Adjacent Karst Research Articles

Behavior of Sb and As in the hydrogeochemistry of adjacent karst underground river systems and the responses of such systems to mining activities.

Through the investigation of Qinglong mining area and adjacent karst underground river system, mining activities and water-rock interactions are found to control the hydrogeochemical evolution of karst underground water. Along the flow direction of the karst underground river, the hydro-chemical type is converted from HCO3-Ca type to SO4-Ca type. The concentrations of Sb and As also gradually decrease. Using PHREEQC to calculate the SI shows that: in the karst underground river system, both gypsum and fluorite are unsaturated, indicating a high degree of water-rock interaction. LogPCO2 is negatively correlated with pH, indicating that the karst underground river systems are both open systems. The dissolution of carbonate minerals and the alternate adsorption of ions are the main water-rock interactions that lead to the rapid decline of Sb and As concentrations. This research also applies principal component analysis to identify the types of pollution in adjacent karst underground river systems. The results show that the LongBaiwei underground river was mainly affected by coal mining activities, and Fe was more prominent; the ShuiYa underground river was more significantly affected by the leachate from the antimony tailings yard. This study provides a scientific basis for the evolution of the water environment as well as strategies for pollution prevention and control in typical karst underground river systems owing to the influence of mining activities.

Origin and fate of dissolved inorganic carbon in a karst groundwater fed peatland using δ13CDIC

Continental hydrosystems and in particular peatlands play an important role in the carbon cycle of the Critical Zone (CZ). Peatlands are important sinks for organic carbon and have therefore been extensively studied. However, peatlands are not only important for the fate of organic carbon, but they also affect the cycle of Dissolved Inorganic Carbon (DIC) of the peatland and the surrounding watershed. The fate of DIC is particularly complex in peatlands in limestone-dominated regions, because bicarbonate concentrations in surface and groundwater are high and the interaction between peatlands and surrounding hydrosystems are facilitated by the presence of highly permeable karst aquifers. In the present paper we study the origin and the fractionation of DIC in a peatland located on top of a karst aquifer. The study is based on hydrochemical and isotopic (δ13CDIC) data from samples recovered during 2 campaigns (low flow, high flow) at various depths within the Forbonnet peatland (Jura Mountains, eastern France), at the peatland outlet and at adjacent karst springs representing the underlying aquifer. In order to evaluate secondary fractionation processes, the measured δ13CDIC compositions were compared to modeled values considering the origin of DIC and potentially associated fractionation and speciation processes. The main results are: (1) DIC is lost at the bog surface by CO2 outgassing. (2) The δ13CDIC compositions of deep catotelm pore waters from the bog were much heavier than the modeled values. We relate this discrepancy to methanogenesis and show that this process is favored by reduced conditions at pH ∼ 6 and a HCO3− content of ∼1 mmol/L, most probably due to punctual groundwater inflows at the base of the bog. Finally, contrasted δ13CDIC compositions between the bog and the fen of the peatland reveal an additional ecohydrological control on DIC speciation.

A comparison of native and non-native small mammals in adjacent karst and volcanic soil regions in NE Luzon, Philippines

Small mammal communities that occur in habitats on volcanic soil substrates have been extensively studied on Luzon Island, but those that occur in forest over limestone are poorly known and have not been directly compared to those over volcanic soils. We conducted field surveys of small mammals in forest over limestone from ca. 100 m to 590 m elevation in the vicinity of Callao Cave, and in adjacent lowland dipterocarp forest over volcanic soil from 490 m to 900 m, near the location of prior surveys from 1300 m to1550 m on Mt. Cetaceo, an extinct volcanic peak in the northern Sierra Madre range. Despite moderately heavy disturbance to the habitats over karst (limestone) and moderate disturbance to forest over volcanic soils, we found native small mammals overall at levels of species richness and abundance similar to what we have documented elsewhere on Luzon over the same elevational range. Non-native mammals were present at all localities in the karstic habitat but were absent in all types of forest over volcanic soils, even in areas recovering from prior disturbance. Although non-natives were moderately common in karstic areas, they rarely were more common than native species, and non-native species were no more successful at invading the disturbed karstic habitat than the native species were at persisting there. The most abundant small mammal in dipterocarp forest over volcanic soil (Apomys sierra) was absent in karstic localities, despite occurring in adjacent areas at overlapping elevation. Overall, the difference between small mammals in karst and lowland dipterocarp forest was mainly due to species composition rather than total abundance. Comparisons with data from a prior study on the upper slopes of Mt. Cetaceo showed that total native species abundance was highest in montane and mossy forest, typically about three times higher than in lowland dipterocarp forest. We confirmed the current presence of one species, Apomys microdon, reported as a fossil from Callao Cave, but the apparent absence of one other, Batomys sp.; both were from deposits dated as ca. 65,000 BP. We also summarize information about large mammals in the study areas. Further study of mammals in the distinctive forest over limestone is clearly needed. KEYWORDS: biodiversity, biogeography, Cagayan Valley, disturbed forest, elevation, fossils, Muridae, Sierra Madre, Soricidae

Source and flux of anthropogenically enhanced dissolved inorganic carbon: A comparative study of urban and forest karst catchments in Southwest China

Anthropogenic disturbance has become an accelerator of dissolved inorganic carbon flux (FDIC), but the magnitude by which FDIC is enhanced by various anthropogenic activities, especially urbanization, remains largely unknown. In this study, rainfall, discharge, pH, and specific conductivity were continuously monitored during a one-year period in two adjacent karst catchments affected by anthropogenic activities in Southwest China. Groundwater, rainwater, and untreated sewage were collected monthly, and their hydrogeochemical characteristics and isotopic compositions (δ13CDIC, δ34SSO4, δ18OSO4, δ15NNO3 and δ18ONO3) were measured. The results showed that the urban catchment exported 70% more FDIC than its forest counterpart, with considerable differences in the concentration and isotopic composition of DIC, SO42− and NO3− between the two subterranean streams. Based on the contribution by various SO42− or NO3− sources estimated with a Bayesian isotope mixing model, carbonate weathering by H2CO3, H2SO4 and HNO3 contributed 67.5%, 26.0% and 6.5% of FDIC in the urban catchment and 93.3%, 3.4% and 3.3% in the forest catchment, respectively. Anthropogenic activities enhanced the FDIC by 24.0% in the urban catchment and 5.8% in the forest catchment. Anthropogenically enhanced DIC flux (FDIC-A) primarily arose from carbonate dissolution due to acid precipitation (especially S deposition), which accounted for approximately 64% of the FDIC-A in the two catchments. Sewage (including manure) and fertilizer applications also enhanced carbonate dissolution through nitrification processes. Furthermore, FDIC-A was much higher (>83%) during the wet and warm season (May to October) in both catchments. The results of this study suggest that anthropogenic impacts on carbonate dissolution should be considered in global carbon cycle assessments, especially in urban areas.

Deducing flow path mixing by storm-induced bulk chemistry and REE variations in two karst springs: With trends like these who needs anomalies?

Karst aquifers are dynamic hydrologic systems which can be sensitive to short-term recharge events (storms) and heterogeneous recharge characteristics (point recharge at sinks, irregular soil thicknesses). In this study, two adjacent karst springs, Tippery Spring and Near Tippery Spring, were monitored to better understand flow and source mixing characteristics in response to two storms in May and June 2017. Monitoring techniques included high-resolution discharge and temperature logging and collection of spring water using automatic samplers to analyze chemical parameters such as stable water isotopes and Mg/Ca ratios along with Ca/Zr ratios and rare earth elements (REEs) which have had limited testing in karst systems. The two springs exhibited behaviors which were both unique to each spring and shared depending on which parameter is considered. Spring-specific behaviors included discharge and isotopic response, with Tippery Spring having a flashier and faster conduit flow behavior relative to Near Tippery Spring’s delayed storm response. Absolute Mg/Ca values were spring-specific, owing to the relative fraction of limestone and dolostone in their respective recharge areas, although both springs showed similar Mg/Ca ratio shifts after storms. While Ca/Zr ratios changed in timing and intensity with storm intensity, both springs exhibited a decline in Ca/Zr ratios as calcium-rich carbonate matrix water was displaced by zirconium-rich storm recharge water from sinking streams off the clastic upland ridges. Flushing of recharged storm water resulted in an increase in total REE concentrations at both springs (from <0.15 ppb to >1.0 ppb), with the timing and magnitude of concentration increases determined by the degree of surface connectivity intrinsic to each spring and the intensity of the recharge event. REEs and Ca/Zr ratios provided additional and complementary tracer techniques to better understand transient recharge and flow behaviors in karst springs.

OCEANOGRAPHIC OBSERVATIONS IN THE LAGOON OF KAIAFA (W PELOPONNESE)

The Kaifa lagoon is a coastal marine ecosystem located in the Kyparisiakos Bay. The purpose of this study is to: (a) To determine the spatial and temporal changes of the physicochemical parameters in the water column of the Kaifa lagoon and (b). To create a base of information for future use for the restoration of the lagoon. Temperature, salinity, pH and dissolved oxygen were measured insitu in 28 stations. Furthermore, water samples were taken for the determination of NO2, NO3, NH4 and PO4 on seasonal bnsin from November '94 to September '95. The temperature was fluctuating from 15,90 °C in March to 30,41 °C in late August and late September. Further the seasonal variation of the temperature showed the expected two thermal periods. The first period is a hot period showing a continuous increase of temperature from March to September. The second period is a cold period showing a continuous decrease of temperature from the September to March. For each period of sampling the temperature of lagoonal water in all the extent of the lagoon remains practically constant because the fluctuation of temperature is very small each time. The salinity varied between 7,2%o and 9,20%o. The salinity like the temperature presented seasonal fluctuation patterns but the lagoon is brackish all the year round. The spatial changes of salinity were absent for every sampling period. The pH values ranged from 6,70 to 8,40. So, the pH values fluctuated in the normal levels for aquatic animals. Further, these are relatively high in spring (arithmetic mean=7.8) owing probably to higher photosynthesis rate. Dissolved oxygen ranges from 3,30 mg/l to 10,00 mg/l. In the sampling periods of September and November the oxygen values were less than 7,00mg/l for a large part of the lagoon except southern margins. This evidence suggests dangerous conditions for the fish life. Phosphate concentrations were low (0,010 mg/l - 0,07 mg/l), in November. On the contrary the phosphate levels were high (on the average 0,111 mg/l) in the sampling period of September and in particular in the southern part of the lagoon. So, this part indicated photosynthetic activity. Further, In March the phosphate concentrations have an intermediate value for every sampling station in relation to the other sampling periods. Ammonia concentrations were considered high (0,24 mg/l - 2,68 mg/l) all the year round. Nitrate levels fluctuated around normal values (0,018 mg/l -0,11mg/l) during the year. The high amount of the ammonia nitrite and nitrate in November suggests the pollution of lagoon from the fertilizers into lagoon through two drainage canals. Nitrite concentrations were high during the cold period (0,041 mg/l - 0,280 mg/l). The spatial and temporal variability of the abiotic parameters of the lagoonal water must be attributed mainly to the strong influence of fresh water witch is discharged into the lagoon from a adjacent karst with hot springs.

Investigation of seepage flow path(s) in the right embankment of Sheshpeer Dam, the Zagros Region, Iran

Gar and Bare Anticlines are located in the Zagros mountain range, southern Iran. The cores of the anticlines are comprised of the calcareous Sarvak formation sandwiched between two impermeable marly formations, namely Pabdeh-Gurpi at the top and Kazhdomi at the bottom. Sheshpeer spring with an average discharge rate of 3.2 m$$^{3}$$ s$$^{-1}$$ emerges from the Gar Anticline, forming the Sheshpeer River. To the west, the Sheshpeer River is delimited by the Albian aged calcareous Sarvak formation, while the Santonian-Oligocene impermeable deposits of the marly Pabdeh-Gurpi formation constitute the eastern limit. Sheshpeer Dam is currently under study and under construction. Parts of the Sheshpeer riverbed lie directly on the Sarvak formation and its water seeps into the adjacent karst aquifer at a rate of approximately 340–650 l s$$^{-1}$$ which will increase undoubtedly after reservoir impoundment. In addition, two tracing tests, for determination of underground seepage flow path(s) were accomplished. However, no dye tracer was detected in any source of ground water located downstream of the reservoir. Interestingly, water levels of the studied boreholes have dropped during drilling operations indicating the existence of a deep karst aquifer in the region. Finally, the seepage flow direction was investigated and assumed to be most likely parallel to Gar Anticline which strikes toward the adjacent Bare Anticline based on the dye tracing, borehole permeability, water table profiles, water budget, hydrochemistry of water resources and due to the presence of extensive crushed zones on the southern flank of the Gar Anticline.

Revealing hydrological relations of adjacent karst springs by partial correlation analysis

Abstract The objective of this work is the study of two adjacent karst springs, Jadro and Žrnovnica, in Croatia. This work focuses on the effects of temperature, relative humidity, rainfall and discharges on the hydrological behavior and relations of two adjacent karst springs. Partial correlation analysis reveals the type of the control signal that affects the cross-correlation function between an input and output signal. It has been confirmed that in the case of the adjacent karst springs Jadro and Žrnovnica, the discharge of the Žrnovnica Spring has an impact on the rainfall-discharge relation of the Jadro Spring. The demonstrated approach represents an improvement in investigating the relations of adjacent karst springs and could be used as an integral part of their hydrological and hydrogeological investigations, considering that the necessary data can occur in a relatively simple and inexpensive manner.

The Traders’ Cave of Niah (NW Borneo): morphology and features as indicators of speleogenesis and karstification

Relict caves which are isolated from regional groundwater flow are common in deeply dissected tropical tower karsts. Their passage morphology and the micro-morphology of their walls can provide valuable information on former karst processes and speleogenesis. The Traders’ Cave at Niah (Sarawak, Malaysia) was selected for a case study including comprehensive survey and observations to establish a model of the cave’s formation which can serve as a basis for comparison with other caves in the region. The research identified six levels of vadose alluvial notches showing evidence of relative water-level drop of at least 15 m during the main vadose phase of speleogenesis. During this phase, the passage reached its maximal dimensions, possibly over 90 m wide. The notches are associated with paragenetic ceiling anastomoses formed by upward or antigravitative erosion. The results indicate that point-recharge allogenic flow, i.e., sinking streams from non-karst terrains, and sediment transport and removal played a major role during cave formation. The position of limestone boulders within the cave suggests that cave-ceiling collapse and un-roofing contributed to erosion of a large part of the cave and formation of the steep-sided valley between adjacent karst towers. The collapse is linked to landscape rejuvenation associated with a significant relative water-level drop leading to the present situation in which the Traders’ Cave is isolated and relict. Most speleothems post-date the opening of the cave into the karst valley and are fed by epikarstic flow. Many speleothems are phototropic, indicating a biological influence.

The impact of halite dissolution of salt diapirs on surface and ground water under climate change, South-Central Iran

The climate change may affect the hydrological behavior and water quality of surface and ground waters across the world. The problem becomes very important in regions that the water quality is deteriorated by the evaporitic formations. One of these regions is South-Central Iran where numerous salt diapirs deteriorate the quality of water resources. The study area includes Konarsiah, Jahani and Khurab salt diapirs, where these diapirs currently deteriorate the quality of the Firuzabad River water. Part of the water of the Konarsiah salt diapir is discharged from eight brine springs, and a small part of it flows into an adjacent karst aquifer, emerging as the saline Konarsiah spring. The objectives of this study are to determine the changes of salt diapir dissolution and salinity of the water resources under the climate change. Daily precipitation generated by the Canadian global coupled model is transiently downscaled at the Firuzabad meteorological station using LARS-WG. The precipitation will decrease by 13, 19 and 28 %, under scenarios B1, A2 and A1B, respectively, for a period of 2015–2095. Consequently, the average annual discharge of the Konarsiah salt diapir springs, Konarsiah spring and Firuzabad River will also decrease. The annual mass of dissolved halite in the water resources under the influence of the three salt diapirs will decrease, but the annual salinity of these resources will increase under climate change. The percentage increase of salinity in the Konarsiah spring is lower than the Firuzabad River due to the different hydrogeological behavior of these two water resources. Most of the aquifers in South-Central Iran are overexploited; therefore, the salinity increase may intensify the present water crisis. It is recommended that salinity increase due to climate change be taken into account in any future water management for areas having evaporitic formations and precipitation reduction.

A multi-compartment hydrologic model to estimate groundwater recharge in an alluvial-karst system

Estimation of groundwater recharge is essential for sustainable groundwater management planning in arid and semiarid areas. Accurate recharge estimation in a distributed scale is a great challenge, especially when multiple recharge sources exist and available data are limited and uncertain. There are various sophisticated direct and indirect methods such as water balance method to estimate this parameter. Conventional spatially and temporally lumped models cannot take into account spatial variation of hydraulic properties of an aquifer, land use, and hydrometeorological conditions in the water balance estimation. In this study, a semi-distributed hydrologic model is developed and applied in a complex alluvial-karst system in Firouzabad catchment (Iran) to estimate groundwater recharge from precipitation, subsurface inflow from adjacent karst aquifer, return flows, and riverbed infiltration. The proposed multi-compartment model considers groundwater balance in alluvial and karstic aquifers and surface soil layer. Furthermore, it contains a multi-cell aquifer model which is used to understand the macro mechanism of the alluvial aquifer. A parameter calibration procedure is implemented wherein groundwater head data are used in parameter estimation. The performance of the proposed model is assessed by evaluating the coefficient of determination (R2) and the coefficient of efficiency. The results of the groundwater balance model are analyzed to quantify the seasonal long-term (16 years, from 1992 to 2008) groundwater recharge components. The proposed model is straightforward, efficient, and easy to apply, and its results are reasonable and acceptable.

Microbial Source Tracking in Adjacent Karst Springs.

Modern man-made environments, including urban, agricultural, and industrial environments, have complex ecological interactions among themselves and with the natural surroundings. Microbial source tracking (MST) offers advanced tools to resolve the host source of fecal contamination beyond indicator monitoring. This study was intended to assess karst spring susceptibilities to different fecal sources using MST quantitative PCR (qPCR) assays targeting human, bovine, and swine markers. It involved a dual-time monitoring frame: (i) monthly throughout the calendar year and (ii) daily during a rainfall event. Data integration was taken from both monthly and daily MST profile monitoring and improved identification of spring susceptibility to host fecal contamination; three springs located in close geographic proximity revealed different MST profiles. The Giach spring showed moderate fluctuations of MST marker quantities amid wet and dry samplings, while the Zuf spring had the highest rise of the GenBac3 marker during the wet event, which was mirrored in other markers as well. The revelation of human fecal contamination during the dry season not connected to incidents of raining leachates suggests a continuous and direct exposure to septic systems. Pigpens were identified in the watersheds of Zuf, Shefa, and Giach springs and on the border of the Gaaton spring watershed. Their impact was correlated with partial detection of the Pig-2-Bac marker in Gaaton spring, which was lower than detection levels in all three of the other springs. Ruminant and swine markers were detected intermittently, and their contamination potential during the wet samplings was exposed. These results emphasized the importance of sampling design to utilize the MST approach to delineate subtleties of fecal contamination in the environment.

Coupling geochemical tracers and pesticides to determine recharge origins of a shallow alluvial aquifer: Case study of the Vistrenque hydrogeosystem (SE France)

The objective of this study is to identify the origin of groundwater in a shallow alluvial aquifer, using a multi-tracer approach including δ18O, δ2H, major elements and 87Sr/86Sr. In addition, triazines are used as a tracer of water draining agricultural areas.Four potential recharge sources are evidenced in the alluvial groundwater: rainfall, karst water from adjacent aquifer, imported Rhône river water and local stream water.Strontium isotopes are used to highlight the adjacent karst water input (Sr=6.4–17.6μmolL−1; 87Sr/86Sr=0.7076–0.7078) showing a contrasting signature with the pristine alluvial groundwater (Sr=3.4μmolL−1; 87Sr/86Sr=0.7088–0.7092). Lateral karst recharge is observed, with high proportions reaching 100%, all along the North Western border of the aquifer. This lateral recharge implies a dilution in triazines content of the Vistrenque groundwater as the karst area is not used for agriculture.Oxygen-18 and deuterium signatures of local rainwater (δ2H=−43.5‰) and imported Rhône River water (δ2H=−72.5‰) differ significantly which allows to quantify the influence of imported water on the alluvial groundwater. Such influence is observed only locally in this study. Contribution of local stream water, influenced by wastewater treatment plant effluents, is also locally detected in the alluvial aquifer, using Cl, K, and Na contents.High triazines, NO3, and Cl concentrations underline the vulnerability of this shallow alluvial aquifer to surface contaminations. Finally, the results of this environmental multi-tracer approach are statistically supported by principal component analyses.

Relationship between carbon dioxide in Balcarka Cave and adjacent soils in the Moravian Karst region of the Czech Republic

Carbon dioxide concentration, air temperature, and humidity were monitored at (1) two cave sites and (2) three adjacent karst soils. The data over a one-year period are supported by dripwater chemistry and cave visiting frequency. The results indicate that the sources of cave CO2 are anthropogenic and epikarstic ones in addition to ordinary soils. Epikarstic CO2 produced under almost stationary conditions probably control dripwater chemistry and cave’s CO2 maxima. Based on breathing and door opening, anthropogenic activity affects instantaneous cave CO2 levels, depending on site volume/position and visitor number. A conceptual model of the CO2 dynamics of the soil-cave system is proposed. The study indicates that karst processes such as limestone dissolution and speleothem growth need not be entirely/directly controlled by external climatic conditions.

Sustainable yield of a karst aquifer system: a case study of Jinan springs in northern China

Based on the long-term monitoring data of rainfall, groundwater levels, groundwater abstraction, spring flow rates and groundwater quality, an assessment has been undertaken of the sustainable yield of a karst aquifer system in Shandong Province, northern China, to maintain perennial outflow of the karst springs while meeting water demands. One of the fundamental indicators for sustainable yield of groundwater is identified as maximum allowable water-level drawdown. A regional three-dimensional finite-difference numerical model has been developed to optimize the schemes associated with well fields and their locations and sustainable yields, in the Jinan spring catchment and its adjacent karst groundwater catchments, with the aim of maintaining the water level higher than the allowable lowest water level of 27.5 m above sea level. Furthermore, measures necessary to move towards sustainable use of the karst groundwater are outlined, drawing on contingency plans of water-source replacement and artificial recharge, dual water supply (based in water quality), use of the spring waters themselves, and groundwater quality protection.

Reconstruction of the pleistocene glaciers of Mt. Durmitor in Montenegro

Mount Durmitor is situated in the southeastern part of the Dinaric mountain system in Montenegro. Throughout the Pleistocene there were many glaciers there, which descended to adjacent karst plateau. Types of glaciers, their number and direction of moving were mostly affected by geological structure (carbonate basis) and pre-glacial relief (karst and fluvial relief). During two phases of intensive glaciation, the surface that had been seized by glacial changes also changed. Over 54% of the surface of Durmitor was exposed to the glacial process of the stronger phase and about 36% of the weaker phase. Cirque type of glaciation dominated the third phase.

Summertime Elevation of 222Rn Levels in Huntsville, Alabama

Indoor Rn concentrations and Rn in adjacent karst terrains were studied at four houses with crawlspaces in Huntsville, AL. In warm summertime weather, Rn-rich air may vent through limestone solution cavities exposed as holes at the surface of the properties. A probable interrelated-finding is that the indoor levels of 222Rn are distinctly higher in the summer than winter. The karst underlying the homes is structurally faulted and, in all probability, facilitates Rn transport from the solution cavities to the crawlspaces. Abrupt day-to-day changes in indoor Rn concentrations were recorded in addition to large seasonal changes. If the owners or residents of these particular homes had attempted to make, and interpret, short-term screening measurements for Rn during the fall season, problems, including false negatives, could have arisen because of order-of-magnitude changes in Rn concentration occurring over a few days. The best time of year to make screening measurements would be during the summer when indoor Rn concentrations are more likely to reach their maximum values.

山口県お福カルスト台上の安藤大理石採石場産ハタネズミ亜科きゅう歯化石

In the present study, 1212 isolated fossil microtine teeth from Ando Quarry at Ofukudai karst plateau, Yamaguchi Prefecture, Japan, were examined for identifictation. Among them 280 specimens were rootless molars, and the other 932 specimens were molars with root. The former were identified as Microtus epiratticeps YOUNG 1934, which is an element of the Choukoutien fossil fauna. The taxonomic validity of M. epiratticeps YOUNG 1934, was discussed in some detail. The molars with roots were referred to Clethrionomys sp. at the present stage of study. In the genus Clethrionomys, they belong to nageri group of HINTON (1926). More precise identification is an open problem.By adding at least a new microtine fossil species of the Choukoutien fossil fauna, the present study gave more evidence to support the view already stated that the formation of the Ofukudai and the adjacent karst plateaus represents the boundary between the late-middle and early-upper Pleistocene in Japan, i. e., the age of Stegodon-Palaeoloxodon faunal transition.