Diverse Geological Settings Research Articles

Mineralogical Marvels: Deciphering the Geological Alchemy from Stones to Wealth

This research endeavors to dissect the mineralogical intricacies governing the alchemical metamorphosis of geological substrates into economic wealth. Employing a multifaceted approach, this study scrutinizes the crystallographic and chemical underpinnings of economically consequential minerals. Crystallographically, an exploration of intricate structures elucidates the nexus between crystal lattice configurations and resultant mineral properties, instrumental in ascertaining economic worth. Concurrently, an in-depth chemical analysis discerns the elemental intricacies dictating mineral value, establishing a nexus between compositional intricacies and economic significance. The investigation extends to the geological crucible where ore formation processes and diverse geological settings are analyzed. This includes an examination of the dynamic interplay of factors engendering the concentration of economically salient minerals. Consequently, this study accentuates the geological environments fostering mineral richness and includes pertinent case studies. Furthermore, an economic trajectory is traced, covering extraction, processing methodologies, and market dynamics. This encompasses an appraisal of contemporary mining and processing technologies, along with a discerning scrutiny of the geopolitical intricacies steering global mineral markets. In conclusion, this research amalgamates its findings into a cohesive narrative, presenting a nuanced understanding of the geological genesis of mineral wealth and its implications for scientific and economic paradigms.

The effect of permeability on Darcy-to-Forchheimer flow transition

Flow through porous media takes place in diverse geological settings. The fluid motion through pores follows Darcy’s Law (linear rate law) in many cases, but at high flows the Forchheimer (nonlinear) flow regime emerges, where fluid flux and the hydraulic gradient are no longer linearly related. The transition to the nonlinear flow regime has many possible causes, making the prediction of its onset nearly impossible. The Reynolds number has been used for identifying the onset of nonlinear flow, but its values span across a few orders of magnitude suggesting it might be an inappropriate or inadequate metric. Through the analysis and synthesis of 2852 single-phase flow experiments in different porous media and supporting numerical pore-scale flow simulations, we observed that the critical hydraulic gradient (Ic) which determines the onset of Forchheimer flow scales with permeability (k) via a power law for high k media (k = 10−12–10−6 m2). However, when k is smaller (1 × 10−12–1 × 10−18 m2), the Forchheimer flow regime emerges at an Ic that is orders of magnitude smaller than expected, which is possibly caused by the slippery solid surfaces. Other flow processes such as flow separation and recirculation might explain the uncertainties in the power law relationship here and these merit future investigations.

LANDSLIDE PROTECTION OF ROADWAY NETWORK DURING THE CONSTRUCTION AND RECONSTRUCTION

The article discusses an example of construction and operation of a high embankment of the road, which was constructed in the central part of Moldova. A detailed historic reference about the behavior of the embankment over 40 years of its operation is given. The reasons for the repeated deformations of the embankment have been identified. The analysis of the effectiveness of the undertaken landslide prevention works has been performed. In order to increase the effectiveness of landslide protection, the authors propose a procedure for multifactorial analysis of the interaction of complex natural systems and various engineering structures, which will allow designers to reasonably predict and make accurate design decisions in diverse geological settings.

Estimation of chemical weather indices of sediments using R program

For estimating major elemental geochemistry of sedimentary packages, various Weathering Indices (WIs) are utilized by researchers involved in geochemical evolution of sediments. Through developing a computer program, GeoChem, based on ‘R’ programming environment, we intend to simplify the evaluation and implementation of various Weathering Indices (WIs), including CIW, CPA, PIA, CIX, CIA, WIP, R, ICV, V, MWPI and STI. Additionally, it generates plots of input data used to quantify chemical weathering of clastic sediments in various compositional space diagrams, such as Al2O3 – CaO – Na2O, Al2O3 – K2O – CaO – Na2O, Al2O3 – CaO + Na2O – K2O, Al2O3 – CaO + Na2O + K2O – Fe2O3 + MgO and M – F – W compositional space diagram. Using GeoChem, one can do all the calculations and artwork associated with the finished report without having to use Microsoft Excel, CorelDraw or similar software. Input data source files and output calculations results data files are in CSV format. Data plots are produced in vector as well as in raster formats, providing additional flexibility to the user. Also, we are trying to figure out the associated statistical parameters, their correlation and specially restricting the major elemental geochemistry in a variety of compositional space diagrams to constrain sediment and rock composites, demonstrating chemical weathering profiles and mineralogical composition of the parent rock. By altering different arguments in the code, the ‘R’ programming environment allows the investigator to change the code, depending on the dataset under consideration and the user requirement to generate user-defined, customized plots. To demonstrate the applicability of the tool, its performance was tested, evaluating the major elemental geochemical data of diverse geological settings and sedimentary provenance different in kind. For the same, sediments selected include channel, suspended and overbank sediments of the Peninsular rivers of Ganga basin; Surma group and Barail group of sandstones; lake sediments of Manasbal, Kashmir; Mizoram Foreland Basin, India.

Advancing Local Distance Discrimination of Explosions and Earthquakes With Joint P/S and ML‐MC Classification

AbstractClassification of local‐distance, low‐magnitude seismic events is challenging because signals can be numerous and difficult to characterize with approaches developed for larger magnitude events observed at greater distances. Yet, accurate classification is important to studies of earthquake processes and detection of potential underground nuclear tests. Here, we combine two classification metrics: the three‐component ratio of high‐frequency P/S amplitudes and the difference between local and coda duration magnitudes (ML‐MC). The metrics use different parts of the high‐frequency wavefield and exhibit complementary sensitivity for classification of M ∼ 0.5–4 natural earthquakes and borehole explosions, which are the best analog for underground nuclear explosions. Using means from bootstrap resampling across four diverse geologic settings, joint classification achieves >94.4% true positives and <8.4% false positives when using ≥8 seismographs within 200 km of the source. This high performance is obtained without local site corrections, indicating that the method may be transportable for local event classification.

Assessment of oil-producing wells by means of stimulation approach through matrix acidizing: a case study in the Azraq region

The acidizing approach belongs to the well workover operations, where acid mixtures are initially implemented to treat damage near the wellbore area after drilling operations have been completed. Acidizing treatment is characterized by removal of fine particles and debris from the porous media of the damaged zone, hence leading to improve oil production from wells. This study evaluates the assessment of the acidizing treatment in vertical oil-producing wells. Gradually, the damage formation was reduced and then eliminated, and to a great extent, was compensated with the better performance of oil production from reservoirs. Target candidate wells were enriched by environmentally friendly additives and special chemicals, in predefined amounts, to achieve enhanced oil production rates from wells. A semi-analytical model was formulated for extrapolating the skin magnitude, depending on the damage formation’s permeability parameter as well as on the physical characteristics and reservoir depth. The figures of skin magnitude for all target wells were decreased, and oil production rates were enhanced after performing the matrix acidizing process. These findings are valid for diverse geological settings of different formations, as all treated intervals within the investigated wells have shown an objective response to the matrix acidizing approach. Eventually, productivity rates are imperative to increase potential economic outcomes.

Geochemical signatures in native gold derived from Au-bearing ore deposits

Native gold is a significant indicator mineral for Au-bearing deposits. The chemical composition of gold in diverse geological settings is a function of fluid composition under various physicochemical conditions. Native gold grains from various Au-bearing deposits and districts, including orogenic, volcanogenic massive sulfide (VMS), porphyry Cu-Au deposits, epithermal Au-Ag, and reduced intrusion-related gold (RIRG) deposits, were investigated by electron probe microanalyzer (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to establish discriminant chemical signatures to apply indicator mineral surveys for exploration for gold-bearing deposits. Detailed textural observation of gold identifies compositional heterogeneities in gold grains from epithermal and VMS deposits. Partial least square-discriminant analysis (PLS-DA) identifies that Pd, Ag, Sb, Pb, Cu, Hg, and Te contents in gold grains have a high potential to discriminate gold from different deposit types. Comparison of gold compositional data from different deposit types using Random Forests classification models can be used as a predictive modeling tool to provide an accurate indication of gold-bearing deposit types.

Geochemistry of Small Canadian Arctic Rivers with Diverse Geological and Hydrological Settings

AbstractA survey of 25 coastal‐draining rivers across the Canadian Arctic Archipelago (CAA) shows that these systems are distinct from the largest Arctic rivers that drain watersheds extending far south of the Arctic circle. Observations collected from 2014 to 2016 illustrate the influences of seasonal hydrology, bedrock geology, and landscape physiography on each river's inorganic geochemical characteristics. Summertime data show the impact of coincident gradients in lake cover and surficial geology on river geochemical signatures. In the north and central CAA, drainage basins are generally smaller, underlain by sedimentary bedrock, and their hydrology is driven by seasonal precipitation pulses that undergo little modification before they enter the coastal ocean. In the southern CAA, a high density of lakes stores water longer within the terrestrial system, permitting more modification of water isotope and geochemical characteristics. Annual time‐series observations from two CAA rivers reveal that their concentration‐discharge relationships differ compared with those of the largest Arctic rivers, suggesting that future projections of dissolved ion fluxes from CAA rivers to the Arctic Ocean may not be reliably made based on compositions of the largest Arctic rivers alone, and that rivers draining the CAA region will likely follow different trajectories of change under a warming climate. Understanding how these small, coastal‐draining river systems will respond to climate change is essential to fully evaluate the impact of changing freshwater inputs to the Arctic marine system.

Crystallographic and textural evidence for precipitation of rutile, ilmenite, corundum, and apatite lamellae from garnet

Abstract Garnet is a common metamorphic and igneous mineral with extensive solid solution that can be stable to mantle depths ≥400 km. High-T and/or high-P garnet may contain oriented lamellae of other minerals, most commonly simple oxides (e.g., rutile, ilmenite), apatite, and, in ultrahigh-P cases, silicates including pyroxene and amphibole. Lamellae have classically been considered to be precipitation features preserving a record of former garnet chemistry richer in the lamellae nutrients (e.g., Ti4+). Such microtextural origins in precipitation systems (e.g., alloys) have long been studied via the crystallographic orientation relationships (COR) that form between a host and a separating phase, and by the shape-preferred orientation (SPO) of the lamellae. Recently, however, alternative hypotheses to precipitation have been suggested that require emplacement of lamellae in garnet by fluids, or co-growth, overgrowth, or inheritance mechanisms. These hypotheses posit that lamellae cannot be used to study former garnet chemistry. Moreover, they predict that lamellae phases, SPO, and COR should differ widely between localities, as lamellae formation will be controlled by various local rock-specific factors such as fluid presence, fluid chemistry, or mineral growth sequence. On the other hand, if lamellae characteristics are largely consistent between localities, it likely reflects control by precipitation energetics, rather than external factors. There have been few comparative COR studies in geologic systems, but the integrative assessment of COR, SPO, and lamellae assemblages should fingerprint lamellae growth process. To test the precipitation and alternative hypotheses, we collected large electron backscatter diffraction (EBSD) data sets for rutile, ilmenite, and apatite lamellae in garnet from the Brimfield Schist, Connecticut (≥1000 °C metamorphism; Central Maine Terrane, U.S.A.). We analyzed these data alongside published EBSD data for rutile, ilmenite, and corundum from metapegmatites metamorphosed in the eclogite facies from the Austrian Alps (Griffiths et al. 2016). The apatite data set is the first of its kind, and reveals that apatite preferentially aligns its close-packed direction parallel to that of garnet (c-axisapatite//<111>garnet). We also recognize a rutile-garnet COR related to those in meteorites with Widmanstätten patterns that are unequivocal products of exsolution. This is the first identification of direct similarities between silicate-oxide and metal-metal COR of which we are aware. Significantly, this rutile-garnet COR is found in diverse geologic settings including Connecticut and Idaho (U.S.A.), Austria, Germany, Greece, and China over a broad range of bulk-rock compositions. Results for all lamellae minerals show that COR are largely consistent between localities and, furthermore, are shared between apatite, ilmenite, and corundum. Moreover, between 70% and 95% of lamellae have COR and there is a dominant COR for each lamellae phase. Calculations show that d-spacing ratios of host-lamellae pairs can successfully predict the most commonly observed specific COR (those COR with two or more axial alignments with the host). These results, especially similarity of COR from markedly different geologic settings and a low diversity of lamellae minerals, are fully consistent with lamellae formation by precipitation (likely via exsolution). In contrast, the alternative hypotheses remain unsupported by COR results as well as by mineralogical and petrological evidence. Lamellae with similar traits as those in this work should thus be considered precipitates formed during unmixing of garnet compositions originally stable at elevated or extreme pressures and temperatures.

A Simplified, Object-Based Framework for Efficient Landslide Inventorying Using LIDAR Digital Elevation Model Derivatives

Landslide inventory maps are critical to understand the factors governing landslide occurrence and estimate hazards or sediment delivery to channels. Numerous semi-automated approaches for landslide inventory mapping have been proposed to improve the efficiency and objectivity of the process, but these methods have not been widely adopted by practitioners because of the use of input parameters without physical meaning, a lack of transparency in machine-learning based mapping techniques, and limitations in resulting products, which are not ordinarily designed or tested on a large-scale or in diverse geologic units. To this end, this work presents a new semi-automated method, called the Scarp Identification and Contour Connection Method (SICCM), which adapts to diverse geologic settings automatically or semi-automatically using interventions driven by simple inputs and interpretation from an expert mapper. The applicability of SICCM for use in landslide inventory mapping is demonstrated for three diverse study areas in western Oregon, USA by assessing the utility of the results as a landslide inventory, evaluating the sensitivity of the algorithm to changes in input parameters, and exploring how geology influences the resulting landslide inventory results. In these case studies, accuracies exceed 70%, with reliability and precision of nearly 80%. Conclusions of this work are that (1) SICCM efficiently produces meaningful landslide inventories for large areas as evidenced by mapping 216 km2 of landslide deposits with individual deposits ranging in size from 58 to 1.1 million m2; (2) results are predictable with changes to input parameters, resulting in an intuitive approach; (3) geology does not appear to significantly affect SICCM performance; and (4) the process involves simplifications compared with more complex alternatives from the literature.

Gem Corundum Deposits of Greece: Geology, Mineralogy and Genesis

Greece contains several gem corundum deposits set within diverse geological settings, mostly within the Rhodope (Xanthi and Drama areas) and Attico-Cycladic (Naxos and Ikaria islands) tectono-metamorphic units. In the Xanthi area, the sapphire (pink, blue to purple) deposits are stratiform, occurring within marble layers alternating with amphibolites. Deep red rubies in the Paranesti-Drama area are restricted to boudinaged lenses of Al-rich metapyroxenites alternating with amphibolites and gneisses. Both occurrences are oriented parallel to the ultra-high pressure/high pressure (UHP/HP) Nestos suture zone. On central Naxos Island, colored sapphires are associated with desilicated granite pegmatites intruding ultramafic lithologies (plumasites), occurring either within the pegmatites themselves or associated metasomatic reaction zones. In contrast, on southern Naxos and Ikaria Islands, blue sapphires occur in extensional fissures within Mesozoic metabauxites hosted in marbles. Mineral inclusions in corundums are in equilibrium and/or postdate corundum crystallization and comprise: spinel and pargasite (Paranesti), spinel, zircon (Xanthi), margarite, zircon, apatite, diaspore, phlogopite and chlorite (Naxos) and chloritoid, ilmenite, hematite, ulvospinel, rutile and zircon (Ikaria). The main chromophore elements within the Greek corundums show a wide range in concentration: the Fe contents vary from (average values) 1099 ppm in the blue sapphires of Xanthi, 424 ppm in the pink sapphires of Xanthi, 2654 ppm for Paranesti rubies, 4326 ppm for the Ikaria sapphires, 3706 for southern Naxos blue sapphires, 4777 for purple and 3301 for pink sapphire from Naxos plumasite, and finally 4677 to 1532 for blue to colorless sapphires from Naxos plumasites, respectively. The Ti concentrations (average values) are very low in rubies from Paranesti (41 ppm), with values of 2871 ppm and 509 in the blue and pink sapphires of Xanthi, respectively, of 1263 ppm for the Ikaria blue sapphires, and 520 ppm, 181 ppm in Naxos purple, pink sapphires, respectively. The blue to colorless sapphires from Naxos plumasites contain 1944 to 264 ppm Ti, respectively. The very high Ti contents of the Xanthi blue sapphires may reflect submicroscopic rutile inclusions. The Cr (average values) ranges from 4 to 691 ppm in the blue, purple and pink colored corundums from Naxos plumasite, is quite fixed (222 ppm) for Ikaria sapphires, ranges from 90 to 297 ppm in the blue and pink sapphires from Xanthi, reaches 9142 ppm in the corundums of Paranesti, with highest values of 15,347 ppm in deep red colored varieties. Each occurrence has both unique mineral assemblage and trace element chemistry (with variable Fe/Mg, Ga/Mg, Ga/Cr and Fe/Ti ratios). Additionally, oxygen isotope compositions confirm their geological typology, i.e., with, respectively δ18O of 4.9 ± 0.2‰ for sapphire in plumasite, 20.5‰ for sapphire in marble and 1‰ for ruby in mafics. The fluid inclusions study evidenced water free CO2 dominant fluids with traces of CH4 or N2, and low CO2 densities (0.46 and 0.67 g/cm3), which were probably trapped after the metamorphic peak. The Paranesti, Xanthi and central Naxos corundum deposits can be classified as metamorphic sensu stricto (s.s.) and metasomatic, respectively, those from southern Naxos and Ikaria display atypical magmatic signature indicating a hydrothermal origin. Greek corundums are characterized by wide color variation, homogeneity of the color hues, and transparency, and can be considered as potential gemstones.

Diversity in Ruby Geochemistry and Its Inclusions: Intra- and Inter- Continental Comparisons from Myanmar and Eastern Australia

Ruby in diverse geological settings leaves petrogenetic clues, in its zoning, inclusions, trace elements and oxygen isotope values. Rock-hosted and isolated crystals are compared from Myanmar, SE Asia, and New South Wales, East Australia. Myanmar ruby typifies metasomatized and metamorphic settings, while East Australian ruby xenocrysts are derived from basalts that tapped underlying fold belts. The respective suites include homogeneous ruby; bi-colored inner (violet blue) and outer (red) zoned ruby; ruby-sapphirine-spinel composites; pink to red grains and multi-zoned crystals of red-pink-white-violet (core to rim). Ruby ages were determined by using U-Pb isotopes in titanite inclusions (Thurein Taung; 32.4 Ma) and zircon inclusions (Mong Hsu; 23.9 Ma) and basalt dating in NSW, >60–40 Ma. Trace element oxide plots suggest marble sources for Thurein Taung and Mong Hsu ruby and ultramafic-mafic sources for Mong Hsu (dark cores). NSW rubies suggest metasomatic (Barrington Tops), ultramafic to mafic (Macquarie River) and metasomatic-magmatic (New England) sources. A previous study showed that Cr/Ga vs. Fe/(V + Ti) plots separate Mong Hsu ruby from other ruby fields, but did not test Mogok ruby. Thurein Taung ruby, tested here, plotted separately to Mong Hsu ruby. A Fe-Ga/Mg diagram splits ruby suites into various fields (Ga/Mg < 3), except for magmatic input into rare Mogok and Australian ruby (Ga/Mg > 6). The diverse results emphasize ruby’s potential for geographic typing.

Crustal structure beneath Tierra del Fuego, Argentina, inferred from seismic P-wave receiver functions and ambient noise autocorrelations

We investigate the structure of the crust beneath the main island of Tierra del Fuego through a teleseismic receiver function analysis and ambient seismic noise autocorrelation using data of four available broad-band stations. The area is situated in a remote region of southern Argentina where the interaction between the South American and Scotia plates define the Magallanes-Fagnano Fault System. Crustal thickness, Vp/Vs ratios and S-wave velocity models were estimated using the H-k stacking method and the inversion of receiver functions with the Neighbourhood Algorithm. Furthermore, we applied an ambient seismic noise autocorrelation procedure to identify PmP Moho reflections at all stations. The three methods provide consistent estimates for the crustal thickness which ranges from about 24.5 km in the northern part of the Island to about 39.2 km in the south. The lowest and highest values of S-wave velocity found, in the most superficial layers of the crust, correlate with the presence of Tertiary and upper Cretacic sediments in the north and with older geological units composed by more consolidated lithologies in the south, respectively. Despite the diverse geological and tectonic settings present, our results do not change significantly for different parameters or subsidiary data sets, i.e., showing the robustness of our models which likely represent closely the local structure beneath the Island. This area is considered a very seismically active one and its crustal structure has been little explored demonstrating the importance of having new models and the necessity to increase the station coverage to allow a more detailed study of the region. Furthermore, the models presented here provide better constraints on the crustal structure, and will facilitate studies of the regional seismicity that can improve our understanding of the seismic hazard posed by earthquakes such as the magnitude 7.5 and 7.8 events that occurred in 1949.

EXAMINING THERMAL CONDUCTIVITIES OF SHALLOW SUBSURFACE MATERIALS FOR GROUND SOURCE HEAT PUMP UTILIZATION IN THE PANNONIAN PART OF CROATIA

Thermogeological and hydrogeological properties of the shallow subsurface in the Croatian part of the Pannonian Basin System (PBS) were investigated in the context of its utilization for ground source heat pump (GSHP) systems installation. Detailed borehole core determinations, sampling and thermal conductivity measurements were conducted for seven boreholes at four locations in diverse geological settings. Results of 418 measurements conducted on 82 sediment and rock samples were compiled and analysed in the context of existing collections of thermal conductivities from Germany and Switzerland which are frequently utilized for borehole heat exchanger (BHE) dimensioning in other countries. Discrepancies have been detected between thermal conductivity data from different geographical regions and geological settings. These results imply that local data sets should be further developed to enable accurate BHE sizing. In four of the boreholes thermal response tests (TRTs) were also conducted so the results were compared to direct measurements on samples. The comparison demonstrated that in the environments with significant groundwater flow (coarser-grained sediments) the laboratory measurements systematically underestimated natural-scale thermal conductivities, while the discrepancies were low in finer-grained sedimentary environments. That is why in the presence of significant groundwater flow the TRTs are recommended for all installations, while at locations with low flow velocities the analogy to values cited in data collections can be used for small-scale installations. It is important to have the collection of measurements for local materials in cases when thermal response testing would not be economically feasible. The values reported in this paper can be a guideline for proper GSHP system dimensioning in order to achieve better performance, especially of small-scale systems in Croatia and other geologically comparable localities in the PBS area.

Hydro-geophysical characterization and performance evaluation of natural wetlands in a semi-arid wastewater irrigated landscape

Natural wetlands are green infrastructure systems that are energy-efficient for wastewater treatment and can be found in diverse geo-environmental settings around the world. Their structure and functions, which defines the treatment efficiencies are highly varied. Wetlands over shallow bedrock and geological lineaments (weak zones) have been known to contribute to groundwater contamination. However, not many studies have been performed to understand the structure in different geological settings to identify the efficiency determining factors. Therefore, it is important to investigate the geological suitability of the natural wetlands. We examined wastewater fed natural wetlands in diverse geological settings aiming at studying the depth, geo-stability, bio-chemical interactions, and hydrogeological attributes that improve the wastewater quality, within the Musi River basin, India. The integrated geophysical scans encompassing electrical resistivity tomography (ERT), hydrogeological test, bathymetric study and hydro-chemical analysis were carried out to explore the physical structure and hydro-dynamic processes in the wetlands. ERT investigations showed that, the depth to bedrock up to 20–25 m devoid of geo-fractures (lineaments) indicated the effective depth of saturated zone as a passable scope for potential bio-chemical interactions, implying the proportionality of the deep seated (deep bedrock) wetland to the pollutant removal efficiency. The lower order of electrical resistivity range 10–35 Ωm and hydraulic conductivity 2.938 md−1 acquired for saturated weathered zone were found catalyzing the bioremediation, sedimentation, adsorption, redox reactions and ion exchange processes. It caused the deep seated wetland removing nitrate 194.34 kgd−1 (97.18%); sulphate 333.75 kgd−1 (77.70%); phosphate 9.66 kgd−1 (82.53%); microbes 99.99%, BOD 80%, and COD 80% load with discharge 1408 m3d-1 of treated wastewater. Further, the strategies for designating the natural wetlands as wastewater treatment systems are also discussed in this paper.

Deciphering Silicification Pathways of Fossil Forests: Case Studies from the Late Paleozoic of Central Europe

The occurrence and formation of silicified wood from five late Paleozoic basins in Central Europe was investigated. Fossil wood from diverse geological settings was studied using field observations, taphonomic determinations as well as mineralogical analyses (polarizing microscopy, cathodoluminescence (CL) microscopy and spectroscopy). The results indicate that silicification is either a monophase or multiphase process under varying physico-chemical conditions. In particular, CL studies revealed complex processes of silica accumulation and crystallization. The CL characteristics of quartz phases in silicified wood can mostly be related to blue (390 and 440 nm), yellow (580 nm), and red (650 nm) emission bands, which may appear in different combinations and varying intensity ratios. Yellow CL is typical for initial silicification, reflecting quick precipitation under oxygen-deficient conditions caused by initial decay of the organic material. Blue CL is predominantly of secondary origin, resulting from replacement of precursor phases by a secondary hydrothermal quartz generation or subsequent silicification of wood. The red CL can be related to a lattice defect (non-bridging oxygen hole center—NBOHC).

Time-dependent variations in vertical fluxes of hydrothermal plumes at mid-ocean ridges

We investigated the short-period variations in vertical fluxes of hydrothermal plumes at mid-ocean ridges through quantitative analysis of digital video images of plumes using the particle image velocimetry method. The analyzed digital video images of hydrothermal plumes were selected from the V Vent and Biotransect Vent at the fast-spreading East Pacific Rise, the Grotto Mound of the Endeavour Segment at the intermediate fast-spreading Juan de Fuca Ridge, and the TAG vent at the slow-spreading Northern Mid-Atlantic Ridge. The PIV was able to track the motion of turbulent parcels instead of individual particles within a hydrothermal plume. The mean plume vertical flux was shown to increase with increasing height above the vent orifice, revealing significant turbulent disperse of the rising hydrothermal plumes. The dominant periods of oscillation in the mean vertical flux were observed to be within a relatively narrow band width of 0.5–5 s despite diverse geological settings. Such pervasive short-period variations in plume flux are hypothesized to be caused by the pressure-drop oscillation within a network of compressible two-phase fluid within a sub-seafloor hydrothermal source zone. It is further argued that both the period and amplitude of plume flux oscillation might increase with decreasing plume vertical flux. The relatively narrow band width of the observed oscillation periods might reflect common characteristics in the plume dynamics despite diverse geological settings.

Mineral Quantification with Simultaneous Refinement of Ca-Mg Carbonates Non-Stoichiometry by X-ray Diffraction, Rietveld Method

Quantitative phase analyses of carbonate rocks containing Mg-rich calcite and non-stoichiometric dolomite by the Rietveld method yielded improved results when the substitutions are refined for either minerals. The refinement is constrained by the c-axis of the lattice for both minerals using the formula c = −1.8603 nMg + 17.061 for calcite, where nMg is the molar fraction of Mg replacing Ca, and c = 16.0032 + 0.8632ΔnCa for dolomite, with ΔnCa being the excess Ca in its B site. The one-step procedure was implemented into the Topas software and tested on twenty-two carbonate rock samples from diverse geological settings, considered analogues to petroleum system lithotypes of the pre-evaporite deposits of Southeastern Brazil. The case study spans over a wide range of calcite and dolomite compositions: up to 0.287 apfu Mg in magnesian calcite, and Ca in excess of up to 0.25 apfu in non-stoichiometric dolomite, which are maximum substitutions the formulas support. The method overcomes the limitations for the quantification of minerals by stoichiometry based on whole-rock chemical analysis for complex mineralogy and can be employed for multiple generations of either carbonate. It returns the mineral quantification with unprecedented detailing of the carbonates’ composition, which compares very well to spot analysis (both SEM-EDS and EMPA) if those cover the full range of compositions. The conciliation of the quantification results based on the XRD is also excellent against chemical analysis, thermogravimetry, and carbon elemental analysis.

Differential preservation of vertebrates in Southeast Asian caves

Caves have been an important source of vertebrate fossils for much of Southeast Asia, particularly for the Quaternary. Despite this importance, the mechanisms by which vertebrate remains accumulate and preserve in Southeast Asian caves has never been systematically reviewed or examined. Here, we present the results of three years of cave surveys in Indonesia and Timor-Leste, describing cave systems and their attendant vertebrate accumulations in diverse geological, biogeographical, and environmental settings. While each cave system is unique, we find that the accumulation and preservation of vertebrate remains are highly dependent on local geology and environment. These factors notwithstanding, we find the dominant factor responsible for faunal deposition is the presence or absence of biological accumulating agents, a factor directly dictated by biogeographical history. In small, isolated, volcanic islands, the only significant accumulation occurs in archaeological settings, thereby limiting our understanding of the palaeontology of those islands prior to human arrival. In karstic landscapes on both oceanic and continental islands, our understanding of the long-term preservation of vertebrates is still in its infancy. The formation processes of vertebrate bearing breccias, their taphonomic histories, and the criteria used to determine whether these represent syngenetic or multiple deposits remain critically understudied. The latter in particular has important implications for arguments on how breccia deposits from the region should be analysed and interpreted when reconstructing palaeoenvironments.

Chromium isotope heterogeneity in the mantle

To better constrain the Cr isotopic composition of the silicate Earth and to investigate potential Cr isotopic fractionation during high temperature geological processes, we analyzed the Cr isotopic composition of different types of mantle xenoliths from diverse geologic settings: fertile to refractory off-craton spinel and garnet peridotites, pyroxenite veins, metasomatised spinel lherzolites and associated basalts from central Mongolia, spinel lherzolites and harzburgites from North China, as well as cratonic spinel and garnet peridotites from Siberia and southern Africa. The δ53CrNIST 979 values of the peridotites range from −0.51±0.04‰ (2SD) to +0.75±0.05‰ (2SD). The results show a slight negative correlation between δ53Cr and Al2O3 and CaO contents for most mantle peridotites, which may imply Cr isotopic fractionation during partial melting of mantle peridotites. However, highly variable Cr isotopic compositions measured in Mongolian peridotites cannot be caused by partial melting alone. Instead, the wide range in Cr isotopic composition of these samples most likely reflects kinetic fractionation during melt percolation. Chemical diffusion during melt percolation resulted in light Cr isotopes preferably entering into the melt. Two spinel websterite veins from Mongolia have extremely light δ53Cr values of −1.36±0.04‰ and −0.77±0.06‰, respectively, which are the most negative Cr isotopic compositions yet reported for mantle-derived rocks. These two websterite veins may represent crystallization products from the isotopically light melt that may also metasomatize some peridotites in the area. The δ53Cr values of highly altered garnet peridotites from southern Africa vary from −0.35±0.04‰ (2SD) to +0.12±0.04‰ (2SD) and increase with increasing LOI (Loss on Ignition), reflecting a shift of δ53Cr to more positive values by secondary alteration.The Cr isotopic composition of the pristine, fertile upper mantle is estimated as δCr53=−0.14±0.12‰, after corrections for the effects of partial melting and metasomatism. This value is in line with that estimated for the BSE (−0.12±0.10‰) previously.