Karst Fissure Research Articles

Hydrogeochemical Characteristics of the Haiyuan-Liupanshan Seismic Belt at the Northeastern Edge of the Tibet Plateau

The hydrogeochemical characteristics and groundwater recharge environments along the deep-cut Haiyuan-Liupanshan fault zone (HLFZ) were investigated by major ion and isotopic compositions (δ18O and δD) of the water samples collected at 14 sites from 2016 to 2017. The Schukalev classification method, fuzzy membership function, the proportion coefficients of major ions and principal component analysis (PCA) were adopted to analysis the hydrogeochemistry, water quality, origins and controlling factors of groundwater. In terms of chemical types, the sites along HLFZ can be divided into two groups. Specifically, the Group 1 is in the north and west part of the HLFZ and the water samples are characterized by higher salinity and enriched in Na+ and SO42-, reflecting the control of evaporate dissolution in cretaceous and tertiary aquifers, reverse ionic exchange, stronger water-rock reaction and deep fluids. The higher concentrations of Ca2+ + Mg2+ and HCO3- were found in Group 2, which is located in the southeast of the HLFZ and may be attributed to carbonate weathering and the recharge of karst fissure water from ordovician dolomite and limestone. Contamination of groundwater in HLFZ is severe, with 78.6% of the sites classified as grade V, which means they cannot be used for drinking water or agriculture. The primary contaminants found in Group 1 are TDS, Na+, Cl- and SO42- and the exceedance in NO3-and pH value affect water quality in the Group 2. The 18O and δD values of groundwater in HLFZ indicated that meteoric water contributed dominantly to the groundwater and it was influenced by the water cycle and water-rock reaction. Furthermore, tectonic movement, seismicity, and the level of deformation along different segments of HLFZ are important factors in the migration of deep to shallow groundwater, and water-rock reactions during groundwater migration, which results in differences in chemical composition of the groundwater between Group 1 and Group 2. Most of the sites with higher TDS in HLFZ fall on the a higher stress state region (represented by a low b value<0.75), which reflected a possible evidence of seismic activity affected the hydrogeochemistry of groundwater.

Transformation process of five water in epikarst zone: a case study in subtropical karst area

Five water stands for five form existence models of water. In karst area, five water means precipitation, groundwater, evapotranspiration water, soil water, and overland flow. The complicated water-bearing hydrogeological media and the inhomogeneous water storage structure lead to low efficiency of water utilization. To reveal intricate water resources transformation in karst areas, a typical epikarst zone was selected. The five water and their conversion processes were studied and the transformation models were built based on the long-term positioning observations. The results show that (1) overland flow can be generated when precipitation reaches 6 mm and lasts for 6 h. Under light and moderate rainfall (LMR) conditions, less than 6% of the precipitation is converted to overland flow. Under heavy rainfall and rainstorm (HRR) conditions, the conversion of precipitation into overland flow in about 3.5–6%. (2) Under LMR conditions, the conversion rate of precipitation to vegetation water, soil water and groundwater was 2–3.5%, 40–60% and 25–35%, and the conversion rate under HHR conditions was 1.5–2.2%, 25–30% and 32–50%. (3) The proportion of different levels precipitation was transformed to soil water is 20–70%. (4) The conversion rate of groundwater and karst fissure water for LMR conditions are 8–15% and 10–15%, and that for HRR is 15–20% and 40–50%. (5) The proportions of different degrees of precipitation transformed into vegetation transpiration and evaporation water are 1.5–3.5% and 6–9%, respectively. (6) Generally, <4% of the precipitation is converted into overland flow, 20–70% into soil water, 25–50% into karst groundwater, and 1–10% into evaporative water.

Construction of a hydrogeochemical conceptual model and identification of the groundwater pollution contribution rate in a pyrite mining area

To effectively restore the groundwater environment of the Shiping Mine (SPM) area, which is contaminated by acid mine drainage (AMD), a hydrogeochemical conceptual model was constructed based on groundwater chemistry and environmental stable isotopes. The contribution rate of various pollution sources in the groundwater environment was quantitatively analyzed using an optimized stable isotope mass balance model. A total of 68 groups of water samples were collected. The sampling period covered the dry, intermediate, and wet periods of a complete hydrological year. Samples were taken from rain, springs, mine drainage, tailings leachate, and surface water; and the detection and analysis indicators included 24 parameters, such as inorganic salts, heavy metals, and isotopes. A hydrogeochemical and statistical data analysis was performed. The main source of groundwater replenishment was found to be atmospheric precipitation, with the water-rock interaction of calcite and pyrite, and mining activities being the main controlling factors of hydrogeochemical processes. Acid mine drainage significantly enhanced the dissolution of various minerals, and the detection rate of Zn, Cu, As, Cd, and Pb increased from 0–30%–100% when compared with groundwater in the area upstream of the mines. The optimized mass balance model results revealed that the contribution rates of upstream groundwater, mine water and leachate were 0.78–0.86, 0.08–0.18, and 0.04–0.06 for Heidong underground river, respectively; were 0.27–0.36, 0.62–0.68, and 0.03–0.05 for Tiantang underground river, respectively. Furthermore, based on the water balance analysis, 34–70% of the mine water was found to infiltrate directly through karst fissures and karst pipes and could not be collected at the mine entrance. Acid mine drainage that directly infiltrated through runoff could easily be ignored due to the hidden migration path, which may cause the groundwater environment to be remediated less effectively than expected.

Disastrous Mechanism of Water Burst by Karst Roof Channel in Rocky Desertification Mining Area in Southwest China

With the development of coal mining in rocky desertification mining area in Southwest China, water burst is becoming an important disaster in coal mine. In order to grasp the evolution characteristics of water gushing channels in coal mining in rocky desertification mining area, the 1402 working face in Xintian Coal Mine is taken as the research object, and the occurrence of aquifers on the roof of the working face is analyzed, and the water filling path of the aquifers is explored. Besides, the evolution characteristics of water passage in coal seam mining are comprehensively analyzed, by the methods of physical similarity simulation, numerical simulation, and microseismic monitoring. The results show that the key water resource is the atmospheric precipitation, which enters the mine through the original karst fissure and mining-induced fissure. With the continuous advance of working face, the fracture height of overburden increases gradually. Specifically, when the advancement distance of working face exceeds 135 m, the water-conducting cracks in the overlying strata develop to the bottom boundary of the Yulongshan limestone aquifer, and then, the mining-induced fracture and aquifer are conducted; when the working face advances 190 m, the overall overburden mining fissure is divided into fissure opening zone and fissure closed zone. Meanwhile, most of the microseismic events occur in the middle part of the karst roof, and the maximum height of microseismic event is 40 m away from the bottom boundary of the Yulongshan limestone, during the advancing process of the working face. When the mining fissure is connected with the original karst fissure, atmospheric precipitation enters the aquifer through the original karst fissure and enters the gob of working face through the mining fissure. The research results provide the references for prediction and prevention for the water burst disaster in rocky desertification mining area in Southwest China.

Similarity Model Test of Coal Mining under Ordovician Limestone Nappe Aquifer

Ordovician limestone in North China coalfield has the characteristics of karst fissure development and strong water yield. Coal mines in North China have been threatened by Ordovician limestone water for a long time. Taking the mining of 32 coal seam in the first eastern mining area of Qianyingzi coal mine in Anhui Province in China as the engineering geological prototype, this paper uses the self-developed fluid solid coupling similarity model test device to carry out the similarity model test of overburden stress and pore water pressure response of coal mining under Ordovician limestone nappe aquifer. Based on the variation law of pore water pressure and overburden stress in a stope, it can be seen that the variation law of pore water pressure in confined aquifer is jointly affected by two factors: the vertical distance between the monitoring point and coal seam and the horizontal distance between the monitoring point and DF200 fault. According to the analysis of experimental results, the maximum height of a water flowing fracture zone in the stope is fifteen times the mining thickness. Compared with the theoretical calculation results of empirical formula, the coupling effect of seepage field and stress field and the geological structure characteristics of the stope promote the development of a water flowing fracture zone. The research results of this paper have important theoretical and practical significance not only for the safe mining of Qianyingzi coal mine but also for the safe mining of the coal mine facing the double threat of roof Ordovician limestone confined aquifer and reverse fault.

Thermo-Hydro-Mechanical Coupling Processes in Carbonate Geothermal Reservoirs and Their Numerical Simulation

Abstract Reinjecting low-temperature tailwater into geothermal reservoirs leads to complex thermo-hydro-mechanical coupling processes, making it more difficult to predict the thermal breakthrough of the reservoirs. By taking the example of the deep carbonate geothermal reservoirs of karst fissure type in the Xianxian geothermal field in China, this paper studied the thermo-hydro-mechanical coupling processes in the case of reinjection based on previous tracer tests. It established a thermo-hydro-mechanical three-field coupling model based on a two-dimensional discrete fracture network and further verified its suitability through inversion analyses. Moreover, this paper discovered the regularity of the effects of temperature and pressure changes on the deformation of the rock masses in geothermal reservoirs and clarified the mechanisms of the seepage and heat transfer in thermo-hydro-mechanical coupling processes. Meanwhile, it presented the effects of the pressure and temperature on the heat extraction efficiency and production well temperature of the geothermal production-reinjection system in the Xianxian geothermal field. As indicated by the results, the pressure and temperature of geothermal reservoirs increased and decreased, respectively, in the initial phase of the reinjection, leading to an increase in fracture aperture and reservoir permeability. Then, they tended to gradually stabilize, and the amplitude change of the reservoir permeability decreased as the reinjection proceeded. Finally, this paper proposed an optimized reinjection scheme of the study area, aiming to provide scientific support for geothermal reinjection.

Geothermal Power Generation Potential in the Eastern Linqing Depression

AbstractChina has been the leading country worldwide in direct geothermal utilization for a rather long time, which has contributed significantly to reducing carbon emissions. But the installed capacity of geothermal power generation in China is very small, and there are only a few geothermal power plants in China, specifically in Tibet, including the well‐known Yangbajing geothermal power plant. Therefore, it is anticipated that more high‐temperature geothermal resources will be discovered in order to promote China's power generation. There is potential for high‐enthalpy geothermal in the Eastern Linqing Depression in Shandong Province, where geothermal energy is stored in Ordovician and Cambrian carbonate strata. Based on the geothermal gradient in Cenozoic strata and the depth of the target geothermal reservoir, the temperature distribution pattern of the reservoir was analyzed, and two “sweet points” were identified in the Yucheng geothermal field and the Guanxian geothermal field, where the reservoir temperature is predicted to be higher than 200°C at a depth of less than 8000 m. Due to the low karst fissure ratio and the insufficient geothermal fluid in the geothermal reservoir, it is recommended that an enhanced geothermal system be set up, to increase the permeability of the natural fracture system in the carbonate formations and provide sufficient fluid for power generation through reinjection of used geothermal fluid. The power generation capacity of the two geothermal fields was estimated using a volumetric method, revealing a power generation capacity of 1621.02 MWe for the Yucheng geothermal field, and 1287.19 MWe for the Guanxian geothermal field.

Compound Karst Cave Treatment and Waterproofing Strategy for EPB Shield Tunnelling in Karst Areas: A Case Study

There is high risk of water inrush and ground collapse accidents when tunnelling in karst areas. Based on the case study of an urban metro tunnel, this paper focuses on karst cave treatment and waterproofing strategies for earth pressure balancing (EPB) shield tunnelling in karst areas containing large amounts of karst caves and fissures. When the shield machine enters the karst area, water gush easily occurs, posing serious threats to tunnelling safety. The distribution characteristic of limestone fractures, karst caves, and fissures in the karst area were analyzed according to the geological survey results. Further, water inrush risk and engineering difficulties were analyzed. Subsequently, a compound karst cave treatment and waterproofing strategy for EPB shield tunnelling was proposed and implemented. Water inflow is successfully reduced and ground collapse accident is avoided using the compound karst cave treatment and waterproofing strategy.

Seasonal Differences in Water-Use Sources of Impatiens hainanensis (Balsaminaceae), a Limestone-Endemic Plant Based on “Fissure-Soil” Habitat Function

The southwestern mountains of Hainan Island are the southernmost region with tropical karst landform in China. The frequent alternation of dry and wet seasons leads to the loss of the mineral nutrients of limestone, creating karst fissure habitats. Plants living in karst fissure habitats for long periods of time have developed local adaptation mechanisms correspondingly. In the paper, hydrogen–oxygen stable isotope technology was applied to determine the water-use sources of Impatiens hainanensis in the dry and wet seasons, hoping to expound the adaptation mechanism of I. hainanensis in karst fissure habitats to the moisture dynamics in the wet and dry seasons. In the wet season (May to October, 2018), the air humidity is relatively high in the I. hainanensis habitat; in the dry season (November 2018 to April 2019), there is a degree of evaporation. In the wet season, fine-root biomass increases with soil depths, while coarse-root biomass decreases with soil depths; in the dry season, fine-root biomass is lower and coarse-root biomass is higher compared with the wet season. It was found that the average rainfall reached 1523 mm and the main water-use sources were shallow (0–5 cm) and middle (5–10 cm) soil water, epikarst water, and shallow karst fissure water during the wet season; the average rainfall reached 528 mm, and the deep (10–15 cm) soil water and shallow karst fissure water were the main water-use sources during the dry season. Fog water has a partial complementary effect in the dry season. The differences in the distribution of root biomass and each source of water in the wet and dry seasons of I. hainanensis also reflect the different water-use strategies of I. hainanensis in the wet and dry seasons. In both dry and wet seasons, I. hainanensis formed a water-use pattern dominated by soil water and shallow fissure water (0–15 cm) under the influence of the “fissure-soil-plant” system in the karst region.

Simulation of solute transport behaviors in saturated karst aquifer system

The karst development makes aquifer have strong anisotropy and heterogeneity. In order to reveal the characteristics of solute transport in the karst fissure–conduit aquifer system, this study presents a physical model of fissure–conduit in laboratory experiments to carry out the solute transport simulation. In this paper, the tracer tests of fissure–conduit combination, fissure, and conduit solute transport process in saturated flow are designed. We found that different aquifer structures and tracer injection points have an influence on the shape of the breakthrough curve. Besides, the two-dimensional dispersion model of tracer injection of the instantaneous point was used to calculate the dispersion parameters of each group of experiments. Then, the dynamic responses of the linear distance (x) between the injection point and the receiving point, initial time (t0), peak time (tm), peak concentration (cm), average tracer transport velocity (V), and porosity (p) of aqueous media to the longitudinal dispersion coefficient are discussed. In addition, according to the measured data, Gaussian multi-peak fitting can be used to reflect the overall shape and change trend of the multi-peak BTC. These results demonstrate the solute transport behaviors in the saturated karst aquifer system, which have important reference significance for solving the engineering environmental problems in the karst area.

First Discovery of Dicerorhinus sumatrensis from Yanjinggou Provides Insights into the Pleistocene Rhinocerotidae of South China

AbstractThe Rhinocerotidae is one of the most common and important families in the Pleistocene mammalian fauna of South China. Since the last century, most of the Pleistocene rhinocerotid fossils were prematurely assigned to Rhinoceros sinensis, which has resulted in confusion of taxonomy for decades, especially in South China. The Yanjinggou area in Chongqing Municipality of China, where the neotype of R. sinensis came from, has yielded abundant rhinocerotid fossils and is a key area to solve this problem. A recently discovered juvenile skull from a karstic fissure in this area can be referred to Dicerorhinus sumatrensis (Fischer, 1814), which is the first confirmed non‐Rhinoceros rhinocerotid from the area. This new finding indicates that non‐Rhinoceros fossils might have been mixed in AMNH collection from Yanjinggou and thus the diagnosis of Rhinoceros sinensis needs reformation. On the other hand, Stephanorhinus ?kirchbergensis is also detected in Granger's collection based on our reobservation. The coexistence of Rhinoceros, Dicerorhinus and Stephanorhinus shows the higher diversity of Pleistocene rhinocerotids in South China.

Mustelids from Sackdilling Cave (Bavaria, Germany) and their biostratigraphic significance

Sackdilling Cave is a karst fissure filled with a fossiliferous breccia including abundant fossil remains, mostly snails and small mammals. The taxonomic status of mustelid remains from this cave was previously regarded as controversial and, consequently, different authors listed different species from the locality. A detailed revision of the material shows the presence of five mustelid species: Meles sp., Martes vetus, Mustela strandi, Mustela palerminea, and Mustela praenivalis. Among them, especially noteworthy is the presence of the type specimen of Martes vetus. The Sackdilling holotype resembles Martes foina and differs from that of Martes martes in a short and broad viscerocranium; wide and less extended forward incisor row; compressed, short and wide temporal region; large, strongly inflated and convex tympanic bullae; and narrow P3 with weak lingual bulge. Some dental characters are specific for Martes vetus and show some intermediate values between Martes foina than Martes martes. Among them are the P4 protocone length and the M1 trigon length. The revised material from Sackdilling Cave of Mustela palerminea and Mustela praenivalis was compared with that from other Early and early Middle Pleistocene sites of Europe and showed the presence of intermediate characters. Subsequently, based on the entire mustelid assemblage and other faunal elements (mainly rodents), the age of this fauna was estimated as ca. 0.9–0.7 Ma.

Hydro-mechanical Coupling Response Behaviors in Tunnel Subjected to a Water-Filled Karst Cave

Tunnel construction usually suffers some water-filled karst caves, which can change the stress and flow fields and bring about unpredictable engineering disasters. A typical form of water inrush disaster caused by combination of steep karst fissures and concealed karst cave is proposed in this paper. The mechanism of this water inrush disaster is studied from aspects of geology and hydro-mechanical coupling response behaviors of surrounding rock. Geological conditions including lithology, attitude of rock formation, supply and runoff conditions, climatic characteristics, etc. of Qiyueshan (QYS) tunnel are analyzed to figure out causes of this disaster. A geological conceptual model is established to describe the causes from geological aspect. Then a numerical model is built through simplifying the geological conceptual model to simulate and study hydro-mechanical coupling response behaviors of tunnel surrounding rock on the platform of PANDAS software. In addition, effects of position and size of the karst cave, and distance between the tunnel and the karst cave on principal stress and displacement of surrounding rock are discussed, which can be used to predict position, size and distance of karst caves in actual engineering.

Evaluation of Groundwater Resources and Exploitation Potential: A Case from Weifang City of Shandong Province in China

With the rapid growth of population and economy, the demand for groundwater resources is also increasing, leading to the exploitation of groundwater in some areas far greater than the recharge, which easily causes a series of environmental geological problems such as groundwater drawdown, water quality deterioration, surface subsidence, and so on. Taking Shouguang water resource in Weifang City, Shandong Province, China, as an example, the water-bearing formation in the study area can be divided into three types: pore water-bearing formation of unconsolidated sediments, karst fissure water-bearing formation of carbonate rock, and bedrock fissure water-bearing formation. According to the pumping test results, the groundwater-richness zones in the study area were delineated first. On this basis, by analyzing the dynamic changes of groundwater, the study area was divided into 40 blocks, and the natural recharge of groundwater in each block was calculated by the analogy method of the infiltration coefficient of precipitation. Then, combined with the actual situation of the study area, the allowable withdrawal of groundwater resources, mainly including pore water-bearing formation of unconsolidated sediments, karst fissure water-bearing formation of carbonate rock, and bedrock fissure water-bearing formation, was calculated using the safe yield modulus method, the improved method of the uniform arrangement of wells, and temporary storage capacity, respectively. Through the calculation, it can be concluded that the total allowable withdrawal of shallow groundwater resources in Shouguang city is 6292.5783 × 104 m3/a, that of middle and deep layer groundwater resources is 2574.92 × 104 m3/a, that of karst fissure water in carbonate rock is 1767.92 × 104 m3/a, and that of bedrock fissure water is 307.89 × 104 m3/a. The results show that within the study area, karst fissure water in carbonate rock and bedrock fissure water have immense exploitation potential.

A multidisciplinary approach in cover-collapse sinkhole analyses in the mantle karst from Guangzhou City (SE China)

Mantled karst is characterized by solution processes in underground conditions, where karst evidence can be masked. In mantled karst environments, cover-collapse sinkhole can be considered one of the most hazardous elements. This study seeks to develop a methodological framework utilizing different techniques and approaches to understand cover-collapse sinkhole genesis and its likely evolution. The study area is located in the Conghua district of Guangzhou city, Guangdong Province, in the south-eastern region of China. A mapping procedure was introduced to combine data from aerial photographs and intensive field investigations. In addition, data interpretations from borehole drilling activities and different geophysical approaches were performed to reconstruct the Quaternary deposit features, rock head morphology, and karst features. During these investigations, the detailed typology, morphometry, and chronology inventory of 49 cover-collapse sinkholes were analysed, and three karst fissure zones covered by Quaternary soil were observed. In the study, the hydrogeological data suggested that karst aquifer pumping triggered the drop in groundwater levels. Cover-collapse sinkholes might be ascribed to erosion of the soil layers due to the groundwater level decline.

Near-Surface Geothermal Reservoir Imaging based on the Customized Dense Seismic Network

Exploration of geothermal resources has become one of the major drivers for urbanization and economic transformation in southeast China, and it calls for temporal and spatial resolution improvements on conventional geophysical techniques under complex near-surface conditions. A dense seismic network including 192 sensors, with its aperture around 4.8 km, was deployed to record ambient noise for local-scale geothermal reservoir imaging in central Zhejiang Province, southeast China. With the ultrashort (less than 5 days) observation, a subset of the total station pairs was extracted to conduct seismic interferometry and dispersion measurements. This customized subnet was qualified to be an overdetermined system to achieve similar performance of entire network for the eikonal tomography with higher efficiency. The recorded high-frequency noise sources turned out to be rather homogeneous distributions, except for the dominant direction of northern Jinhua urban area. Azimuthal effects and wavelength restriction of dispersion measurements were quantified by simulating source–receiver responses under non-equipartitions of energy. The azimuth–velocity variations of field dataset verified that phase velocity measurements using the tested wavelength restriction were robust under different source–receiver orientations. The obtained phase velocity maps were comparable with the geological map. Furthermore, the inverted body wave velocities coincide well with the borehole data. Shear wave velocity profiles revealed corresponding fracture and depression structures of the reservoir. Finally, multiple geophysical properties delineate the shallow geothermy to be karst fissure water heated at certain earth temperature gradient.

Analysis on Treatment Effect of Mine Tunnel Construction Spring in Karst Area

The investigation of ultrashallow buried mining method in an interval revealed the existence of the karst fracture zone. The flow rate of 9 springs exposed in the initial excavation was relatively large, and the total water output per hour was nearly 300 m3. The filling materials in karst channels or fissures had the risk of bursting during excavation. Moreover, the ultrashallow buried tunnel undercrossed a special railway line, and the construction required higher surface deformation control. In view of the abovementioned risk problems, based on the grouting ideas of “assessment of influence,” “determination of surrounding rock,” “zone positioning,” and “dynamic grouting,” the grouting design scheme is dynamically optimized, and the grouting construction of surrounding water is cut off. Combined with the tunnel inspection, monitoring data, and numerical analysis, it is verified that the construction technology adopted in the project can ensure the stability of the project, which can provide a reference for similar projects.

Heloderma (Helodermatidae; Squamata) from the Apache Local Fauna, Pleistocene, Southwestern Oklahoma

Paleontological occurrences of helodermatid lizards (Helodermatidae) are relatively uncommon and scattered in the North American fossil record. A recently discovered concentration of vertebrate fossils was exposed in a karstic fissure filling in an active rock quarry in southwestern Oklahoma. Underwater screening of the ancient cave fill yielded numerous isolated and fragmentary skeletal elements of a diversity of small, and a few large, vertebrates including unexpected remains of Heloderma sp. as well as extinct large mammals (horse, peccary, Dwarf Pronghorn), indicating Pleistocene age. Radiometric dating of the locality is not possible because of the leaching, but fossils of the Prairie Vole, Microtus ochrogaster, from the locality help to constrain the age of the deposit between 1.21 Ma and 0.01 Ma. The fossils are the first of Heloderma in the Pleistocene of Oklahoma and the southern Great Plains. Based on taphonomic evidence and the relative abundance of rodent teeth, we infer that the fossils accumulated at least partly as the remains of vertebrates fed upon by Ringtails (Bassariscus; Procyonidae) and other small carnivorous mammals. The Pleistocene occurrence of Heloderma in the southern Great Plains of North American has potential implications for the paleobiogeography of the genus and begs further investigation of fossil herpetofaunas in North America.

The age and formation mechanisms of Late Triassic fissure deposits, Gloucestershire, England: Comments on Mussini, G. et al. (2020). Anatomy of a Late Triassic Bristol fissure: Tytherington fissure 2

In the Late Triassic the landscape NE of present-day Bristol, SW England was dominated by Carboniferous Limestone ridges and cuestas that became progressively buried by continental Mercia Mudstones and finally inundated during the Rhaetian marine transgression. Mussini et al. (2020) adopt the assertions of earlier collaborators back to Whiteside and Marshall (2008) that terrestrial vertebrate assemblages from sediments contained within karstic fissure systems in the former limestone ridges at Cromhall, Tytherington and elsewhere are restricted to the Rhaetian. We review and reject the sedimentological, stratigraphic, geomorphological and topographic arguments for this and reassert a long pre-Rhaetian (Norian) history for the vertebrate-bearing fissure systems at both Tytherington and Cromhall. We also reject the contemporaneous Rhaetian freshwater-seawater mixing zone dissolution model for the fissure systems adopted by Mussini et al. (2020) and reaffirm that the Tytherington and Cromhall fissures developed as conduit caves with a long Triassic history. Applying a new regional study of the Rhaetian transgressive surface, we also show that whilst the fissures at Cromhall remained sealed after the Norian, those at nearby Tytherington were re-exposed in the Late Rhaetian. Already partially filled with Norian sediments, the Tytherington fissures were subject to reworking on the seabed. Internal collapses, probably triggered by well documented repeated regional seismicity, led to the chaotic state of the Tytherington fills when downward moving Rhaetian marine components came to lie amongst and mix with earlier Norian terrestrial sediments. The vertebrate associations in the Tytherington fissures therefore contain a substantial Rhaetian input whilst those at Cromhall do not.

Evolution Analysis of Microseismic Events before and after Mining through Large‐Scale Weak Zone with High Confined Water

The existence of large‐scale weak zone will have a great adverse impact on coal mining in high confined aquifer. Taking the Wutongzhuang Coal Mine which is threatened by high‐pressure water as an example, this paper studies the difference between the microseismic events before and after mining and analyzes the influence of the large size weak zone on the coal mining on the confined aquifer. The research results show that the microseismic characteristics of the large soft weak belt are small number of events, the spatial distribution of events is concentrated, and the energy level is large. The amplitude of microseismic events is higher, and the proportion of large events in microseismic events is larger than that of small events; the characteristics of microseismic events caused by mining face mining are that the number of events is more, the distribution of events is loose, the distribution of roof and floor is more, the energy level is less, the amplitude is smaller, and the proportion of small and medium events in microseismic events is larger than that of large events. Due to the joint influence of large‐scale weak zone of floor and mining, the floor in the middle area of working face is affected by mining, the number of microseismic events in each aquifer increases suddenly, the karst fissures between the aquifers are further developed, and there is a trend of transfixion. Therefore, measures such as floor grouting should be taken to reinforce the large‐scale weak zone before mining.