Building robust age models for speleothems – A case-study using coeval twin stalagmites

We use the uranium-series (U-Th) dating method to investigate the accuracy of a relative chronology based on laminae correlation between a pair of coeval twin stalagmites and compare their stable isotope and trace element records based on the two chronologies. U-Th dating shows that a relative chronology based on laminae correlation can be inaccurate: a hiatus in one of the stalagmites was not recognised, as well as more subtle changes in growth rates. Use of the stratigraphic correlation alone resulted in significant differences in the timing of stable isotopes and trace element peaks, with implications for their interpretation. Our results reveal the importance of a robust and direct chronology with which to interpret proxy data. Poor relative chronologies can lead to a misinterpretation of palaeoclimate data. The study reveals potential implications for speleothem records where proxy data and samples for dating were not taken in close proximity to each other and/or were correlated via laminae over distances of more than a few centimetres

A novel approach for construction of radiocarbon-based chronologies for speleothems

Robust chronologies are crucial for the correct interpretation of climate proxy records and for detailed reconstructions of palaeoclimate. Stalagmites have garnered strong interest as recorders of past climate in part due to their amenability to U-series dating. However, many stalagmites are not dateable using this technique due to low 238U and/or high detrital Th concentrations (e.g., many tropical cave systems (Adkins et al., 2013)), and occasionally these issues affect stalagmites across wide geographical regions (e.g., large parts of Australia (Green et al. 2013)) complicating the use of stalagmites in these areas. Radiocarbon (14C) offers an alternative method of dating stalagmites, but issues associated with the ‘dead carbon fraction’ (DCF) have historically hindered this approach. Here, a novel 14C-based method for dating stalagmites is presented and discussed. The technique calculates a best-fit growth rate between a time-series of stalagmite 14C data and known atmospheric 14C variability. The new method produces excellent results for stalagmites that satisfy four requirements: i) the absence of long-term secular variability in DCF (i.e., stalagmite DCF varies around a mean value with no long-term trend), ii) stalagmite growth rate does not vary significantly (the technique identifies stalagmites with substantial growth rate variability), iii) the stalagmite record is long enough that measurable 14C decay has occurred, and iv) one ‘anchor’ point exists where the calendar age is known. The model produces good results for a previously U–Th dated stalagmite from Heshang Cave, China, and is then applied to an undated stalagmite from southern Poland. The new method will not replace high-precision U–Th measurements, because the precision of the technique is difficult to quantify. However, it provides a means for dating certain stalagmites undateable by conventional U–Th methods and for refining coarse U–Th chronologies

Transmission electron microscopy (TEM) as a tool for identification of combustion products : application to black layers in speleothems

The present study deals with the application of High Resolution Transmission Electron Microscopy (HRTEM) to dark layers, occurring in the speleothems of Domica Cave (Slovakia). Chemical pre-treatment was necessary for sample purification and the effective extraction of carbon soot. For purposes of comparison, soot aggregates obtained from laboratory experiments on the combustion of beech wood and collected from a diesel engine also were studied. HRTEM analyses of combustion products permit a distinction to be made between soot aggregates that originated in different combustion processes. The diameter of spherical, primary particles depends on the conditions of combustion, notably temperature. Burning in diesel engines produces soot with relatively small, primary particles (diameter dp = 34 ± 4 nm). Primary, spherical particles of soot aggregates, obtained from the combustion of beech wood, were larger (diameter dp = 42 ± 5 nm). The diameters of primary particles of soot separated from Domica flowstones (samples DOM1 and DOM2) were similar to the wood samples (dp = 50 ± 9 nm). Another type of carbonaceous particle, obtained in the combustion process, had a spherical shape, but the diameter of about 50–500 nm was significantly larger than that of soot. Analyses performed on two samples (DOM S1 and DOM S2) confirmed that the black laminae owed their colour to particles, formed during wood combustion and later retained in the speleothems

New isotopic data on karst development in the northern Kraków-Wieluń Upland (southern Poland)

The Kraków-Wieluñ Upland is one of the major palaeokarst regions in Poland. However, the stages of karst development in this area are neither well documented nor reconstructed. A series of samples from a new location in the vicinity of Raciszyn was analysed. On the basis of the results of U-series dating, four phases of speleothem deposition were distinguished: (1) older than 600 ka, (2) from more than 600 ka to 290 ka, (3) around 150 ka, and the youngest (4), younger than 3 ka. On the basis of all geochronological data from the region, eight stages of karst development were described. The structure of the oldest speleothems indicates even more stages of deposition and erosion that cannot be recognized using the 230Th/234U dating method. These results indicate that the initial creation of empty spaces in the limestone took place in pre-Pleistocene time. After 600 ka ago, climatic conditions were stable for more than 300 ka, allowing the continuous deposition of speleothems. Several episodes of erosion, deposition of clastic sediments and speleothem growth during the Middle and Early Pleistocene were described. This variability of the sedimentation regime clearly reflects climate changes during that period

EPR Dating of Hydroxyapatite from Fossil Bones. Transient Effects after γ and UV Irradiation

ESR measurements at room temperature have been performed on fossil bones of cave bear (from Magurska Cave of the Tatra Mountains) and mammoth (from Dniestr River). Various paramagnetic centres related to defects in hydroxyapatite were identified. The ESR spectrum is dominated by Mn$\text{}^{2+}$ lines and free radical centres CO$\text{}_{2}^{-}$ and CO$\text{}_{3}^{-}$. Suitability of various EPR lines for the dating was evaluated. The spectra are affected by γ-ray and UV irradiation which produce new relatively unstable (transient) radical centres. From their decay curves we determined the delay period (waiting time) between irradiation and ESR dating measurements. For γ-rays the period is about 15 days and depends on the chosen ESR line. UV generates mainly surface O$\text{}^{-}$ centres which decay practically after a few days. The ESR dating of the bear bones using an additive dose method given the age t = 21.7 kiloyears (ky), whereas from radionuclide Th/U method t= 34 ky and from radiocarbon $\text{}^{14}$C method t > 33.1 ky

Evolution of the Bystrej Valley caves (Tatra Mts, Poland) based on corrosive forms, clastic deposits and U-series speleothem dating

The origin and age of cave deposits, as well as palaeogeographical changes in the Bystrej catchment during the last ca. 250 ka, were reconstructed in Magurska, Kasprowa Niżnia, Goryczkowa, Kalacka and Bystrej caves (the Bystrej Valley). The reconstruction is based on the study of corrosive forms, heavy mineral analyses and U-series dating of speleothems. Two generations of palaeoflows were distinguished by observations of scallops and heavy mineral analyses. In the older stage, now abandoned caves drained massifs surrounding the Bystrej Valley and part of an adjacent valley. The direction of palaeoflow changed as a result of the water capture after Kasprowa Niżnia Cave came into being. In the later stages, the evolution of cave systems was controlled by glaciation-deglaciation cycles. Probably at this time, some caves located in the lowest parts of the massifs also started to be formed. U-series speleothem dating allows the determination of five phases of speleothem deposition: ca. 220–150 ka, ca. 135–105 ka, ca. 95–70 ka, ca. 40–23 ka and during the Holocene

Cryogenic cave carbonates from the Cold Wind Cave, Nízke Tatry Mountains, Slovakia: Extending the age range of cryogenic cave carbonate formation to the Saalian

Cold Wind Cave, located at elevations ranging between 1,600 and 1,700 m a. s. l. in the main range of the Nízke Tatry Mountains(Slovakia), is linked in origin with the adjacent Dead Bats Cave. Together, these caves form a major cave system located within anarrow tectonic slice of Triassic sediments. Both caves have undergone complex multiphase development. A system of sub-horizontalcave levels characterized by large, tunnel-like corridors was formed during the Tertiary, when elevation differences surroundingthe cave were less pronounced than today. The central part of the Nízke Tatry Mountains, together with the cave systems, wasuplifted during the Neogene and Lower Pleistocene, which changed the drainage pattern of the area completely. The formation ofnumerous steep-sloped vadose channels and widespread cave roof frost shattering characterized cave development throughout theQuaternary.In the Cold Wind Cave, extensive accumulations of loose, morphologically variable crystal aggregates of secondary cave carbonateranging in size between less than 1 mm to about 35 mm was found on the surface of fallen limestone blocks. Based on the C andO stable isotope compositions of the carbonate (δ13C: 0.72 to 6.34 ‰, δ18O: –22.61 to –13.68 ‰ V-PDB) and the negative relationbetween δ13C and δ18O, the carbonate crystal aggregates are interpreted as being cryogenic cave carbonate (CCC). Publishedmodels suggest the formation of CCC in slowly freezing water pools, probably on the surface of cave ice, most probably duringtransitions from stadials to interstadials. Though the formation of these carbonates is likely one of the youngest events in thesequence of formation of cave sediments of the studied caves, the 230Th/234U ages of three samples (79.7±2.3, 104.0±2.9, and180.0±6.3 ka) are the oldest so far obtained for CCC in Central Europe. This is the first description of CCC formation in one caveduring two glacial periods (Saalian and Weichselian)

Holocene tufa in the Slovak Karst : facies, sedimentary environments and depositional history

Several tufa complexes are known in the Slovak Karst which is a typical karst area of a temperate climate. This area is built of Mesozoic carbonates, mainly Triassic in age. The karst systems drain carbonate plateaux and lead water to resurgences located in valleys which are up to 300 m deep. Below the resurgences there are Holocene fossil tufa deposits that exceed 12 m in thickness. The tufas include stromatolite, moss, phytoclastic, oncoidal, and intraclastic facies. Extensive barrages which once dammed the upper reaches of the streams were formed in narrow valleys. They are composed predominantly of moss facies and stromatolites, with subordinate oncoidal and phytoclastic facies. Phytoclastic, oncoidal and intraclastic facies are dominant in dammed segments of streams, and include gastropod shells and charcoal fragments. Some small moss cushions are also developed. Barrages and dammed areas formed in a longitudinal fluvial depositional system. Conversely, below resurgences located on plateau slopes tufas of a perched springline depositional system were formed. These comprise deposits of prograding cascades constructed by moss, phytoclastic and stromatolitic facies. Presently, the tufas analysed are inactive. They stopped growing in the Late Holocene time, after which there was abrupt incision of the streams. This caused downcutting into Holocene tufas, in some places reaching Mesozoic bedrock. At present tufa is being precipitated from streams in all the sites studied

Peculiar calcite speleothems filling fissures in calcareous sandstones and their palaeohydrological and palaeoclimatic significance: an example from the Polish Carpathians

Peculiar calcite speleothems developed in fissures in the Cergowa Sandstones were found in the Klęczany Quarry (Polish Western Carpathians). They represent flowstone and stalactites, rafts and various sparry crusts. Such speleothems, especially phreatic ones, are uncommon in the Outer Carpathians that are composed mainly of siliciclastic rocks of flysch type, with only limited calcium carbonate content. The speleothems analysed grew in vadose and phreatic conditions as well as at the air-water interface. Phreatic speleothems and thin rafts comprise calcite crystals of eccentric morphology. Based on their stable isotope composition the majority of the speleothems form two clusters. The first is characterized by d18O values between –9.8 and –8.5‰ and of d13C values between –5.7 and –0.6‰ whereas the second cluster of samples yields d18O values between –9.4 and –7.3‰ and d13C values from –11.5 to –9.7‰. Speleothems grew between 230+14–13 ka and Holocene time. Phreatic speleothems, including massive rafts, precipitated from ascending water of deep circulation whereas vadose and water table speleothems crystallized from local infiltration water charged with soil CO2. Mixing of both waters in the shallow phreatic zone is plausible