All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
2759.
Initial results of coring at Prees, Cheshire Basin, UK (ICDP JET project): towards an integrated stratigraphy, timescale, and Earth system
understanding for the Early Jurassic
Scientific Drilling,
321--25
2023
2758.
Incompatibility between serpentinization and epidote formation in the
lower oceanic crust: Evidence from the Oman Drilling Project
JOURNAL OF METAMORPHIC GEOLOGY,
41
(5)
2023
Keywords:▾
epidote; lower oceanic crust; olivine gabbro; Oman ophiolite; prehnite;
serpentinization
2757.
Machine-learning-based morphological analyses of leaf epidermal cells in
modern and fossil ginkgo and their implications for palaeoclimate
studies
PALAEONTOLOGY,
66
2023
Keywords:▾
Ginkgo; epidermal cell; micro-character; machine learning; palaeoclimate
parameter
2756.
Implications of a short carbon pulse on biofilm formation on mica schist in microcosms with deep crystalline bedrock groundwater
Frontiers in Microbiology,
14
2023
ISSN: 1664302X
Publisher: Frontiers Media S.A.
Keywords:▾
acetic acid; carbon; ground water; methane; methanol; mica; RNA 16S; Actinobacteria; archaeon; Article; Ascomycetes; Basidiomycetes; bedrock; biofilm; Desulfobulbus; DNA extraction; Escherichia coli; Firmicutes; fungal community; gene sequence; microbial community; microbial diversity; microcosm; nonhuman; Proteobacteria; real time polymerase chain reaction
Abstract: ▾ Microbial life in the deep subsurface occupies rock surfaces as attached communities and biofilms. Previously, epilithic Fennoscandian deep subsurface bacterial communities were shown to host genetic potential, especially for heterotrophy and sulfur cycling. Acetate, methane, and methanol link multiple biogeochemical pathways and thus represent an important carbon and energy source for microorganisms in the deep subsurface. In this study, we examined further how a short pulse of low-molecular-weight carbon compounds impacts the formation and structure of sessile microbial communities on mica schist surfaces over an incubation period of ∼3.5 years in microcosms containing deep subsurface groundwater from the depth of 500 m, from Outokumpu, Finland. The marker gene copy counts in the water and rock phases were estimated with qPCR, which showed that bacteria dominated the mica schist communities with a relatively high proportion of epilithic sulfate-reducing bacteria in all microcosms. The dominant bacterial phyla in the microcosms were Proteobacteria, Firmicutes, and Actinobacteria, whereas most fungal genera belonged to Ascomycota and Basidiomycota. Dissimilarities between planktic and sessile rock surface microbial communities were observed, and the supplied carbon substrates led to variations in the bacterial community composition. Copyright © 2023 Nuppunen-Puputti, Kietäväinen, Kukkonen and Bomberg.
2755.
Evaluating geophysical logs as proxies for cyclostratigraphy in lacustrine deposits using power ratio accumulation
Palaeogeography, Palaeoclimatology, Palaeoecology,
614
2023
2754.
Hydrogeochemical and isotopic signatures elucidate deep subsurface hypersaline brine formation through radiolysis driven water-rock interaction
Geochimica et Cosmochimica Acta,
34065-84
2023
ISSN: 0016-7037Keywords:▾
Groundwater, Brine, Radiolysis, Isotope geochemistry, Deep biosphere
Abstract: ▾ Geochemical and isotopic fluid signatures from a 2.9–3.2 km deep, 45–55 °C temperature, hypersaline brine from Moab Khotsong gold and uranium mine in the Witwatersrand Basin of South Africa were combined with radiolytic and water–rock isotopic exchange models to delineate brine evolution over geologic time, and to explore brine conditions for habitability. The Moab Khotsong brines were hypersaline (Ca-Na-Cl) with 215–246 g/L TDS, and Cl− concentrations up to 4 mol/L suggesting their position as a hypersaline end-member significantly more saline than any previously sampled Witwatersrand Basin fluids. The brines revealed low DIC (∼0.266–∼1.07 mmol/L) with high (∼8.49–∼23.6 mmol/L) DOC pools, and several reduced gaseous species (up to 46 % by volume H2) despite microoxic conditions (Eh = 135–161 mV). Alpha particle radiolysis of water to H2, H2O2, and O2 along with anhydrous-silicate-to-clay alteration reactions predicted 4 mol/L Cl− brine concentration and deuterium enrichment in the fracture waters over a period > 1.00 Ga, consistent with previously reported 40Ar noble gas-derived residence times of 1.20 Ga for this system. In addition, radiolytic production of 7–26 nmol/(L × yr) H2, 3–11 nmol/(L × yr) O2, and 1–8 nmol/(L × yr) H2O2 was predicted for 1–100μ g/g 238U dosage scenarios, supporting radiolysis as a significant source of H2 and oxidant species to deep brines over time that are available to a low biomass system (102–103 cells/mL). The host rock lithology was predominately Archaean quartzite, with minerals exposed on fracture surfaces that included calcite, pyrite, and chlorite. Signatures of δ18Ocalcite, δ13Ccalcite, Δ33Spyrite, δ34Spyrite and 87Sr/86Sr obtained from secondary ion mass spectrometry (SIMS) microanalyses suggest several discrete fluid events as the basin cooled from peak greenschist conditions to equilibrium with present-day brine temperatures. The brine physiochemistry, geochemistry, and cellular abundances were significantly different from those of a younger, shallower, low salinity dolomitic fluid in the same mine, and both were different from the mine service water. These results indicate the discovery of one of few long-isolated systems that supports subsurface brine formation via extended water–rock interaction, and an example of a subsurface brine system where abiotic geochemistry may support a low biomass microbial community.
2753.
Holocene variations in Lake Titicaca water level and their implications for sociopolitical developments in the central Andes
Proceedings of the National Academy of Sciences of the United States of America,
120
(2)
2023
Keywords:▾
Climate; Lakes; Water; biological marker; organic carbon; water; Andes; archeology; Article; cultural anthropology; environmental parameters; geochemical analysis; geographic and geological phenomena; geographic elevation; Holocene; human; lake; lake basin; lake sediment; lake water level; Late Holocene; Middle Holocene; paleoecology; paleoeshoreline; politics; population migration; scientist; shoreline; social evolution; stable isotope labeling; chemistry; climate
Abstract: ▾ Holocene climate in the high tropical Andes was characterized by both gradual and abrupt changes, which disrupted the hydrological cycle and impacted landscapes and societies. High-resolution paleoenvironmental records are essential to contextualize archaeological data and to evaluate the sociopolitical response of ancient societies to environmental variability. Middle-to-Late Holocene water levels in Lake Titicaca were reevaluated through a transfer function model based on measurements of organic carbon stable isotopes, combined with high-resolution profiles of other geochemical variables and paleoshoreline indicators. Our reconstruction indicates that following a prolonged low stand during the Middle Holocene (4000 to 2400 BCE), lake level rose rapidly ~15 m by 1800 BCE, and then increased another 3 to 6 m in a series of steps, attaining the highest values after ~1600 CE. The largest lake-level increases coincided with major sociopolitical changes reported by archaeologists. In particular, at the end of the Formative Period (500 CE), a major lake-level rise inundated large shoreline areas and forced populations to migrate to higher elevation, likely contributing to the emergence of the Tiwanaku culture. Copyright © 2023 the Author(s).
2752.
Hierarchical Milankovitch and sub-Milankovitch cycles in the environmental magnetism of the lower Shahezi Formation, Lower Cretaceous, Songliao Basin, northeastern China
Frontiers in Earth Science,
11
2023
ISSN: 22966463
Publisher: Frontiers Media S.A.
Keywords:▾
China; Songliao Basin; Cretaceous; cyclostratigraphy; geomagnetism; hierarchical system; lacustrine deposit; Milankovitch cycle; paleoclimate; paleoenvironment
Abstract: ▾ SK-2 borehole in Songliao Basin provides unprecedented geological materials for investigating the Early Cretaceous continental paleoenvironment and paleoclimate in northeastern China. The lacustrine successions of the lower Shahezi (K1sh) Formation at the depth from 4,542 to 5,695 m was systematically studied using environmental magnetism and cyclostratigraphy in this study. Magnetic analysis reveals an inverse correlation between magnetic susceptibility (MS) and lithological ranks in fine clastic sediments, with the highest values in mudstones and the lowest in sandstones. The main magnetism carriers in the lower K1sh are pseudo-single-domain (PSD) and/or multi-domain (MD) magnetite with minor presence of hematite. MS was used to further explore the genesis of the environmental and climatic variations through cyclostratigraphic analysis. Sedimentary cycles of 113 m, 34 m, 13 m and 6 m can be identified in the power spectrum, which were interpreted as long and short eccentricity, obliquity, and precession cycles, demonstrating the impact of astronomical cyclicity on sedimentary rhythmicity. Floating astronomical time scale (FATS) of 4,090 kyr and 4,148 kyr were established by tuning the inferred long and short eccentricity cycles to the artificial 405-kyr and 105-kyr orbital eccentricity curves respectively. The estimated sediment accumulation rate around 28 cm/kyr confirms the rapid deposition process within the faulted lacustrine basin. Based on this study, the lake level oscillations in Songliao Basin are assumed to be shaped by long and short eccentricity, precession and semi-precession cycles during Early Cretaceous. This study also indicates that the sand-mudstone alternations deposition in K1sh is most likely driven by the seasonal discrepancies of summer insolation during semi-precession periods. Copyright © 2023 Zhang, Wu, Zhang, Yang, Li, Fang and Shi.
2751.
Environmental changes during the onset of the Late Pliensbachian Event (Early Jurassic) in the Cardigan Bay Basin, Wales
Climate of the Past,
19
(5)
979 – 997
2023
Keywords:▾
Cardigan Bay; United Kingdom; Wales; carbon cycle; chemical weathering; climate forcing; environmental change; orbital forcing; organic matter; paleoenvironment; palynology; Pliensbachian; thermohaline circulation
Abstract: ▾ The Late Pliensbachian Event (LPE), in the Early Jurassic, is associated with a perturbation in the global carbon cycle (positive carbon isotope excursion (CIE) of ∼2‰), cooling of ∼5C, and the deposition of widespread regressive facies. Cooling during the late Pliensbachian has been linked to enhanced organic matter burial and/or disruption of thermohaline ocean circulation due to a sea level lowstand of at least regional extent. Orbital forcing had a strong influence on the Pliensbachian environments and recent studies show that the terrestrial realm and the marine realm in and around the Cardigan Bay Basin, UK, were strongly influenced by orbital climate forcing. In the present study we build on the previously published data for long eccentricity cycle E459±1 and extend the palaeoenvironmental record to include E458±1. We explore the environmental and depositional changes on orbital timescales for the Llanbedr (Mochras Farm) core during the onset of the LPE. Clay mineralogy, X-ray fluorescence (XRF) elemental analysis, isotope ratio mass spectrometry, and palynology are combined to resolve systematic changes in erosion, weathering, fire, grain size, and riverine influx. Our results indicate distinctively different environments before and after the onset of the LPE positive CIE and show increased physical erosion relative to chemical weathering. We also identify five swings in the climate, in tandem with the 405kyr eccentricity minima and maxima. Eccentricity maxima are linked to precessionally repeated occurrences of a semi-arid monsoonal climate with high fire activity and relatively coarser sediment from terrestrial runoff. In contrast, 405kyr minima in the Mochras core are linked to a more persistent, annually wet climate, low fire activity, and relatively finer-grained deposits across multiple precession cycles. The onset of the LPE positive CIE did not impact the expression of the 405kyr cycle in the proxy records; however, during the second pulse of heavier carbon (13C) enrichment, the clay minerals record a change from dominant chemical weathering to dominant physical erosion. © 2023 Teuntje P. Hollaar et al.
2750.
Ground Surface Temperature History Since the Last Glacial Maximum in Northeast Asia: Reconstructions From the Borehole Geotherms of the International Continental Scientific Drilling Program
Geophysical Research Letters,
50
(8)
2023
2749.
Experimental study on nonlinear mechanical behavior and sampling damage characteristics of rocks from depths of 4900–6830 m in Well Songke-2; [松科二井4900~6830 m不同深度岩石非线性力学行为和取样损伤特性试验研究]
Journal of Central South University,
30
(4)
1296 – 1310
2023
ISSN: 20952899
Publisher: Central South University of Technology
Keywords:▾
Minerals; Sedimentary rocks; Sedimentology; Burial depths; Characteristic stress; Deep rocks; Deformation and failures; Different depth; Magmatic rock; Mechanical behavior; Sampling damage; Uni-axial compression tests; Well songke-2; Compression testing
Abstract: ▾ Based on the deep cores of Well Songke-2 (SK-2), uniaxial compression tests of deep rock from 8 different depths in the 4900–6830 m range were carried out, and deformation and failure characteristics were analyzed in detail. It was found that in the range of 4900–6830 m, the mechanical parameters of uniaxial compression tests of rocks changed nonlinearly with depth, and the strength was positively correlated with the hard mineral content. Comparing the rock failure of these samples with the 4500–7000 m core disc segment in SK-2, it was found that the failure of magmatic rock samples in both cases was smoother than that of sedimentary rock, indicating that deep magmatic rocks more easily released energy during the failure process. From depths of 4900–6000 m, prepeak characteristic stresses increased with increasing depth, while from depths of 6000–6830 m, they decreased with increasing depth. Fracture closure stress was used to characterize rock sampling damage at depths of 1000–6830 m, and it was found that sampling damage varied linearly with burial depth in sedimentary strata, while in igneous strata, sampling damage remained stable with increasing burial depth. © 2023, Central South University.
2748.
Hyperspectral core scanner: An effective mineral mapping tool for apatite in the Upper Zone, northern limb, Bushveld Complex
Journal of the Southern African Institute of Mining and Metallurgy,
123
(2)
81--92
2023
2747.
New Rock Magnetic Analysis of Ultramafic Cores From the Oman Drilling Project and Its Implications for Alteration of Lower Crust and Upper Mantle
Journal of Geophysical Research: Solid Earth,
127
(7)
e2022JB024379
2022
2746.
No evidence of multiple impact scenario across the Cretaceous/Paleogene boundary based on planktic foraminiferal biochronology
Special Paper of the Geological Society of America,
557415 – 448
2022
2745.
Numerical Simulation of Coastal Sub-Permafrost Gas Hydrate Formation in the Mackenzie Delta, Canadian Arctic
Energies,
15
(14)
2022
ISSN: 19961073
Publisher: MDPI
Keywords:▾
Flow of fluids; Gas hydrates; Hydration; Methane; Numerical models; Permafrost; Proven reserves, Canadian Arctic; CH 4; Conventional hydrocarbons; Dissolved CH; Fault; Fault system; Gas hydrates formation; Hydrate accumulations; Mallik; Thermogenic methane, Climate change
Abstract: ▾ The Mackenzie Delta (MD) is a permafrost-bearing region along the coasts of the Canadian Arctic which exhibits high sub-permafrost gas hydrate (GH) reserves. The GH occurring at the Mallik site in the MD is dominated by thermogenic methane (CH4), which migrated from deep conventional hydrocarbon reservoirs, very likely through the present fault systems. Therefore, it is assumed that fluid flow transports dissolved CH4 upward and out of the deeper overpressurized reservoirs via the existing polygonal fault system and then forms the GH accumulations in the Kugmallit–Mackenzie Bay Sequences. We investigate the feasibility of this mechanism with a thermo– hydraulic–chemical numerical model, representing a cross section of the Mallik site. We present the first simulations that consider permafrost formation and thawing, as well as the formation of GH accumulations sourced from the upward migrating CH4-rich formation fluid. The simulation results show that temperature distribution, as well as the thickness and base of the ice-bearing permafrost are consistent with corresponding field observations. The primary driver for the spatial GH distribution is the permeability of the host sediments. Thus, the hypothesis on GH formation by dissolved CH4 originating from deeper geological reservoirs is successfully validated. Furthermore, our results demonstrate that the permafrost has been substantially heated to 0.8–1.3 °C, triggered by the global temperature increase of about 0.44 °C and further enhanced by the Arctic Amplification effect at the Mallik site from the early 1970s to the mid-2000s. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.
2744.
Obliquity-forced aquifer-eustasy during the Late Cretaceous greenhouse world
Earth and Planetary Science Letters,
596
2022
ISSN: 0012821X
Publisher: Elsevier B.V.
Keywords:▾
Boreholes; Gamma rays; Geochronology; Greenhouses; Groundwater resources; Lakes; Modulation; Reservoirs (water); Sea level; Zircon; Aquifer-eustasy; Cretaceous; Eustasy; Gamma-rays; Lake levels; Marine incursion; Nenjiang formation; Obliquity; The songliao basin; Aquifers
Abstract: ▾ The mechanisms of short-term (105–106 years) and high-magnitude (>20 m) sea-level oscillations have long been debated involving glacio- and aquifer-eustasy, largely owing to the sparse robust evidence for the presence and significance of aquifer-eustasy, and lack of knowledge about the hydrological dynamics behind it. Non-marine/continental greenhouse archives (e.g., lake level) and their temporal correlation to marine successions (e.g., sea level) could provide clues to aquifer-eustasy. The Songliao Basin (SLB) in Northeast China is one of the largest Mesozoic terrestrial inland basins and provides a terrestrial archive of nearly all Cretaceous successions. The greenhouse late Santonian–early Campanian lower Nenjiang Formation (K2n1+2), recovered from three boreholes in the SLB, provides a unique opportunity for validating and decoding aquifer-eustasy. Initially, the cyclostratigraphy of logging gamma ray (GR) and thorium (Th) series from three boreholes was implemented, which in conjunction with precise geochronological (U/Pb zircon) ages renewed the chronology framework of the SLB. Using the astronomically tuned GR and Th datasets, the lake level of the SLB, which was recovered from sedimentary noise modeling and presented as a proxy for the water table of the groundwater reservoir, showed a clear out-of-phase relationship with the coeval sea level, validating the aquifer-eustasy hypothesis. The lake level of SLB shows prominent ∼1.2 Myr cycles and a well-coupled relationship with sea level and obliquity modulation, indicating that orbital obliquity drove the lake level and modulated water exchange between ocean and continent during the Cretaceous greenhouse period. Strong precipitation events indicated by negative excursions of ostracod δ18O correlate well with high lake levels, high obliquity, and low sea level, suggesting that more moisture was precipitated into the high-latitude continents during obliquity modulation maxima, consequently recharging the aquifer and raising the lake level while drawing down the sea level and vice versa. The close correlation between the reported marine incursion layers and the lowstand of sea level casts a doubt on the marine incursion hypothesis in the SLB; thus, more work is needed to reconcile this paradox. Overall, this study provides the first robust geological evidence for aquifer-eustasy and decodes its role in Cretaceous short-term eustasy. © 2022 Elsevier B.V.
2743.
Oil and gas basin analysis based on airborne gravity and magnetic data
Applied Geophysics
2022
ISSN: 16727975
Publisher: Higher Education Press Limited Company
Abstract: ▾ In this study, we discuss the methods and results for the tectonolayer of a hydrocarbon basin using airborne gravity and magnetic data in the Qijia-Gulong area of the Songliao Basin. Using the latest airborne gravity and magnetic data combined with seismic and drilling data, we determined the density and magnetic measurement data of strata (rocks) in the study area. Next, density and structural stratifications were conducted. The structural sections of the strata-structure-magmatic rocks in the shallow, middle, and deep strata of the basin were determined, and a three-dimensional framework with multiple levels of the basin was constructed. Combining qualitative analysis and quantitative calculation, we explained the depths of the bottom of the Cenozoic layer, the bottom of the Upper Cretaceous layer, the bottom of the Mesozoic layer, and the top of the magnetic basement. We also determined the thicknesses of the Cenozoic layer, the Upper Cretaceous layer, the Upper Jurassic-Lower Cretaceous layer, and the Upper Paleozoic layer. These provide important achievements for the new petroliferous strata survey of regional Upper Paleozoic and Upper Jurassic-Lower Cretaceous strata. At the same time, it provides a new exploration method for studying are as with magmatic rocks and unclear deep seismic reflections. The results show that the new Upper Paleozoic strata (with a thickness of 0–9200 m) are mainly distributed in the central and eastern regions but absent in the western region. This yields significant differences in different regions of the study area. The thickness and depth of the Upper Jurassic-lower Cretaceous layer were different between the eastern and western regions; thicker and deeper in the middle eastern region but thinner and shallower in the western region. © 2022, The Editorial Department of APPLIED GEOPHYSICS. All rights reserved.
2742.
Ongoing alteration of mantle peridotite in the weathering horizon: Initial results from the Oman Drilling Project Multi-Borehole Observatory
Authorea Preprints
2022
2741.
Paleoenvironmental evolution during the Early Eocene Climate Optimum in
the Chicxulub impact crater
EARTH AND PLANETARY SCIENCE LETTERS,
589
2022
Keywords:▾
biomarker; C/N/S-stable isotopes; TEX86; primary productivity;
paleosalinity; pigments
2740.
Orbital control of Pleistocene euxinia in Lake Magadi, Kenya
Geology,
50
(1)
42 – 47
2022
DOI:10.1130/G49140.1
2739.
Orbital controls on eastern African hydroclimate in the Pleistocene
Scientific Reports,
12
(1)
2022
2738.
Orbitally forced chemical weathering in the Late Cretaceous northeastern China: Implications for paleoclimate change
Global and Planetary Change,
218
2022
ISSN: 09218181
Publisher: Elsevier B.V.
Keywords:▾
China; Songliao Basin; Climate change; Geochemistry; Chemical weathering; Continental scientific drillings; Drilling projects; Late cretaceous; Orbital forcing; Paleoclimate change; Paleoclimatic pattern; Quantou formation; Sedimentary records; Songliao basin; chemical weathering; Cretaceous; orbital forcing; paleoclimate; seasonal variation; Weathering
Abstract: ▾ The International Continental Scientific Drilling Project of Cretaceous Songliao Basin has recovered a complete Cretaceous terrestrial sedimentary record in northeastern China, providing a unique opportunity to understand the terrestrial climate change during the Cretaceous period. In this study, we present high-resolution geochemical records from Members 3 and 4 of the Quantou Formation in the SK-1 South borehole. The findings show that samples from Members 3 and 4 of the Quantou Formation originated from a source area of a homogeneous composition. Most of the samples were sediments that underwent the first round of weathering. The geochemical proxies (Th, CIA, CIW, τNa) and average value of the CIA proxy indicate that the strata have been subjected to moderate chemical weathering. The weathering intensity trend was divided into four evolutionary stages based on the CIA proxy: the steady lower part (1915–1878 m), the slowly rising lower and middle part (1878–1815 m), the middle and upper part (1815–1800 m) showing the highest values, and the gently fluctuating upper part (1800–1783 m). Precession, obliquity, and short-eccentricity signals were recognized in the proxies of Th, τNa, corrected CIA, and corrected CIW from Members 3 and 4 of the Quantou Formation, including about seven short-eccentricity cycle periods with a duration of ∼700 ka. The high peaks in short-eccentricity correspond to the high values of Th, corrected CIA, and corrected CIW proxies, and are consistent with the amplitudes of precession signals preserved in τNa during humid periods. During strong precession, the enhanced seasonal contrasts increased humidity, which intensified chemical weathering. The paleoclimatic pattern of interaction between the monsoon-like system and westerlies in the Cretaceous Songliao Basin may be the underlying interpretation that causes cyclic variation in the chemical weathering proxies in Members 3 and 4 of the Quantou Formation. © 2022 Elsevier B.V.
2737.
Petrophysics of Chicxulub Impact Crater's Peak Ring
Journal of Geophysical Research: Solid Earth,
127
(5)
2022
Abstract: ▾ A new set of physical property measurements was undertaken on 29 peak-ring samples from the IODP-ICDP Expedition 364. Among the studied lithologies, the dominant one recovered in the peak ring consists of shocked granitoid rocks (19 samples). Porosity measurements with two independent methods (triple weight and 14C-PMMA porosity mapping) concur and bring new observations on the intensity and distribution of fracturing and porosity in these shocked target rocks. Characterization of the porous network is taken a step further with two other independent methods (electrical and permeability measurements). Electrical properties such as the cementation exponent (1.59 < m < 1.87) and the formation factor (21 < F < 103) do not compare with other granites from the published literature; they point at a type of porosity closer to clastic sedimentary rocks than to crystalline rocks. Permeabilities of the granitoid rocks range from 0.1 to 7.1 mD under an effective pressure of ∼10 MPa. Unlike other fresh to deformed and altered granitoid rocks from the literature compared in this study, this permeability appears to be relatively insensitive to increasing stress (up to ∼40 MPa), with implications for the nature of the porous network, again, behaving more like cemented clastic rocks than fractured crystalline rocks. Other analyzed lithologies include suevite and impact melt rocks. Relatively low permeability (10−3 mD) measured in melt-rich facies suggest that, at the matrix scale, these lithologies cutting through more permeable peak-ring granitoid rocks may have been a barrier to fluid flow, with implications for hydrothermal systems. © 2022 The Authors.
2736.
Phases of stability during major hydroclimate change ending the Last Glacial in the Levant
Scientific Reports,
12
(1)
2022
2735.
Physical property studies to elucidate the source of seismic reflectivity within the ICDP DSeis seismogenic zone: Klerksdorp goldfield, South Africa
International Journal of Rock Mechanics and Mining Sciences,
155105082
2022
ISSN: 13651609
Publisher: Elsevier Ltd
Keywords:▾
South Africa; Acoustic wave velocity; Boreholes; Earthquakes; Geophysical prospecting; Infill drilling; Petrophysics; Porosity; Reflection; Rocks; Seismic response; Seismic waves; Shear waves; Stratigraphy; Wave propagation; Well logging; Downholes; Metabasalts; Mining induced earthquake; P-wave velocity; Petrophysical datum; S-wave velocity; Seismic datas; Seismic reflectivity; Sonic logs; Synthetic seismogram; gold mine; mining-induced seismicity; P-wave; physical property; S-wave; seismic reflection; seismic velocity; seismic zone; seismogram; ultrasonics; Lithology
Abstract: ▾ Petrophysical properties of cylindrical core specimens from three boreholes from the International Continental Scientific Drilling Program, the DSeis project, measured at ambient pressure and room temperature conditions in various laboratories are presented and compared with downhole petrophysical data (sonic and density). The measured properties are from sixty-six rock specimens constituting metasediments, metabasalts and intrusives. Seismic velocities were measured using 0.5 MHz P- and S-wave transducers. To investigate the source of seismic reflectivity observed on the 2D legacy seismic data, we computed synthetic seismograms for adjacent rock units using downhole petrophysical data and compared them with seismic reflections from the reflection seismic profile. The experimental measurements show that the metasediments exhibit lower bulk densities and seismic velocities than the metabasalts and intrusive specimens. The porosity was found to be less than 2% for all the samples. No clear trends emerge when the Poisson's ratio is plotted against the P-wave velocities and porosities of the samples. A positive relationship is observed between the bulk modulus and P-wave velocities of the rock samples. The highest calculated reflection coefficients (RC) are associated with the metasediment-intrusive interfaces in all three boreholes. The intrusive-metabasalt and the metasediment-metabasalt interfaces exhibit low RC. Synthetic seismograms reveal strong reflections that coincide with high RC calculated using the bulk density and velocity data. The synthetic seismograms also revealed additional strong reflections that were not identified using the reflection coefficients calculated from the rock specimens, due to core loss in some lithological units. Successful correlations are carried out between the synthetic seismic data and the real seismic data, enabling us to correlate the stratigraphic sequence drilled in the boreholes to the seismic reflections observed on the legacy 2D reflection seismic data. © 2022 Elsevier Ltd