Sedimentary Sequence Research Articles

Low resistivity anomalies in the upper crust of the Midlands of Tasmania from combined magnetotelluric datasets

Heat flow data obtained in connection with geothermal resource exploration suggests anomalous upper crustal structure and processes in parts of central east Tasmania. The regional scale crustal geology of the Midlands of Tasmania is, however, mostly obscured at the surface by the Permo-Triassic sedimentary sequences of the Tasmania Basin together with extensive exposures of Jurassic dolerite. We investigate controls on undercover crustal processes in this region by combining long period and broadband magnetotelluric (MT) datasets in 3D inversions for the geoelectric structure; followed by an interpretation that is informed by aspects of the pre-existing 3D regional geological and geophysical model. The new 3D model allows improved resolution of low resistivity anomalies together with a qualitative appraisal of spatially variable model sensitivity. The most robust features ( < 1 Ω m ) in the 2–3 km depth interval occur where N–S and E–W faults intersect with a high point in the topography of the upper surface of a deep seated granite body. Enhancement of conductivity in this zone by clay, graphite or mineralisation, or a combination thereof, is likely. Other low resistivity features suggest that conductive pathways exist where major or multiple faults are present. These interpretations provide support for continued exploration in the Midlands of Tasmania for a variety of resources related to crustal fluids and fracturing.

Compound-specific radiocarbon analysis of sedimentary fatty acids: Potential as a dating tool for lake sediments of Mt. Fuji volcanic region, Japan

Compound-specific radiocarbon analysis (CSRA) is a promising tool for dating sediment sequences where traditional dating methods are impractical. However, the applicability of CSRA of short-chain fatty acids as a dating tool remains poorly understood, especially in lacustrine settings. Accordingly, we determined the radiocarbon content (Δ14C) of individual fatty acids in sediments of Lake Yamanaka (central Japan), as well as their stable carbon and hydrogen isotope ratios, to evaluate the potential of CSRA as a dating tool in volcanic lake environments. We found that the Δ14C values of plant-derived (C24, C26, and C28) n-fatty acids (–99‰ to –149‰) were considerably lower than the Δ14C of charred plants (139‰) within the sediments and those of living aquatic plants (–52‰ to –58‰) in Lake Yamanaka, suggesting that contributions from pre-aged terrestrial and aquatic plant materials likely affect these acids. Similarly, the Δ14C of C16n-fatty acid (–95‰) in surface sediments was much lower than the Δ14C of modern aquatic plants (–52‰ to –58‰), as well as the Δ14C of dissolved organic carbon (DIC) in surface water (–48‰). Together with the stable isotope results, we conclude that in addition to autochthonous aquatic sources, contributions from pre-aged terrestrial carbon sources significantly affect the Δ14C of C16n-fatty acids. Comparing fatty acid Δ14C and concentration data across lakes within the Mt. Fuji region suggests that CSRA of the C16 acid provides valid chronological information only when the C16 originates exclusively from autochthonous aquatic sources, with minor allochthonous terrestrial input.

Seismic Monitoring near Ithaca, New York, Reveals Nonuniform Distribution of Microseismicity in an Intraplate Region

Abstract Cornell University intends to use a deep direct-use geothermal system to heat its Ithaca, New York, campus. In preparation for this project, the Cornell Seismic Network has been monitoring the background seismicity in this intraplate region since 2019. From January 2020 to June 2023, 95 events were detected within 20 km of the proposed geothermal well site, with local magnitudes ranging from −1.02 to 0.56. None of these events appear in regional or national catalogs. Events locate in a narrow geographic band, with one-fourth exhibiting multimodal hypocentral probability peaks both near the surface and at 1–4 km depth. We relocate events with a joint hypocenter and 1D velocity model inversion, in addition to a fully nonlinear method, and then compare observations with synthetic waveforms. Together, these approaches provide strong evidence for &amp;gt;95% of events locating at the surface or within the 3-km-thick sedimentary sequence. We explore how anthropogenic activity and regional topographic stress may contribute to frequent surficial events. This information is critical for characterizing the background microseismicity for comparison during future geothermal operations. Ithaca’s geology of Paleozoic sediments overlying Precambrian crystalline basement is typical of many continental interiors, so these results also provide insight into intraplate microseismicity patterns.

Benthic macroinvertebrate communities change along a karstic barrage-lake system

Barrage-lake systems are a rare natural phenomenon with specific ecological characteristics that are greatly affected by tufa formation. Our main goal was to investigate benthic macroinvertebrate communities and their longitudinal variations within the lakes arranged in cascades in the Dinaric karst hydrosystem. Each lake within the Plitvice Lakes system studied presented with a distinct community, showing the effects of the barrage-lake system on the macroinvertebrates in these lakes. We observed a downstream decrease in taxa richness, abundance and Shannon diversity index along the longitudinal profile of the studied barrage-lake system. This pattern is most probably a result of decreased organic matter and increased tufa deposition. Overall, our results suggest that the hydrosystem studied represents a sequence of sediment sinks in which lakes retain and accumulate organic matter and fauna. Therefore, each lake acts as a filtering screen and consequently appears to be a small ecosystem. Each lake has its own community characteristics, regardless of the fact that water flows from one lake to the next, connecting them and creating very similar abiotic conditions in each lake along the system.

Application of Geophysical Methods in the Identification of Mineralized Structures and Ranking of Areas for Drilling as Exemplified by Alto Guaporé Orogenic Gold Province

Mineral exploration works conducted in the Alto Guaporé Gold Province (AGGP), situated in the southwest region of the Amazon Craton in Brazil, faces the challenges of many gold provinces around the world, i.e., declines in the discoveries of new economic deposits and increases in exploration costs. Ground geophysical methods, combined with structural analyses and geological mapping, are valuable tools that have potential to improve accuracy in selecting exploration targets and in determining drilling locations. AGGP deposits are primarily associated with regional N20°–W50° inverse faulting and sheared geologic contacts between Meso-Neoproterozoic siliciclastic metasedimentary rocks and Mesoproterozoic basement (granite and volcano–sedimentary sequences). Mining currently occurring in the central portion of the province drives exploration works towards the many existing targets at the area. Among them, the ABP target is one of the most promising for being located few kilometers north of the Pau-a-Pique mine. At the ABP target, gold is associated with hydrothermal alteration located in the sheared contacts and in the hinge zone of folded metasedimentary sequence. Hydrothermal phases include Fe-oxides, sulfide (py), muscovite and quartz veins. In this study, we use magnetic and geoelectric (induced polarization) surveys coupled with structural and geological mapping to identify potential footprints within the ABP target. The results from induced polarization (IP) profiles successfully mapped the shape and orientation of the main structures down to approximately 350 m at the ABP target, indicating potential locations for hydrothermal alteration hosting gold. Additionally, 3D magnetic data inversions illustrated the distribution of magnetic susceptibilities and magnetization vectors associated with shear zone structures and isolated magnetic bodies. Magnetic data highlighted fault zones along the contacts between metamorphic rocks and granites, while IP data identified areas with high chargeability, correlating with sulfidation zones mineralized with gold. These findings suggest a metallogenic model where gold deposits are transported through deep structures connected to regional faults, implying significant tectonic and structural control over gold deposition. The results underscore the potential of multiparameter geophysics in identifying and characterizing deposits in both deep and strike, thereby advancing our understanding of mineral occurrences in the region and enhancing the search for new mineralized zones.

Assessment of Middle Jurassic sedimentary sequence’s petroleum system at Imhotep-W-1X well, Northwestern desert, using integrated geochemical, geomechanics, XRD, and basin modeling

Assessment of Middle Jurassic sedimentary sequence’s petroleum system at Imhotep-W-1X well, Northwestern desert, using integrated geochemical, geomechanics, XRD, and basin modeling

Effect of the deposition sequence of Ti and W on the Ni-based Ohmic contacts to n-type 4H-SiC

The paper investigated the deposition sequence-dependent behavior of Ni (50 nm)/Ti (60 nm)/W (60 nm) and Ni (50 nm)/W (60 nm)/Ti (60 nm) Ohmic contacts on n-type 4H-SiC after annealing at 1050 °C for 3 min in Ar atmosphere by in-depth electrical and physical characterization. The contact resistivity of the Ni/Ti/W structure (∼ 8.43 × 10−6 Ω·cm2) was found to be lower than that of the Ni/W/Ti structure (∼ 21.9 × 10−6 Ω·cm2). For the Ni/W/Ti structure, the W layer closer to the contact interface led to an increase in the preferred orientation degree of the δ-Ni2Si (220) plane at the interface, favoring a lower contact resistivity according to previous studies. However, the content and interfacial coverage of δ-Ni2Si is reduced by the WxNiyC phase and the interfacial strain/stress is greatly increased by the WxNiyC phase as well, which ultimately leads to an increase in the contact resistivity. The larger interfacial strain/stress in the Ni/W/Ti structure also results in a rough surface morphology with more microcracks and a large area of delamination. In addition, the shearing strength of Al wire bonding points on the Ni/W/Ti surface is slightly weaker than that on the Ni/Ti/W surface due to the higher surface roughness. The above experimental findings can provide a guideline for further structural optimization of the 4H-SiC Ohmic contacts.

Investigating the potential of unconventional resources in the Midland Basin: A comprehensive chemostratigraphic analysis of a Cline Shale (Wolfcamp-D) core

Basinal mudrocks assigned to the Wolfcamp Group in the Midland Basin are prolific producers of oil and gas. Technological advancements in horizontal drilling and hydraulic fracturing have been successful in the exploitation of oil and gas from these tight mudrocks. However, many challenges remain unsolved in capturing their macroscale compositional variations to enhance recovery factors and delineate “sweet spots”. To gain improved insights into this fine-grained system, high resolution chemostratigraphic (XRF) data was integrated with mineralogical measurements (XRD), logs, thin sections, and TOC readings, as well as hierarchical cluster analysis to: 1) develop a sequence stratigraphic framework, and 2) reconstruct paleo-redox, as well as ancient water-mass, conditions within the Cline Shale (Wolfcamp-D) from a core in the Midland Basin.This study revealed the presence of three chemo-stratigraphically distinct depositional sequences in the Cline Shale, herein termed Lower, Middle, and Upper Cline from the base upwards. All three units exhibit distinct mineralogical and petrophysical characteristics, were correlated across the basin, and interpreted as third-order sequences. Superimposed onto the three interpreted third-order sequences within the Cline, are potential higher frequency (fourth-order) sequences. These fourth-order sequences typically consist of a lower interval, interpreted as lowstand deposits and an upper interval, which is interpreted as transgressive and highstand deposits. The lower interval is interpreted to be deposited during highly reducing conditions while the upper interval is interpreted to be deposited under suboxic conditions. The highest organic matter preservation is associated with the interpreted lowstand deposits, especially in the Upper Cline. Optimal landing zones (20 ft) are recognized in the upper zone of the Cline Shale based on their high resistivity, total organic richness, elevated siliceous content, and reduced percentage of clay minerals. These zones have been correlated with several nearby wells.The current study demonstrates the wealth of information that can be gained from a single core/well when properly investigated at high resolution with measurements on a cm-scale. The observed shifts in the chemistry of the sediments character and composition are distinct, with implications for sequence stratigraphic analysis, the reconstruction of ancient water-mass conditions, and the identification of “sweet spots” for hydrocarbon resources. The provided analysis lays a foundational basis for further studies in the region, serving as critical data input for expansive regional research efforts.

Rapid barrier estuary infill in a geologically-constrained setting: Aireys Inlet/Painkalac Creek, Victoria, Australia

The Holocene infill of an intermittently open-closed barrier estuary (Painkalac Creek/Aireys Inlet) was examined on the southern margins of Australia, through aerial LiDAR, coring, sedimentology, radiocarbon dating and pollen analysis. It is found that almost all the accommodation space within the estuary has been occupied, with a thick sequence (&gt;9 m) of sediments being deposited rapidly soon after flooding by the sea. The rate of sedimentation was 4.8 mm/year which closely matches the rate of sea level rise (4.5 mm/year) during the 1200 year period that the estuary infilled, from around 8000–6800 years ago. The evidence of estuarine deposition above the elevation of the modern intertidal zone provides significant further evidence for the presence of the mid-Holocene highstand sea level in this relatively unstudied part of the Australian coast. The pattern of infill departs from the traditional barrier evolution models. The first phase of infill was likely tide dominated with subtidal sand shoals being found landward of a subtidal bedrock sill. Once a beach-barrier sequence formed, the estuary infilled in a more traditional manner, with lateral progradation of a flood tide delta and central mud basin infill. The barrier estuary of Painkalac Creek therefore has undergone a complex evolutionary history, characterised by a change in process dominance from classic tidal to wave-dominated form. Infill occurred in a keep-up (or fast catch-up) mode, with geological control occurring in regard to the presence of an intertidal bedrock sill at the mouth of the estuary.

The Palaeozoic of a future high potential hydrocarbon fold-thrust belt through the Zagros Basin, Iran

The Zagros Fold-and-Thrust Belt is one of the world's richest hydrocarbon regions, with Palaeozoic sediments being a key element in hydrocarbon plays. The main aim of this research is to provide a model for the formation and development of the sedimentary basin during the Palaeozoic Era in the Zagros and Persian Gulf regions. We utilize data from exploratory wells and surface outcrops of Palaeozoic sediments specifically in the northern parts of Iran's Zagros Mountains. The seismic profiles of the eastern region of the Persian Gulf provide more detailed information due to their distance from the Zagros hinterland. The investigation reveals that folds with wavelengths of several tens of km were formed on the Infra-Cambrian Hormuz Salt or its equivalent décollement.This study has identified halokinetic activities as the primary cause of Palaeozoic deformations in the Zagros region, with tectonic and orogenic factors playing a secondary role. The Palaeozoic sediments are divided into pre-kinematic, syn-kinematic and post-kinematic categories. Sedimentary sequences possibly including the Palaeozoic hydrocarbon source rock could be present throughout the study area.

Multiproxy faunal analysis of the middle – upper Eocene deposits in the Fayum area, Egypt: Insights into sequence stratigraphy, trophic conditions, and oxygenation

The Eocene epoch experienced significant fluctuations in climate, ranging from intense greenhouse warming to icehouse cooling, which profoundly impacted the global depositional systems. The middle – upper Eocene deposits in Garet Gehannam, Fayum area, Egypt, present an exciting opportunity to explore paleoenvironmental dynamics using a multiproxy dataset of calcareous nannofossils, benthic foraminifera, ostracods, and molluscan assemblages. Calcareous nannofossil biostratigraphy constrained the studied sequence to the NP17 and NP-19-20 zones. Furthermore, three 3rd-order depositional sequences, BAR.SQ.1, BAR.SQ.2, and PR.SQ.3 were identified. The BAR.SQ.1 sequence encompasses the Gehannam Formation, with a transgressive systems tract (TST) and a highstand systems tract (HST). The BAR.SQ.2 sequence corresponds to the lower Birket Qarun Formation and exhibits a TST/HST pattern. The PR.SQ.3 sequence, however, consists solely of a TST spanning the upper Birket Qarun and Qasr El Sagha formations. The main trend of our multiproxy-based sea level curve shows an overall stepped Tethyan sea level regression within the 2nd-order cycle. This regression is characterized by a transition from outer neritic to inner settings, interrupted by two minor 3rd-order transgressive pulses. This sea level trend was likely driven by global eustatic changes and regional tectonic uplift related to the final collisional phase between Africa/Arabia and Eurasia, which led to the closure of the Neotethys Ocean. Multiproxy faunal analysis reveals a pronounced upsection shift from low-oxic and mesotrophic conditions to well-ventilated, oligotrophic settings tracking long-term sea level fall. The lowering of the sea level may have expanded aerobic ventilation windows on the continental shelf while potentially reducing nutrient influx. Our multiproxy sequence stratigraphic and paleoenvironmental analysis provides insights into the complex interplay of tectonic, eustatic, and climatic influences on the region during the middle – late Eocene episode along the southern Tethyan margin.

Iron species and sulfur isotopic compositions of authigenic pyrite in deep-sea sediments at southern Hydrate Ridge, Cascadia margin (ODP Leg 204): implications for non-steady-state depositional and diagenetic processes

Two accretionary sediment sequences from Sites 1245 and 1252 recovered during Ocean Drilling Program (ODP) Leg 204 at southern Hydrate Ridge were investigated to explore the response of geochemical partitioning of iron and sulfur isotopic composition of authigenic pyrite to non-steady-state depositional and diagenetic scenarios. Five iron species were characterized by a modified sequential extraction procedure that covers almost all iron-bearing minerals in sediment cores, including: (1) iron-bearing carbonates, mainly siderite; (2) ferric (hydr)oxides, probably ferrihydrite and/or lepidocrocite; (3) magnetite; (4) iron-bearing silicates; and (5) pyrite. Highly reactive iron has been accumulated for a long-term steady-state history and its pyritization, to varying degrees, is limited by availability of dissolved sulfide. This causes pyrite and siderite occurred in the same sedimentary layer and shows an inverse relationship between their concentrations. From this, their proportions to highly reactive iron can be chosen for evaluating the degree of sulfidization. A significant change in sulfur isotopic composition of pyrite (-42.4 to +16.8‰ VCDT) indicates that the steady-state conditions are dramatically limited, where the δ34S values higher than -20‰ may result from an upward shift of SMT zone close to the seafloor or a sudden, massive depositional event. To explain the downcore sulfidization effects and pyrite δ34S values, we developed two categories of conceptual scenarios based on variations in sedimentation rate and methane flux. The geochemical features similar to those derived from each scenario were searched in the sediment columns and the non-steady-state events behind the scenarios were proved to be consistent with the real observations. Thus, iron species and pyrite δ34S values can be regarded as a proxy to differentiate different non-steady-state depositional and diagenetic controls on the sedimentary record.

Determination of the Nature of Hydrocarbons in the Barents Sea (Verification of Remote Sensing Data)

Based on remote sensing data on the distribution of oil spills obtained using synthetic aperture radar (SAR) imagery of the Sentinel-1A and Sentinel-1B satellites in 2016–2022 and the results of the analysis of aliphatic hydrocarbons (AHCs) and polycyclic aromatic hydrocarbons (PAHs) in bottom sediments taken in 2019–2022, the nature of oil slicks in various areas of the Barents Sea has been established. It is shown that the distribution of oil slicks in coastal areas is greatly influenced by anthropogenic hydrocarbon inflow (mainly from shipping and fishing), which is confirmed by elevated AHC concentrations in coastal sediments (up to 73 μg/g) and in the composition of Corg (up to 3.6%). In the central and northern regions of the Barents Sea (station 7105, in the coordinates 75.2–75.3 N, 31.5–31.8 E), the grouping of oil slicks is due to natural seepage of oil and gas. This is confirmed by the anomalous concentration of PAHs in the lower horizons of the obtained sediment column, and their composition (the dominance of 2-methylnaphthalene, a marker of their oil genesis). At the same time, the proportion of light homologues in the composition of alkanes increased, which may indicate their formation in the sedimentary sequence.

Provenance changes of the holocene deposits of Oga and Tsivolki bays (Novaya Zemlya archipelago) according to SR, ND, PB isotope data

The paper is devoted to the Sr-, Nd-, Pb-isotope data obtained for two cores of bottom sediments taken in the Oga and Tsivolki bays of the Severny Island of the Novaya Zemlya archipelago. The studied sequence of sediments from Oga Bay has been accumulated over the last thousand years. The 87Sr/86Sr ratio decreases from top to bottom down the section from 0.72225 to 0.71995, the value of εNd varies from –6.1 to –5.5. The Pb isotopic composition varies within narrow limits: the 206Pb/204Pb ratio from 19.107 to 19.139, the 207Pb/204Pb ratio from 15.632 to 15.635, and the 208Pb/204Pb ratio from 38.568 to 38.635. A rapid decrease in the 87Sr/86Sr ratio at a relatively stable neodymium and lead isotope composition indicates a change in the source of the clastogenic material. This can be explained by the fact that the material of the destruction of Permian clay shales, and then the Devonian-Silurian sedimentary carbonates, first entered the area of glacier abrasion and further, respectively, into the sedimentation zone. The sediment column from the Tsivolki Bay was formed over a little more than 10 thousand years. Based on the Sr, Nd, and Pb isotope ratios, these bottom sediments are divided into lower and upper parts: before and after 150 cm (or ~3500 years). In the lower part of the column, the 87Sr/86Sr ratio increases from 0.72055 to 0.72580, the value of εNd remains approximately the same and varies around –8.2. In the upper part, the 87Sr/86Sr ratio drops to 0.72049 in the near-surface layer; at the same time, the value of εNd increases to –6.4. At the boundary of these two units, the 206Pb/204Pb ratio abruptly changes from about 18.0 in the lower part to 19.3 in the upper part and 208Pb/204Pb from about 36.5 in the lower part to 38.7 in the upper part of the section. The change in the Sr, Nd, and Pb isotope characteristics is likely a reflection of changes in the composition of the rocks in the area where the basin was removed, which is now being eroded by the glacier. Comparison with modern sources supplying clastic material to the Kara Sea showed that the material inputs the Oga and Tsivolki bays only from Novaya Zemlya.

Sedimentary ancient DNA sequences reveal marine ecosystem shifts and indicator taxa for glacial-interglacial sea ice conditions

Sedimentary ancient DNA (sedaDNA) analysis is a promising new approach for reconstructing the impact of past climate and environmental changes on marine paleobiodiversity. By recovering, amplifying, and sequencing taxonomically informative sedaDNA fragments preserved in sediments, it is possible to assess the response of a broad range of eukaryote taxa, including non-fossilizing lineages, to past climate change. Here we present a unique marine derived sedaDNA metabarcoding record, spanning the penultimate glacial-interglacial transition across Marine Isotope Stages 6 to 5d (>135–107 ka) from an Eirik Drift core-site in the Labrador Sea. We identified a range of marine groups including dinoflagellates, diatoms, coccolithophores, chlorophytes, and copepods. There were representatives of primary/secondary producers, grazers, and parasites, which may represent remnants of complex ecosystems and ancient food webs. There were significant biodiversity shifts following the penultimate deglaciation and changing sea ice conditions throughout the Last Interglacial. These shifts reflected the striking increase in community richness during periods of seasonal sea ice and reduction under extensive perennial sea ice cover and open ocean. We identify two potential sedaDNA indicator taxa sequences associated with past seasonal sea ice which are most likely pico-eukaryote representatives of Micromonas and Pyramimonas, both green algae with known sea ice associations in modern ecosystems. Our work demonstrates the importance of high resolution marine sedaDNA metabarcoding for unravelling climate-ecosystem linkages and strengthens the potential of sedaDNA signals for past sea ice reconstructions through indicator sequences.

Unveiling the geoheritage, cultural geomorphology and geotourism potential of Zanskar region, NW Himalaya, India

The Zanskar region, nestled in the heart of the Tethyan Himalaya, represents a significant geological and cultural repository that has remained relatively unexplored by the global tourism industry. This study investigates Zanskar's geoheritage and cultural geomorphology, highlighting its importance for geotourism and advocating for the implementation of sustainable development to preserve its fragile ecosystem. Flowing northward from the Higher Himalayas, the Zanskar River, one of the largest northeast-flowing tributary of the Upper Indus River Basin (UIRB), traverses the complex, strongly folded, and thrusted Zanskar Range via a steep, narrow 60-kilometer-long gorge. Zanskar has consistently garnered attention from geoscientists and tourists owing to its unique geographic location and remoteness. Many areas and routes in Zanskar are challenging to reach, but it stands out as a prime location where glaciers can be accessed by road, making it an ideal destination for studying geoscience. Geologically, the study area is part of the Zanskar Range, with its boundaries defined by the Ladakh Range to the northeast and the Great Himalayan Range to the southwest. The Indus Tsangpo Suture Zone, the Tethyan Sedimentary Sequence, and the Higher Himalayan Crystalline Sequence are exposed from north to south. Zanskar serves as a pristine field museum for studying young Himalayan orogenic tectonics, featuring prominent exposures such as the Zanskar Shear Zone (ZSZ)/South Tibetan Detachment System (STDS) and the structural outcrop of Zangla, showcasing a variety of folding types. These folds signify different phases of deformation resulting from the Indo-Eurasian collision. Moreover, it serves as a prime sequence of Quaternary Glacial Periods (QGP), providing an ideal natural laboratory and an open, practical classroom for geoscientists and Earth science students. We propose ten geoheritage sites in Zanskar, which encompass cultural, geomorphological, and geological attractions with potential for geotourism in this region.

Magnetotelluric imaging of an iron-oxide copper gold (IOCG) deposit under thick cover

The presence of thick (>100 m) and electrically conductive (< 10 Ω.m) ground cover is a major impediment in mineral exploration of deep resources. Iron-oxide copper gold (IOCG) systems in Australia are often associated with a pronounced potential field anomaly, depending on the oxidation state of iron, but the gravity and magnetic field signatures have little vertical resolution unless constrained by drill hole petrophysics. Additionally, IOCG systems have deep magmatic sources, with their conductivity anomalies extending at least to the lithospheric mantle. The Vulcan IOCG prospect lies about 30 km northeast of the Olympic Dam IOCG mine and is defined by a significant gravity anomaly associated with brecciated haematite beneath 850 m of sedimentary cover sequences. To image the physical properties and structural geometry of the Vulcan IOCG prospect, a 100-site broadband MT and passive seismic array was deployed in a 1 km grid over a 9 by 9 km area. Three-dimensional inversion of MT responses resolve structure in three distinct domains. Firstly, broad limestone-quartzite-shale stratigraphy (1–30 Ω.m) in the 850 m cover is delineated in resistivity and corresponds well with changes in shear-wave velocity. Secondly, the region of brecciated haematite below the cover sequences is shown to have lower resistivity (< 60 Ω.m) than surrounding country rock (> 100 Ω.m). Thirdly, a more electrically conductive (< 30 Ω.m) vertical zone that extends > 5 km is imaged a few kilometers to the northeast of the Vulcan haematite breccia, and appears to be linked by a region of low shear-wave velocity in the depth range 1–2 km. Two-dimensional inversion of more regional MT responses along a 200-km line passing through the Vulcan prospect suggest this vertical region of low resistivity links to the lower-crust with anomalous resistivity of < 60 Ω.m in a similar way as imaged beneath the Olympic Dam mine. It is suggested that this conductive region is associated with graphite precipitated from magmatically derived CO2-rich fluids cooling in a reducing environment.

Measurements of radon exhalations and radiological doses using LR-115 (II) nuclear track detectors in Tiru region of the Naga Schuppen Belt, India.

In this present study, the nuclear track detector LR-115 (II) was employed to assess radon (222Rn) exhalation rate, effective radium (226Ra) content, and the annual effective dose from coal and soil samples collected in and around the coal mining area of Tiru region of Nagaland, India. The 222Rn mass and surface exhalation rates and 226Ra contents were found to be in the ranges of 7.3-17.3 mBq kg-1 h-1, 242.9-573.6 mBq m-2h-1 and 1.0-2.3Bqkg-1, respectively, for coal and 15.8-22.0 mBq kg-1 h-1, 523.8-730.4 mBq m-2h-1 and 2.1-2.9Bqkg-1, respectively, for soil. The 222Rn exhalation rates and 226Ra contents in soils were found to be higher than in coal. The estimated annual effective doses for coal and soils were found to be in the ranges of 17.6-41.6 and 38.0-53.0μSv y-1, respectively. This study is an important contribution to the understanding of radiation exposure in the coal mining area of the thrust-bound sedimentary sequence of the Naga Schuppen Belt, and it would have potential impact on further human health studies. However, the measured values for all the samples were found to be within the globally recognised permissible range.

Comparative study on pore-connectivity and wettability characteristics of the fresh-water and saline lacustrine tuffaceous shales: triggering mechanisms and multi-scale models for differential reservoir-forming patterns

Although particular attention has been paid to responses of hydrocarbon storage and percolation capacity to the devitrification concerning lacustrine tuffaceous shale reservoirs in recent years, there is still a lack of systematical and comparative investigation on differential patterns and potential triggering mechanisms concerning development of the pore-microfracture systems and characteristics of surface wettability between the fresh-water and saline lacustrine settings, which is of considerable importance in fully understanding of genesis and spatial distribution of dessert reservoir intervals of tuffaceous shale reservoirs, and to provide further conceptual basis for deciphering shale-oil movability of saline lacustrine fine-grained mixed sedimentary sequences. In this study, tuffaceous shales from both the Upper Triassic Yanchang Formation in the Ordos Basin and Middle Permian Jingjingzigou Formation in the Junggar Basin are targeted to unravel the differential behavior of tuff devitrification and potential impacts on reservoir wettability and pore connectivity concerning fresh-water and saline lacustrine settings, and we present new results here from integrated analyses and combined interpretation of FE-SEM, Image Pro Plus (IPP) software image processing, contact angle and spontaneous imbibition experiments. In view of comparative analysis from representative samples, the tuffaceous shales from saline lacustrine environments are characterized by well-developed intergranular-intercrystalline and dissolution pores, and inorganic microfractures, generally yield a higher plane porosity of representative pore-fracture spaces and spontaneous imbibition slopes, a relatively lower average of n-decane contact angles and corresponding wettability parameters. The saline lacustrine tuffaceous shales are thus suspected to have undergone more intense devitrification resulting in a higher amount of devitrification and associated dissolution pores, and a relatively better connectivity between isolated micropore systems with adjacent microfractures. This would significantly facilitate the interface wettability reversal and occurrence of movable hydrocarbon fluid in microscopic reservoir spaces. Finally, a comprehensive and conceptual model is established illustrating the effects of differential devitrification on reservoir-forming patterns concerning tuffaceous shales developed in the fresh-water and saline lacustrine settings, respectively. These findings are of great theoretical and practical significance to enrich theory of high-quality reservoir formation and shale-oil accumulation in saline lacustrine tuffaceous shale reservoirs, and lay the foundation for guiding efficient exploration of continental fine-grained mixed sedimentary sequences.

Sedimentary Facies, Depositional Environment, and High-resolution Sequence Stratigraphy of Dernah Formation, N Cyrenaica Promontory, NE Libya

The depositional environment and high-order stratigraphic architecture of the Eocene Dernah Formation in N Cyrenaica Promontory, NE Libya, were interpreted through detailed sedimentary facies and sequence stratigraphic analyses of four measured sections located several kilometers apart. Five distinct lithofacies were delineated based on variations in lithology, grain composition, fossil content, texture, color, and stacking pattern. Dernah Formation mainly contains nummulitic limestone with a noticeable amount of Discocyclina and rare gastropods. The extraordinary presence of Nummulites indicates shallow-marine carbonate settings, perhaps a Nummulite bank environment, where the reworking of sediments by wave- or tide-induced currents and storms is high. Two complete fifth-order depositional sequences were defined. Each sequence was subdivided into a transgressive and a regressive hemicycle based on the vertical lithological variation and stacking pattern of facies. We conclude that each sequence may have formed as a result of a fifth-order sea-level cycle. This study reconstructs a three-dimensional model for the Nummulite bank environment in the Mediterranean region, which can serve as an analog for similar depositional systems elsewhere.