Karst Cave System Research Articles

A phylogeographic approach to Sulawesi’s Maros karst shrimp fauna (Decapoda, Atyidae) reveals several cave invasions and challenges current taxonomic hypotheses

Abstract The unique endemic cave fauna of the Maros karst cave system (Sulawesi, Indonesia) includes atyid freshwater shrimps only known from their species descriptions. An extensive survey revealed a total of ten species in epigean and subterranean rivers: Two non-endemic, four species endemic to Sulawesi (genus Caridina) and four stygobiont species (genus Caridina, Marosina, and Parisia) only endemic to the Maros karst. A molecular phylogeny revealed (1) two independent colonizations of Sulawesi’s Maros karst caves by species of Caridina (Clade 1) derived from endemic ancestors, and (2) an exclusively stygobiont group (Clade 2, Marosina, Parisia) possibly derived from an amphidromous, anchialine cave-dweller. Our approach revealed another cryptic cave species of Caridina and challenges the taxonomic status of four Sulawesi endemics. In conclusion, the freshwater shrimps of the Maros karst are a challenging but rewarding group that can contribute to our understanding of the evolution of cave-dwelling species and atyid phylogenetics.

Remarks on the diversity and echolocation calls of hipposiderid bats (Chirroptera: Hipposideridae) in Cuc Phuong National Park, northeastern Vietnam

Cuc Phuong is the oldest and most well-known National Park in Vietnam. With its large primary forest area and karst cave systems, it is assumed to be an ideal home to a highly diverse bat fauna. However, species diversity and echolocation of bats in this park are poorly characterized. Between April 2021 and April 2022, three bat surveys were conducted in the park with special attention on the species of the family Hipposideridae. The bat specimens collected previously from the park were also examined. According to past records, hipposiderids in the park comprised at least seven species: Aselliscus stoliczkanus, Coelops frithii, Hipposideros alongensis, Hipposideros armiger, Hipposideros gentilis, Hipposideros lylei and Hipposideros poutensis. In this series of field surveys, six of these seven species were captured while Coelops frithii was only confirmed from specimen examination. Each species is clearly distinguishable by their morphology and echolocation calls. This study provides the first comparison of echolocation calls of all seven species which will be useful for potential acoustic identification and monitoring bats in the park and surrounding areas in future.

Cooling of hydrothermal fluids rich in carbon dioxide can create large karst cave systems in carbonate rocks

Karst systems, comprising interconnected voids and caves, are ubiquitous in carbonate formations and play a pivotal role in the global water supply. Accumulating evidence suggests that a significant portion of the global karst is hypogenic, formed via rock dissolution by groundwater ascending from depth (rather than by infiltration from the surface), yet the exact formation mechanism remains unclear. Here we show that cooling of carbon dioxide-rich geothermal fluids, which turns them into highly corrosive agents due to their retrograde solubility, can dissolve and sculpt large caves on short geological timescales. A conceptual hydro-thermo-geochemical scenario is numerically simulated, showing cave formation by rising hot water discharging into a confined layer. Our models predict field observations characteristic of hypogenic caves, including enigmatic locations of the largest passages and intricate maze-like networks. Finally, we suggest that deep-seated carbon dioxide consumption during karst formation may constitute a link to the global carbon cycle.

Evidence of recent sea-level rise and the formation of a classic Maya canal system inferred from Boca Paila cave sediments, Sian Ka'an biosphere, Mexico

Cave sediments along the eastern coast of the Yucatán Peninsula contain important records of paleoenvironmental change that have not been fully explored. Reconstructing environmental changes in Boca Paila lagoon reveals details about sea level, flooding of the Sian Ka'an Biosphere, and the timeline of occupation at Muyil, an important Classic Maya maritime trading site. Three sediment cores (BP1, BP2, and BP3) were collected from a cave system beneath Boca Paila lagoon in the Sian Ka'an Biosphere. Radiocarbon dating, geochemical (X-Ray Fluorescence Core Scanning, δ13C, C/N), and microfossil (foraminifera, diatoms, pollen) analyses were performed. The combined results show three distinct phases of coastal evolution. Phase 1 (1157 BCE or earlier), an upland area with mangrove associate Conocarpus erectus, grasses, and ferns, is characterized by: organic-rich detrital peat; a relative absence of foraminifera and diatoms; organic geochemistry results within terrestrial ranges (δ13C values of −28‰ to −26‰); and low Sr/Ca, Si/Ti, and Ti/K ratios. These indicate dry conditions at the karst surface. Phase 2 (1157 BCE – 312 CE), a shallow wetland, is represented by: an increase in weathering products (Ti/K) and diatom productivity (Si/Ti); more positive δ13C values (−27‰ to −22‰) and decreasing C/N ratios; and increased marine foraminifera (e.g., Ammodiscus sp.). These indicate more open water conditions. Phase 3 (>312 CE), a wetland/lagoon environment, is characterized by: carbonate-rich marl; a greater diversity of foraminifera (Ammonia spp., Elphidium spp., Rosalina spp., and Bolivina spp.), diatoms (Cyclotella meneghiniana, Craticula spp., Amphora spp., Hyalosynedra laevigata, and Grammatophora spp.) and pollen (from mangroves, ferns, grasses, palms, and pine); increased Si/Ti and Sr/Ca values; and mixed marine and terrestrial organic geochemistry values (δ13C values of −22‰ to −20‰). These indicate increased input of marine organic sediment during sea-level rise. Sea-level and climate records support the interpretation of a dry upper karst environment prior to ∼1157 BCE, with sea-level rise forming shallow (<50 cm) wetlands by ∼312 CE. Previous archaeological analysis estimates that the first settlers arrived at Muyil ∼350 BCE, but that population expansion and construction of most structures occurred during the Postclassic (925–1550 CE). Sea-level rise would have been an important factor in the expansion of coastal settlements and trade routes; continued sea-level rise after ∼312 CE allowed for the formation of deeper lagoons and channels connecting the coast to Muyil and other inland sites which would likely not have been navigable prior to the Early Classic period (250–600 CE) as they would be too shallow. This study highlights the impacts of environment on society, as well as the importance of karst cave systems for obtaining paleoenvironmental records.

Semi-analytical solution for bottomhole pressure transient analysis of a hydraulically fractured horizontal well in a fracture-cavity reservoir

This paper study the role of hydraulic fracture properties on the transient bottomhole pressure (BHP) behavior of a horizontal well producing from a tight fracture-cavity reservoir. A combination of point source function, Laplace transformation and Perturbation transformation are used to obtain BHP step by step. Through literature comparison and numerical simulation, the results of BHP have a good consistency, which indicates the proposed method is scientific and reasonable. We divide the fluid flow into five stages, namely the wellbore storage stage, the karst cave fluid flows to the fracture stage, the radial flow stage of karst cave and fracture system, the matrix fluid flows to the fracture stage and the quasi-steady state stage. We come to the conclusion that the number of fractures and fracture direction mainly affect radial flow stage. In contrast, the length of horizontal subsection and skin factor mainly affect the karst cave fluid flows to the fracture stage. The matrix fluid flows to the fracture stage is more obvious when the fracture half-length and the horizontal segment spacing of the horizontal well are small. The study believes special attention should be paid to reforming the formations at both ends of the horizontal well. The advantage of this method is to incorporate well geometry (skin factor) and hydraulic fracturing design (fracture parameters), which is useful for well test interpretation through generating a new set of type curves. What’s more, this new method has the characteristics of easy calculation. The findings of this study can help for better understanding of well test analysis in fracture-cavity reservoir. However, the limitation of this study is that it is only suitable for this situation the horizontal well does not encounter karst caves and the karst caves in the reservoir are connected to the wellbore through fractures.

Study on vertical migration of CO2 in a karst cave system

Study on vertical migration of CO₂ in a karst cave system

Integration of multiple hydrogeological survey technologies for exploring the groundwater distribution in karst areas: A case study in Xingfu Spring, Chaohu City, China

Exploring the developing characteristics and spatial distribution of fractures and conduits in the karst system is of great significance for utilizing groundwater resources and preventing geological disasters. This study took the field of Xingfu Spring, Chaohu City, China as a target zone, three geophysical methods including MALM, TEM, and ERT were used to disclose the distribution regulation of the karst system. Based on the geophysical methods results, a hydrogeological borehole with a depth of 24.4 m was constructed to observe the structure of stratum. Then, the point velocity probe (PVP) technique was used to reveal the structure characteristics of stratum in borehole and measure the flow velocity and direction of the karst system. Finally, the tracer test was carried out in the borehole to explore the connection between borehole area and spring system. The main results show: (1) the extension direction of the karst cave in borehole is about 20° west by south and the direction of spring water flow path is about 30° north by east; (2) the groundwater in this karst cave and spring water flow path system has a similar flow direction, roughly from northeast to west; (3) there is no direct hydraulic connection between the borehole area and the spring water flow path based on the result of the tracer test. In this paper, the spatial distribution of groundwater in the study area has been successfully revealed based on the ensemble hydrogeological survey technologies. The good application of the integrated geophysical method and PVP technique can provide the reliable technology means for researching the spatial distribution and development regulation of groundwater in karst system.

Petrographic, mineralogical and geochemical constraints on the fluid origin and multistage karstification of the Middle-Lower Ordovician carbonate reservoir, NW Tarim Basin, China

The Middle-Lower Ordovician carbonate formation is the most important hydrocarbon-bearing unit in the Tarim Basin, China. Previous studies have predominately attributed the fracture-cave carbonate reservoirs to epigene karstification, and few involved polygenic karstification. Until now, mechanism and evolution model of the fracture-cave reservoirs has not been very robust. Based on detailed petrographic, mineralogical, karstological and geochemical analysis at the outcrop, this research provides new insights into the characteristics of the karst reservoir, origin of diagenetic fluids and multistage karstification in the Middle-Lower Ordovician. The results indicate that matrix porosity and permeability of the reservoir rock are low, ranging from 0.03% to 1.35% (mean 0.46%) and from 0.000864 mD to 9.15 mD (mean 0.33 mD), respectively, and that karst cave and fracture systems account for the dominant secondary reservoir porosity in the Middle-Lower Ordovician. Meteoric water and hydrothermal fluids are the two most important diagenetic fluids in the Middle-Lower Ordovician, and two stages of dissolution are responsible for the development of the fracture-cave reservoirs in the region. Extensive dissolution by meteoric water resulted in the formation of large volumes of fracture-cave reservoirs during the Middle Caledonian. Hydrothermal dissolution induced by the hydrothermal event during the Early Permian formed additional fracture-cave reservoirs in the Middle-Lower Ordovician carbonate as well. The meteoric dissolution is primarily controlled by the karst unconformity, and the fracture-cave system resulting from meteoric dissolution has a stratiform distribution below the unconformity. The fracture-cave system formed by hydrothermal fluids is mainly controlled by the deep-seated faults and the previous permeable layers, which determine that its distribution is closely related to faults. Moreover, hydrothermal dissolution may occur at high temperature and at great depths, while mineral precipitation may be the dominate process at relatively low temperature and at shallow depths. In this study, a reservoir development model of multistage karstification was established that could further enhance the knowledge of karstification process and assist in petroleum exploration in deep carbonate strata. • Two types of diagenetic fluids are revealed by integration of Geochemical, Petrographic and Mineralogical analysis. • The effects of multistage karstification on the carbonate reservoir are determined. • Hydrothermal karstification plays a positive role in the deeply burial environment. • A development model of the carbonate reservoir covered by the overlying impermeable strata is established.

A rapid sediment pulse induced by glacial melting during the MIS 8/7e transition buried well‐developed karst in the Railton Valley, Tasmania, Australia

Recent catastrophic sinkhole collapse caused by regional water table lowering induced by quarrying has led to the partial exhumation and reactivation of a buried karst cave system in the floor of the Railton Valley in the lowlands of northern Tasmania, Australia, and widespread sinkhole development. Extensive silty sediments exposed in sinkholes, OSL dated to approximately 237 ka, are interpreted to be lacustrine deposits derived from rapidly deposited glacial outwash. The silty sediments have mineralogy consistent with derivation from a source in the upper Mersey catchment rather than locally and are interpreted to be the product of rapid melting of the Mersey Valley glacier during the MIS 8/7e transition. Thick Last Glacial alluvial fan and Holocene flood‐plain deposits mantle the lacustrine sediments. Exposures of glacial erratics and weathered till in streambeds provide further evidence that the valley was impacted by earlier Pleistocene glaciations.

Variations and significance of Mg/Sr and 87Sr/86Sr in a karst cave system in southwest China

The geochemical compositions of cave drip water and speleothems such as Mg, Sr, Mg/Ca, Sr/Ca, and 87Sr/86Sr are considered to be responsive to changes in the local climate and hydrological conditions. Systematic monitoring was performed on the Mg and Sr contents, Mg/Sr ratio and 87Sr/86Sr of soil, soil water, cave drip water, and the active speleothems (AS) in Furong Cave in Chongqing, southwest China, during 2009–2018 (A.D). The results were interpreted in conjunction with the changes in the 87Sr/86Sr ratios to explore the main sources and controlling factors of Sr and other trace elements in drip water. (1) Due to the decrease in winter and spring rainfall, the residence time of water in the soil was prolonged, which resulted in increasing of Mg and Sr concentrations and 87Sr/86Sr ratios in soil water. It indicates that the trace element contents of soil water reflect seasonal changes of the rainfall. (2) The Mg and Sr contents were higher in drip water than in the soil water, as well as the 87Sr/86Sr ratios of the cave drip-water was closer to that of the bedrock, which indicated that the overlying bedrock was the main source of the trace elements in the drip water and the speleothems in Furong Cave. (3) Mg contents and Mg/Sr ratios in drip water and AS showed decreasing trend, which may be affected by the shorter water-rock contact time due to the increasing annual rainfall in the monitoring period. (4) The Sr contents in AS might be affected by the growth rate of AS because of the similar increasing trend. (5) The Mg and Sr contents and the Mg/Sr ratios of the drip water and AS did not exhibit seasonal variations due to the mixing of the fissure water and complex hydrology condition of the overlying bedrock, however, the geochemical indexes (Mg and Mg/Sr ratio) showed an opposite trend to the annual rainfall variation. In short, this study highlights the responses of the changes of Mg, Sr contents and Mg/Sr ratios of drip water and AS to the rainfall on the multi-year timescale, which contributes critical insights into the paleoclimate interpretation of proxies of speleothems in the cave with hundreds of meters’ thick bedrock.

Model-based Seismic Imaging and Analysis of Karst Water Hazards in Coal Mining

Accurate detection of karst water is the premise of karst water disaster control in coal mines. It is difficult to identify karst geological characteristics based on seismic data, so to solve this problem, a digital model including the coal measure strata and complete karst system was established based on the karst status of a coal mine in the Huaibei area of China. The entire process of seismic acquisition, processing, and interpretation was simulated and then the model was restored according to the seismic interpretation. Based on the results, karst identification and water inrush risk prediction were tried. The results allowed the overall karst geological framework, karst cave system, and stratum contact relationships to be restored more truly. Thus, seismic data can provide accurate geological information for large-scale hydrogeological mine exploration.

The transport mechanism of carbon isotopes based on 10 years of cave monitoring: Implications for paleoclimate reconstruction

Cave monitoring is crucial to unraveling the factors controlling carbon isotope compositions and their transportation in karst systems. Here, we report a 10-year (2010 ~ 2019) cave monitoring of carbon isotopes from the plants, soil, cave water, and speleothems in Jiguan Cave, Central China, located on the Chinese north–south divide in an area that is sensitive to the Asian monsoon. The results show that the cave ventilation and soil air CO2 controlled by the local temperature and humidity conditions are responsible for the seasonal variability in the δ13CDIC values. The variation in the δ13CDIC values and trace element ratios of the cave water are sensitive to the local hydrological conditions. Although there is the lag time from precipitation to cave water in drought year, the δ13CDIC and trace element ratios (Mg/Ca, Ba/Ca and Sr/Ca) of cave water are strongly coupled and reflect the extreme drought due to the influence of prior calcite precipitation (PCP) and water–rock interaction. The 10-year monitoring period covered two complete El Niño Southern Oscillation (ENSO) cycles. During the two strong El Niño years (2010 and 2015), the cave drip water δ13CDIC values were negative but the δ18O values were positive. This opposite trend is mainly due to their different controlling mechanisms. The rainfall amount and moisture sources are responsible for the δ13CDIC and δ18O values of the drip water, respectively. Throughout the karst cave system, the carbon isotopes in Jiguan Cave are continuously enriched when migrating from the vegetation to the soil to the cave drip water to the modern speleothems. Comparisons with the stalagmite δ13C records for the nearby Jiguan Cave suggest that stalagmite carbon isotopes may reflect the regional precipitation changes induced by the ENSO on the decadal scale. Overall, we demonstrate that the δ13C is a potentially reliable proxy that records the changes in the regional environment, especially precipitation changes, and is also a sensitive indictor that indirectly reflects ENSO.

Study on the characteristics of karst development in Beijing

The distribution area of carbonate rocks in Beijing is about 5071.44 km2, accounting for 30.19% of the land area in Beijing. The distribution areas of bare, covered and buried carbonate rocks are 2862.21 km2, 401.86 km2, 1803.37 km2, respectively. The carbonate rocks mainly includes dolomite in Changcheng Group of Jixian System (Jxg), dolomite in Wumishan Group of Jixian System (Jxw), dolomite in Tieling Group of Jixian System (Jxt), Cambrian limestone (Є), Ordovician limestone (O) and carbonate rocks with different ages. The characteristics of karst development in Beijing differ from region to region. In the mountainous areas of dolomite in Changcheng System and Jixian System of Proterozoic, the karst landforms such as hoodoos, series of peaks and gorges are formed by the influence of rock differential solution and shear joints. In the Cambrian and Ordovician limestone distribution areas, middle-low mountains and uvalas are formed; the covered karst is affected by rock composition, regional structure control and environment, and the degree of karst development varies in different regions. According to the ground karst, karst caves distribution and karst spring distribution in Beijing area, the karst development in Beijing is summarized into three types: karst system-based (mainly developed karst cave system), fissure-based (basically undeveloped caves and karst springs, mainly for the development of underground joint fissures in the concealed area) and composite type (the karst spring with relatively large distribution, and a small number of ground karst caves, and the development of underground joint fissures). According to the distribution characteristics of 271 karst water boreholes, 563 geothermal boreholes, 258 ground surface karst caves and 499 karst springs in Beijing, the karst development in Beijing also has typical characteristics of heterogeneity, stratification and staging.

Sporadic occupation in Armiña cave during the Upper Magdalenian: What for?

The cave of Armiña is the lower level of the same karst cave system as Atxurra Cave, which has a habitat site in the entrance, covering from the Gravettian to the Late Magdalenian periods, and an important Palaeolithic rock art ensemble in the inner part of the cave. The current entrance of Armiña was opened artificially at the end of the 19th century.Between 2016 and 2017 several tests and a 6 m2 excavation were performed in the main hall of Armiña to evaluate its archaeological record. The excavated stratigraphic sequence is sealed by a succession of sterile units (Ia-Ic) with no archaeological or faunal remains. At the bottom of this sterile unit a continuous flowstone separates it from Unit III, an almost sterile unit containing a few transported bones, charcoal fragments and a few lithics found in contact with Unit IV, where the bulk of archaeological remains were found. In Unit IV, a number of bone fragments and lithic tools are associated with a small hearth and an ocher stain.The available archaeological evidence, and the first results of the ongoing multiproxy analyses, suggest that the deposit is the result of a very short occupation event or even shorter visits to this spot inside the cave. These visits were more or less contemporaneous with the occupation levels in Atxurra and probably correspond chronologically to the artistic activity in the deep part of the cave. However, although Armiña Cave is quite suitable for human settlement, only a short-term occupation has been recognized. This could partially be related to the morpho-topographic conditions of the cave which would imply that access from the exterior was difficult at the time of the occupation. Thus, the occupation site might be defined as an Inner Archaeological Context (I.A.C.). Therefore, our main hypothesis is that this short-term occupation was an activity spot for Magdalenian explorers inside the cave, in which the activities they carried out were not exclusively related to technological and subsistence practices, nor to the execution of art, given the particular nature of the finds and the absence of Palaeolithic artistic manifestations in Armiña.

Groundwater microbial diversity and antibiotic resistance linked to human population density in Yucatan Peninsula, Mexico.

Microbial community composition in selected karst groundwater sites in the Yucatan Peninsula, Mexico, was assessed to determine the environmental variables influencing groundwater microbial diversity. The karst aquifer system is a groundwater-dependent ecosystem and is the world's second largest underwater karst cave system. The area's geology allows precipitation to infiltrate into the groundwater system and prevents accumulation of surface water; as such, groundwater is the only source of fresh water on the peninsula. The sampling locations consisted of three karst sinkholes that extend through the freshwater zone into the saline water, and an abandoned drinking water well of an ocean-side resort, during the dry and rainy seasons. The analysis showed that highly diverse microbial communities are present in the Yucatan groundwater, sustained by permanently warm temperatures and high nutrient input from human activity. Proximity to densely populated areas, such as tourist resorts, is the most important factor influencing both the diversity and presence of fecal bacteria and the antibiotic resistance profile.

Diversity, Distribution and Co-occurrence Patterns of Bacterial Communities in a Karst Cave System.

Caves are typified by their permanent darkness and a shortage of nutrients. Consequently, bacteria play an important role in sustaining such subsurface ecosystems by dominating primary production and fueling biogeochemical cycles. China has one of the world’s largest areas of karst topography in the Yunnan-Guizhou Plateau, yet the bacteriomes in these karst caves remain unexplored. In this study, bacteriomes of eight karst caves in southwest China were examined, and co-occurrence networks of cave bacterial communities were constructed. Results revealed abundant and diversified bacterial communities in karst caves, with Proteobacteria, Actinobacteria, and Firmicutes being the most abundant phyla. Statistical analysis revealed no significant difference in bacteriomes among the eight caves. However, a PCoA plot did show that the bacterial communities of 128 cave samples clustered into groups corresponding to sampling types (air, water, rock, and sediment). These results suggest that the distribution of bacterial communities is driven more by sample types than the separate caves from which samples were collected. Further community-level composition analysis indicated that Proteobacteria were most dominant in water and air samples, while Actinobacteria dominated the sediment and rock samples. Co-occurrence analysis revealed highly modularized assembly patterns of the cave bacterial community, with Nitrosococcaceae wb1-P19, an uncultured group in Rokubacteriales, and an uncultured group in Gaiellales, being the top-three keystone members. These results not only expand our understanding of cave bacteriomes but also inspires functional exploration of bacterial strains in karst caves.

Discovery of syngenetic and eogenetic karsts in the Middle Ordovician gypsum-bearing dolomites of the eastern Ordos Basin (central China) and their heterogeneous impact on reservoir quality

Abstract The Middle Ordovician Majiagou Formation in the eastern Ordos Basin (central China) represents a typical case of karst in gypsum-bearing carbonate strata. It is unique in a long karst history of ca. 120 Ma since the deposition to the Late Carboniferous. The lithology is complex with the development of both fine-grained and granular dolomites. Thus, the karstification and its impact on reservoir quality is challenging. To improve the understanding of this critical issue and further provide data for exploration, we collected core samples within the representative first and second sub-members of the fifth Member of the Majiagou Formation (herein referred to as Ma 51+2) and conducted comprehensive analyses of their physical and geochemical properties. Results show that Ma 51+2 is generally composed of gypsum-bearing micritic dolomites and grain dolomites. Karst breccias were observed and two periods of karstification were recognized. The first period is syngenetic and shows typical features such as gypsum molds and intragranular pores. It is predominantly developed within gypsum-bearing micritic dolomites due to selective fabric dissolution. Isotopic data indicate the influence of syngenetic meteoric water and seawater, as indicated by slightly depleted δ13C values (average −0.03‰), relatively low δ18O values (average −8.35‰), and slightly elevated 87Sr/86Sr values (average 0.70999). The second period is interpreted as inland eogenetic karstification and shows typical features such as non-selective fabric dissolution, including pores and vugs, breccias, and karst fillings in grain rocks. The rocks were subjected to differential dedolomitization. Grain dolomites were strongly altered by meteoric water and record a terrestrial input, as suggested by negative carbon and oxygen isotope excursions (average δ13C and δ18O values are respectively −3.07‰ and −8.97‰) as well as high 87Sr/86Sr values (average 0.71093). The two periods of karstification had a profound and heterogeneous influence on the reservoir quality. Gypsum molds formed due to the alteration of gypsum-nodule-bearing micritic dolomite by early syngenetic karstification, and represent the best reservoir space in Ma 51+2. This reflects the key role of syngenetic karstification in the formation of high-quality reservoirs. In contrast, the late inland eogenetic karstification is mainly manifested as strong alteration of grain dolomites, with little effect on micritic dolomites due to its relatively poor physical properties. The collapse resulting from strong dissolution destroys the continuity of reservoirs. In addition, relatively high porosity and permeability promote fluid movement, resulting in the infilling of the karst cave system by mud and carbonate sand. Thus, a so-called inversion of physical property occurs, namely the filling of original large pores in the grain dolomites leads to poor reservoir at last, and the preservation of initially small pores in the micritic dolomites leads to relatively good reservoir at last. This indicates that the evolution of reservoir is complex under the influence of karst.

Impact of Tourism on Bacterial Communities of Karst Underground River: A Case Study from Two Caves in Fengdu, Chongqing

In this research, the bacterial community compositions of underground water in a tourist and pristine cave were studied. Xueyu Cave and Shuiming Cave are tourist and pristine caves, respectively, in the same karst cave system located in Chongqing, southwest China. To understand the impact of tourism on bacterial community compositions in underground water that flows through the caves, filtered materials from water were collected, and 16S rDNA gene sequences were obtained by high-throughput sequencing. The Shuiming Cave (the pristine cave) had less diversity than Xueyu Cave (the tourist cave) based on the Shannon's diversity index according to Illumina operational taxonomic units (OTUs). Proteobacteria, represented mostly by γ-Proteobacterium and Bacteroidetes, dominated both systems. OTUs from Shuiming Cave were dominated by 38% Proteobacteria, 24% Chlorobi, and 19% Bacteroidetes. In the Xueyu Cave, OTUs from upstream samples were comprised of 62% Proteobacteria but comprised 64% in the downstream samples. In the Xueyu Cave, Bacteroidetes accounted for 11% of the total OTUs in the upstream sample and 16% in the downstream. Among the γ-Proteobacterium and Bacteroidetes, Acinetobacter, Pseudomonas spp., and Flavobacteriaceae, which are related to potentially pathogenic species, were prevalent in the Xueyu Cave, while Methylococcaceae-uncultured, Methylomonas spp., and Methylobacter, all methane-oxidizing bacteria, had high relative abundances in the Shuiming Cave. These results revealed that potentially more pathogenic bacteria are present in the stream waters from the tourist cave, which has important implications for the protection of tourist caves. The RDA analysis of the environmental factor and bacteria community in groundwater showed that the distribution of pathogenic bacteria was positively correlated with the cave air CO2, and the Spearman correlation analysis of the two environmental factors indicated that the influence of the number of tourists on the structure of the bacterial community in the groundwater was more obvious and led to the disappearance of a large number of native bacteria. We proposed that tourist caves control the number of daily tourists and that they enter in batches and increase the import and export of closed devices to avoid the cave air exchange inside and outside. In addition, it was recommended that they increase the import and export of sterilization devices to reduce tourists with bacteria and organic matter, and avoid leaving garbage in the hole to avoid cave microbial exchange inside and outside. A reduction in the fixed lighting inside caves should be required to reduce long exposure, since the tourists can bring individual source lighting.

Human exposure to radon radiation geohazard in Rong Cave, Dong Van Karst Plateau Geopark, Vietnam

Human exposure to radon radiation geohazard in Rong Cave, Dong Van Karst Plateau Geopark, Vietnam

A new fossil peccary from the Pleistocene-Holocene boundary of the eastern Yucatán Peninsula, Mexico

Here we describe the left mandibular ramus of a fossil peccary from the submerged karst cave system in the southeastern Mexican state of Quintana Roo. The specimen, which was discovered in the Muknal cave northwest of Tulúm, is a new genus and species of peccary termed Muknalia minima. The taxon likely dates from the latest Pleistocene and differs significantly from all extant peccaries and their Pleistocene relatives by a concave notch at the caudal edge of the mandibular ramus and prominent ventrally directed angular process. These diagnostic osteological differences suggest that the masticatory apparatus differed from all other peccaries, which may hint to an ecological isolation on the late Pleistocene Yucatán Peninsula.