Phreatic Zone Research Articles

Late-stage evolution of hypogene caves at Tyuya-Muyun (Kyrgyzstan): Quantitative insights from mineral deposits

The Tyuya-Muyun massif in SW Kyrgyzstan hosts a number of caves some of which contain Ra- and U-bearing minerals that were extensively mined in the early 20th century. Previous studies have suggested that the caves of the Tyuya-Muyun have experienced a complex speleogenetic history, including epigene and hypogene processes. Here, we reconstruct the late stages of hypogene processes by studying subaqueous (calcite and barite spars, cave clouds), near-water table (rafts, folia) and vadose (flowstone) mineral deposits in Great Barite and Surprise caves. We determined the chronology (230Th dating), stable isotope composition (δ18O, δ13C and Δ47), and formation temperature (fluid inclusion microthermometry and Δ47) of these minerals and reconstructed the oxygen isotopic composition of the paleo-water (δ18Ow). In contrast to previous hypotheses about cave evolution, we found no evidence of an initial epigenic karst phase. The earliest mineral deposits suggest already hydrothermal conditions, with calcite and barite forming at ~40–50 °C prior to 600 ka. Cave clouds in Great Barite Cave mark the beginning of the lowering of the groundwater table and also record a decrease in water temperature from 29.7 ± 8.3 °C to 12.7 ± 5.6 °C, as shown by Δ47 thermometry. The latter temperature remained stable, within analytical uncertainties, during the past 600 ka, as indicated by Δ47 results of near-water table and vadose speleothems in Surprise Cave. At the same time, the decrease in δ18Ow suggests a reduced contribution of thermal water and an increased input of colder meteoric water. By around 540–450 ka Surprise Cave emerged from the phreatic zone, as indicated by 230Th ages of the highest folia and flowstone. This lowering of the water table continued until 84 ka and may have been related to the final uplift phase of the Tyuya-Muyun massif and the concomitant incision of the Aravan River forming the Dangi Gorge.

Phreatic zone wastewater irrigation: Sensitivity analysis of contaminant fate

Phreatic zone wastewater irrigation: Sensitivity analysis of contaminant fate

Multiscale discrete fracture network modelling of shallow-water carbonates: East Agri Valley Basin, Southern Italy

We investigate the multiscale geometrical and dimensional properties of fracture and fault networks crosscutting Lower Jurassic to Cretaceous shallow-water carbonate rocks. The carbonates are exposed along the flanks of the Viggiano Mt., on the eastern side of the High Agri Valley Basin of southern Italy. Furthermore, we employ the results of field and digital structural analyses to derive the input parameters for subsequent Discrete Fracture Network modelling (DFN) of geocellular volumes whose dimension and architecture resemble those of the investigated sites. DFN modelling is carried out for geocellular volumes representing the studied bed packages (5m-side volumes), outcrops (50m-side volumes), and reservoir-scale carbonate cliffs (500m-side volumes). Notably, modelling is obtained considering the minimum mechanical aperture value obtained in the field for porosity computations and theoretical values of fracture hydraulic aperture for permeability computations. This is because the mechanical aperture values and roughness profiles collected in the field along single fractures are unreliable due to weathering and localized karst-related dissolution. Our findings reveal that a scale-dependent geometry characterizes the Cretaceous carbonates over three orders of magnitude. These results support previously published data, and contrast with those obtained for the Lower Jurassic carbonates, which suffer of some bias due to the quality of the exposures. After DFN modelling, we show that the amount of computed fracture porosity is mainly due to the SB and NSB fractures, and that equivalent permeability is greater within faulted rock volumes. In terms of horizontal permeability, which is the most reliable result after DFN modelling, we document near isotropic horizontal permeability ellipses at all scales of observations. At individual outcrops, we note that the permeability ellipses are elongated parallel to the dominant fault sets that denotes how localized strain affects the directionality of fluid flow. Finally, we summarize the original data in a conceptual model illustrating the modalities of meteoric fluid infiltration through the vadose zone, and then subsequent horizontal flow in the phreatic zone present within the fracture carbonates at shallow depths.

Dual clumped isotopes (Δ47 and Δ48) reveal non-equilibrium formation of freshwater cements

Low-Mg calcite, precipitating from meteoric fluids, is a common mineral that forms in a variety of near-surface diagenetic environments. However, recent studies, based on a combination of analyses of δ18O and Δ47 values, have suggested that this mineral might form in disequilibrium and consequently yield kinetic bias in Δ47-derived temperatures and fluid δ18O values. Here, we use dual clumped isotope proxies (Δ47 and Δ48) to investigate the influence of kinetic isotope effects within different meteoric diagenetic zones of Holocene and Pleistocene carbonates from the southern Florida and the Dominican Republic. In the Miami Oolite, the primary aragonite ooids and secondary low-Mg calcite cements in the bulk sample were separated from each other and their isotopic compositions (δ13C, δ18O, Δ47 and Δ48 values) were measured. The Δ47 and Δ48 values of the separated aragonite are consistent with the modern ooid sediments and in approximate equilibrium with the surface seawater. In contrast, the low-Mg calcite cement shows the higher Δ48 and lower Δ47 values, than expected, with the disequilibrium arising as a result of CO2 degassing in the vadose zone. Such deviations of Δ47 and Δ48 values are also observed in low-Mg calcite vadose cements in the Dominican Republic. While low-Mg calcites formed in the lower freshwater phreatic zone in the Dominican Republic have the Δ47- and Δ48-derived temperatures close to expected, the same mineral forming near the water-table and upper phreatic zone shows much higher Δ48-derived temperatures (up to ∼ 90 °C). The possible origin of such elevated temperatures can be attributed to non-equilibrium processes caused by changes in pH and pCO2, mediated by microbial sulfate reduction. Such differential kinetic behavior of Δ48 values between vadose and phreatic zones could be used as a proxy marker for the presence and the location of a water-table. This study demonstrates the great potential of dual clumped isotopes in the investigation of meteoric diagenesis and will help understand the alteration of ancient sequences and the interpretation of stable C isotope trends that they contain.

A speleogenetic history of Novoafonskaya Cave in the Western Caucasus

Speleogenesis in hypogene karst settings may be closely tied to regional tectonic dynamics and concomitant hydrochemical evolution of karst waters. However, placing temporal constraints on these processes can require a wider array of field observations and techniques than for typical karst systems. Herein, we present a comprehensive study of Novoafonskaya Cave (Western Caucasus, Abkhazia). The updated speleogenetic history of the cave comprises four stages: (1) the most ancient, a low-T hydrothermal (ca. 40–50°C) priming stage; (2) the main stage enabled by mixing of upwelling thermomineral and locally recharged common karst waters; (3) the late sulfuric-acid speleogenesis (SAS) stage, which left significant mineralogical overprint (gypsum and a suite of minerals resulting from the alteration of silicate sediments) but did not alter the morphology of the cave appreciably; and (4) the contemporary stage, occurring predominantly in the phreatic and epiphreatic zones. Ages of speleogenetic stages were constrained by radiometric dating (230Th-U and 40Ar/39Ar) and paleomagnetic data, alongside the Quaternary geological history of the region and paleodynamics of the Black Sea level. Conditions for the low-T hydrothermal karstification occurred from Miocene – Middle Pliocene. The main stage, which created the main volumes of the cave, took place from Late Pliocene – Middle Pleistocene. The cave emerged from the phreatic into the vadose zone after ca. 400 ka ago, due to the combined effect of the Black Sea regression and intensification of tectonic uplift in the Caucasus. The presence of sulfidic waters during dewatering led to the development of transient SAS processes during Middle to Late Pleistocene. Dating of calcite underlying SAS-associated overgrowths constrains the cessation of this SAS activity to within the last 147 ka. In its present state, the cave has no connection with thermomineral waters; however, such waters are found deeper in the southern parts of the karst massif (based on the hydrochemistry of Psyrtskha spring), implying that hypogene karstification, primarily driven by mixing corrosion, may still be active deep in the phreatic zone.

U‐Pb Geochronology of Paleosol Carbonate Cements by LA‐ICP‐MS: A Proof of Concept and Strategy for Dating the Terrestrial Record

AbstractThis study investigates the potential of laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) U‐Pb dating for carbonate nodules in the Late Triassic Ischigualasto Formation of northwestern Argentina. We establish a fully characterized paragenetic sequence to guide the analysis of three pedogenic carbonates and compare the U‐Pb ages with published geochronology from volcanic ashes within the sedimentary succession. Our findings demonstrate the importance of interpreting U‐Pb data within a well‐defined paragenetic framework for accurate age interpretation of pedogenic carbonates. We observe variations in U‐Pb isotopic signatures across different generations of carbonate precipitates and identify syn‐pedogenic and early burial calcite cements as most suitable for precise dating. Respectively, these two calcite cements are interpreted as microcodium and crack‐lining calcite cements formed early in the paragenetic sequence during pedogenesis to early burial of the paleosols as they transitioned from the unsaturated vadose to saturated phreatic zone below the water table. The U‐Pb ages obtained from the carbonate nodules agree with the radioisotopic ages of volcanic ashes, supporting the validity of our dating strategy. These results contribute to advancing U‐Pb carbonate geochronology and highlight its increased potential for dating sedimentary records in the terrestrial realm. Future research should focus on replicating similar work on different carbonate nodules within the Ischigualasto Fm and expanding the application of LA‐ICP‐MS U‐Pb dating to other carbonate‐bearing formations, especially in successions with limited absolute ages or where volcanic ashes are sparse or absent.

Wastewater irrigation beneath the water table: analytical model of crop contamination risks

Wastewater irrigation alleviates freshwater scarcity. However, conventional (near)surface irrigation techniques directly expose crops to contaminants. Irrigating wastewater into shallow phreatic zones to raise the water table enhances groundwater evapotranspiration, while using the vadose zone as a bioreactor that attenuates contaminants through dilution, adsorption, and biodegradation. Nevertheless, contaminants may spread across the groundwater, soil, and vegetation. In this study, we focus on the crop contamination risks, and derive a simple analytical model to estimate crop solute uptake. Although crops are not directly exposed to the irrigated wastewater, contaminants (and nutrients) may spread to the root zone. Results show that crop contamination is primarily determined by the root zone water balance, and by solute dispersion and biogeochemical reaction parameters. The model contributes towards identifying hydrogeologically and climatically suitable locations for phreatic zone wastewater irrigation, determining acceptable levels of irrigation water quality, and evaluating crop contamination hazards against the fertigative value of wastewater.

Ephemeral Puddles—Potential Sites for Feeding and Reproduction of Hyporheic Copepoda

The hyporheic (phreatic) zone connects groundwater and surface water and hosts a diverse community of organisms that are adapted to its unique conditions. In order to investigate the hitherto poorly understood biotic connections between the hyporheic zone and temporary ponds, we analyzed changes in the community of Copepoda in a small and shallow ephemeral puddle in a meadow for one year, with comparison to the groundwater fauna of the surrounding region in northeastern Poland. In the puddle, three species of Cyclopoida (Acanthocyclops vernalis, Diacyclops bisetosus, and Cyclops furcifer) were present in large numbers throughout the year. These species were also common components of the region’s groundwater fauna, but in much lower densities in the groundwater than in the puddle. These results suggest that temporary puddles can be a convenient place for copepods to feed and reproduce, while groundwater may serve as an important corridor for their dispersal. This study contributes to a more comprehensive understanding of copepod ecology and the functioning of ephemeral aquatic habitats.

The Outstanding Geology And Geoheritage Of The Niah Caves And Karst Area

This paper provides an overview of current information (including research results since 2011) on outstanding geological features of Niah karst region and caves, to support nomination of the property for World Heritage status. The geomorphology visible today is due to geological processes affecting the predominantly Miocene Subis Limestone since uplift: dissolution in vadose and phreatic zones, sediment deposition and removal, mechanical breakdown, speleothem formation and surface weathering. The caves developed at several levels in tropical tower karst (fenglin), with vertical cliffs, swamp notches and a semi-flooded epiphreatic cave network, evidence of ongoing karstification. The walls of relict Traders’ Cave have anastomosing ceiling grooves associated with wall notches indicating that it was partially filled with sediment and flow from large streams several times during its formation, prior to more recent mechanical breakdown. The numerous large and complex caves have high aesthetic value, with ceiling skylights and impressive entrances connecting to the surrounding forest. They contain speleothems (stalagmites and stalactites) of types rarely found elsewhere in the world. The Painted Cave holds one of the world’s largest cluster of unique crayback-like stalagmites, which are influenced by constructive activity of calcifying cyanobacteria and only form under limited environmental conditions of specific light levels and wind. Microbial activity can also be erosive and is likely responsible for pancake pinnacles and rare photokarren, reported here in Niah for the first time. In addition to their undisputed archaeological, cultural, ecosystems and conservation values, the Niah caves and karst region also have many interesting geological and geomorphological features, some of which are rare and hence have geoheritage value.

Assessment of Salinity in Fresh and Saline Aquifers in the Coastal Area of Jiangsu Province

Within the littoral alluvial expanse of the Yangtze River Delta, the phreatic zone encompassing the aquifer represents a prolific ecosystem, which has been subjected to an enduring epoch of marine sediment deposition, and is conspicuously susceptible to the escalating phenomenon of urbanization. The prodigious abstraction of the groundwater reserves has engendered a recent encroachment of seawater and leakage of connate saline water, culminating in the salinization of freshwater sources. For an incisive comprehension of the gradations of salinity (viz., fresh, brackish, and saline) and to execute evaluations of the groundwater’s quality, the spatial distributions of the total dissolved solids (TDS) were interpolated employing bifurcate power functions that establish a relationship between the Vertical Electrical Sounding (VES)-predicated transformation average resistivity and the assayed TDS from the systematically sampled boreholes corresponding to the aquifer stratum. The scrutiny of the groundwater’s physicochemical attributes is of paramount significance to efficaciously steer the exploitation and management of hydric resources within the area under investigation.

Petrological, Geochemical and Chronological Characteristics of Dolomites in the Permian Maokou Formation and Constraints to the Reservoir Genesis, Central Sichuan Basin, China

The Middle Permian Maokou Formation in the Sichuan Basin has huge resources and is an important target for natural gas exploration. In recent years, significant exploration breakthroughs have been made in the dolomite field of member Mao-2 in central Sichuan, and the gas production of several wells has exceeded 1 × 106 m3/d, indicating promising prospects for exploration. However, the origin of the dolomite reservoir in member Mao-2 remains ambiguous, which restricts the accurate prediction of favorable reservoirs. This study focuses on drilling in the Hechuan area as its research object, by using a detailed description of the cores from member Mao-2 of seven wells; samples were selected for tests of the degree of dolomite cation ordering, stable carbon and oxygen isotopic compositions, strontium isotopic composition, rare earth elements, LA-ICP-MS element mapping and U-Pb dating. It is clarified that: (1) The crystalline dolomite of member Mao-2 in the Hechuan area is the main reservoir rock, and the heterogeneous vugs and fractures are the main reservoir space. The dolomite in member Mao-2 has been characterized by a low degree of cation ordering value (avg. 0.59), with values of δ13C (avg. 3.87‰), δ18O (avg. −7.15‰) and 87Sr/86Sr (avg. 0.707474) having similar geochemical characteristics to Middle Permian seawater; the REEs normalized distribution patterns have similar characteristics to limestone; and the U-Pb age (261.0~262.0 Ma) corresponds to the age in the Capitanian stage of the Permian Guadalupian Series. (2) Petrological studies show that member Mao-2 has vertical karstification zonation characteristics; syngenetic karstification controls the formation of a large-scale fracture-cave system in the phreatic zone; the dolomitization of sediment in the fracture-cave system occurred during the penecontemporaneous period with locally restricted seawater. (3) The main controlling factors of the reservoir were syngenetic karstification, early dolomitization and hydrothermal dissolution related to Emei taphrogenesis. The research results are of great significance for dolomite reservoir prediction; the highlands of paleogeomorphology with syndepositional faults are favorable areas for dolomite reservoirs.

Unraveling the persistence of deep podzolized carbon: Insights from organic matter characterization

Over a billion tons of terrestrial carbon (C) is stored in deep soils from the Southeastern Coastal Plain of the United States. While the size and extent of this pool, known as deep podzolized carbon (DPC), have been reported in recent studies, the stabilization mechanisms responsible for its persistence are unclear. The main hypothesis of DPC stabilization is that hydrology, specifically water table fluctuations in the phreatic zone, slow microbial degradation and promote C accumulation. This accounts for the characteristic properties and distribution of DPC and provides a mechanistic distinction between DPC and shallow podzolized C in the region's soils, however it has yet to be tested. We characterized the organic matter composition of the bulk and dissolved fractions of DPC using elemental analysis, solvent extraction, infrared spectroscopy, and high-resolution mass spectrometry. Consistent with past work, the majority of DPC organic matter was extractable by sodium pyrophosphate solution; the influence of metal association was also observable in the water extractable fraction of DPC with large species being preferentially removed and a low compound diversity compared to those from other horizons overlying DPC. Only water extractable species with low molecular mass (m/z < 375 Da) showed significant change in average nominal oxidation state of carbon (NOSC) values, indicative of oxygen-limitation influence on the processing of these species. Infrared spectroscopy revealed an increase in abundance of aliphatic (C-H:C-O) bonds relative to polysaccharide bonds with depth whereas aromatic (C=C:C-O) bonds decreased with depth in DPC relative to other subsurface horizons. Our work shows that DPC is significantly more refractory than overlying surface soil C, and yet slightly more labile than the subsoils above DPC. Together our results suggest that the maintenance of low redox conditions via persistent water saturation contributes to the stabilization and persistence of DPC.

Managed phreatic zone recharge for irrigation and wastewater treatment

Managed phreatic zone recharge with marginal water, using (existing) drainage systems, raises the water table and increases water availability for crops. This is a newly developed method of freshwater conservation and marginal water treatment and disposal, but risks crop and environmental contamination. The fate of contaminants of emerging concern (CECs) within the irrigated water is addressed. We introduce numerical and analytical models, inspired loosely by a field site where treated domestic wastewater is used for subsurface irrigation. The treated wastewater would otherwise have been discharged into rivers, thereby spreading downstream. Model results show that minimal amounts of CECs are transported to deeper aquifers. Crops are not contaminated, except during dry years where small amounts of mobile CECs rise to the root zone, but then only directly above each irrigation drain. Under an annual precipitation surplus, less-mobile solutes are thus unlikely to ever enter the root zone. The primary mechanism of solute transport is lateral advection within the phreatic aquifer. Despite spatio-temporal heterogeneity in water flux magnitudes and directions, contaminant retardation does not significantly alter mass balance outcomes, only how fast it gets there. Therefore, persistent CECs pose the greatest risks, though overall environmental and crop contamination risks appear low. To maximize complementarity with subsurface irrigation systems, future advances in water treatment technologies should focus on removing persistent CECs. However, the system may be unsuitable for climates with annual precipitation shortages, as CECs may accumulate in the root zone and crops.

The Obir caves adjacent to the Periadriatic Fault in southern Austria: Uplifted hypogene caves formed by carbonic acid speleogenesis

Hypogene karst caves, formed independently of surface processes, have garnered increasing attention in recent decades, revealing a wider distribution than previously assumed. While most studies have relied on morphological observations, this research combines morphological and geochemical approaches to present new insights from the Obir caves in the Northern Karawank Mountains, Austria. These caverns, discovered during mining activities, lack natural entrances and developed along a prominent master horizon about 500 m above the current spring level. Notably, large shafts within the caves originate in narrow fissures and terminate blindly at the top, also suggesting a phreatic regime during their formation, with some areas being modified by vadose waters later on. A comprehensive study of drill cores indicates a stable isotope halo in the first few centimeters of the wall rock, characterized by significantly depleted δ13C and moderately depleted δ18O values compared to the pristine limestone, accompanied by bleaching of the host rock. This geochemical evidence of wall rock alteration is only present where the original phreatic solutional morphology is preserved and absent where vadose waters resulted in rugged cave wall surfaces.Considering the lack of evidence for the involvement of sulfuric acid or thermal waters, the formation of the Obir caves is attributed to carbonic acid speleogenesis. This interpretation is supported by the observed strong C isotope shift in the wall rock and the presence of CO2-bearing springs both north and south of the Periadriatic Fault. In contrast to previous studies of carbonic acid speleogenesis suggesting large-scale upwelling of aggressive waters, we propose an alternative mechanism: the injection of carbon dioxide gas into limestone situated in the phreatic zone. These injections likely occurred along subvertical tectonic fissures, triggered by the tectonic transpression of the Northern Karawank Mountains during the middle Miocene. Subsequent tectonic uplift and the incision of valleys led to a drop in the groundwater table, widespread collapse of larger cave rooms and localized vadose overprint.This study highlights the strength of combining mega- to the microscale cave morphological observations with systematic geochemical analyses of wall rock alteration in identifying caves formed by carbonic acid speleogenesis.

Genesis, Distribution, and Characterization of a Paleokarst Subsurface River System in the Tahe Area, Tarim Basin, Western China

Summary Subsurface river systems constitute one of three major paleokarst types that make up Ordovician reservoirs in the Tahe area of the Tarim Basin. The total length of the river system is approximately 400 km, and the reserves associated with this karst type are more than 200 million tons. However, it is manifested that 47% of drilled wells have not encountered river paleokarst, while 50% of wells that have encountered river paleokarst are fully filled due to the poor understanding of the paleokarst of this region, resulting in a significant variation of production capacities. In this study, we propose a detailed data integration approach with outcrops, drilling, logging, seismic profiles, and dynamic data to delineate the complex paleokarst river system in the Tahe area. The karst geological theory with reservoir characterization is combined in particular. The workflow of clarifying the main controlling factors, architecture types, and development distribution modes of the subsurface river system is established. Fill material type, sequence of fill structure, and fill controlling factors are also revealed. A quantitative characterization method of the subsurface rivers is established adopting predictions based on seismic data and high-resolution geostatistical and geological modeling. The Ordovician reservoirs in the Tahe area comprise three paleokarst river systems with different characteristics. Karst paleogeomorphology is the main control over the overall flow direction and plane distribution of the subsurface rivers. Changes in the surface of the phreatic zone are crucial in controlling the vertical layers and scale of the rivers. The combined action of faults plays a decisive role in controlling the anastomosing pattern of the rivers. Single-branch channels, reticulated channels, and structural corridors in single-layer or multilayer styles are the main subsurface river types. Trunk channels, branch channels, hall caves, and inlets/outlets are dominant structures in the architecture of the river system. Sand-mud, breccia, and chemically precipitated materials are the most common fill types. Three typical sequences of fill structure and four spatial combination modes exist in the subsurface river system. The morphology and fill characteristics of rivers are predictable using seismic attributes, such as frequency division energy, frequency division inversion, and coherent energy gradient. 3D models are constructed by multivariate control multipoint geostatistical method, which can characterize the strong heterogeneity characteristics of subsurface river systems. This complex paleokarst system enables remarkable results for the adjustment of the reservoir development plan through quantitative characterization.

Advances, challenges and perspective in modelling the functioning of karst systems: a review

We present a discussion of the state-of-the art on modelling geometrical characteristics, hydrogeological behavior and geochemical evolution of karst aquifers of meteoric origin. The considered key karst processes include: (1) the recharge processes, (2) the various hydrodynamic processes in the vadose and phreatic zones, (3) the related transport processes and (4) the speleogenesis processes. Different types of approaches for modelling geometrical characteristics of karst conduit networks are summarized. Integrated numerical studies on hydrogeological behavior of karst aquifers with functional and physically based models are then reviewed. Challenging issues in karst modelling are further discussed based on previous modelling progresses. The paper finally offers recommendations for advancing the modelling of hydrogeological behavior of karst systems and lists several open questions for future research.

An alternative approach to investigation of sediment transport through a karst aquifer

Information about the transport of suspended sediment through a karst aquifer is obtained by the time series analysis of the input and outputs from the conduit system of vadose and phreatic zone. The input is the internal runoff from epikarst zone at the analyzed location. The outputs are the discharge from karst spring, as well as the turbidity and electrical conductivity of spring water. The diffuse drainage from epikarst zone is considered as a control process that changes the quantity of water in the conduit system, and consequently it affects the outputs. The time series of internal runoff and diffuse drainage are obtained by a simple water-balance model of epikarst zone based on the concept of saturation threshold. The proposed model has two parameters: maximal capacity of epikarst storage, and maximal diffuse drainage from epikarst storage, which are estimated by using the cumulative rainfall and turbidity data, as well as the value of runoff coefficient. The time series are analyzed by means of the correlation and partial correlation functions. The presented results show that the overall capability and accuracy of the time series analysis are significantly improved by considering the conduit system separately. It is possible to register and to characterize processes in karst aquifer that are not recognizable by using classical approaches. The results for Jadro Spring show that the memory of hypothetical discharge generated by the internal runoff is practically same as the memory of time series of turbidity. The memory of hypothetical discharge generated by the diffuse drainage is very similar to the memory of time series of discharge. The duration of turbidity response is 22 days, which entirely corresponds to the duration of fresh rainwater withdrawal from the conduit system. During the first 5 days, turbidity is generated mostly by the internal runoff from the central part of catchment. During the last 12 days, turbidity has been generated by the internal runoff from the eastern part of catchment. Two components in turbidity are recognized, which are manifested as two peaks in the turbidity graph. Both peaks are produced dominantly by autochthonous sediment.

Histotaphonomy of a Pleistocene megamammal assemblage from Argentine Pampas

This work involves a multy-proxy approach of taphonomic features of the extinct giant ground sloth Lestodon armatus (Xenarthra, Mylodontidae). The study is based on paleohistological, mineralogical, and geochemical analyses from the Late Pleistocene Playa del Barco site (Buenos Aires Province, Argentina). Transverse thin sections of ribs and vertebrae were studied under light microscope, polarizing petrographic microscope, and scanning electron microscope (SEM), combined with chemical analysis using energy dispersive spectroscopy (EDS) and micro-X-ray diffraction (μXRD). The internal crystalline structure and mineral composition remains almost unaltered. The bone microstructure is well preserved in all the samples, although it was affected by different types of microfractures and infillings. Numerous radial microcracks were identified in the secondary osteons of all specimens evidencing wet depositional environment. The mineralogical and geochemical composition of the infillings and encrustations indicates that the enrichment with new elements was due to direct exchange with the sediments in which they were buried. Mineralogical evidence from the infillings allows to identify different diagenetic pathways; most of the skeletal elements were quickly buried in the vadose zone, while others were buried in the phreatic zone, directly or after some time immersed in a continental aquatic context. The fossildiagenetic information obtained from the Lestodon armatus fossils provides novel information to interpret and reconstruct the whole taphonomic history and the environmental and climatic conditions that favored the preservation of the Playa del Barco fossil assemblage during the end of the Last Glacial Maximum.

Diagenesis Analysis of Padengo Limestone Area, Gorontalo Regency Based on Petrographic Method

Carbonate rocks are rocks composed of carbonate minerals that are chemically formed in the form of solutions, and there are organisms involved in their formation. The limestone found around Lake Limboto is very interesting, because the water in the lake is freshwater while the limestone is characteristic of a marine environment. Diagenesis is a natural process in sedimentary rocks that occurs from the initial deposition until it reaches the limit of metamorphism will be formed. The research area is located in Padengo Village, West Limboto Subdistrict, Gorontalo Regency with a research area of 7.72 Km2. This research aims to analyze the diagenesis of limestone in the Padengo area of Gorontalo Regency using the petrographic method. The methods used are field geological survey and petrographic analysis. The results showed that the geology of the Padengo area is composed of a wackestone limestone facies unit, a crystalline limestone facies unit, and an alluvial sediment unit. The diagenesis type of the study area consists of neomorphism, micritization, dissolution, cementation, and dolomitization. From the type of diagenesis, it can be determined that the limestone diagenesis environment of the study area starts from the marine phreatic zone, then the burial zone, and ends at the meteoric vadose zone.

Subterranean Fauna of the Lukina Jama–Trojama Cave System in Croatia: The Deepest Cave in the Dinaric Karst

The Dinaric Karst is a global hotspot for subterranean diversity, with two distinct peaks of species richness in the northwest and southeast, and an area of a lower species richness in the central part. In this article, we present a species list and describe the ecological conditions of the Lukina jama–Trojama cave system, located in the central part of the Dinaric Karst. This cave system is the deepest and one of the most logistically challenging cave systems sampled so far in the Dinaric Karst. Repeated sampling resulted in a list of 45 species, including 25 troglobionts, 3 troglophiles, 16 stygobionts, and 1 stygophile. Most of the recorded species are endemic to the Velebit Mountain, while three species are endemic to the Lukina jama–Trojama cave system. Within the system, species richness peaks in the deepest third of the cave, most likely reflecting the harsh ecological conditions in the upper parts, including ice, cold winds, and occasional waterfalls. Milder and more stable deeper parts of the cave contain a rich subterranean species community, part of which is associated with two very distinct aquatic habitats, the cave hygropetric and the phreatic zone. The newly recognized hotspot of subterranean biodiversity in the central Dinaric Karst, which has emerged between the two known centers of biodiversity, further highlights the species richness in large cave systems, but also challenges the diversity patterns in the Dinaric Karst overall.