<p>A proper quantitative statistical characterization of fracture length or height is of paramount importance when analysing outcrops of fractured rocks. Past literature suggests adopting a non-parametric approach, such as circular scanlines, for the unbiased estimation of the fracture-length mean value. This is due to the fact that, in the past, estimating any type of statistical distribution was difficult and there was no real interest in defining precise parametrical models. However, due to the recent rise in popularity of digital outcrop models (DOMs) and of stochastic discrete fracture networks (DFNs), there is an increasing demand for distribution-based solutions that output a correct estimation of parameters for a given proposed model (e.g. mean and standard deviation). This change in demand highlights in the geological literature the absence of properly structured theoretical works on this topic. Our methodology, presented for the first time in this contribution, represents a powerful alternative to non-parametrical methods, aimed at specifically treating censoring bias and obtaining an unbiased trace-length statistical model. As our first objective, we propose to tackle the censoring bias by applying survival analysis techniques: a branch of statistics focused on modelling time-to-event data and correctly estimating model parameters with data affected by censoring. As a second objective, we propose a novel approach for selecting the most representative parametric model. We combine a direct visual approach and the calculation of four statistics to quantify how well proposed models reflect the data. We apply survival analysis to correctly estimate statistical parameters of a censored length dataset in three different case studies and show the effects of the censoring percentage on parametrical estimations that do not use this paradigm. The presented analyses are carried out using an open-source Python package called FracAbility, which we purposefully created to carry out the described workflow (<span class="uri">https://github.com/gecos-lab/FracAbility</span>, last access: 8 September 2024).</p>
<p>More advanced data (gravity field model EIGEN 6C4 including the GOCE gradiometry data instead of EGM 2008) and a more sophisticated method (using a set of gravity aspects instead of gravity anomalies and the radial second derivative of the disturbing potential only) enable a deeper study of various geological features. Improved techniques were applied to study the impact craters Chicxulub and Popigai. We confirm our results from 2010, extend them, and offer more complicated models, namely by means of the gravity strike angles. Both craters are interpreted to be double or multiple craters. The probable impactor azimuth was from NE (to SW) for Chicxulub and SE (to W) for Popigai. The formation of both the craters seems to be associated with impact-induced tectonics that triggered the development of impact grabens.</p>
Introduction: China has the world’s largest amount of antimony resources and plays a vital role in the global antimony industry. The Huangyangling area in Xinjiang belongs to the Lazhulong-Huangyangling antimony mineralization belt; this area is rich in antimony ore resources, with potential for discovery of additional ore. This high-elevation mountainous area is located in the northwestern region of the northern Tibetan Plateau, with a harsh natural environment and poor transportation access; thus, the use of traditional geological exploration methods is limited, and remote sensing technology provides unique advantages.Methods: Using Landsat 8 OLI and Gaofen-6 (GF-6) data, we extracted stratigraphic, lithologic and fault information from the study area through information enhancement processing of the images. Based on Landsat 8 OLI, Sentinel-2 and ASTER images and the use of remote sensing image preprocessing and interference information masking, the spectral characteristics of limonite, as well as hydroxyl, carbonate, and silicified alteration minerals were utilized; the characteristics included reflection or absorption in specific spectral bands. The spectral characteristics were then combined with principal component analysis (PCA) and the band ratio method to extract the alteration information for the study area.Results: The stratigraphy and boundaries between stratigraphic and lithologic units extracted in this study were defined, and numerous small faults were identified based on a comparison with 1:250,000 geologic maps. And the overall distribution trends of the indicators of alteration extracted in this study were located along fault zones; additionally, the hydroxyl and carbonate alteration anomalies matched well with known deposits (occurrences). Thus, the alteration information is a good indication of antimony ore bodies. Based on the geological interpretation, alteration information extraction and geochemical exploration data, four prospecting areas were identified.Discussion: The method of extracting geological and hydrothermal alteration information by remote sensing has practical significance because it provides the possibility for geological work and mineral exploration in difficult high-elevation environments.
This contribution reviews the newly revised biostratigraphy of MiddleâUpper Ordovician marine shelf successions from the JuneeâNarromine Volcanic Belt in central New South Wales, based on conodont studies from four areas covering the northern, central and southern sectors of the Belt. Seven conodont biozones ranging from the middle Darriwilian (Histiodella holodentata-Eoplacognathus pseudoplanus Biozone) to the lower Katian (Taoqupognathus blandus Biozone) are recognized in the Billabong Creek Formation exposed in the Gunningbland area. This includes the first known biostratigraphic succession in Australia that extends continuously from the middle Darriwilian to the basal Sandbian. These new data are crucial for a better understanding of the geological evolution of this region in central New South Wales, and for the enhanced correlation of Ordovician rocks throughout the Macquarie Volcanic Province, which hosts substantial porphyry CuâAu mineral deposits.
<p>To explore the effect of various solvents extraction on the chemical property of shale, several lacustrine shale samples from the Chang 7 member of the Upper Triassic Yanchang Formation, Ordos Basin, with maturities, from marginally mature (<span class="inline-formula"><i>T</i><sub>max</sub>=439</span><span class="inline-formula"><sup>∘</sup></span>) to late mature (<span class="inline-formula"><i>T</i><sub>max</sub>=456</span><span class="inline-formula"><sup>∘</sup></span>), were extracted by using acetone, tetrahydrofuran (THF), carbon disulfide (CS<span class="inline-formula"><sub>2</sub></span>), and benzene, respectively. Fourier transform infrared spectroscopy (FTIR) was employed to examine the functional groups of the samples before and after extraction with different solvents. The results showed that the extraction yield from shale with THF is significantly higher than that of other solvents, which may be related to the properties of the THF, including the aromatic structure, high boiling point, excellent Hansen solubility parameters, and strong polarity. The total organic carbon (TOC)-normalized yield of the mature sample J1 is significantly higher than that of other samples, which may be related to the fact that the J1 sample is at the peak of hydrocarbon generation; thus, a large number of kerogens were cracked into oil and bitumen. The aromaticity of organic matter (OM) increases with the increase in the maturity. The length of the aliphatic chains of the OM first increased with the increase in the maturity before late maturity stage and then decreased in late maturity stage. The extraction of shale samples with solvents hardly changes the length of aliphatic chains. Higher aromaticity is observed in shale residues after THF extractions than for other solvents (i.e., acetone, CS<span class="inline-formula"><sub>2</sub></span>, and benzene).</p>
<p>Raman spectroscopy is commonly used to estimate peak temperatures
in rocks containing organic carbon. In geological settings such as
fold–thrust belts, temperature constraints are particularly important as
complex burial and exhumation histories cannot easily be modelled. Many
authors have developed equations to determine peak temperatures from Raman
spectral parameters, most recently to temperatures as low as 75 <span class="inline-formula"><sup>∘</sup></span>C. However, recent work has shown that Raman spectra can be affected by
strain as well as temperature. Fold–thrust systems are often highly deformed
on multiple scales, with deformation characterised by faults and shear
zones, and therefore temperatures derived from Raman spectra in these
settings may be erroneous. In this study, we investigate how some of the
most common Raman spectral parameters (peak width, Raman band separation)
and ratios (intensity and area) change through a thrust-stacked carbonate
sequence. By comparing samples from relatively low-strain localities to
those on thrust planes and in shear zones, we show maximum differences of
0.16 for <span class="inline-formula"><i>I</i><sub>D</sub> </span>/<span class="inline-formula"> <i>I</i><sub>G</sub></span> and 0.11 for <span class="inline-formula"><i>R</i><sub>2</sub></span>, while full width at half-maximum (FWHM[d]) and Raman band separation
show no significant change between low- and high-strained samples. Plausible
frictional heating temperatures of faulted samples suggest that the observed
changes in Raman spectra are not the result of frictional heating. We also
consider the implications of these results for how temperatures are
determined using Raman spectra in strained and unstrained rock samples.</p>
<p>Geodynamic modelling provides a powerful tool to investigate processes in the Earth's crust, mantle, and core that are not directly observable. However, numerical models are inherently subject to the assumptions and simplifications on which they are based. In order to use and review numerical modelling studies appropriately, one needs to be aware of the limitations of geodynamic modelling as well as its advantages. Here, we present a comprehensive yet concise overview of the geodynamic modelling process applied to the solid Earth from the choice of governing equations to numerical methods, model setup, model interpretation, and the eventual communication of the model results. We highlight best practices and discuss their implementations including code verification, model validation, internal consistency checks, and software and data management. Thus, with this perspective, we encourage high-quality modelling studies, fair external interpretation, and sensible use of published work. We provide ample examples, from lithosphere and mantle dynamics specifically, and point out synergies with related fields such as seismology, tectonophysics, geology, mineral physics, planetary science, and geodesy. We clarify and consolidate terminology across geodynamics and numerical modelling to set a standard for clear communication of modelling studies. All in all, this paper presents the basics of geodynamic modelling for first-time and experienced modellers, collaborators, and reviewers from diverse backgrounds to (re)gain a solid understanding of geodynamic modelling as a whole.</p>
Evangelos M. Mouchos, Evangelos M. Mouchos, Penny J. Johnes
et al.
Phosphorus (P) is a key element which can contribute to the eutrophication of waters draining intensively farmed or populated catchments, driving adverse impacts on ecosystem and human health. An often overlooked source of P in permeable catchments is weathering of P-bearing minerals in bedrock. P release from primary minerals, present when the rock formed, controls background P concentrations in groundwater, but secondary P-bearing minerals may form in aquifers in the presence of anthropogenic P fluxes from agriculture and septic tanks. Using cores from the Upper Greensand (UGS) aquifer, United Kingdom, we show the relative contributions of P from primary and secondary minerals. Bulk rock chemical analysis indicates solid P concentrations of 0–0.8 wt%, while porewater analyses from the same samples indicate phosphate-P concentrations of <5 μg/L - 1 mg/L and dissolved organic P concentrations of <5 μg/L - 0.7 mg/L. These data, coupled with core stratigraphy, reveal the presence of multiple primary and secondary P-bearing minerals in the UGS, and suggest that secondary P-bearing minerals are largely of anthropogenic origin. The weathering of primary P nodules produces a very low background P flux to surface waters, while the anthropogenic P-bearing minerals undergo rapid dissolution, re-precipitation and re-dissolution cycles, controlled by porewater pH and P concentrations, in turn controlling dissolved P flux to groundwater. We show that secondary P-bearing minerals are a dynamic component of the P transfer system linking anthropogenic activities on the land surface to P in groundwater and surface waters and contributing to the eutrophication of surface waters.
Abstract The Central Elysium Planitia (CEP) is one of the youngest geological units on Mars and displays evidence of volcanic and fluvial activities on the surface. The origin of the CEP material has long been debated with a range of hypotheses from purely fluvial to solely volcanic origins. This study presents a comprehensive investigation of SHAllow RADar (SHARAD) data to reveal subsurface radar reflectors over the CEP region. Distribution of the detected radar reflectors show possible connections between the CEP and outflow channels, such as Athabasca Valles and Marte Vallis. Analysis of the radar reflectors in the CEP region show six subsurface layers implying multiple depositional and erosional episodes. One detected subsurface layer is found to correspond to the upper exposed layers of one terraced crater. By measuring the depth accurately of these exposed layers in the derived HiRISE (High Resolution Imaging Scientific Experiment) and CTX (Context Camera) DTMs (Digital Terrain Models) and inverting the dielectric constant combining the layers in radargrams, an interpretation that the filling material contains water ice is favored.
Fernanda Setta, Sérgio Bergamaschi, René Rodrigues
et al.
Abstract This assessment of the volumetric potential of the oil shales of Tremembé Formation (Oligocene, Taubaté Basin, Brazil) was based on the sedimentological study of 2457 total organic carbon and 1007 Rock–Eval pyrolysis analyses of core samples from nine survey wells drilled in the central portion of Taubaté Basin. Along a 240-m-thick package in the upper part of Tremembé Formation, thirteen chemostratigraphic units with thicknesses varying from 10 to 35 m were identified. The upper interval (unit L), 30 m thick, exhibited the highest organic content and original generation potential and was thus studied in detail. In unit L, oil yield maps were constructed, seeking to identify the most attractive areas for industrially exploiting the oil shales, and volumetric calculations employing a probabilistic Monte Carlo method were conducted to quantify the potentially recoverable oil volume. Three exploratory scenarios based on yield values (S1 + S2) were considered for calculating the oil volumes, seeking to offer different exploratory scenarios for decision making. For the scenario that considered only average yields above 100 mg HC/g rock, the recoverable oil volume is 525 million bbl (P90) to 884 million bbl (P10); for the scenario that considered only average yields above 80 mg HC/g rock, the recoverable oil volume is 1.4 billion bbl (P90) to 2.6 billion bbl (P10); and for the scenario that considered only average yields above 60 mg HC/g rock, the recoverable oil volume is 3.6 billion bbl (P90) to 5.4 billion bbl (P10).
Unlike other estuaries Nationally in Australia, the Walpole-Nornalup Inlets is unique complex twin-basin ria estuary in the most humid part of Western Australia. The estuary fronts the oceanographically-dynamic Southern Ocean and, with the high annual rainfall, it provides a range of estuarine landforms, estuarine peripheral wetlands, a dynamic sand barrier that records climate changes and, with its microtidal setting, it provides examples of complex riverine-to-marine dynamics such as intra-basinal gyring. A range of geological to estuarine features that are of geoheritage significance and available for exploration and explanation as geotrails include: (1) the Precambrian geology, (2) the stratigraphy of the Cainozoic Werillup Formation, 4. Cainozoic weathering, sedimentation, and climate history, with a very wet climate to produce erosionally-resistant quartz grain lags, (5) Cainozoic to Quaternary formation of a rock tombolo, (6) the complex estuarine shorelines and history, and (7) complex estuarine processes and history. As an ensemble of geological and other natural history features, Walpole-Nornalup Inlets system also provides a case study of a systematic approach, using the Geoheritage Tool-kit, of identifying and evaluating different natural values. This forms the foundation for to baseline monitoring (for environmental management) and tourism to explore through geological time the natural history of this geologically, and biologically rich location. Keywords: Walpole-Nornalup inlets, Western Australia, Estuary, Geoheritage, Marine Park
<p>The magmatism (including volcanism) in East Asia (or China) could provide key clues and age constraints for the subduction and
dynamical process of the Paleo-Pacific Plate. Although many absolute
isotope ages of extrusive rocks have been published in the 1980s–2000s,
large uncertainties and large errors prevent the magmatism in southeast (SE) China from
being well understood. In this study, we investigate the zircon
geochronology of extrusive rocks and temporospatial variations in the late
Mesozoic volcanism in SE China. We reported zircon U–Pb ages of
new 48 extrusive rock samples in the Shi-Hang tectonic belt. Together with
the published data in the past decade, ages of 291 rock samples from
<span class="inline-formula">∼40</span> lithostratigraphic units were compiled, potentially
documenting a relatively complete history and spatial distribution of the
late Mesozoic volcanism in SE China. The results show that the extrusive
rocks spanned <span class="inline-formula">∼95</span> Myr (177–82 Ma), but dominantly
<span class="inline-formula">∼70</span> Myr (160–90 Ma), within which the volcanism in the early
Early Cretaceous (145–125 Ma) was the most intensive and widespread
eruption. We propose that these ages represent the intervals of the
Yanshanian volcanism in SE China. Spatially, the age geographic pattern of
extrusive rocks shows that both the oldest and youngest age clusters occur
in the coastal magmatic arc (eastern Zhejiang and Fujian), and the most
intensive and widespread age group (145–125 Ma) occurs in a back arc or rifting basin (eastern Jiangxi, central Zhejiang, and northern Guangdong), implying
that the late Mesozoic volcanism migrated northwest and subsequently
retreated southeast. This volcanic migration pattern may imply that the
Paleo-Pacific Plate subducted northwestward and the roll-back subduction did
not begin until the Aptian (<span class="inline-formula">∼125</span> Ma) of the mid-Cretaceous.</p>
<p>The majority of Antarctic ice shelves are bounded by grounded ice rises.
These ice rises exhibit local flow fields that partially oppose the
flow of the surrounding ice shelves. Formation of ice rises is
accompanied by a characteristic upward-arching internal stratigraphy
(“Raymond arches”), whose geometry can be analysed to infer information
about past ice-sheet changes in areas where other archives such as rock
outcrops are missing. Here we present an improved modelling framework to
study ice-rise evolution using a satellite-velocity calibrated,
isothermal, and isotropic 3-D full-Stokes model including grounding-line
dynamics at the required mesh resolution (<span class="inline-formula"><</span>500 m). This overcomes
limitations of previous studies where ice-rise modelling has been
restricted to 2-D and excluded the coupling between the ice shelf and ice
rise. We apply the model to the Ekström Ice Shelf, Antarctica, containing
two ice rises. Our simulations investigate the effect of surface mass
balance and ocean perturbations onto ice-rise divide position and
interpret possible resulting unique Raymond arch geometries. Our results
show that changes in the surface mass balance result in immediate and
sustained divide migration (<span class="inline-formula">>2.0</span> m yr<span class="inline-formula"><sup>−1</sup></span>) of up to 3.5 km. In contrast,
instantaneous ice-shelf disintegration causes a short-lived and delayed
(by 60–100 years) response of smaller magnitude (<span class="inline-formula"><0.75</span> m yr<span class="inline-formula"><sup>−1</sup></span>). The model
tracks migration of a triple junction and synchronous ice-divide
migration in both ice rises with similar magnitude but differing rates.
The model is suitable for glacial/interglacial simulations on the
catchment scale, providing the next step forward to unravel the
ice-dynamic history stored in ice rises all around Antarctica.</p>