Drill Core Data Research Articles

Middle to Late Pleistocene multi-proxy record of environmental response to climate change from the Vienna Basin, Central Europe (Austria)

Tectonic basins can represent valuable archives of the environmental history. Presented here are the stratigraphy and multi-proxy analyses of two adjacent alluvial fans in the Quaternary active parts of the Vienna Basin, situated at the interface of the Atlantic, European continental and Mediterranean climate. Deposits comprise a sequence of coarse-grained fluvial deposits intercalated by laterally extensive horizons of pedogenically altered fine sediments. To establish palaeoenvironmental reconstructions, fine-grained sequences from a drill core and outcrop data were analysed according to its malacofauna, palaeopedology, susceptibility and sedimentology. The chronological framework is provided by 38 luminescence ages and supported by geomagnetic polarity investigations. Distinct warm periods each associated with a geomagnetic excursion, are recorded in three pedocomplexes formed during the Last Interglacial and two earlier interglacial periods, indicted to correlate with Marine Isotope Stage (MIS) 9 and MIS 11, respectively. Environmental conditions during the early last glacial period (MIS 5, c. 100–70 ka) are reconstructed from mollusc-shell rich overbank fines deposited along a former channel belt, covered by massive sheetflood deposits during MIS 2. Analysed warm phases suggest strong variations in humidity, ranging from steppe to forest dominated environments. The study presents one of the few numerically dated Middle Pleistocene multi-proxy records and one of the most comprehensive malacological datasets covering the early phases of last glacial period of continental Europe.

The significance of Upper Cretaceous hardgrounds and other discontinuity surfaces for basin-wide correlations, based on drillcore data from boreholes in northern Poland

The paper presents the hardgrounds and some other correlative discontinuity surfaces found in Upper Cretaceous (Cenomanian–Maastrichtian) borehole sections of northern Poland. They were briefly described, and depositional environment was identified for both the underlying deposit (UD) and the overlying deposit (OD). The significance of these features for both basin-wide correlations and broadly understood sequence stratigraphic techniques is highlighted. They were correlated with other major discontinuity surfaces identified in boreholes of northern Poland in both drill cores and well logs if such identification was reliable based on geophysical borehole data. All these discontinuity surfaces were referred to the boundaries of the individual depositional cycles determined within the Upper Cretaceous succession: K3-II/K3-III, K3-III/K3-IV, K3-IV/K4-I, K3-IV/K4-II, K4-I/K4-II (or II or IV or V), K4-III/K4-IV (or V), K4-IVa/K4-IVb, probably K4-IVb/K4-V, and K4-V/Pc-I. The discontinuity surfaces can be related to both sea level fluctuations and tectonic activity during the Subhercynian phases. Most of them developed in relatively calm sedimentary conditions, outside the central part of the Mid-Polish Trough. The exceptions are three hardgrounds from the Czlopa–Szamotuly Zone, which seem to be associated mainly with the Late Cretaceous tectonic (including salt tectonics) activity of this zone. The most common UD/OD configuration of sedimentary environments is the open-marine carbonate shelf both beneath and above the discontinuity surface. The second most common situation is the open-marine carbonate shelf beneath and the open-marine shelf with carbonate-siliceous sedimentation above. The gaps at the surfaces span variously long intervals, ranging from short periods (spanning a fraction of a depositional cycle) to long periods (comprising one or more depositional cycles). The position of the discontinuity surfaces facilitates searching for any possible hiatuses in the sections of other boreholes, and paying attention to local changes in sediment distribution patterns, and local tectonic activity.

Analysis of Reservoir Architecture of Shallow-water Delta Front Based on Process—A Case of S2L410 in Southern 79 Block in Wennan Oilfield

The sand body distribution is relatively limited in this block, the lens-shaped sandbodies are more developed, the change of intergranular sandbody is fast and the internal architecture of the sand body is complex, which results in the difficulties of the arrangement of horizontal wells in the study area and the tapping of remaining oil in high water reservoirs. In this paper, taking an example of S2L410 sandbodies in Wen 79 Southern Block, rich drilling data, core data, logging data and geological research results accumulated over many years in Wennan Oilfield were applied to discuss the anatomical method of the reservoir architecture unit in the underwater distributary channel in the shallow delta front, the hierarchy of the internal architecture of the reservoir and the anatomy of the single sand body. On the basis of this, the sequence of the underwater distributary channel in the composite channel is determined by the cross section and the source profile. Under the guidance of the sedimentology principle, the formation process of the underwater distributary channel is restored and the evolution process of underwater distributary channel is recovered.

The model of fracture development in the faulted folds: The role of folding and faulting

Tectonic fractures are otherwise known as joints or fissures. The density of tectonic fractures is governed by the lithology, layer thickness and structures. The distribution and density of tectonic fractures in the Kuqa Depression in the northern Tarim Basin of Northwest China are dominantly controlled by the regional faulted fold belt. Our purpose of this paper is to analyze how folding and faulting control the development of tectonic fractures, based on outcrop and logs of drill data. In the folded tight sandstone reservoirs in the Kuqa Depression, the extensional area, transition area and shortening area have been separated by two neutral lines, which control the distribution and density of tectonic fractures in the buckle folds. From the twelve sites of field measurements, six logs of drill core data and analysis of the micro-texture of tectonic fractures, it can be deduced that the fracture development in the sub-salt faulted fold belt is related to the neutral lines and related faults. The high-density tensile fractures in the vicinity of fold hinges are more developed than in the limbs of the fold. Folding is thus the first level of control over the general pattern of fracture distribution. The fractures in the hanging wall of the thrust faults are more developed than those in the footwall. Further more, the fractures in the hinge zone and steeply tilted limbs of folds close to thrust faults are more developed than the gently tilted limbs which are far from faulting. This suggests that faulting is a secondary control over the development of local fractures within the faulted fold belt. The development of fractures related to faulted folds in the Kuqa Depression can be also divided into three episodes: pre-folding, syn-folding and post-folding, which are identified by field observation.

A new genetic interpretation for the Caotaobei uranium deposit associated with the shoshonitic volcanic rocks in the Hecaokeng ore field, southern Jiangxi, China

Combined with in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon UPb geochronology, published and unpublished literature on the Caotaobei uranium deposit in southern Jiangxi province, China, is re-examined to provide an improved understanding of the origin of the main ore (103 Ma). The Caotaobei deposit lies in the Hecaokeng ore field and is currently one of China's largest, volcanic-related uranium producers. Unlike commonly known volcanogenic uranium deposits throughout the world, it is spatially associated with intermediate lavas with a shoshonitic composition. Uranium mineralization (pitchblende) occurs predominantly as veinlets, disseminations, and massive ores, hosted by the cryptoexplosive breccias rimming the Caotaobei crater. Zircons from one latite define four distinct 206Pb/238U age groups at 220–235 Ma (Triassic), 188 Ma (Early Jurassic), 131–137 Ma (Early Cretaceous), and 97–103 Ma (Early-Late Cretaceous transition, hereafter termed mid-Cretaceous). The integrated age (134 ± 2 Ma) of Early Cretaceous zircons (group III) is interpreted as representing the time of lava emplacement. The age data, together with the re-examination of literature, does not definitively support a volcanogenic origin for the generation of the deposit, which was proposed by the previous workers based mainly on the close spatial relationship and the age similarity between the main ore and volcanic lavas. Drill core and grade-control data reveal that rich concentrations of primary uranium ore are common around the granite porphyry dikes cutting the lavas, and that the cryptoexplosive breccias away from the dikes are barren or unmineralized. These observations indicate that the emplacement of the granite porphyries exerts a fundamental control on ore distribution and thus a genetic link exists between main-stage uranium mineralization and the intrusions of the dikes. Zircon overgrowths of mid-Cretaceous age (99.6 ± 5.7 Ma) in the shoshonitic volcanic rock is broadly coeval with main-stage U mineralization, which is probably attributable to a tectonothermal event related to the intrusion of the granite porphyries and further supports our genetic reinterpretation. It is thus concluded that the granite porphyry intrusions and associated magma may provide the fluids, ore components, and the thermal energy for U mineralization. However, some other types of fluids and metal sources (e.g., meteoric-derived fluids, which are yet to be identified) could have been substantially involved in the mineralization process. Our new genetic explanation may point to significant potential for mid-Cretaceous granite-related hydrothermal U deposits in Jiangxi and other parts of Southeast China.

Evolution of the transtensional structure in Huimin sag of Bohai Bay basin, eastern China

Transtensional basins containing petroleum reserves are common in eastern China. To better understand the evolution of the oil reservoirs, we investigated the generation mechanism of the Huimin sag transtensional structure, eastern China. We analyzed three-dimensional seismic surveys and drill-core data and concluded that most faults in the Huimin sag are planar or listric with negative flower-structured vertical profiles. The main faults are ENE- and E-striking: the Linshang fault belt to the north and the Xiakou fault belt to the south. Seismic profiles indicate three sets of basement faults in the Huimin sag, striking NNE, ENE, and NNW. The NNW-striking basement faults originated in the middle Triassic; the ENE and NNE faults formed during the late Jurassic. During the Paleogene, the Huimin sag was subjected to N–S extensional forces that reactivated the ENE faults, leading to dextral strike-slip displacement in the Linshang and Xiakou faults, which were oblique to the extensional direction. This generated the conjugate brushed-shaped Linshang and Xiakou fault system, producing a typical oblique extensional basin with characteristic transtensional structure. To reconstruct the evolution of the transtensional structure in Huimin sag, we used Lagrangian analysis software to model the main faults in the western Huimin sag. The simulation verified the re-activation of the NE-, ENE-, and NNW-striking faults under the N–S extension. The NNW fault faded, while the other two strengthened, producing brush-shaped fault systems and E–W- and ENE-striking normal faults. The simulation results show good agreement with the field-data analysis.

Nucleation process of magnitude 2 repeating earthquakes on the San Andreas Fault predicted by rate‐and‐state fault models with SAFOD drill core data

AbstractRecent laboratory shear‐slip experiments conducted on a nominally flat frictional interface reported the intriguing details of a two‐phase nucleation of stick‐slip motion that precedes the dynamic rupture propagation. This behavior was subsequently reproduced by a physics‐based model incorporating laboratory‐derived rate‐and‐state friction laws. However, applying the laboratory and theoretical results to the nucleation of crustal earthquakes remains challenging due to poorly constrained physical and friction properties of fault zone rocks at seismogenic depths. Here we apply the same physics‐based model to simulate the nucleation process of crustal earthquakes using unique data acquired during the San Andreas Fault Observatory at Depth (SAFOD) experiment and new and existing measurements of friction properties of SAFOD drill core samples. Using this well‐constrained model, we predict what the nucleation phase will look like for magnitude ∼2 repeating earthquakes on segments of the San Andreas Fault at a 2.8 km depth. We find that despite up to 3 orders of magnitude difference in the physical and friction parameters and stress conditions, the behavior of the modeled nucleation is qualitatively similar to that of laboratory earthquakes, with the nucleation consisting of two distinct phases. Our results further suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the magnitude ∼2 earthquakes by strain measurements close (a few hundred meters) to the hypocenter, in a position reached by the existing borehole.

Numerical Simulations of the Lunar Penetrating Radar and Investigations of the Geological Structures of the Lunar Regolith Layer at the Chang’E 3 Landing Site

In the process of lunar exploration, and specifically when studying lunar surface structure and thickness, the established lunar regolith model is usually a uniform and ideal structural model, which is not well-suited to describe the real structure of the lunar regolith layer. The present study aims to explain the geological structural information contained in the channel 2 LPR (lunar penetrating radar) data. In this paper, the random medium theory and Apollo drilling core data are used to construct a modeling method based on discrete heterogeneous random media, and the simulation data are processed and collected by the electromagnetic numerical method FDTD (finite-difference time domain). When comparing the LPR data with the simulated data, the heterogeneous random medium model is more consistent with the actual distribution of the media in the lunar regolith layer. It is indicated that the interior structure of the lunar regolith layer at the landing site is not a pure lunar regolith medium but rather a regolith-rock mixture, with rocks of different sizes and shapes. Finally, several reasons are given to explain the formation of the geological structures of the lunar regolith layer at the Chang’E 3 landing site, as well as the possible geological stratification structure.

Reflectance spectroscopic characterisation of mineral alteration footprints associated with sediment-hosted gold mineralisation at Mt Olympus (Ashburton Basin, Western Australia)

ABSTRACTHydrothermal ore deposits are typically characterised by footprints of zoned mineral assemblages that extend far beyond the size of the orebody. Understanding the mineral assemblages and spatial extent of these hydrothermal footprints is crucial for successful exploration, but is commonly hindered by the impact of regolith processes on the Earth's surface. Hyperspectral drill core (HyLogger™-3) data were used to characterise alteration mineralogy at the Mt Olympus gold deposit located 35 km southeast of Paraburdoo along the Nanjilgardy Fault within the northern margin of the Ashburton Basin in Western Australia. Mineralogy interpreted from hyperspectral data over the visible to shortwave (400–2500 nm) and thermal (6000–14500 nm) infrared wavelength ranges was validated with X-ray diffraction and geochemical analyses. Spaceborne multispectral (ASTER) and airborne geophysical (airborne electromagnetic, AEM) data were evaluated for mapping mineral footprints at the surface and sub-surface. At the deposit scale, mineral alteration patterns were identified by comparing the most abundant mineral groups detected in the HyLogger data against lithology logging and gold assays. Potential hydrothermal alteration phases included Na/K-alunite, kaolin phases (kaolinite, dickite), pyrophyllite, white mica, chlorite and quartz, representing low-T alteration of earlier greenschist metamorphosed sediments. The respective zoned mineral footprints varied depending on the type of sedimentary host rock. Siltstones were mainly characterised by widespread white-mica alteration with proximal kaolinite alteration or quartz veining. Sandstones showed (1) distal white mica, intermediate dickite, and proximal alunite + kaolinite or (2) widespread white-mica alteration with associated intervals of kaolinite. In both, sandstones and siltstones, chlorite was distal to gold mineralisation. Conglomerates showed distal kaolinite/dickite and proximal white-mica/dickite alteration. Three-dimensional visualisation of the gold distribution and spatially associated alteration patterns around Mt Olympus revealed three distinct categories: (1) several irregular, poddy, SE-plunging zones of >0.5 ppm gold intersected by the Zoe Fault; (2) sulfate alteration proximal to mineralisation, particularly on the northern side of the Mt Olympus open pit; and (3) varying AlIVAlVISiIV–1(Mg,Fe)VI–1 composition of white micas with proximity to gold mineralisation. Chlorite that developed during regional metamorphic or later hydrothermal alteration occurs distal to gold mineralisation. ASTER mineral mapping products, such as the MgOH Group Content used to map chlorite (±white mica) assemblages, showed evidence of correlation to mapped, local structural features and unknown structural or lithological contacts as indicated by inversion modelling of AEM data.

Responses of submarine groundwater to silty-sand coast reclamation: A case study in south of Laizhou Bay, China

Coastal reclamation can result in considerable changes in the quality and quantity of submarine groundwater at the land/sea interface. In this study, submarine groundwater monitoring wells and water samples were designed and implemented to get data of groundwater level, electrical conductivity, temperature, and hydrochemistry data to examine the responses of silty-sand submarine groundwater in different sedimentary strata to reclamation in south of Laizhou Bay. The submarine groundwater is mainly saline water and its salinity in the deep aquifer is higher than that of seawater and close to brine. It was formed in the Late Pleistocene and Holocene. Drilling core data indicates that there is a stratigraphic boundary at a depth of 18.58 m, with Holocene strata above, and Late Pleistocene strata below, this level. Continuous electrical conductivity data indicates that the submarine groundwater properties are stratigraphically distributed in this study area. And there is an interface at a depth of 38 m. Above the 38 m depth, the water quantity of submarine ground-saline water is freshening. The major ions showed a tendency to change continually above 25 m, but the tended to stabilize below 25 m depth. Freshwater is the major recharge source in the upper section of the Holocene strata, between the surface and 8.00 m depth, and the hydrochemical type has changed from ClNa to Cl·HCO3Na. In the lower section of Holocene strata (8.00–23.00 m) and upper section of late Late Pleistocene strata (23.00–38.00 m), groundwater is influenced by seawater and groundwater of upper aquifer. The freshwater, seawater, and groundwater recharge in the upper aquifer has no influence on the groundwater in the section below the late Late Pleistocene (between 38.00 and 49.15 m) and the early Late Pleistocene strata (between 49.15 and 75.00 m). The filling layer, added in the coastal reclamation project, is comprised of clayey silt and fine sand, and its high porosity means that it is suitable for water storage. After the reclamation, meteoric water was stored in the filling layer that became the stable recharge resource. The recharge resource and the filling layer can improve the properties of the confined aquifer to increase the groundwater level. They may also influence the groundwater quantity and the flow direction. The groundwater in the Holocene strata is clearly influenced by recharge and the previously saline water aquifers receive freshwater on an on-going basis, such that the water is now becoming fresh.

Reply to 'Unclear causes for subduction'

Keenan and Encarnacion suggest that the absence of pre-subduction inception basement in the drill core data taken from site U1438 raises ambiguity in our conclusion of spontaneous subduction initiation in the Izu–Bonin–Mariana system. However, there is no evidence for uplift in the earliest products of the Izu–Bonin–Mariana system preceding rifting preserved anywhere in the region. Three sub-parallel ridges — from north to south, the Amami plateau, Daito and Oki-Daito ridges (Fig. 1 from ref. 1) — comprise magmatic products of Mesozoic–Tertiary arcs formed prior to the Izu–Bonin–Mariana system. These ridges generally strike east–west orthogonally to the Kyushu–Palau ridge — the earliest stratovolcano chain of the Izu–Bonin–Mariana system. If compression preceded inception, as implied by the forced subduction model, we anticipate uplift of the old arc ridges, diminishing in effect westwards, and sediment shedding from uplifted regions into adjacent basins.

Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23-14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3-4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2 These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

A New Methodology for Open Pit Slope Design in Karst-Prone Ground Conditions Based on Integrated Stochastic-Limit Equilibrium Analysis

Using the Chengmenshan Copper Mine as a case study, a new methodology for open pit slope design in karst-prone ground conditions is presented based on integrated stochastic-limit equilibrium analysis. The numerical modeling and optimization design procedure contain a collection of drill core data, karst cave stochastic model generation, SLIDE simulation and bisection method optimization. Borehole investigations are performed, and the statistical result shows that the length of the karst cave fits a negative exponential distribution model, but the length of carbonatite does not exactly follow any standard distribution. The inverse transform method and acceptance–rejection method are used to reproduce the length of the karst cave and carbonatite, respectively. A code for karst cave stochastic model generation, named KCSMG, is developed. The stability of the rock slope with the karst cave stochastic model is analyzed by combining the KCSMG code and the SLIDE program. This approach is then applied to study the effect of the karst cave on the stability of the open pit slope, and a procedure to optimize the open pit slope angle is presented.

Identification of mineralized zones in the Zardu area, Kushk SEDEX deposit (Central Iran), based on geological and multifractal modeling

AbstractThe aim of this paper is to delineate the different lead–zinc mineralized zones in the Zardu area of the Kushk zinc–lead stratabound SEDEX deposit, Central Iran, through concentration–volume (C–V) modeling of geological and lithogeochemical drillcore data. The geological model demonstrated that the massive sulfide and pyrite+dolomite ore types as main rock types hosting mineralization. The C–V fractal modeling used lead, zinc and iron geochemical data to outline four types of mineralized zones, which were then compared to the mineralized rock types identified in the geological model. ‘Enriched’ mineralized zones contain lead and zinc values higher than 6.93% and 19.95%, respectively, with iron values lower than 12.02%. Areas where lead and zinc values were higher than 1.58% and 5.88%, respectively, and iron grades lower than 22% are labelled “high-grade” mineralized zones, and these zones are linked to massive sulfide and pyrite+dolomite lithologies of the geological model. Weakly mineralized zones, labelled ‘low-grade’ in the C– V model have 0–0.63% lead, 0–3.16% zinc and > 30.19% iron, and are correlated to those lithological units labeled as gangue in the geological model, including shales and dolomites, pyritized dolomites. Finally, a log-ratio matrix was employed to validate the results obtained and check correlations between the geological and fractal modeling. Using this method, a high overall accuracy (OA) was confirmed for the correlation between the enriched and high-grade mineralized zones and two lithological units — the massive sulfide and pyrite+dolomite ore types.

Continuous 1.3-million-year record of East African hydroclimate, and implications for patterns of evolution and biodiversity

The transport of moisture in the tropics is a critical process for the global energy budget and on geologic timescales, has markedly influenced continental landscapes, migratory pathways, and biological evolution. Here we present a continuous, first-of-its-kind 1.3-My record of continental hydroclimate and lake-level variability derived from drill core data from Lake Malawi, East Africa (9-15° S). Over the Quaternary, we observe dramatic shifts in effective moisture, resulting in large-scale changes in one of the world's largest lakes and most diverse freshwater ecosystems. Results show evidence for 24 lake level drops of more than 200 m during the Late Quaternary, including 15 lowstands when water levels were more than 400 m lower than modern. A dramatic shift is observed at the Mid-Pleistocene Transition (MPT), consistent with far-field climate forcing, which separates vastly different hydroclimate regimes before and after ∼800,000 years ago. Before 800 ka, lake levels were lower, indicating a climate drier than today, and water levels changed frequently. Following the MPT high-amplitude lake level variations dominate the record. From 800 to 100 ka, a deep, often overfilled lake occupied the basin, indicating a wetter climate, but these highstands were interrupted by prolonged intervals of extreme drought. Periods of high lake level are observed during times of high eccentricity. The extreme hydroclimate variability exerted a profound influence on the Lake Malawi endemic cichlid fish species flock; the geographically extensive habitat reconfiguration provided novel ecological opportunities, enabling new populations to differentiate rapidly to distinct species.

Blind Test of Muon Geotomography for Mineral Exploration

SUMMARY Muon geotomography is a new geophysical imaging technology that creates 3D images of subsurface density distributions. Similar in concept to computed tomography scanning, muon geotomography uses naturally occurring cosmic radiation that gets attenuated when traversing matter. Cosmic ray muon data were acquired in the Pend Oreille Zn-Pb mine in Metaline Falls, Washington State, USA without prior knowledge of the presence or absence of ore bodies. The resulting 3D density distribution indicated a substantial volume of rock with higher density than the host stratigraphy above the survey location. Subsequently, a model of existing ore shells based on drill core data was provided and a simulation of the expected muon tomography data was found to be consistent with the muon geotomography measurements. This is the first blind test demonstration of muon geotomography applied to mineral exploration.

Reflectance spectroscopy and alteration assemblages at the Leven Star gold deposit, Victoria, Australia

Hylogger-2 reflectance spectroscopy data from two drill holes at the Leven Star gold deposit, provides an insight into the hydrothermal alteration associated with vein sets and faults that host gold mineralisation. The metasedimentary host rock is a biotite-rich hornfels, which overprints a regional greenschist facies metamorphism. Gold mineralisation is associated with quartz (±carbonate) stockwork-breccia zones. HyLogging short-wave infrared reflectance spectra detected carbonates, chlorites, epidote (propylitic: carbonatisation, chloritisation, epidote), muscovite (phyllic/sericitic) and kaolinite, illite, ammonium alunite, montmorillonite and dickite (intermediate argillic alteration) assemblages that were confirmed using petrographic observations, drill core and geochemical data. The gold occurs within a sulfidation halo with carbonate phases (ankerite–siderite–dolomite) in structurally controlled veins and faults, which also host a late Sb–As–Bi–Cu–W assemblage, attributed to an intrusion-related style of mineralisation superimposed on a hydrothermal orogenic gold event.

Seismic stratigraphy of the Heuksan mud belt in the southeastern Yellow Sea, Korea

To establish the seismic stratigraphy of the Heuksan mud belt (HMB) and reconstruct its depositional history, approximately 1,600 km of high-resolution seismic data were newly obtained using chirp acoustic sub-bottom profiler, sparker, and air-gun seismic systems. Based on seismic stratigraphic analysis, the HMB can be divided into three major seismic units (I, II, and III, from top to bottom) and four subunits (II-a, II-b, III-a, and III-b) overlying transgressive sands, pre-last glacial maximum (LGM) deposits, and the acoustic basement. Each unit and subunit show different seismic facies and geometry, being clearly separated from each other by bounding surfaces formed since the LGM. The spatial distribution, thicknesses and volumes of the seismic units were determined and plotted to document the sequential formation of the HMB. The correlation between deep drill core data (HMB-101, HMB-102, HMB-103, YSDP-101, and YSDP-102) and the seismic data suggests that subunits III-b and III-a were formed by the continuous accumulation of fine-grained sediment with partial sandy sediment in an estuarine/deltaic environment during the early to middle transgressive stage, accompanied by landward migration of the shoreline. Subunits II-b and II-a were probably formed by re-deposition of large volumes of sediment eroded from unit III during the middle transgressive to early highstand stage. Unit I is interpreted as the most recent mud deposit representing the highstand systems tract when sea-level rise terminated. The careful definition of seismic units and their interpretation proposed in this study, on the basis of the large and partly new seismic dataset covering the entire HMB together with deep drill core data, have been instrumental in reconstructing the depositional environment and formation mechanisms of the HMB.

The role of sedimentation history and lithology on fluid flow and reactions in off-axis hydrothermal systems: A perspective from the Troodos ophiolite

Off-axis hydrothermal systems are thought to carry globally significant chemical fluxes but different ocean crust sections show widely differing extents of alteration making the quantification of these fluxes complex. With the aim of better understanding the origin of this diversity in alteration extent we have studied two sections of the lava pile in the Troodos ophiolite with distinct sedimentation history and volcanic architecture. The Akaki section is dominated by pillow lavas and the oldest sediments overlying the crust are ~20Myr younger than the ophiolite. Here there is a 300m thick zone at the top of the lavas that is enriched in CO2 and alkali elements, and has high 87Sr/86Sr and δ7Li. These features indicate extensive chemical exchange with seawater. In contrast to the Akaki area, the Onophrious section is dominated by sheet flows and the oldest sediments are of the same age as the ophiolite. Here the CO2 and alkali element enriched zone is much thinner (<100m), is less enriched in these elements (e.g. by a factor of three for CO2), and has lower 87Sr/86Sr and δ7Li. The O-isotopic compositions of calcites from these CO2- and alkali-enriched zones were precipitated from fluids with bottom water temperatures (~10°C). Maintaining such low temperatures to 300m depth in the crust in the Akaki area suggests that this was a region of recharge. Below these CO2- and alkali-enriched zones temperatures increase with depth such that calcite precipitation in the Onophrious area occurred at ~10°C higher temperature, at any given depth, than in the Akaki area. The increase in precipitation temperature with depth indicates poor thermal mixing within the crustal aquifer, likely due to laterally continuous sheet flows restricting the permeability. The chemical and thermal constraints suggest that both timing of the onset of sedimentation and volcanic architecture play important roles in controlling fluid and chemical fluxes. The same signal can be seen in drill core data from the modern ocean basins, with higher sedimentation rates leading to lower fluid fluxes and higher temperatures in the crustal aquifer.

Modern and ancient hiatuses in the pelagic caps of Pacific guyots and seamounts and internal tides

Incidences of non-deposition or erosion at the modern seabed and hiatuses within the pelagic caps of guyots and seamounts are evaluated along with paleo-temperature and physiographic information to speculate on the character of Late Cenozoic internal tidal waves in the upper Pacific Ocean. Drill core and seismic reflection data are used to classify sediment at the drill sites as having been either accumulating or eroding/nondepositing in the recent geological past. When those classified sites are compared against predictions of a numerical model of the modern internal tidal wave field (Simmons, 2008), the sites accumulating particles over the past few million years are found to lie away from beams of the modeled internal tide, while those that have not been accumulating are in internal tide beams. Given the correspondence to the modern internal wave field, we examine whether internal tides can explain ancient hiatuses at the drill sites. For example, Late Cenozoic pelagic caps on guyots among the Marshall Islands contain two hiatuses of broadly similar age, but the dates of the first pelagic sediments deposited following each hiatus do not correlate between guyots, suggesting that they originate not from ocean chemical changes but from physical processes, such as erosion by internal tidal waves. We investigate how changing conditions such as ocean temperature and basin physiography may have affected internal tides through the Cenozoic. Allowing for subsequent rotation or uplift by plate tectonics, ancient submarine ridges among the Solomon, Bonin and Marianas Island chains may have been responsible for some sediment hiatuses at these distant guyot sites.