Hasil untuk "Stratigraphy"

Guolai Li, Zeina Naim, Luis Gibert et al.

Abstract This study examines the climatic controls on dolomite precipitation through a multiproxy investigation of a carbonate‐rich sediment core from Salinas Lake, a hypersaline playa in Alicante, south‐eastern Iberia. The ~120,000 year record captures depositional cycles and palaeoenvironmental changes driven by late Pleistocene to Holocene climate variability. Integrated analyses of sedimentology, lithology, geochemistry (elemental concentrations, total organic carbon, stable carbon and oxygen isotopes), scanning electron microscopy, microbial community characterisation and palynology reconstruct lake hydrology and its influence on carbonate mineralogy. The sediment succession is marked by alternating calcite‐ and dolomite‐rich intervals, with dolomite crystals displaying morphological evolution from spherical to rhombohedral forms with depth. Stable isotope signatures (δ13C: −6.5‰ to −2.4‰ VPDB; δ18O: −2.3‰ to +4.9‰ VPDB), alongside microbial structures such as extracellular polymeric substances (EPS) and internal crystal voids, suggest a biologically mediated precipitation mechanism. These mineralogical shifts closely correspond to rapid hydrological changes driven by Dansgaard–Oeschger climate oscillations, with dolomite formation favoured under arid, evaporative conditions that concentrate Mg and Ca ions and promote microbial mat development. Halophilic microbial communities, capable of catalysing carbonate precipitation, probably enhance dolomite nucleation and growth through EPS production and geochemical modulation. This work underscores the complex interplay between climate, hydrology, microbial activity and sedimentary mineral formation, providing new insights into the longstanding ‘dolomite problem’ within sedimentary environments.

Stanley Uchechukwu Eze, Okezie Uchegbulam, Rotimi Salami et al.

The study investigated the importance and image behavior of integrated geophysical methods in mapping contaminant spread beneath the surface of a pollution site in Ogoniland, Southern Nigeria. Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) techniques constrained by Vertical Electrical Sounding (VES) data were employed to investigate the electrical properties of hydrocarbon contaminated soils that resulted from recent oil spills/leakage into the environment. Five (5) ERT and GPR lines and twenty-nine (29) VES data were acquired at the spill site. Basically, the electrical signatures from the resistivity measurements were able to image the subsurface layers and the associated contamination zone. GPR equally imaged the subsurface stratigraphy to a depth of 10.0 m beneath the surface. The interpretation of the five (5) ERT data showed consistency in the resistivity structure indicative of contaminant plumes with anomalously high electrical resistivity in the range of 1000-10,000 Ωm, a possible indication of hydrocarbon contamination. On the GPR radargram, regions of high electrical resistivities were in agreement with reduced GPR reflection behavior (shadow zones) and were limited to the near surface of the surveyed areas. Vertical electrical sounding delineated layers with high resistivity predominantly within the second and fourth geoelectric layers within pollution depths of 2.4 m and 11.9 m, respectively. As a result, the underground aquifer, relatively between 7.5 and 10.5 m, has been infiltrated by hydrocarbons. It can be seen from the study that geoelectric measurements on the surface can describe the distribution of hydrocarbon resistive zones as well as their conductive behavior that may be linked with the biodegradation of oil spills in the subsurface. Thus, the employment of these integrated methods for contaminant monitoring, hydrogeologic studies and remediation planning reduced the uncertainties, and they are of extensive relevance in mapping the geological behavior of polluted soils in contamination sites.

D. Spengler, M. Koch-Müller, A. Włodek et al.

<p>A total of 10 western Norwegian eclogites, whose mineral chemistry records metamorphism of up to 850 <span class="inline-formula">°C</span> and 5.5 <span class="inline-formula">GPa</span>, were investigated for structural hydroxyl content in nominally anhydrous minerals. Garnet shows pronounced absorption in the wavenumber ranges of 3596–3633, 3651–3694, and 3698–3735 <span class="inline-formula">cm⁻¹</span> and minor absorption centred at about 3560 <span class="inline-formula">cm⁻¹</span>. Clinopyroxene with aligned inclusions of either quartz, albite, or quartz <span class="inline-formula">+</span> pargasite has major absorption at 3450–3471 and 3521–3538 <span class="inline-formula">cm⁻¹</span> and minor absorption centred at 3350 and approximately 3625 <span class="inline-formula">cm⁻¹</span>. The latter band is strongest in a sample with minute lamellar inclusions rich in Al, Fe, and Na and was excluded from hydroxyl quantification. Orthopyroxene has large, narrow absorption peaks centred at 3415 and 3515 <span class="inline-formula">cm⁻¹</span> and smaller peaks at 3555, 3595, and 3625 <span class="inline-formula">cm⁻¹</span>. Five orthopyroxene-bearing eclogites exhibit relatively homogeneous amounts of structural hydroxyl in garnet (13–32 <span class="inline-formula">µg g⁻¹</span>), clinopyroxene (119–174 <span class="inline-formula">µg g⁻¹</span>), and orthopyroxene (4–17 <span class="inline-formula">µg g⁻¹</span>). The outer 200 <span class="inline-formula">µm</span> wide rims of the orthopyroxene grains illustrate a late hydroxyl loss compared to core values of about 30 %, which is not evident in garnet and clinopyroxene. In contrast, the other five orthopyroxene-free eclogites exhibit variable amounts of hydroxyl in garnet (8–306 <span class="inline-formula">µg g⁻¹</span>) and clinopyroxene (58–711 <span class="inline-formula">µg g⁻¹</span>). Apart from extreme values, the structural hydroxyl content of clinopyroxene in the eclogites studied is lower than in comparable ultra-high-pressure metamorphic samples, e.g. both metasomatised and pristine eclogite xenoliths from the lithospheric mantle underneath several cratons and coesite- and quartz-eclogites from the Erzgebirge and the Kokchetav massifs, by up to several hundreds of micrograms per gram (<span class="inline-formula">µg g⁻¹</span>). The low structural hydroxyl contents, the deficiency of molecular water, and the preservation of diffusion-sensitive evidence from the mineral chemistry for metamorphism well beyond the stability field of amphibole suggest that oriented inclusions of quartz <span class="inline-formula">+</span> pargasite were formed isochemically during decompression. In addition, structural hydroxyl content in clinopyroxene is inversely correlated with metamorphic pressure estimates obtained from orthopyroxene of the same samples. Therefore, structural hydroxyl in nominally anhydrous eclogite minerals can serve as an indicator of the effectiveness of retrogression.</p>

Fusaroli, Federica

This article presents the critical edition and philological analysis of the Occitan translation of John XII-XVII preserved in BNF, fr. 2427. It reassesses the textual transmission of the Gospel passage, underscoring affinities with the fourteenth-century Catalan Bible. Particular attention is given to the linguistic features of the Parisian witness, examined from both scriptological and stratigraphic perspectives. The edition is supplemented by philological and linguistic notes.

Jialin XU, Weibing ZHU, Dayang XUAN et al.

Ground control is a science of mitigating or eliminating mining damage by controlling the breaking motion of mining rock strata, with the aim of ensuring safe, efficient and green mining. There are two limitations in the traditional thoughts and methods of ground control research: only studying the local rock movement instead of the overall movement of the overlying rocks in the whole stratum, and homogenizing the overlying rocks instead of grasping the main contradictions. In view of these problems, in the process of key stratum theory research and engineering application, the ‘full-stratigraphy’ thought of ground control has been formed, whose basic connotation is as follows: firstly, ‘grasping the main contradiction’, to find the key stratum (i.e. the main contradiction) that plays a major role in controlling the overburden movement without homogenizing the overlying rocks. Secondly, it is ‘overall view’, which takes the overburden as a global object, considers all the factors that may have a significant impact on the breakage and instability of the key stratum from a global view, and analyses the manifestation of mining pressure, water and gas transport, and surface subsidence from the point of view of the whole activity of the overburden movement. According to the basic connotation of the thought of full-stratigraphy, when carrying out ground control research, it is necessary to collect full-stratigraphy data and key stratum discrimination studies within different mining scales (mine, mining area, workings and blocks), the complete coring columnar that contains all the information of the rock strata from the vicinity under the mined coal seam all the way to the surface, and then form an overall portrait of the rock stratum endowment characteristics in the research area through the comparison of the columnar of multiple drill holes. The comparison of multiple drill hole columns will form an overall picture of the characteristics of the rock strata in the study area, rather than using only partial columns or comprehensive columns, or homogenizing the whole column. It is necessary to consider the possible effects of changes in the location of the columns and key stratum in different regions on the movement of the rock layer. Secondly, it is also necessary to fully consider the original rock stress, geological structure, topography, water load, mining deployment and so on, which may lead to abnormal loads on the key stratum and its breakage. On this basis, the relation between key stratum movement and various mining engineering phenomena or disasters is established, based on which the mechanism of the problem is analyzed and the targeted rock control methods are put forward. The full-stratigraphy thought has promoted the theoretical development and practical innovation of ground control, solved a series of engineering problems of disaster prevention and control such as supports crushing, water-inrush, subsidence, etc., and achieved remarkable results. The main innovations in the theory of rock stratum control achieved by using the full-stratigraphy thought include revealing the accumulative effect of overburden strata expansion induced by stress relief, establishing a structural model of ‘key stratum - loose stratum arch’ of the mining overburden, proposing a new method to predict the height of fractured water-conducting zone by location of key stratum, and initially establishing a method for estimating the surface subsidence based on the structure of key stratum, and so on. It lays a foundation for engineering application. Typical examples of the full-stratigraphy thought in engineering application include: finding out the root cause of pressurized racking in the uphill section of shallow buried coal seam gully and mining under unconsolidated confined aquifer, completely solving the engineering problems of pressurized racking prevention and control; quantifying the influence of the location of the key stratum on the ‘water flowing fracture height’, solving the problems of preventing and controlling the abnormal water breakout of the roof; proposing the ‘three-zone’ distribution of the unloaded gas in coal seam, which has guided the practice of unloaded gas extraction; it has developed isolated overburden grout injection and filling technology, and created a new mode of ground drilling and one-injection high-efficiency filling and green mining, which has solved the problems of surface subsidence control, and has been comprehensively popularized and applied.

Roberto Casado-Vara, M. Candelaria Martín-Luis, Ramón Casillas-Ruiz et al.

Lithofacies analysis is essential for sequence stratigraphy as it provides crucial insights into facies identification, facies associations, stratigraphic relationships and paleoenvironmental reconstructions. The use of X-ray fluorescence (XRF) scanning techniques provides large elemental geochemical datasets that could help to improve our understanding of depositional processes. This study explores two common methods for sedimentary stratigraphic analysis via XRF: major elements analysis and all-elements analysis. Major elements analysis quickly identifies lithofacies, while all-elements analysis provides detailed chemical composition breakdowns, particularly through trace elements. Although methods for lithology classification with machine learning techniques are available, there are currently limited options for open-source alternatives with the choice of major elements or all-elements analysis. This study presents an open-source Python code for lithofacies classification by comparing major elements and all-elements analysis methods using established machine learning algorithms. The AdaBoost algorithm achieved high performance with both methodologies when trained on a fluvial-lacustrine-sedimentary sequence from a volcanic basin in Tenerife, Canary Islands. In addition, we applied the trained algorithm to two other volcano-sedimentary sequences in the same basin using a transfer learning strategy, achieving an average accuracy of 80 %. However, transfer learning did not work for these two new sequences due to the presence of a basaltic level in addition to the fluvial-lacustrine-facies. Additionally, we conducted a study on the performance of each methodology using ML and explainable artificial intelligence (XAI) algorithms. Our results demonstrate that the AdaBoost algorithm accurately classifies lithofacies regardless of the methodology employed if the sequence only includes fluvial-lacustrine-sedimentary facies. The selected algorithm has bad performance in classifying lithofacies using transfer learning strategy when volcanic basalt facies occur in the same sequence.

A. Margalef, P. Clariana, J. M. Casas et al.

In this work we present a 1:50,000 geological map of the basement rocks of Andorra that is the harmonization of the results of two decades of field work and data analyses in the frame of the 1:25,000 Geological Map of Andorra Project by CENMA–IEA (at present AR + I, Andorra Research + Innovation). The study area lies entirely in the Axial Zone of the Pyrenees, where only late Neoproterozoic and Paleozoic rocks and Quaternary deposits crop out. The map is produced at 1:25,000 scale and Quaternary deposits have been removed, in order to obtain a continuous basement map that can be used as the basis for stratigraphical and structural works. The main results of this work are the publication of new cartographic and structural data, as well as a better understanding of the stratigraphy in this sector.

Bienvenido Martínez-Navarro, Joan Madurell-Malapeira, Sergio Ros-Montoya et al.

On 2015, after the direct study of the most important Late Villafranchian fossil collections of Europe and Western Asia, including Orce (Spain), Pirro Nord and Upper Valdarno (Italy), Appollonia (Greece), Dmanisi (Georgia) and ‘Ubeidiya (Israel), among others, our team proposed the hypothesis that suids disappeared from Europe during the time span between 1.8 and 1.2 Ma. The implications of our conclusions were significant, the arrival of Early <i>Homo</i> into Western Europe, dated to 1.4 Ma at the site of Barranco León in Orce (Spain), preceded the return of pigs into the continent at 1.2 Ma. This hypothesis has been recently challenged because of the finding of an incomplete metatarsal ascribed to <i>Sus</i> sp., with no clear stratigraphic origin, found in the XIX Century Croizet collection of Peyrolles (France), which is housed in the Natural History Museum, London, together with other weak arguments based on the absence of reliable dating for many Early Pleistocene European sites, and other hypothetical records of pigs, with no real fossil support. We answer all these questions and defend that our 2015 hypothesis is correct.

Matthias Urban

Nasrolah Kalantari, Zahra Sajadi, Abbas Charchi et al.

Proper water resources management requires recognizing and evaluating the factors that affect the quantity and quality of water resources. The Ilam-Sarvak (Upper Cretaceous) and Asmari (Oligocene to Miocene) limestone- dolomite formations in the Zagros structural belt have formed a promising karst groundwater horizon. In the present study, the hydraulic relationship between the karst structures of the Izeh territory in the northeast of Khuzestan province was investigated using hydrogeochemical and isotopic information of springs and wells. The results enabled to understand various components influencing the recharge of water resources. In this study, samples were collected from the karst springs and wells of Mongasht, Shavish-Tanosh and Kamarderaz anticlines and Naal-e-Asbi (Horseshoe) syncline and meteoric water to understand the hydrochemical and isotopic characterization, and hydrogeological and hydraulic behavior of the Izeh karst system. The meteoric and groundwater samples were analyzed to determine major and minor ion concentrations and δ18O and δ2H isotope ratios. Isotopic content ranged from -31.6 to -2.9‰ and from -6.32 to -1.87‰ for δ2H and δ18O, respectively, and d-excess values were high and positive. The study of the isotopic content of water samples of springs and wells in the region shows three groups of water sources. The first group, related to the Mongasht anticline springs, has lower isotopic values, indicating that it is recharged by rainfall at high altitudes and snow melting. The isotopic value of the second group is richer than that of the first group, indicating rainfall recharge as well as groundwater mixing (ex­amples of Naal-e-Asbi syncline and Shavish-Tanosh anticline). The highest value in the third group (samples of Kamarderaz anticline) is attributed to evaporation and longer distance from the recharge site to the discharge point, as well as to the diffu­sion system. The trend of decrease in Sr+2 and increase in Ba+2 in the samples of dolomitic limestone formations (Shavish Ta­nosh and Mongasht anticlines) compared to the water samples of Kamarderaz anticline and Naal-e-Asbi syncline indicates the possibility that karst aquifers of the region are recharged from the Mongasht anticline and that there is a hydraulic relation­ship between these structures. D-excess and δ18O show a linear trend, illustrating the effect of altitude difference on isotopic content and recharge sources. The major and minor changes in the concentration of ions, the isotopic content of groundwa­ter and the relationship between TDS and δ18O and d-excess and δ18O indicate the mixing and recharging of karst aquifers (Shavish-Tanosh, Kamarderaz and Naal-e-Asbi aquifers) from the Mongasht karst aquifer and their hydraulic connection.

Mohammadnabi Gorgij, Somayyeh Shahraki Mirzaei

Of the most important characteristics of the Ranikothalia genus, as large benthic foraminifera, are the existence of ornamentation in the external part of the shell especially around the central umbilicus knob, marginal mesh channels (MMC) in the marginal chord, trabeculate system with channels, V-shape plate in the floor of chambers and accumulation of septum that differentiated this genus from Nummulites genus and placing it in the Palaeonummulitinae sub-family. The Ilerdian transgression near the P5 Zone (Pelagic P5) is a stratal key surface for the determination of the Paleocene-Eocene boundary in the neritic deposits. Ranikothalia nuttalli as an index species is used for recognition of the Paleocene–Eocene boundary in the Neo-Tethys shallow water successions. This species, in the Padagi section, resembling the Pakistan Indus Basin, accompanied with Miscellanea miscella, Discocyclina sp., Discocyclina sp., Assilina sp. that indicated SBZ5/6 and suggested lower Ilerdian (earliest Eocene) age. Keywords: Ranikothalia , Ilerdian, systematic, Sistan Suture Zone     Introduction Large benthic foraminifera, such as Fusulinidae, Oritoididae, Alveolinidae, Rotaliidae and Nummulitidae, are important fossil and extant forms that with respect to systematic and biostratigraphic widespread, are studied and some biozonation schemes based on them are suggested. Nummulitidae (such as Ranikothalia) are a group of large benthic foraminiferas developed in the Paleocene and Eocene of the Tethys basin. Larger benthic foraminiferas biozonation is represented by Serra-Kiel et al. (1998) which based on these group of foraminifera Paleocene and Eocene series are divided into 20 shallow benthic zones (SBZ1–SBZ20). The Paleocene–Eocene boundary is considered between SBZ4–SBZ5 (Scheibner & Speijer 2009). Ranikothalia nuttalli as an index species is used for recognition of the Paleocene–Eocene boundary in the Neo-Tethys shallow water successions. This species, in the Padagi section, resembles the Pakistan Indus Basin, accompanied with Miscellanea miscella, Discocyclina sp., Discocyclina sp., Assilina sp. that indicated SBZ5/6 and suggested the lower Ilerdian (earliest Eocene) age. The purpose of this study is to identify and introduce the Ranikothalia nuttali species and investigate its expansion in the adjacent sedimentary basin in the Neo-Tethys Ocean.   Material & Method To do research and biostratigraphic investigations of the Paleocene–Eocene deposits in the Sefid-Abeh basin, the Padagi section, ten rock samples are collected that 60 thin sections prepared from them. The systematic determination of Ranikothalia, in the level of genus and species, is done by using binocular microscope, and then based on identified Ranikothalia nutalli, the age of the Padagi section is suggested.   Discussion of Results & Conclusions Studies of different genera of Nummulitidae in the thin sections and isolated forms led to the identification of different species of Ranikothalia especially Ranikothalia nutalli accompanied by other large benthic foraminiferas suggested the late Paleocene–early Eocene age for the Padagi section in the Sefid-Abeh basin. Ranikothalia nutalli as a specific species for identification of the Paleocene–Eocene boundary in the Neo-Tethys shallow water succession is suggested. This specific species, in the Padagi section, is seen with Miscellanea miscella and the different species of Assilina and Discocyclina, such as the Indus basin, that show SBZ 5/6 and the earliest Eocene (lower Ilerdian) age. The most important characteristics of Ranikothalia genus, as large benthic foraminifera, are the existence of ornamentation in the external part of the shell especially around the central umbilicus knob, marginal mesh channels (MMC) in the marginal chord, trabeculate system with channels, V-shape plate in the floor of chambers and accumulation of septum that differentiated this genus from Nummulites genus and placing it in the Palaeonummulitinae sub-family. The Ilerdian transgression in near the P5 Zone (Pelagic P5) is a stratal key surface for the determination of the Paleocene–Eocene boundary in the neritic deposits. Ranikothalia nuttalli as an index species is used for recognition of the Paleocene–Eocene boundary in the Neo-Tethys shallow water successions. With regards to affinity and similarity of larger benthic foraminifera assemblages (widespread of Ranikothalia and Miscellanea) in the Sefid-Abeh basin (Padagi section) with Indus basin (in Pakistan and India) we can concluded that palaeobiogeographically, the mentioned basin is related to the eastern Neotethys.

Andrew D. Miall

J. Diaz, M. Ruiz, J.-A. Jara

<p>During the COVID-19 pandemic lockdown, the city of Barcelona was covered by a dense seismic network consisting of up to 19 seismic sensors. This network has provided an excellent tool to investigate in detail the background seismic-noise variations associated with the lockdown measures. Permanent stations facilitate comparing the seismic noise recorded during the lockdown quieting with long-term variations due to holiday periods. On the other hand, the data acquired by the dense network show the differences between sites located near industrial areas, transportation hubs or residential areas. The results confirm that the quieting of human activity during lockdown has resulted in a reduction in seismic vibrations in the 2–20 Hz band that is clearly higher than during holiday seasons. This effect is observed throughout the city, but only those stations not affected by very proximal sources of vibration (construction sites, industries) are clearly correlated with the level of activity denoted by other indicators. Our contribution demonstrates that seismic amplitude variations can be used as a proxy for human activity in urban environments, providing details similar to those offered by other mobility indicators.</p>

James B. Innes, Yongqiang Zong

The surface of the lowland deltaic plain around Taihu (Lake Tai), south of the Yangtze river mouth in eastern China, lies near sea level and until recent drainage and development by human societies was mostly covered by wetlands of various types. It was created by regular overbank flooding, mainly from the Yangtze, and the deposition of mostly mineral sediments over the several millennia since sea level regained its current altitude in the early mid-Holocene and progradation of the Yangtze delta began. Fluvial activity has therefore been the dominant influence on sedimentation in the Taihu lowlands, and in the lower Yangtze valley generally, and has determined the character of the mainly inorganic sediment sequences that have accumulated there, with autochthonous deposition of organic sediments within the local wetland plant communities playing a minor role. The presence of both clastic flood horizons and peat layers within the deposits of the Taihu plain attests to great variability in the magnitude of fluvial input from the Yangtze, with repeated extreme floods occurring at some periods, but with periods when the growth of peat layers shows low water tables, little exogenic sediment input and so little fluvial influence. We have examined the published evidence for these different depositional environments in the lower Yangtze and the Taihu plain during the Holocene, comparing the flood history with the middle and upper reaches of the Yangtze catchment. Discrete phases of high or low flooding influence are recognised, and these correspond with large-scale Holocene climate history. Intensified human land use in recent millennia has complicated this relationship, amplifying the flooding signal. Our palynological research shows that algal microfossil type and abundance is a useful proxy for changing water depth and quality in the aquatic environments of the Holocene Taihu wetlands, and can recognise flooding events that are not registered in the floodplain lithological sequences.

L. Li, L. Li, P. Boué et al.

<p>Deep body waves have been reconstructed from seismic noise correlations in recent studies. The authors note their great potential for deep-Earth imaging. In addition to the expected physical seismic phases, some spurious arrivals having no correspondence in earthquake seismograms are observed from the noise correlations. The origins of the noise-derived body waves have not been well understood. Traditionally, the reconstruction of seismic phases from inter-receiver noise correlations is attributed to the interference between waves from noise sources in the stationary-phase regions. The interfering waves emanating from a stationary-phase location have a common ray path from the source to the first receiver. The correlation operator cancels the common path and extracts a signal corresponding to the inter-receiver ray path. In this study, with seismic noise records from two networks at teleseismic distance, we show that noise-derived spurious seismic signals without correspondence in real seismograms can arise from the interference between waves without a common ray path or common slowness. These noise-derived signals cannot be explained by traditional stationary-phase arguments. Numerical experiments reproduce the observed spurious signals. These signals still emerge for uniformly distributed noise sources, and thus are not caused by localized sources. We interpret the presence of the spurious signals with a less restrictive condition of quasi-stationary phase: providing the time delays between interfering waves from spatially distributed noise sources are close enough, the stack of correlation functions over the distributed sources can still be constructive as an effect of finite frequencies, and thereby noise-derived signals emerge from the source averaging.</p>

S. Tapster, J. W. G. Bright, J. W. G. Bright

<p>Cassiterite (<span class="inline-formula">SnO₂</span>) is the most common ore phase of Sn. Typically containing 1–100 <span class="inline-formula">µg g⁻¹</span> of uranium and relatively low concentrations of common Pb, cassiterite has been increasingly targeted for U–Pb geochronology, principally via microbeam methods, to understand the timing and durations of granite-related magmatic–hydrothermal systems throughout geological time. However, due to the extreme resistance of cassiterite to most forms of acid digestion, there has been no published method permitting the complete, closed-system decomposition of cassiterite under conditions in which the basic necessities of measurement by isotope dilution can be met, leading to a paucity of reference and validation materials. To address this a new low blank (<span class="inline-formula">&lt;</span> 1 pg Pb) method for the complete acid decomposition of cassiterite utilising HBr in the presence of a mixed U–Pb tracer, U and Pb purification, and thermal ionisation mass spectrometry (TIMS) analyses has been developed. Decomposition rates have been experimentally evaluated under a range of conditions. A careful balance of time and temperature is required due to competing effects (e.g. HBr oxidation), yet the decomposition of 500 <span class="inline-formula">µ</span>m diameter fragments of cassiterite is readily achievable over periods comparable to zircon decomposition. Its acid-resistant nature can be turned into an advantage by leaching common Pb-bearing phases (e.g. sulfides, silicates) without disturbing the U–Pb systematics of the cassiterite lattice. The archetypal Sn–W greisen deposit of Cligga Head, SW England, is used to define accuracy relative to chemical abrasion–isotope dilution–thermal ionisation mass spectrometry (CA-ID-TIMS) zircon U–Pb ages and demonstrates the potential of this new method for resolving high-resolution timescales (<span class="inline-formula">&lt;0.1</span> %) of magmatic–hydrothermal systems. However, data also indicate that the isotopic composition of initial common Pb varies significantly, both between crystals and within a single crystal. This is attributed to significant fluid–rock interactions and the highly F-rich acidic nature of the hydrothermal system. At microbeam precision levels, this issue is largely unresolvable and can result in significant inaccuracy in interpreted ages. The ID-TIMS U–Pb method described herein can, for the first time, be used to properly characterise suitable reference materials for microbeam cassiterite U–Pb analyses, thus improving the accuracy of the U–Pb cassiterite chronometer as a whole.</p>

Shuo Yang, Frank T.-C. Tsai

Study region: The Greater New Orleans in southeastern Louisiana, USA. Study focus: Flooding is a major threat to New Orleans due to its geographic location and geologic condition. However, potential groundwater flooding is seldom studied and poorly understood. This study investigated potential groundwater flooding and seepage-induced hazards to levees in New Orleans. High-fidelity stratigraphy and groundwater models were developed to investigate groundwater dynamics and identify areas prone to groundwater flooding and low levee factor of safety. New hydrological insights for the region: The stratigraphy model showed that 74 % of shallow sediments in New Orleans are fine grains and noticeable amounts of coarse sediments connect to surface waters. The groundwater model showed that shallow sands, such as beach sands and point bar sands, have strong hydraulic connections with lakes, canals, and Mississippi River. Groundwater flow simulation in 2018 found that 40 % of New Orleans metropolitan area may have groundwater level above ground surface all year round. Low-lying areas with relatively permeable surficial sediments and high groundwater head in shallow sands are concerned about potential groundwater flooding. The simulation results also indicated that levees in these areas have high probabilities of low factors of safety. Not only did the model prediction agree well to the previous levee assessments for the Hurricane Katrina disaster, but it also indicated additional areas with potential levee safety issues.

A. Grobe, A. Grobe, C. von Hagke et al.

<p>We present a study of pressure and temperature evolution in the passive continental margin under the Oman Ophiolite using numerical basin models calibrated with thermal maturity data, fluid-inclusion thermometry, and low-temperature thermochronometry and building on the results of recent work on the tectonic evolution. Because the Oman mountains experienced only weak post-obduction overprint, they offer a unique natural laboratory for this study.</p> <p>Thermal maturity data from the Adam Foothills constrain burial in the basin in front of the advancing nappes to at least 4&thinsp;<span class="inline-formula">km</span>. Peak temperature evolution in the carbonate platform under the ophiolite depends on the burial depth and only weakly on the temperature of the overriding nappes, which have cooled during transport from the oceanic subduction zone to emplacement. Fluid-inclusion thermometry yields pressure-corrected homogenization temperatures of 225 to 266&thinsp;<span class="inline-formula">^∘C</span> for veins formed during progressive burial, 296–364&thinsp;<span class="inline-formula">^∘C</span> for veins related to peak burial, and 184 to 213&thinsp;<span class="inline-formula">^∘C</span> for veins associated with late-stage strike-slip faulting. In contrast, the overlying Hawasina nappes have not been heated above 130–170&thinsp;<span class="inline-formula">^∘C</span>, as witnessed by only partial resetting of the zircon <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mrow class="chem"><mi mathvariant="normal">U</mi><mo>-</mo><mi mathvariant="normal">Th</mi></mrow><mo>)</mo><mo>/</mo><mrow class="chem"><mi mathvariant="normal">He</mi></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d8ce3bb5b8d51bea1aaabe8dd1323f4c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="se-10-149-2019-ie00001.svg" width="58pt" height="14pt" src="se-10-149-2019-ie00001.png"/></svg:svg></span></span> thermochronometer.</p> <p>In combination with independently determined temperatures from solid bitumen reflectance, we infer that the fluid inclusions of peak-burial-related veins formed at minimum pressures of 225–285&thinsp;<span class="inline-formula">MPa</span>. This implies that the rocks of the future Jebel Akhdar Dome were buried under 8–10&thinsp;<span class="inline-formula">km</span> of ophiolite on top of 2&thinsp;<span class="inline-formula">km</span> of sedimentary nappes, in agreement with thermal maturity data from solid bitumen reflectance and Raman spectroscopy.</p> <p>Rapid burial of the passive margin under the ophiolite results in sub-lithostatic pore pressures, as indicated by veins formed in dilatant fractures in the carbonates. We infer that overpressure is induced by rapid burial under the ophiolite. Tilting of the carbonate platform in combination with overpressure in the passive margin caused fluid migration towards the south in front of the advancing nappes.</p> <p>Exhumation of the Jebel Akhdar, as indicated by our zircon <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mrow class="chem"><mi mathvariant="normal">U</mi><mo>-</mo><mi mathvariant="normal">Th</mi></mrow><mo>)</mo><mo>/</mo><mrow class="chem"><mi mathvariant="normal">He</mi></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="2657dacc3c136e36ed8984af5e5cc5e5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="se-10-149-2019-ie00002.svg" width="58pt" height="14pt" src="se-10-149-2019-ie00002.png"/></svg:svg></span></span> data and in agreement with existing work on the tectonic evolution, started as early as the Late Cretaceous to early Cenozoic, linked with extension above a major listric shear zone with top-to-NNE shear sense. In a second exhumation phase the carbonate platform and obducted nappes of the Jebel Akhdar Dome cooled together below ca. 170&thinsp;<span class="inline-formula">^∘C</span> between 50 and 40&thinsp;<span class="inline-formula">Ma</span> before the final stage of anticline formation.</p>