Showing papers on "Speleothem published in 1998"

Climate and vegetation history of the midcontinent from 75 to 25 ka: A speleothem record from crevice cave, missouri, USA

Abstract: Four Missouri stalagmites yield consistent overlapping records of oxygen and carbon isotopic changes and provide a climate and vegetation history with submillennial resolution from 75 to 25 thousand years ago (ka). The thorium-230-dated records reveal that between 75 and 55 ka, the midcontinental climate oscillated on millennial time scales between cold and warm, and vegetation alternated among forest, savanna, and prairie. Temperatures were highest and prairie vegetation peaked between 59 and 55 ka. Climate cooled and forest replaced grassland at 55 ka, when global ice sheets began to build during the early part of Marine Oxygen Isotope Stage 3.

Speleothem-based paleoclimate record from northern Oman

Abstract: U-Th age dating and stable isotope measurements of speleothems from Hoti Cave in northern Oman yield paleoclimate information from the region extending to 125 ka. The results (1) provide further confirmation of an early Holocene wet period in southern Arabia extending from some time prior to 9.7 ka and ending at 6.2 ka; (2) demonstrate a second period of wetness closely coinciding with the last interglacial period, marine isotope stage (MIS) 5e; (3) indicate that during MIS 5e, southern Arabia was considerably wetter than during the early Holocene; and (4) demonstrate that periods of increased monsoon wind strength, based on data from marine sediments, do not always coincide with evidence of greatly increased precipitation even from nearby continental areas.

High-resolution records of soil humification and paleoclimate change from variations in speleothem luminescence excitation and emission wavelengths

Abstract: Recent advances in the precision and accuracy of the optical techniques required to measure luminescence permit the nondestructive analysis of solid geologic samples such as speleothems (secondary carbonate deposits in caves). In this paper we show that measurement of speleothem luminescence demonstrates a strong relationship between the excitation and emission wavelengths and both the extent of soil humification and mean annual rainfall. Raw peat with blanket bog vegetation has the highest humification and highest luminescence excitation and emission matrix wavelengths, because of the higher proportion of high-molecular-weight organic acids in these soils. Brown ranker and rendzina soils with dry grassland and woodland cover have the lowest wavelengths. Detailed analysis of one site where an annually laminated stalagmite has been deposited over the past 70 yr during a period with instrumental climate records and no vegetation change suggests that more subtle variations in luminescence emission wavelength correlate best with mean annual rainfall, although there is a lag of ∼10 yr. These results are used to interpret soil humification and climate change from a 130 ka speleothem at an upland site in Yorkshire, England. These data provide a new continuous terrestrial record of climate and environmental change for northwestern Europe and suggest the presence of significant variations in wetness and vegetation within interglacial and interstadial periods.

Speleothems as high-resolution paleoenvironment archives: Records from northeastern China

Abstract: The isotopic compositions of oxygen and carbon and trace concentrations of magnesium and strontium in speleothems formed in limestone caves respond to climate changes outside the caves. Measurements of these properties on a stalagmite from Shihua Cave near Beijing, China, allowed reconstruction of the regional changes in precipitation, temperature and nature of vegetation. Over the last ∼ 500 years, there were fourteen precipitation cycles with a periodicity of 30–40 years, which may well reflect fluctuations in the strength of the East Asian summer monsoons reaching northeastern China. Relative to the mean temperature of this time interval, the period 1620–1900 AD was cold and periods 1520–1620 and 1900–1994 were warm. Over the last ∼ 3000-years, about eight wet/cool-dry/warm climatic cycles of 300–400 years duration occurred, the latest wet/cool half cycle corresponding to the Little Ice Age. The δ13C record registers the anthropogenic activities of fossil fuel CO2 combustion in recent decades and regional deforestation between 13 and 16 centuries when Beijing was bustling with palatial constructions and being developed into the world’s most populated city.

Karst development and speleogenesis, isla de mona, puerto rico

Abstract: The coincidence of the primary cave development zone with the Lirio Limestone/Isla de Mona Dolomite contact may result from syngenetic speleogenesis and dolomitization rather than preferential dissolution along a lithologic boundary. Tectonic uplift and glacioeustatic sea level fluctuations produced caves at a variety of elevations. Speleothem dissolution took place in many caves under phreatic conditions, evidence these caves were flooded after an initial period of subaerial exposure and speleothem growth. Several features around the perimeter of the island are interpreted to be caves whose roofs were removed by surficial denudation processes. Several large closed depressions and dense pit cave fields are further evidence of surficial karst features. The cliff retreat around the island perimeter since the speleogenesis of the major cave systems is small based upon the distribution of the remnant cave sections.

Applications of interannual-resolution stable isotope records of speleothem: climatic changes in Beijing and Tianjin, China during the past 500 years──the δ 18 O record

Abstract: δ18O of a stalagmite collected from Shihua Cave, 50 km southwest of Beijing is analyzed. The uppermost 2 cm was sampled at about 3-year intervals by a computer-controlled microsampling device. A total of 133 samples were analyzed, covering the last 480 years. A comparison of the δ18O record with the instrumentally recorded precipitation in Beijing and Tianjin back to 1840 AD shows that high precipitation correlates with negative δ18O peaks. The long-term δ18O trend records temperature changes. Between 1620 and 1900 AD, the temperature was cooler than the average value for the 480-year record, corresponding to the Little Ice Age. Temperatures warmer than the average prevailed during 1520–1620 and 1900—present. Superimposed on the long-term trend are about 14 δ18O cycles of 30–40-year periodicity, with wet periods centered around 1985, 1955, 1910, 1880, 1840, 1800, 1760, 1730, 1690, 1660, 1630, 1600, 1560 and 1530 AD.

Radiometric dating of the Middle Palaeolithic tool industry and associated fauna of Pin Hole Cave, Creswell Crags, England

Abstract: Uranium-series dating of derived speleothem suggests that the sediments enclosing a Middle Palaeolithic stone artefact assemblage in Pin Hole Cave probably accumulated after about 64 ka, and 14C dates indicate a likely age of > 40 ka for the large mammal fauna associated with it Electron spin resonance data from the fauna conform with these age constraints and are consistent with accumulation between 38 and 50 ka This evidence supports the view that Britain was recolonised by hominids during Oxygen Isotope Stage 3 Stratigraphically higher stone tool industries demonstrate the local presence of both early Upper and late Upper Palaeolithic cultures © 1998 John Wiley & Sons, Ltd

Datation des concrétions carbonatées de la Grotte du Serpent (Thaïlande) par la méthode Th/U

Abstract: Snake Cave, which is located in Northeastern Thailand, has been intensively excavated during the last few years. Excavations led to the recovery of human remains associated to 31 species of large mammals and to over 30 species of small mammals. It represents therefore a reference site for the history of biodiversity in Southeast Asia. Using the Th/U dating method we succeeded in age-dating two carbonated levels sampled in the cave. Because most speleothem samples consist of a mixture of calcite and detrital contamination we used the isochron technic approach to yield valuable ages. The calcitic level sampled in the deep part of the cave is of particular interest because it contains fossil teeth embedded in a calcitic matrix. Successful dating of this level indicates a lower age limit of 130 ky for the associated fossiliferous level,

A submerged stalactite from Belize: Petrography, geochemistry, and geochronology of massive marine cementation

Abstract: Submerged sink holes and cave systems associated with oceanic limestone platforms often contain speleothems and dripstone features which formed during subaerial exposure during glacially lowered sea level. A large stalactite, collected from a 50 meter deep terrace within the “Blue Hole” on Lighthouse Reef, offshore from Belize, records the geochronology of the transition from subaerial exposure to marine submergence during Holocene sea level rise. The stalactite originally formed on the ceiling of a large cavern when sea level was at least 60 meters below its present stand. As sea level rose, flooding the cavern, the fresh water phase of dripstone formation terminated and a 12 cm-thick rind of botryoidal splays of radial-fibrous marine aragonite coated the stalactite. This is the most massive encrustation of Holocene marine cement known, and it precipitated from seawater which had been considerably modified during circulation through the carbonate platform. By approximately 3000 yBP, when sea water flooded the bank top, cement accretion had ended, and the complex speleothem was encrusted by a marine biolithite prior to falling to the mud-covered floor of the cavern.

Spatial and temporal variations in the dissolved organic carbon concentrations in the vadose karst waters of marengo cave, indiana

Abstract: In order to better understand the organic content of microbands in speleothems, seasonal variations in the organic concentrations of vadose drip waters were examined in relation to climatic and environmental variables. Seasonal variations in the organic concentrations of the vadose waters were observed by documenting the fluctuations of Dissolved Organic Carbon (DOC) and its corresponding fluorescence. Tracer dye tests established that the larger drips depositing calcite in Marengo Cave were fed by waters with a short residence time. A strong seasonal variation in DOC concentrations and natural fluorescence was detected at quickly responding sites. Slow, constant drip sites displayed a weaker seasonality. Further investigation is required to distinguish low fluorescing DOC and to determine if the same fluorophors identified in the vadose water can be identified in the organics trapped in the recipient calcite. The overall conclusions are that fluorescence is well correlated with DOC when the fluorescence range is high but it is not a strong indicator of DOC at low fluorescence values; that the value of fluorescence as a predictor of DOC may vary significantly with individual sampling sites; and that the highest fluorescence values occur in springtime and the weakest in summer and fall. The organic content of microbands in speleothems is a promising but poorly understood field for paleoclimatic interpretation. Paleoclimatic studies of stalagmites and flowstones have included the isotopic records contained in the calcite of vadose-zone speleothems (Schwarcz 1986; Gascoyne 1992; Dorale et al. 1992, Baker et al. 1993). Many speleothems show varve-like submillimeter-scale color bands. Gascoyne (1977) and White (1981) determined that the color of such speleothems is chiefly due to the presence of variable amounts of clay or humic substances which coprecipitated or absorbed onto calcite surfaces from drip waters that passed through soil before entering the cave. Lauritzen et al. (1986) found that humic and fulvic acids are readily soluble and may be expected to enter speleothem feed waters preferentially during growing seasons. The two groups found in speleothems may be taken as indices of productivity in the overlying soil and plant cover and, therefore, as a proxy measure of paleoclimate (Lauritzen et al. 1986). Shopov et al. (1994) found a welldefined annual cycle in many vadose-zone speleothems that could be used to define the chronology of short-term events. This cycle is probably a response to hydrological events in the recharge to the cave. The most basic research on the response of organic material to climatic and environmental variables is still lacking. In this study, seasonal variations in the organic concentrations of vadose drip waters were examined in relation to climatic and environmental variables. The results will help to set up transfer functions for paleoenvironmental interpretation of organic content of speleothems, at least from Marengo Cave, Indiana. Organic (humic) substances occluded in the calcite crystals of many vadose speleothems cause luminescence in UV light. This may produce varve-like bands parallel to growth, and visible color layers are often resolvable down to micrometer scales. Shopov (1987) and White and Brennan (1989) showed that the luminescence is caused by calcium salts of humic and fulvic acids along with some low-molecular-weight organic esters. Shopov (1987) provided the first indirect evidence that the banding may reflect paleoenvironmental parameters. By assuming that the finest bands were annual, 11 to 22 year cycles were demonstrated in some samples. It appears that some variable of the paleo-ecosystem caused variations in the amounts of clay or humic substances to be coprecipitated with, or adsorbed onto, calcite. The first step in order to understand this paleoenvironmental signal is to study the relationship of ecosystem parameters and organics in drip water today. In the study reported below, drip water sites were monitored over the spring and summer of 1995 in order (i) to characterize the organic matter in the vadose waters and its fluorescence, and (ii) to determine any seasonal variations in organic concentrations.

Preliminary study on climatic signals of stable isotopes from Holocene speleothems under monsoon condition

Abstract: Within the East Asian monsoon zone the change in oxygen isotope of Holocene stalagmite is mainly related to monsoon rain rather than to temperature. And carbon isotope can be taken as a comprehensive signal which contains the natural information and the information of anthropogenic activity. Isotopic analysis is also compared with the annual layer records.

Gypsum trays in torgac cave, new mexico

Abstract: The gypsum trays in Torgac Cave, New Mexico are only the second reported occurrence of this speleothem type in the world. They differ from most other (carbonate or gypsum) trays in that they often have stalactites growing on their flat undersides (thereby forming “claw” shapes), and in that they can exhibit multiple tray growth in the vertical direction on a single stalactite. This deviation from “normal” tray development indicates that for gypsum trays to form, equilibrium must be reached between infiltration and evaporation of water. If infiltration exceeds evaporation, then gypsum stalactites (“claws”) will form; if evaporation exceeds infiltration, then trays (with flat-bottomed surfaces) will form. Drier climatic conditions during the Holocene (last 10,000 years) may have influenced the growth of gypsum trays in Torgac Cave. Torgac Cave is located in central New Mexico, ~100 km northeast of the town of Capitan, on Bureau of Land Management property. The cave is developed in the Permian Fourmile Draw member of the San Andres Formation, a siltylimy dolomitic unit containing gypsum interbeds. Short-grass prairie vegetation and a semiarid climate exist in the vicinity of the cave. The entrance area is a collapse sinkhole approximately 100 m in diameter and 30 m deep (Fig. 1). The entrance sink funnels cold, dry air down into the cave, especially in the winter. The temperature and humidity of Torgac Cave were monitored by Forbes (1998) in January and February of 1995. Temperatures at that time ranged from 5.5 ° to 10.9°C. Relative humidity ranged from 56% to 96% in different parts of the cave. The cave serves as a hibernaculum for several species of bats (Jagnow, 1998). Hill (1982) was the first to discuss the mineralogy of the cave, reporting gypsum stalactites (“claw” and anemolite), stalagmites, popcorn and crust, and epsomite flowers, cotton and crust. This report expands on Hill’s earlier description; in particular it discusses the gypsum trays in the cave, a type of speleothem not previously recognized there. Other speleothems/minerals in the cave not previously reported are gypsum rims (“eggshell” variety; Fig. 2), gypsum flowers, gypsum blisters, gypsum flowstone, and epsomite stalactites (growing on the tips of gypsum stalactites). The gypsum dripstone and flowstone has a macrocrystalline texture, with individual gypsum crystals up to 3 cm in diameter. This texture gives these speleothems a “bumpy” appearance. Gypsum spar crystals, up to 10 cm long and dating from an earlier phreatic episode (Fig. 3), are found within bedrock cavities (vugs) in the Football Room (Fig. 1). DESCRIPTION OF TRAYS

The Younger Dryas Event and Holocene Climate Fluctuations Recorded in a Stalagmite from the Panlong Cave of Guilin

Abstract: Comprehensive studies on a stalagmite from the Panlong cave, Guilin, have shown that the isotopic records and sedimentary characteristics can reflect the changes of both palaeotemperatures and palaeorainfall, that is to say, it is possible to get some information about the changes in climate of the area from the speleothem. The results suggest that: (1) the Younger Dryas event might have persisted in the area from 11 300 to 10 800 a B.P.; (2) from 9000 to 7000 a B.P., the climate got warmer and wetter, and the summer monsoon was gradually enhanced; (3) from 7000 to 4500 a B.P., the climate was warm and wet, and the summer monsoon prevailed; and (4) from 4500 a B.P. on, the summer monsoon was weakened and the modern climate pattern appeared, but there were several cold and dry periods, namely, from 4000 to 2500 a B.P., ca. 2400 a B.P. and < 1000 a B.P.

Speleothem deposits developed in caves and tunnels of Deccan-Trap basalts, Maharashtra, India

Abstract: Calcite speleothems composed of stalactites of about 1/2 cm to 1 1/2 cm in length and stalagmites of approximately 15 cm are found in the ancient caves and tunnels in the Deccan-Trap basalts. Thin-section analysis reveals that they dominantly consist of clay-rich micrite, microspar, or sparry calcite layers. These layers are either finely laminated and planar, or irregular and exhibit sutured contacts.

A Mineralogical Analysis of Karst Sediments and its Implications to the Middle-Late Pleistocene Climatic Changes on the Tibetan Plateau

Abstract: The minerals in various categories of Tibetan karst sediments were divided into three groups: carbonate, iron and silicate. The carbonate minerals, including calcite, aragonite and dolomite, consist mainly of speleothem, tufa and sinter. Most of the speleothems indicates wetter and warmer periods in early and middle Pleistocene, the youngest being 194,000 years old. The second formation of carbonate mineral, tufa, implies an arid period starting 91,000 years BP. The iron minerals, goethite and hematite, are often mixed up with cave alluvial sediments that are interbedded with flowstones, and the depression sediments. They indicate strong oxidizing environments during their deposition, which is absent at present. The clay minerals, specially kaolinite, were contained in cave alluvial, flowstone and the depression sediments as well. Combined with stratigraphic study and U-series dating, the mineral analysis shows that warmer and wetter climates, which were suitable for speleothem development, probably disappeared 200 ka ago, and drier and colder climates dominated this plateau since then.