Ordovician Limestone Research Articles

Heavy metals in deep groundwater within coal mining area, northern Anhui province, China: concentration, relationship, and source apportionment

The present study was conducted to investigate the concentrations of heavy metals (HMs) in deep groundwater from coal mining area, including cadmium (Cd), chromium (Cr), copper (Cu), zinc (Zn), lead (Pb), and nickel (Ni). The samples were collected from different aquifers in four coal mines of northern Anhui province, China, which were unconsolidated formation (UF), coal measure aquifer (CA), Taiyuan limestone aquifer (TA), and Ordovician limestone aquifer (OA), respectively. HM concentrations from the four different sources were analyzed by atomic absorption spectrometer, and were found in the order of Zn>Ni>Pb>Cu>Cd>Cr (in UF), Ni>Zn>Pb>Cu>Cr>Cd (in CA), Ni>Zn>Pb>Cu>Cd>Cr (in TA), and Zn>Ni>Pb>Cu>Cr>Cd (in OA), respectively. Concentrations of Cu, Zn, and Cr were found within the quality guidelines set by Bureau of Quality and Technical Supervision of China (GB/T 14848-93) and World Health Organization, while the concentrations of Cd, Pb, and Ni were higher than their respective permissible limits. The enhanced concentrations of Ni, together with Cr, were considered to be affected by anthropogenic sources, since they both had high variable coefficient. Moreover, the inter-dependence of HMs and their pollution sources were further discussed using statistical techniques, including one-factor analysis of variance, Pearson correlation analysis, and principle component analysis.

The Baltic Klint beneath the central Baltic Sea and its comparison with the North Estonian Klint

Along its contact with the Baltic Shield, the margin of the East European Platform reveals a well-developed, flooded terraced relief. The most striking and consistent set of escarpments at the contact of the Lower Palaeozoic calcareous and terrigenous rocks, known as the Baltic Klint (BK), extends from northwest of Russia to the Swedish island of Öland. Marine seismic reflection profiling in 1990–2004 revealed the central Baltic Sea Klint (BSK) section in detail and enabled comparison of its geology/geomorphology with a classical klint-section onshore, namely the North Estonian Klint (NEK). The conception of the BK onshore, which is based on the land-sea separating terraced relief in northern Estonia, is not fully applicable beneath the sea. Therefore, we consider that the BSK includes the entire terraced Cambrian outcrop. We suggest the term “Baltic Klint Complex” to include the well-terraced margin of the Ordovician limestone outcrop, which is weakly developed in Estonia. Because of a steady lithological framework of the bedrock layers across the southern slope of the Fennoscandian Shield, the central BSK in the western and the NEK in the eastern part of the Baltic Homocline have largely identical morphologies. The North Estonian Ordovician limestone plateau with the calcareous crest of the BK extends across the central Baltic Sea, whereas morphological changes/variations along the Klint base occur due to the east-westerly lithostratigraphic/thickness changes in the siliciclastic Cambrian sequence. The verge of the NEK, located some 30–50m above sea level, starts to drop in altitude as its east-westerly course turns to northeast-southwest in western Estonia. Further westwards, the BK shifts gradually into southerly deepening (0.1–0.2°) layers as its crest drops to c. 150m below sea level (b.s.l.) near Gotska Sandön. This course change is accompanied by a considerable decrease in thickness of the platform sedimentary cover, as below the central Baltic Sea the stratal sequence is 150–250m thinner than in northern Estonia. This has facilitated a deviation of the terraced relief-forming Cenozoic rivers traversing east-westerly across the southern slope of the Fennoscandian Shield and forming different morphostructures in its eastern and western parts. Thus, a low-lying central Baltic Sea depression with well-developed asymmetrical cuesta valleys and terraces occur in the western half of the Baltic Homocline. In its eastern part, however, the only explicitly shaped cuesta valley along the shield-platform boundary forms a narrow east-westerly branch/gulf of the Baltic Sea (Gulf of Finland). The well-terraced southern margin of this gulf runs along the contact of the outcropping terrigenous and calcareous rocks, rises above the sea and forms a complex landform known as the NEK.

Impact of particle transfer on flow properties of crushed mudstones

Karst collapse pillar (KCP) is widespread in North China coalfields, where coal extraction above the Ordovician limestone aquifer is threatened by the abundant supply of water and a very high hydraulic pressure. KCP is composed of rock skeleton and fine fillings, which can be transferred under the effect of water flow, thus KCP usually functions as a channel for groundwater inrush. In order to investigate the mechanism of mining-induced groundwater inrush of KCP which was caused by fine fillings transfer, a self-designed particle transfer permeability testing system was used to test the crushed mudstones’ flow properties, which included fine filling particle transfer rate, porosity increase rate and permeability under the conditions of varying pore pressure, particle size mixture and compaction level (initial porosity). The tests indicate fine fillings transfer is the essential reason for mining-induced groundwater inrush (flow instability) of KCP. The flow properties changeability during fine particle transfer could be divided into four stages, i.e., initial flow stage, flow inrush stage, continued particle flow stage and stable flow stage, and flow inrush stage which is the key point to cause water inrush. Due to the crushing of edges and corners and the adjustment of the structure, the fluctuation of permeability–time relationship mainly distributed in the first two stages, which make a change to flow channel. Moreover, with the increasing of pore pressure, particle size mixture and initial porosity, the water inrush time and stable seepage time decreased more rapidly; the fine fillings, porosity and permeability increased gradually. The efficiency criteria analysis between measurement and calculation permeability shows an empirical equation can fit the relationship between porosity and permeability well, and not all of the pore structures were in flow; this means there was a part of pores that were invalid, but the effective porosity in flow can be treated as calculation value approximately.

The source of Fengjia and Langxi barite–fluorite deposits in southeastern Sichuan, China: evidence from rare earth elements and S, Sr, and Sm–Nd isotopic data

The barite–fluorite metallogenic belt in southeastern Sichuan is one of the most important barite–fluorite ore‐concentrated areas in China. In order to find the ore‐forming source and the mineralization age of the Fengjia and Langxi barite–fluorite deposit, we systematically evaluated the rare earth element (REE) contents and isotopic characteristics of S, Sr, and Sm–Nd. The results show that the δ34S values of barites and pyrites are high and similar to S isotopic values of gypsum in the Cambrian Qingxudong Formation (∈1q), suggesting that the sulphur source was from Cambrian evaporite strata. The initial 87Sr/86Sr ratios of fluorites and barites range from 0.708800 to 0.712999, and these values are similar to Cambrian carbonate rocks and Lower Ordovician limestone. Except for black shales of the Lower Cambrian Niutitang Formation, the Ba content of other strata was generally low. The REE characteristics of barite and fluorite have close relationships, in regard to the source of ore‐forming materials, to the Lower Cambrian Niutitang Formation black shales. Hence, we have concluded that the Cambrian carbonate rocks and Lower Ordovician limestone provide the source of calcium for mineralization and that the source of barium comes from the Lower Cambrian Niutitang Formation black shales. The fluorine contents of the Upper Sinian Doushantuo Formation and the Lower Cambrian Mingxinshi Formation are much higher than other strata, and these formations could provide the source for fluorine. The Sm–Nd isochron age of fluorites is 104 ± 11 Ma, which demonstrates that the mineralization mainly occurred during the late Yanshanian. Copyright © 2016 John Wiley & Sons, Ltd.

Multi-factor evaluation for the water yield properties of coal floor aquifers, based on GIS

Groundwater inrush in mines directly threatens safe coal production. Aquifer yield plays a crucial role during water inrush. Significant accidents occur in areas where aquifer yields are strong. The yield of an aquifer is influenced by many things and, in this study, five for which data are easily acquired were selected as evaluation indices for coal-seam floor aquifer yield. They comprise specific yield, permeability, drilling fluid consumption, aquifer thickness, and fault and fold distribution. Based on these indices, a comprehensive model for evaluating water yield was constructed. Using the Ordovician limestone aquifer below the coal floor of Danhou coal mine, Hebei province, China, as an example, index data relating to aquifer yield were collected and the index weight determined. A geographic information system was used to prepare a thematic map for each driving factor and, subsequently, to superimpose them. Comprehensive water yield evaluation indexes were obtained and, finally, a zonal map of different water yield properties was developed for the research area.

Dolomitisation of the Lower-Middle Ordovician Yingshan Formation in the Tazhong area, Tarim Basin, western China

The carbonate unit in the Lower-Middle Ordovician Yingshan Formation in the Tazhong region of the Tarim Basin in western China is partially to completely dolomitised. Three types of dolomite were identified in this unit: microcrystalline (<20 μm) to finely crystalline (20–50 μm) subhedral dolomite rhombs (Rd1), finely crystalline (50–250 μm) anhedral to subhedral mosaic dolomites (Rd2), and medium to finely crystalline (200–500 μm) euhedral to subhedral sucrosic dolomites (Rd3). Three types of calcite cement were also identified: coarsely crystalline mosaic calcite cement in mouldic pores (Cc1), coarsely crystalline intergrown calcite cement (Cc2), and coarsely crystalline sparry and veined calcite cement in the fractures (based on hand sample observation) (Cc3). The δ13C values and 87Sr/86Sr ratios of the Rd1 dolomite in the Yingshan Formation are consistent with those of Lower to Middle Ordovician marine limestone, suggesting that the isotopic ratios were inherited from the precursor limestone. Stratigraphic, petrographic and geochemical data constrain the formation of the Rd1 dolomite to a shallowly buried environment involving seawater with elevated salinity. The Rd2 dolomite yields lower δ18O values (−7.5 to −4.7 ‰) and contains less Sr and Na and more Fe and Mn than the Rd1 dolomite (−5.3 to −3.2 ‰). Therefore, the dolomitising fluids of the Rd2 dolomite were likely derived from the infiltration and diffusion of residual evaporitic water resulting from intense compaction at elevated temperatures. The Rd3 dolomite generally features lower δ18O values (−9.0 to −7.0 ‰) than the Rd2 dolomite, but the δ18O values of portions of the Rd2 and Rd3 dolomites overlap. Thus, the Rd3 dolomite may represent recrystallisation of the Rd2 dolomite. The Rd3 dolomite contains significantly lower Sr and Na contents and significantly higher Fe and Mn contents than the Rd1 and Rd2 dolomites, suggesting that the dolomitic fluids precipitated under reducing conditions during burial. The late-stage, medium-coarse to very coarse calcite postdates all the dolomites and is present as cement in fractures and pores. The δ18O values of the Rd3 dolomite and Cc2 calcite cements (−12.6 to −7.9 ‰) are similar, suggesting that the calcite cement in the pores may represent calcite supersaturation associated with burial dolomitisation. The Cc3 calcite cements feature slightly higher δ13C values (+0.2 to +0.4 ‰) and higher radioactive 87Sr/86Sr ratios (0.709280 to 0.709483) than those of the limestone (0.707955 to 0.708231) and Rd3 dolomite (0.707723 to 0.708345) and, in places, lower δ18O values (−11.6 to −6.3 ‰) than the latter. Consequently, the Cc3 calcite cement either formed from the upward migration of basinal fluids in a burial environment or was impacted by hydrothermal activity.

Compaction and seepage properties of crushed limestone particle mixture: an experimental investigation for Ordovician karst collapse pillar groundwater inrush

As mining activity rapidly develops to deeper and deeper ground, there have been an increasing number of groundwater inrush events occurring in China. The Ordovician limestone karst collapse pillar (KCP), which contains a lot of crushed rocks, usually functions as a channel for groundwater inrush. The factors, such as the geological conditions, groundwater flow and extraction percentage of coal seam in underground mines, are the main causes of recompaction and permeability change of crushed rock particles in KCP. The high permeability of rock will cause large volumes of groundwater flow, thus posing a great threat of loss of lives in the mines. It is important to take into account the compaction and seepage behaviors of the crushed rocks in Ordovician limestone KCP. The MTS815.02 system and a self-designed water flow apparatus were used to investigate the effect of particle size distribution on compaction and seepage behavior of crushed limestone particle mixture. The Reynolds number calculation of particle mixture shows that the seepage has been influenced by non-Darcy flow. Testing results indicate that the effective porosity of crushed limestone sample is strongly influenced by compaction and particle size distribution. The effective porosity decreases with the increase in compaction and decrease in larger particle size, respectively. Particle crushing during compaction is a main cause of size 0–2.5 mm materials, whereas some fine particles are washed away due to the effect of water seepage, which is a main cause of weight loss. Non-Darcy seepage properties of the crushed limestone are strongly influenced by compaction and particle size distribution. In general, during the compaction, the permeability decreases while the non-Darcy coefficient increases with the decreasing of effective porosity. The effective porosity, particle crushing and seepage properties of crushed limestone are not only related to compaction levels and mixture sizes but also to style of arrangement and initial pore structure.

The Sub-Cambrian Peneplain in southern Norway: its geological significance and its implications for post-Caledonian faulting, uplift and denudation

The Sub-Cambrian Peneplain in southern Norway formed in the Cryogenian–early Cambrian. It was transgressed in the Cambrian–early Ordovician, and subsequently broken up by Caledonian thrusting, post-Caledonian normal faulting and regional uplift. In southern Norway the Sub-Cambrian Peneplain is generally expressed as an angular unconformity or nonconformity surface with no apparent deep weathering. In some localities the basement is characterized by a weathered top. Furthermore, the basement may have a mineralized top in some cases. The peneplain is commonly overlain by in situ regolith, and/or Cryogenian glacial diamictite, Lower–Middle Cambrian siliciclastic sediments, Lower–Upper Cambrian black shale or Lower Ordovician limestone. It has commonly mildly tectonized contacts, but occasionally displays contacts that have been completely destroyed by Caledonian thrusting and reworked into fault rocks. Tracing the peneplain across southern Norway reveals a fault-affected and fault-delineated plateau with a sloping eastern margin. Onshore cumulative offsets record vertical movements of &gt; 2000 m. A 1–5° dip below Caledonian nappes suggests a flexural component related to tectonic overburden. As the oldest identifiable and dateable surface covering much of Scandinavia the peneplain constitutes the reference surface for studies of the younger regional morphotectonic evolution. Its shape supports the interpretation that Cenozoic uplift combined with faulting, not smooth flexural doming, caused the Southern Scandes high in South Norway.

Best practices for the determination of low-pressure/permeability coalbed methane reservoirs, Yuwu Coal Mine, Luan mining area, China

Permeability and pressure are two important parameters for characterizing coal reservoirs and for evaluating coalbed methane (CBM) production potential. In this study, the reservoir pressure and permeability of six steel-cased CBM wells at Yuwu Coal Mine (Luan coal mining area, Qinshui Basin, China) were studied using new injection falloff testing (IFOT) methodology. The tested reservoir represents coal #3 of the lower Permian Shanxi Formation, the main target coal seam for coalbed methane exploration and production in Qinshui Basin. The results show that on average coal #3 has an ultra-low permeability (0.001–0.043mD) and a low pressure gradient (4.0kPa/m). These values are significantly lower than those of previously collected data from open holes in adjacent wells. However, the validity of the new results was confirmed using two additional lines of evidence: (1) analysis of 10 CBM production wells adjacent the current test area and; (2) data from a long-term monitoring well in an Ordovician limestone aquifer, located below coal #3. On the basis of the results, it can be concluded that (1) using the IFOT method in cased wells, in which shut-in times were extended by 7–11 times that of the injection time, provides reliable data on reservoir parameters (including pressure and permeability); (2) coal #3 is characterized by very low permeability and very low pressure; (3) the low reservoir pressure is related to the Xinan Spring Group, located on the eastern edge of the Qinshui Basin, which discharges reservoir groundwater to the surface hydrological system; and (4) low permeability may be caused by low reservoir pressure and by a cleat system filled with post-structural mineralization. These conclusions were used to further optimize stimulation design and production management for this CBM play. As a result, there has been a good production rate for these wells since 2011.

New paleomagnetic results from Late Ordovician rocks of the Yangtze Block, South China, and their paleogeographic implications

AbstractThe paleogeographic relationship between South China and Australia during the Ordovician is important for understanding the configuration of South China in Gondwana. However, high‐quality Ordovician paleomagnetic results for the Yangtze Block are scarce. Here we report the results of a new paleomagnetic study of the Late Ordovician limestones of Wangcang County in the northern Yangtze Block, performed in order to constrain the paleoposition of South China. Two magnetic components were isolated by detailed stepwise thermal demagnetization. The low‐temperature component falls close to the local current Earth's field direction. The site‐mean direction obtained from the high‐temperature component (HTC) carried by magnetite is D/I = 132.6°/−35.2° (α95 = 3.6°) after bedding correction, yielding a paleomagnetic pole at 45.8°S, 191.3°E (dp = 2.4°, dm = 4.2°). The HTC direction passed reversal and fold tests, and its corresponding pole differs from the available paleomagnetic poles since the Silurian of the South China Block. These results suggest that the remanent magnetization was probably acquired during the earliest stage of sedimentation. The high‐temperature component yields a paleolatitude of 19.5°S, implying that the Yangtze Block was at tropic latitudes during the Late Ordovician. These new and reliable paleomagnetic results bridge the Ordovician data gap and favor the proximity between South China and Australia during the Late Ordovician.

Heavy metals in coal mine groundwater responding to mining activity: concentration, temporal variation and speciation

Six groundwater samples were collected from four aquifers in Renlou coal mine, northern Anhui Province, China, and concentration, temporal variation and speciation of five heavy metals (Cr, Cu, Ni, Pb and Zn) were analyzed. The results of physicochemical parameters and major ions showed that the selected groundwater were representative samples of Quaternary aquifer (QA), coal measure aquifer (CA), Taiyuan limestone aquifer (TA) and Ordovician limestone aquifer (OA). Cr, Ni and Zn increased in the four aquifers from 2002 to 2014, but Pb decreased from 2006 to 2014. Cu concentration increased in QA and TA, but decreased in CA and OA. Although all monitoring results met the standards recommended by WHO and GB5749-2006, Cr and Cu in some groundwater samples exceeded GB/T 14848-93, especially in CA. Soluble metallic hydroxides were the dominant species of heavy metals in QA, while free ions were the main species in TA and OA. Excepted Ni2+ and Zn2+, CuCO3(aq) and PbCO3(aq) were the dominant species of Cu and Pb in CA, respectively, indicating more CO2 had been flooded and dissolved in groundwater from ground atmospheric environment. The enhanced concentration and special dominant species of heavy metals revealed that the ‘closed’ characteristics of CA in Renlou coal mine might have been broken due to coal mining activity.

The development of new composite material for the grouting treatment of ordovician limestone aquifer and performance tests

Fluidity and draining time of clay–coal waste rocks–cement aggregate composite grouting material were evaluated in this study. The characteristics of setting time and temperature, internal distribution of pore structure of the consolidation as well as impermeability, strength and softening coefficient were analysed. It was determined that the composition of the new composite material was clay 5–15%, coal waste rocks 45–60% and cement aggregate 20–50%. The permeability factor is <5·746×10−7 m s−1, the softening coefficient is larger than 0·8, and it is capable for the treatment of limestone water with a pressure of up to 8 MPa.

In situ Measurement of Hydraulic Properties of the Fractured Zone of Coal Mines

A review of the literature on the water inrush of underground openings under a condition of water flow reveals that insufficient attention has been devoted to the measurement of hydraulic properties of fractured zones, such as faults and zones of plastic damage generated by excavation or mining. A conceptual sketch of the fractured zone is presented in Fig. 1. The zone of floor damage is a zone of deformation and failure of the floor rock formation resulting from mining. In particular, groundwater inrush from aquifers underlying mining coal seams are usually induced when uncovering the fractured zone, which is a geological structure extensively distributed in the coalfields of eastern China (Bai et al. 2013). Moreover, the Ordovician limestone underlying the coal seams of coalfields in eastern China forms a confined karst aquifer containing an abundant supply of water and having very high water pressure (Zhang 2005). In this regard, the hydraulic properties in the fractured zone are important to deep underground engineering, particularly when an aquifer surrounds an excavation, for the reason that most water inrush accidents relate to the fractured zone (Fahimifar and Zareifard 2009; Qiao et al. 2013). Laboratory tests are commonly conducted to determine the hydraulic properties of soft soils and rocks (e.g., Ponziani et al. 2011; Bo et al. 2014). There has been an increasing emergence of in situ testing methods as alternatives to laboratory testing methods for assessing the hydraulic characteristic of the fractured zone in civil engineering (Bo et al. 2014); e.g., the water injection test (WIT) is conducted to determine the hydraulic characteristics of the fractured zone (Mukai and Fujimori 2007; Kitagawa et al. 2007). However, laboratory tests of the fractured zone are subject to uncertainties due primarily to disturbances that cause an important difference in hydraulic conductivity between the in situ and laboratory test methods (Bo et al. 2014). In situ tests are particularly useful in the determination of the in situ hydraulic conductivity of the fractured zone. In situ tests have an advantage over other methods in that they effectively measure the in situ hydraulic conductivity. The key objective of this technical note is to report the measured hydraulic properties in the fractured zone under mutative water pressures by conducting an in situ WIT.

Geochemical evolution and residence time of porewater in low-permeability rocks of the Michigan Basin, Southwest Ontario

Drill cores collected from an 860-m-thick Paleozoic (Cambrian to Devonian) sedimentary sequence of the Michigan Basin in southwest Ontario, Canada, were used to develop vertical profiles of natural tracers in porewater from the sedimentary sequence and build a conceptual model regarding processes and timing of solute migration. In this paper, the conceptual model is quantitatively assessed with numerical simulations of diffusion-dominated solute transport (Cl− and 18O). The conceptual model suggests that the tracer profiles result from mixing between a deep shield brine with isotopic characteristics consistent with water–rock interaction over a long period of geologic time, Ordovician seawater at intermediate depth, and an overlying hypersaline brine formed by evaporation of seawater in a restricted basin during the Silurian. Between the peak of basin consolidation at 300MaBP and the Pleistocene (2.6MaBP), salinity and isotopic concentration gradients are thought to have driven mixing, dominantly by diffusion. Water isotope data indicate that in the Pleistocene, melt water infiltrated to a maximum depth of 330m in the Silurian Salina Formation, likely in response to transient glacial loading and elevated sub-glacial hydraulic pressures. Also in the Pleistocene, over-pressured conditions in deep regions of the basin drove high-salinity brine eastward in the basal Cambrian aquifer, interrupting pre-existing tracer-diffusion profiles.A base case set of boundary and initial conditions provides a good fit between simulated and measured tracer profiles, but requires effective diffusion coefficients (De) in the Ordovician limestones that are lower than the average values obtained in laboratory measurements by as much as a factor of 10. The base-case values are still within the overall range of measured values. At the formation scale, relatively low in-situ De values are attributed to the intermittent occurrence of gas and liquid hydrocarbons in the Ordovician carbonate units and the effect of lithostatic confining pressure; neither of which are accounted for in the laboratory measurements but both would have the effect of decreasing De for aqueous solutes. The numerical model is most sensitive to the formation-specific De values and geologically reasonable variations in initial and boundary conditions have a relatively small influence on the results. Additional simulations indicate that hydraulic disturbance and ingress of meltwater during the Pleistocene can explain second-order features observed in the measured tracer profiles. This work provides supporting evidence for previous research indicating that the porewater residence time in the Ordovician sequence approaches the age of the rocks.

Development Law and Watery Features of Collapse Column in Pansan Mine

The collapse column is widely developed and distributed in North China coalfield, has been a threat for coal mine production safety. According to the existing collapse columns in pansan mine, using the combination with geology analyzing and geophysical exploration technology, the cause and development regularity of the collapse columns is discussed in a way of palaeogeographic and palaeoenvironment, the inner filling material features of the collapse columns in the coalfield are introduced, The watery features of collapse columns are studied. The results show that collapse columns have a law of zonation in the horizontal and vertical , and have a certain subsiding distance, collapse column widths ranging periphery have the peripheral edge of the impact zone and transition zone, In the collapse column, the cementation degree is poor at the top, highly compressed at the middle and relatively poor in the bottom. The top and middle sections are less in water bearing, the rich water in the bottom was caused by the vertically leakage recharge from Ordovician limestone in the deep. The research results provide scientific basis for the prevention of collapse column in coal mine.

Paleokarst crust of Ordovician limestone and its utilization in evaluating water inrushes in coalmines of North China

Detailed analysis of exploratory borehole data suggests presence of a paleokarst crust at the top of Middle Ordovician Fengfeng Formation in North China. Because of its mechanical strength and low permeability to water, the paleokarst crust can function as an additional water-resisting layer in evaluating water inrush risks in mining the Carboniferous-Permian coal seams in the area. The paleokarst crust is characterized by heterogeneity and may not be ubiquitous. This paper takes Sihe Mine of Shanxi Province as an example to study the geotechnical and hydrogeological characteristics of the paleokarst crust. Incorporation of this additional hydrological barrier into water inrush risk assessment led to more minable coal seams in the coalmine.

Hydrogeochemical and isotopic evidence for flow paths of karst waters collected in the Heshang Cave, Central China

Understanding of hydrological processes in caves is important to help us interpret paleoclimate records from speleothems. In this study, we integrated hydrogeological and hydrogeochemical properties to characterize the hydraulic behavior of karst waters in the Heshang Cave, Central China. Using geological and topographical analyses, we identified regional watershed boundaries and hydrogeological connections that were controlled by anticlinal geometry and faults. Water samples were collected from the Heshang Cave and potential recharge sites. Geochemical data of c(Sr2+)/c(Ca2+) and c(Mg2+)/c(Ca2+) ratios suggest that the drainage system in Heshang Cave consists of two flow paths. For vadose waters, including drip water and rimstone pool water, c(Sr2+)/c(Ca2+) ratio ranges from 0.000 6 to 0.001 1, and c(Mg2+)/c(Ca2+) ratio ranges from 0.97 to 1.1, indicating that recharge was mainly from rainfall infiltration through the overlying Cambrian dolomite stratum. In contrast, slope current and underground river waters have higher c(Sr2+)/c(Ca2+) ratios (values from 0.002 2 to 0.002 8), and lower c(Mg2+)/c(Ca2+) ratios (values from 0.50 to 0.64). These waters show homogeneous isotopic composition (δ18O: −7.15‰–−6.95‰; δD: −52.73‰–−51.31‰), implying recharge of allogeneic water from the Xiaoer River via karst conduits that pass through Ordovician limestone and Cambrian dolomite stratum.

Prediction and assessment of the disturbances of the coal mining in Kailuan to karst groundwater system

Coal resources and water resources play an essential and strategic role in the development of China's social and economic development, being the priority for China's medium and long technological development. As the mining of the coal extraction is increasingly deep, the mine water inrush of high-pressure confined karst water becomes much more a problem. This paper carried out research on the hundred-year old Kailuan coal mine's karst groundwater system. With the help of advanced Visual Modflow software and numerical simulation method, the paper assessed the flow field of karst water area under large-scale exploitation. It also predicted the evolution ofgroundwaterflow field under different mining schemes of Kailuan Corp. The result shows that two cones of depression are formed in the karst flow field of Zhaogezhuang mining area and Tangshan mining area, and the water levels in two cone centers are −270 m and −31 m respectively, and the groundwater generally flows from the northeast to the southwest. Given some potential closed mines in the future, the mine discharge will decrease and the water level of Ordovician limestone will increase slightly. Conversely, given increase of coal yield, the mine drainage will increase, falling depression cone of Ordovician limestone flow field will enlarge. And in Tangshan's urban district, central water level of the depression cone will move slightly towards north due to pumping of a few mines in the north.

Records of the Moon‐forming impact and the 470 Ma disruption of the L chondrite parent body in the asteroid belt from U‐Pb apatite ages of Novato (L6)

AbstractNovato, a newly observed fall in the San Francisco Bay area, is a shocked and brecciated L6 ordinary chondrite containing dark and light lithologies. We have investigated the U‐Pb isotope systematics of coarse Cl‐apatite grains of metamorphic origin in Novato with a large geometry ion microprobe. The U‐Pb systematics of Novato apatite reveals an upper intercept age of 4472 ± 31 Ma and lower intercept age of 473 ± 38 Ma. The upper intercept age is within error identical to the U‐Pb apatite age of 4452 ± 21 Ma measured in the Chelyabinsk LL5 chondrite. This age is interpreted to reflect a massive collisional resetting event due to a large impact associated with the peak arrival time at the primordial asteroid belt of ejecta debris from the Moon‐forming giant impact on Earth. The lower intercept age is consistent with the most precisely dated Ar‐Ar ages of 470 ± 6 Ma of shocked L chondrites, and the fossil meteorites and extraterrestrial chromite relicts found in Ordovician limestones with an age of 467.3 ± 1.6 Ma in Sweden and China. The lower intercept age reflects a major disturbance related to the catastrophic disruption of the L chondrite parent body most likely associated with the Gefion asteroid family, which produced an initially intense meteorite bombardment of the Earth in Ordovician period and reset and degassed at least approximately 35% of the L chondrite falls today. We predict that the 470 Ma impact event is likely to be found on the Moon and Mars, if not Mercury.

Origin of Late Palaeozoic bauxites in the North China Craton: constraints from zircon U–Pb geochronology and in situ Hf isotopes

Bauxite deposits that lie between Middle Ordovician limestones and Late Carboniferous clastic sediments (known as the ‘G’ layer bauxites) are widespread throughout the northern part of the North China Craton. The origin of these bauxites has remained uncertain and has been attributed either to alteration of the underlying limestone or to tephra deposited on the limestone erosional surface. We use U–Pb ages and in situ Hf isotopic analyses of detrital zircons from the ‘G’ layer bauxite deposits (both by laser ablation inductively coupled plasma mass spectrometry) to constrain the major source materials of the bauxites. The zircon ages are dominated by Palaeozoic ages, especially Carboniferous to Early Permian (338–291 Ma), coeval with the Palaeozoic subduction-related volcanism in the Inner Mongolia Palaeo-Uplift on the northern margin of the North China Craton. Zircon ϵ Hf ( t ) values range from 2.2 to −24.5 and are dominated by negative values, similar to those of Palaeozoic magmatic rocks in the Inner Mongolia Palaeo-Uplift, but distinct from those of Palaeozoic magmatic rocks in the Central Asian Orogenic Belt with positive ϵ Hf ( t ) values. Thus, we argue that the bauxites were derived mainly from volcanic dust produced during the Palaeozoic, particularly in the Carboniferous to Early Permian (338–291 Ma), by volcanism in the Inner Mongolia Palaeo-Uplift along the northern margin of the North China Craton, rather than in the Central Asian Orogenic Belt to the north. The underlying Middle Ordovician limestones, however, had provided only minor, if any, source materials for the bauxites.