of Punic and Turdetanian tradition, or already Roman typologies. The main objectives of this research include their technological and compositional characterization as well as the comparison of the characteristics of each manufacture tradition.An assemblage of 13 samples has been studied through petrographic analysis of thin sections, chemical analysis (X-ray fluorescence) and mineralogical analysis (X-ray diffraction). The chemical results showed the silico-aluminous and calcitic character of the samples, with variable contents of iron oxide as well as other minor elements and traces. The statistical treatment of the data by multivariant analysis has differentiated 3 conglomerates and one sample as an outsider. The mineralogical analysis has identified 8 crystalline phases, several of them already present in the raw materials and others formed by thermal treatment. It is interesting to note the illite, identified as dehydroxylated phase, anorthite, diopside and gehlenite. The petrographical analysis has identified 3 different petro-groups, which are correlated by a compositional point of view with the original context of the samples. Thus, according to these results, it has been possible to distinguish the manufactures of Sevilla from the Roman shapes, the common ware and the imitation types of Carmona.It has been discussed the possible solid-state reactions which yielded the crystalline phases identified by X-ray diffraction, besides an estimation of firing temperatures between 820-850 °C in an oxidant atmosphere. Finally, the possible sources for the raw materials used in the fabrication of these amphorae have been proposed in the Guadalquivir River valley, considering their illitic-calcitic characteristics.
Studies of sequence stratigraphy and cycle stratigraphy in carbonate formations increasingly improve our understanding of depositional systems and basinal to global correlations. However, there is ...still a scarcity of dated sequences to determine the time length of sequences and cycles. The durations of sequences and cycles provide tests of the processes that produce them. Poor age resolution mostly stems from the lack of recognizable volcanic ash deposits in many sections. Through continuing advances in analytical techniques and approaches to sampling, the current state of UPb dating of carbonate sedimentary rocks provides opportunities to fill in age gaps. The approach should build on well-constrained 3-dimensional stratigraphic architectures and diagenetic stratigraphies.
Over the last 10 years there has been an explosion in the application of UPb dating of carbonates with the introduction of Laser Ablation (LA) ICPMS analyses. What these studies show is that measured carbonate ages are often younger than the age of deposition and in many cases, multiple ages are derived from individual samples, indicative of multiple events. Often these younger events can be tied to known tectonic activity or sea level changes that would have influenced hydrology, perhaps bringing in new reactive fluids to dissolve or replace some existing minerals and precipitate new minerals. UPb dating of carbonates offers unprecedented potential to work out the timing of deposition and diagenesis in carbonate sequences. As more samples are investigated, particularly in the context of field, petrographic, and geochemical constraints, our views on how to sample and the reliability of ages will be strengthened. Additionally, as more primary and secondary natural reference materials with different textures and mineralogy are made available, our ability to evaluate the reliability of LA ICPMS ages of unknowns will improve. While ages of UPb carbonate will likely never approach the precision of UPb zircon and ArAr sanidine dating of tuffs, carbonates have the advantage of being abundant in space and time, often occurring where volcanic ash deposits are not recognized.
Here we review geochronology from Carboniferous-Permian cyclothems that have been shown in numerous studies to be driven by glacio-eustacy, presumably paced by Milankovitch cycles, and that can be understood in a sequence stratigraphic framework. We compare UPb carbonate ages with other radiometric ages and biostratigraphy to demonstrate the reliability of the carbonate ages and thus highlight potential. We show new Laser Ablation UPb Carbonate data for a particularly well-studied paleosol carbonate with outstanding UPb systematics and compare with published isotope dilution ages, particularly focusing on the power of the image-based approach to carbonate dating advanced by Drost et al. (2018). Finally, we compare results between UPb zircon dating and UPb carbonate dating of cyclothems with Bayesian modeling and conclude that numerous lower precision dates throughout a stratigraphic section provide age constraints that can be similar in precision to a few highly precise ages, depending on the stratigraphic distribution throughout the section.
As a latest Pleistocene repository of Indus River sand at the entry point to the Himalayan foreland basin, the Thal dune field in northern Pakistan stores crucial information that can be used to ...reconstruct the erosional evolution of the Himalayan-Karakorum orogen and the changes in the foreland-basin landscape that took place between the Last Glacial Maximum and the early Holocene. This comprehensive provenance study of Thal Desert sand integrates previously existing petrographic, heavy-mineral, mineral-chemical, isotopic, and geochronological databases with original bulk-sediment geochemistry, zircon-age, and Nd-isotope data. Dune sand is low in quartz and rich in feldspars, volcanic, metavolcanic and metabasite grains, contains a very rich transparent heavy-mineral suite including hypersthene and common zircon grains dated as Late Cretaceous to early Paleogene, and is characterized by high Mg, Sc, V, Co, Ni, Cu concentrations and by εNd values as high as −3.5. Together, these data indicate that ~40% of Thal dune sand was supplied by erosion of the Kohistan arc, a proportion that far exceeds the one assessed for modern Upper Indus sand. Greater detrital supply from the Kohistan arc indicates notably different conditions of sediment generation, during a period in which the sediment-transport capacity of the Upper Indus in the dry lowlands was reduced and volumes of sand were extensively reworked by wind and accumulated in dune fields across the foreland basin. In the early Holocene, the renewed strength of the South Asian monsoon and consequently markedly increased water and sediment discharge led to incision of the Thal and Thar dune fields by the Indus River and its Punjab tributaries draining the Himalayan front directly hit by heavy monsoonal rains.
•The Thal Desert is an inland archive of Indus sand from the western Himalaya syntaxis.•Sand stored in the Thal dunefield reveals major detrital supply from the Kohistan arc.•High variability of εNd values is controlled by minimal changes in monazite content.•The Thal Desert formed in a dry landscape between the LGM and the wet early Holocene.
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•The Middle Iron Age ceramics from Van Fortress, Turkey have been investigated.•The analyses identified the composition and the firing temperature of the ceramics.•Amorphous carbon, ...hematite, magnetite and calcite based pigments were identified.
This work presents the characterization results of Middle Iron Age pottery fragments excavated in Van Fortress, the historical capital of the Urartu Kingdom, located on the eastern coast of Lake Van in Turkey. A multi-analytical approach combining optical microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR) has been employed to investigate the mineralogical composition of ceramics. Micro-Raman spectrometer was also used for the characterization of the pigments used for decoration. The data collected from the analyses offered information on the minerals that were discovered in the ceramics, as well as the temperature at which the ceramics were fired and the atmosphere that they were exposed to. The existence of hematite suggests that they were subjected to firing in an oxidizing environment, with the exception of one sample, which has a sandwich shape characterized by a red-edge and a black center, indicating exposure to both reducing and oxidative atmospheres during the fire process. The ceramics utilized in this investigation are hypothesized to have been crafted from elemental substances procured from two to three distinct clay origins.
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