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1
Meyer, Juliane, Claudia Wrozyna, Albrecht Leis, and Werner E. Piller. "Modeling calcification periods of <i>Cytheridella ilosvayi</i> from Florida based on isotopic signatures and hydrological data." Biogeosciences 14, no. 21 (November 7, 2017): 4927–47. http://dx.doi.org/10.5194/bg-14-4927-2017.
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Abstract. The isotopic signatures of ostracod shells are the result of the temperature and composition of their host water and the phenology and ecology of the target species. Investigations addressing the influence of site-specific environmental variations on the isotopic ranges of ostracod shells are still rare but can provide important information on habitat-dependent variations and may signify a seasonally restricted timing of calcification periods. Here we present isotopic signatures (δ18Oostr, δ13Costr) of living Cytheridella ilosvayi (Ostracoda) and physical, chemical, and isotopic (δD, δ18Owater, δ13CDIC) compositions of 14 freshwater habitats (rivers, lakes, canals, marshes, sinkholes) in South Florida from winter 2013 and summer 2014. We also present instrumental data of river temperatures and δ18O of precipitation (δ18Oprec) from this region. The physicochemical and isotopic compositions of the selected sites characterize the different habitats and show the influence of the source water, biological activity, and duration of exposure to the surface. Mean δ18Oostr and δ13Costr signatures of C. ilosvayi shells correlate well with the isotopic composition of their host waters. Within-sample variabilities in repeated isotopic measurements of single ostracod shells reflect habitat-dependent ranges. The similarly high range of ostracod δ18O in rivers and one marsh sample indicates that both temperature and δ18Oprec are responsible for their variation in the whole study area. Rivers and canals, which are predominantly influenced by the input and mixing of inorganic carbon from the catchment, show smaller δ13Costr ranges than the marsh dominated by local fluctuations in biological activities. Based on these observations, background data of water temperatures and δ18Oprec were used to calculate monthly δ18O variations in a theoretical calcite formed in rivers in Florida assuming a direct reaction on precipitation changes. The calculated values showed a high variation coupled with low mean values during the summer wet season, while during the winter dry season the variation remains small and mean values increased. Inferred configurations were used to approximate possible calcification periods of C. ilosvayi. For a plausible calcification period, mean values and ranges of δ18Oostr had to be equal to the theoretical calcite with a slight positive offset (vital effect). The applied model suggests a seasonal calcification period of C. ilosvayi in early spring that is probably coupled to the hydrologic cycle of Florida.
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Wansard, Guy, Josep R. Roca, and Francesc Mezquita. "Experimental determination of strontium and magnesium partitioning in calcite of the freshwater ostracod Herpetocypris intermedia." Fundamental and Applied Limnology 145, no. 2 (May 27, 1999): 237–53. http://dx.doi.org/10.1127/archiv-hydrobiol/145/1999/237.
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Bornemann, André, Claudius M. Pirkenseer, Patrick De Deckker, and Robert P. Speijer. "Oxygen and carbon isotope fractionation of marine ostracod calcite from the eastern Mediterranean Sea." Chemical Geology 310-311 (June 2012): 114–25. http://dx.doi.org/10.1016/j.chemgeo.2012.03.028.
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Bodergat, Anne-Marie, Christophe Lécuyer, François Martineau, Atike Nazik, Kemal Gürbüz, and Serge Legendre. "Oxygen isotope variability in calcite shells of the ostracod Cyprideis torosa in Akyatan Lagoon, Turkey." Journal of Paleolimnology 52, no. 1-2 (April 23, 2014): 43–59. http://dx.doi.org/10.1007/s10933-014-9777-3.
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Devriendt, Laurent S., Helen V. McGregor, and Allan R. Chivas. "Ostracod calcite records the 18O/16O ratio of the bicarbonate and carbonate ions in water." Geochimica et Cosmochimica Acta 214 (October 2017): 30–50. http://dx.doi.org/10.1016/j.gca.2017.06.044.
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Börner, Nicole, Bart De Baere, Roger Francois, and Antje Schwalb. "Application of flow-through time-resolved analysis (FT-TRA) to isolate the elemental composition in ostracod calcite." Chemical Geology 467 (September 2017): 53–63. http://dx.doi.org/10.1016/j.chemgeo.2017.07.019.
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Silva, Loreine Hermida da Silva e., Anderson Andrade Cavalcanti Iespa, and Cynthia Moreira Damazio Iespa. "Composição dos estromatólitos estratiformes da lagoa Salgada, Rio de Janeiro, Brasil." Anuário do Instituto de Geociências 31, no. 2 (December 1, 2008): 42–49. http://dx.doi.org/10.11137/2008_2_42-49.
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Lagoa Salgada is situated in the north coast of State of Rio de Janeiro, between the districts of Campos dos Goitacazes and São João da Barra, some 41º00'30" W and 21º54'10"S. In the margins of the lagoon the presence of recent stromatolitic constructions was verified. The stromatolite may be defined as lithifying biosedimentary structure, growing through of sediment blade trapping by the carbonate precipitation as result of microbian organism activity. The aim of this study was to characterize the cyanobacteria assemblage in stratiform stromatolites found on the floor of lagoa Salgada. Within the stratiform stromatolites 21 species of cyanobacteria were found, Microcoleus chthonoplastes (Thuret) Gomont 1892 and Lyngbya aestuarii (Liebman) Gomont 1892 are frequent in these stromatolites. The presence of calcite was observed in the stratiform stromatolites. The filamentous cyanobacteria are responsible for the union and imprisonment of sediment to form the layers in the stromatolites. The skeleton remains of mollusks, foraminifers and ostracod found in the area, work as a source of calcium carbonate and of sediment to structure the stromatolites
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Lawrence, James R., Kiseong Hyeong, Rosalie F. Maddocks, and Kwang-Sik Lee. "Passage of Tropical Storm Allison (2001) over southeast Texas recorded in δ18O values of Ostracoda." Quaternary Research 70, no. 2 (September 2008): 339–42. http://dx.doi.org/10.1016/j.yqres.2008.04.004.
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AbstractFreshwater Ostracoda collected in ephemeral pond-waters derived from Tropical Storm Allison (2001, Texas) recorded the unusually low oxygen-isotope values of that storm. Therefore, the potential clearly exists, in locations where tropical cyclones make landfall, to obtain a long-term record of tropical cyclone activity from fossil ostracode calcite.
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Wetterich, Sebastian, Ulrike Herzschuh, Hanno Meyer, Lyudmila Pestryakova, Birgit Plessen, C. M. Larry Lopez, and Lutz Schirrmeister. "Evaporation effects as reflected in freshwaters and ostracod calcite from modern environments in Central and Northeast Yakutia (East Siberia, Russia)." Hydrobiologia 614, no. 1 (July 2, 2008): 171–95. http://dx.doi.org/10.1007/s10750-008-9505-y.
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Schultze, Hans-Peter, Christopher G. Maples, and Christopher R. Cunningham. "The Hamilton Konservat-Lagerstätte: Stephanian terrestrial biota in a marginal-marine setting." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 84, no. 3-4 (1993): 443–51. http://dx.doi.org/10.1017/s0263593300006246.
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ABSTRACTThe Stephanian Konservat-Lagerstätte of Hamilton, Kansas, deposited in a marine-estuarine environment preserves a mixture of terrestrial, fresh-water, and marine fossil organisms. The marine component is the most diverse taxonomically, whereas one ostracod species, commonly interpreted as a fresh-water form, together with vascular plant debris dominates volumetrically. Well-preserved terrestrial and aquatic vertebrates and arthropods were embedded in rapidly deposited calcareous mud conducive to microbial early-diagenesis of vertebrate soft tissues in a tidal estuarine setting. Many vertebrate fossils show no evidence of preburial decay or disarticulation. Dark-coloured body silhouettes (‘skin preservation’) are composed of calcitic bacteria, calcite crystals and organic material, and have been interpreted to reflect preservation under saline conditions. The aquatic vertebrates had a broader tolerance of salinity than today. The fishes were perhaps migratory (anadromous or catadromous), and some used the estuarine environment for spawning. The tetrapods (dissorophid amphibians) retained their tolerance to salinity from their marine ancestors and were able to spawn in near-shore environments. The terrestrial biota was dominated by the conifer Walchia and was subjected to forest fires, as evidenced by preserved charcoal fragments.
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Barros, Cecília, Enelise Piovesan, Mário Lima Filho, and Sonia Agostinho. "FIRST RECORD OF OSTRACODS IN THE ESTIVA FORMATION (PERNAMBUCO BASIN, UPPER CRETACEOUS), NORTHEAST OF BRAZIL." Estudos Geológicos 31, no. 1 (June 21, 2021): 16–26. http://dx.doi.org/10.18190/1980-8208/estudosgeologicos.v31n1p16-26.
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The present work deals with the first record of ostracods in the Estiva Formation, Pernambuco Basin (Cupe, 1 LABIO-PE1 borehole). The Pernambuco Basin extends throughout the southern coast of the state of Pernambuco and is limited by the Pernambuco Shear Zone, in the north and by the Maragogi High, in the south. The Estiva Formation consists of continental shelf carbonates dated as Upper Cretaceous. The analysis and interpretation of the data were performed through literature review, stratigraphic data surveys, and sampling. The methodology used for the treatment of the samples consisted of the following steps: collection, weighing and fragmentation of the samples; washing and drying of the calcined materials; and screening and picking of the carbonatic microfossils. Rare ostracods were found, probably belonging to the brackish genus Fossocytheridea Swain & Brown, 1964. The recognition of the ostracod fauna and its paleoecology aims to contribute to the understanding of the Pernambuco Basin evolution.
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Sharpe, Saxon E., and Jordon Bright. "A high-elevation MIS 5 hydrologic record using mollusks and ostracodes from Snowmass Village, Colorado, USA." Quaternary Research 82, no. 3 (November 2014): 604–17. http://dx.doi.org/10.1016/j.yqres.2014.01.014.
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AbstractSediments containing terrestrial and aquatic mollusks and ostracodes from the Ziegler Reservoir fossil site (2705 m elevation) near Snowmass Village, Colorado, span ~130–87 ka (MIS 5e through 5b). The southeastern area of the site where taxa were recovered was a relatively fresh, shallow, well-vegetated wetland during MIS 5e through 5c time, approximately 2 m deep, with a total dissolved solids value of ~200–1000 mg L− 1. The wetland was seasonally or annually variable and groundwater discharged along the margins of the bounding moraine. Groundwater likely contributed solutes to the system and may have contributed 18O-enriched water. Based on stable isotopes from ostracode calcite (δ18OOST and δ13COST), seasonal evaporation occurred and the dissolved inorganic carbon pool was unexpectedly enriched in 13C. The mollusk and ostracode faunas changed little across the MIS 5e/5d/5c boundaries, whereas a distinct change in the ostracode fauna occurred between the deposition of Unit 11 and Unit 13, which corresponds in time to the MIS 5c/5b boundary, indicating some combination of increased surface and/or groundwater flow, a decrease in water temperature, and a freshening and a possible deepening of the wetland.
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Stevens, Lora R., Emi Ito, Antje Schwalb, and Herbert E. Wright. "Timing of Atmospheric Precipitation in the Zagros Mountains Inferred from a Multi-Proxy Record from Lake Mirabad, Iran." Quaternary Research 66, no. 3 (November 2006): 494–500. http://dx.doi.org/10.1016/j.yqres.2006.06.008.
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AbstractA sediment core 7.2 m long from Lake Mirabad, Iran, was examined for loss-on-ignition, mineralogy, oxygen-isotopic composition of authigenic calcite, and trace-element composition of ostracodes to complement earlier pollen and ostracode-assemblage studies. Pollen, ostracode-inferred lake level, and high Sr/Ca ratios indicate that the early Holocene (10000 to 6500 cal yr BP) was drier than the late Holocene. Low δ18O values during this interval are interpreted as resulting from winter-dominated precipitation, characteristic of a Mediterranean climate. Increasing δ18O values after 6500 cal yr BP signal a gradual increase in spring rains, which are present today. A severe 600-yr drought occurred at ca. 5500 cal yr BP, shortly after the transition from pistachio-almond to oak forest. During the late Holocene, two milder droughts occurred at about 1500 and 500 cal yr BP. Within the resolution of the record, no drought is evident during the collapse of the Akkadian empire (4200–3900 cal yr BP). Rather, a decrease in δ18O values to early-Holocene levels may indicate the return to a Mediterranean precipitation regime.
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Hajdas, Irka, Georges Bonani, Susan Herrgesell Zimmerman, Millie Mendelson, and Sidney Hemming. "14C Ages of Ostracodes from Pleistocene Lake Sediments of the Western Great Basin, Usa—Results of Progressive Acid Leaching." Radiocarbon 46, no. 1 (2004): 189–200. http://dx.doi.org/10.1017/s0033822200039515.
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Progressive dissolution experiments were performed on samples of ostracode shells from lacustrine sediments from the western Great Basin to remove contamination of the surface by secondary calcite. The observed age differences between the external and residual fractions were as great as 2000 to 6000 yr. A “plateau” in ages of the last fractions was obtained only for 1 sample; however, results of repeated experiments resulted in very good agreement of the final ages. A comparison with previously published chronologies based on bulk radiocarbon ages of ostracodes from Wilson Creek (Benson et al. 1990) shows that leaching is imperative for dating samples older than 20 ka B P. This study focuses on the problem of contamination and its removal. However, the final chronology of the Wilson Creek Formation (and other late Pleistocene lacustrine sediments) will require additional dating of other sections as well as establishment of a reservoir effect correction.
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Curry, B. Brandon. "Paleochemistry of Lakes Agassiz and Manitoba based on ostracodes." Canadian Journal of Earth Sciences 34, no. 5 (May 1, 1997): 699–708. http://dx.doi.org/10.1139/e17-056.
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The ionic composition and salinity of Lake Manitoba and its late-glacial precursor, Lake Agassiz, changed significantly over the past 11 000 years. The paleochemical record reported here is based on modern analog environments of ostracodes identified in a new 14.5 m core from southern Lake Manitoba. The ionic composition of Lake Manitoba today is dominated by Na+, Cl−, and HC03−, with much less Ca2+, Mg2+, and K+. Evaporative concentration of modern Lake Manitoba water would lead to greater salinity and the near depletion of Ca2+ due to continued precipitation of calcite. During periods of highest salinity in the Holocene, however, Lake Manitoba supported Limnocythere staplini. Today this species inhabits waters in which [Ca2+] > [HCO3−], including springs associated with groundwater in Paleozoic bedrock discharging into Lake Winnipegosis (and eventually, after much dilution, into Lake Manitoba). Further complicating the Holocene record are intervals containing Limnocythere friabilis that suggest periodic influxes of dilute water, probably from the Assiniboine River, which bypasses Lake Manitoba today. The variations in Holocene paleochemistry indicated by the ostracode record imply changes in the proportion of overland flow plus precipitation relative to groundwater inputs to Lake Manitoba, independent of changes in evaporation relative to precipitation.
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Forester, Richard M. "OSTRACODE ASSEMBLAGES FROM SPRINGS IN THE WESTERN UNITED STATES: IMPLICATIONS FOR PALEOHYDROLOGY." Memoirs of the Entomological Society of Canada 123, S155 (1991): 181–201. http://dx.doi.org/10.4039/entm123155181-1.
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AbstractOstracodes are a diverse group of marine and continental crustaceans that have radiated into virtually all oxygenated aquatic environments that persist for more than about a month. Continental ostracodes live in both surface water and groundwater.Ostracodes living in springs and seeps have typically been the subject of systematic rather than ecologic studies. These taxa may or may not occur in other surface-water bodies. Similarly, lacustrine taxa may or may not be found in springs. Spring taxa occurring in other surface waters are often found in ponds, marshes, streams, or on the edges of lakes where groundwater discharge is important. Groundwater discharge, unlike lake water, shows limited and predictable variability in chemistry and temperature during the year. That level of variability relative to lake water may define particular ostracode environmental gradients. The gradients would range from stable, high-volume discharge springs occupied principally by spring species to high variability lakes occupied largely by lacustrine species.Ostracode occurrences may also be described by parameters such as temperature, solute (dissolved ion) composition, solute concentration (salinity, conductivity, ionic strength), and calcite saturation indices. A plot of these parameters associated with the presence of a taxon illustrates its physiologic response to the environment, a field. Three general fields bounded by chemical parameters are delineated by existing data. Those fields are as follows: (1) a restricted range and (2) a full range of fresh water, and (3) both fresh and saline water. Fields bounded by temperature and chemistry are also recognized. The fields also offer a way of describing ostracode occurrences in terms of hydrogeology and climate.If ostracode occurrences are limited by major chemical and physical properties of the aquatic environment, then their habitat may be defined by certain physical–chemical principles. The same physical–chemical principles must apply to the past. The ecology of extinct taxa may, therefore, be defined in the same environmental terms as those for extant taxa.
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Lowenstein, Tim K., and Bärbel Hönisch. "The Use of Mg/Ca as a Seawater Temperature Proxy." Paleontological Society Papers 18 (November 2012): 85–100. http://dx.doi.org/10.1017/s1089332600002564.
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The underlying basis for Mg/Ca paleothermometry is that the amount of magnesium in calcite precipitated from seawater is dependent on temperature. Here we review the state of the art of the Mg/Ca seawater paleotemperature proxy, summarized by the following: 1) Calcite, whether formed abiotically or biologically as foraminifera and ostracode shells, incorporates variable amounts of magnesium into the crystal structure. 2) Uptake of Mg varies positively with temperature. 3) The relationship between temperature and the amount of Mg in calcite has been quantified by experiments on synthetic calcite growth and by culture, core top, and sediment trap experiments using living organisms. 4) The most careful calibrations of the Mg/Ca paleothermometer have been done for planktic foraminifera, then benthic foraminifera; there are species-specific variations in the amount of Mg incorporated into foraminifera shells. 5) The Mg/Ca ratio of calcite from planktic foraminifera in deep-sea cores has been widely used to interpret sea surface temperatures. 6) Measurement of both Mg/Ca and δ18O in planktic foraminifera have been used to calculate δ18O in seawater, and after correction for global ice volume, salinity could be inferred. 7) Mg/Ca from benthic foraminifera have been used to reconstruct deep-sea temperatures and cooling of ~12° over the last 50 million years. 8) One problem with the Mg/Ca seawater temperature proxy is partial dissolution of foraminifer shells, which lowers the Mg/Ca, and leads to an underestimation of ocean temperature. Benthic foraminifers appear to be more resistant to partial dissolution. 9) Past changes in the Mg/Ca ratio of seawater are an important factor in determining the amount of Mg in fossil skeletal calcite, and thus add another variable to the Mg/Ca temperature proxy. All Mg/Ca paleotemperature studies on fossil calcite older than Pleistocene should take into account the Mg/Ca of the seawater from which it precipitated.
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Xia, J., E. Ito, and D. R. Engstrom. "Geochemistry of ostracode calcite: Part 1. An experimental determination of oxygen isotope fractionation." Geochimica et Cosmochimica Acta 61, no. 2 (January 1997): 377–82. http://dx.doi.org/10.1016/s0016-7037(96)00351-1.
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Schwarcz, Henry P., and Nicholas Eyles. "Laurentide Ice Sheet Extent Inferred from Stable Isotopic Composition (O,C) of Ostracodes at Toronto, Canada." Quaternary Research 35, no. 3-Part1 (May 1991): 305–20. http://dx.doi.org/10.1016/0033-5894(91)90047-9.
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AbstractEarly and Middle Wisconsin glaciolacustrine sediments exposed at Scarborough Bluffs, Toronto, Canada, contain a low-diversity benthic ostracode fauna dominated by Candona subtringulata and C. caudata. We have studied the oxygen and carbon isotopic compositions of the two ostracode species from the base of the Scarborough section to its top immediately below a Late Wisconsin till. We find an upward decrease in δ18O in both species that is more marked in C. caudata. The shift in δ18O of ostracode calcite from interglacial values of −6 to −8‰, to values of −17‰ immediately below the Late Wisconsin till is the result of (1) lowering of δ18O of the lake as a result of addition of isotopically light meltwater from an advancing and thickening Laurentide Ice Sheet combined with (2) lowering of δ18O of local precipitation entering the lake, due to falling temperatures. In the last stages of the lake, δ18O of the lake water was between −17 and −21‰, corresponding to a lake body composed of between 35 and 55% glacial meltwater. The lake appears to have been isotopically and thermally stratified for part of its history. Differences in δ13C values between C. caudata and C. subtriangulata increase upward in the stratigraphic section. This may record enhanced partitioning of carbon isotopes between surface and bottom waters as a result of increased water depths, photosynthesis by algae, and changes in the input of dissolved organic carbon from the oxidation of organic matter. If the age assessments of these sediments are correct, then these data provide valuable information regarding the isotopic composition of ancestral Lake Ontario and also confirm that the basin was only fully glaciated during the Late Wisconsin.
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Labuhn, Inga, Franziska Tell, Ulrich von Grafenstein, Dan Hammarlund, Henning Kuhnert, and Bénédicte Minster. "A modern snapshot of the isotopic composition of lacustrine biogenic carbonates – records of seasonal water temperature variability." Biogeosciences 19, no. 11 (June 2, 2022): 2759–77. http://dx.doi.org/10.5194/bg-19-2759-2022.
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Abstract. Carbonate shells and encrustations from lacustrine organisms provide proxy records of past environmental and climatic changes. The carbon isotopic composition (δ13C) of such carbonates depends on the δ13C of dissolved inorganic carbon (DIC). Their oxygen isotopic composition (δ18O) is controlled by the δ18O of the lake water and by water temperature during carbonate precipitation. Lake water δ18O, in turn, reflects the δ18O of atmospheric precipitation in the catchment area, water residence time and mixing, and evaporation. A paleoclimatic interpretation of carbonate isotope records requires a site-specific calibration based on an understanding of these local conditions. For this study, samples of different biogenic carbonate components and water were collected in the littoral zone of Lake Locknesjön, central Sweden (62.99∘ N, 14.85∘ E, 328 ma.s.l.) along a water depth gradient from 1 to 8 m. Carbonate samples of living organisms and subfossil remains in surface sediments were taken from the calcifying alga Chara hispida, from bivalve mollusks of the genus Pisidium, and from adult and juvenile instars of two ostracod species, Candona candida and Candona neglecta. Our results show that neither the isotopic composition of carbonates nor the δ18O of water vary significantly with water depth, indicating a well-mixed epilimnion. The mean δ13C of Chara hispida encrustations is 4 ‰ higher than the other carbonates. This is due to fractionation related to photosynthesis, which preferentially incorporates 12C into the organic matter and increases the δ13C of the encrustations. A small effect of photosynthetic 13C enrichment in DIC is seen in contemporaneously formed valves of juvenile ostracods. The largest differences in the mean carbonate δ18O between species are caused by vital offsets, i.e., the species-specific deviations from the δ18O of inorganic carbonate which would have been precipitated in isotopic equilibrium with the water. After subtraction of these offsets, the remaining differences in the mean carbonate δ18O between species can mainly be attributed to seasonal water temperature changes. The lowest δ18O values are observed in Chara hispida encrustations, which form during the summer months when photosynthesis is most intense. Adult ostracods, which calcify their valves during the cold season, display the highest δ18O values. The seasonal and interannual variability in lake water δ18O is small (∼ 0.5 ‰) due to the long water residence time in the lake. Seasonal changes in the temperature-dependent fractionation are therefore the dominant cause of carbonate δ18O differences between species when vital offsets are corrected. Temperature reconstructions based on paleotemperature equations for equilibrium carbonate precipitation using the mean δ18O of each species and the mean δ18O of lake water are well in agreement with the observed seasonal water temperature range. The high carbonate δ18O variability of samples within a species, on the other hand, leads to a large scatter in the reconstructed temperatures based on individual samples. This implies that care must be taken to obtain a representative sample size for paleotemperature reconstructions.
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A. Delizy, Bzhar, and Waleed S. Shingaly. "Microfacies Analysis and Depositional Environment of Sarki Formation (Early Jurassic), Rawanduz Area, Kurdistan Region, Northern Iraq." Tikrit Journal of Pure Science 27, no. 1 (January 16, 2022): 27–38. http://dx.doi.org/10.25130/j.v27i1.1245.
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A detail sedimentological analysis of the Sarki Formation (Early Jurassic) in Warte and Zarwan sections in the Imbricated Zone, northern Iraq has been conducted for the first time. The Sarki Formation in both studied sections are consisting of dolomite, dolomitic limestone and recrystallized breccia. The petrographic study of the 80 thin sections analyzed in both outcrops showed the skeletal and non-skeletal components. The skeletal components are including ostracods, bivalves and echinoderms. While the main non skeletal grains are peloids, ooids, extraclasts and intraclasts. The diagenetic processes which affected the carbonate rocks of the Sarki Formation was dolomitization, compaction, cementation, micritization, solution and slicification. The result of XRD and SEM of eight samples of dolomite and dolomitic limestone show that the main minerals are dolomite and calcite. In the carbonate rocks nine main microfacies have been identified, which are classified into three facies groupings that correspond to three depositional environments; peritidal, lagoon and high energy shoal within ramp settings.
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Bzhar A. Delizy and Waleed S. Shingaly. "Microfacies Analysis and Depositional Environment of Sarki Formation (Early Jurassic), Rawanduz Area, Kurdistan Region, Northern Iraq." Tikrit Journal of Pure Science 27, no. 1 (December 2, 2022): 24–35. http://dx.doi.org/10.25130/tjps.v27i1.79.
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A detail sedimentological analysis of the Sarki Formation (Early Jurassic) in Warte and Zarwan sections in the Imbricated Zone, northern Iraq has been conducted for the first time. The Sarki Formation in both studied sections are consisting of dolomite, dolomitic limestone and recrystallized breccia. The petrographic study of the 80 thin sections analyzed in both outcrops showed the skeletal and non-skeletal components. The skeletal components are including ostracods, bivalves and echinoderms. While the main non skeletal grains are peloids, ooids, extraclasts and intraclasts. The diagenetic processes which affected the carbonate rocks of the Sarki Formation was dolomitization, compaction, cementation, micritization, solution and slicification. The result of XRD and SEM of eight samples of dolomite and dolomitic limestone show that the main minerals are dolomite and calcite. In the carbonate rocks nine main microfacies have been identified, which are classified into three facies groupings that correspond to three depositional environments; peritidal, lagoon and high energy shoal within ramp settings.
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Bonny, Sandy, and Brian Jones. "Relict tufa at Miette Hot Springs, Jasper National Park, Alberta, Canada." Canadian Journal of Earth Sciences 40, no. 11 (November 1, 2003): 1459–81. http://dx.doi.org/10.1139/e03-050.
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At the Miette Hot Springs site, relict tufa stretches for nearly 500 m along the west side of Sulphur Creek valley and rises up to 30 m above the valley floor. The tufa, composed of low-Mg calcite, precipitated from waters discharged from a line of perched springs.14C dating of bone material embedded in the tufa indicates that tufa precipitation took place between ~4500 and 2500 years BP under cool and moist climatic conditions. The spring biota was dominated by filamentous microbes (mainly Phormidium and Oscillatoria), with fewer diatoms (including Cymbella), testate protozoans (including Quadrulella), ostracodes (including Darwinula, Heterocypris, Cadonia, and Cyclocypris), and various bryophytes. The ecological preferences of these microbes indicate that the spring water had near-neutral pH, was Ca, HCO3, and H2SSO4rich, and emerged at 5065 °C. Landslides disrupted the west wall of Sulphur Creek valley during and after tufa growth. The relict tufa is divided into six morphotypes that reflect variations in water flow down the steep and rugged flow path. Domal tufa is located around the spring vents, roll-over tufa developed where water flowed over sharp lips or structural barricades, vertical tufa formed where calcite was precipitate from water flowing down steep to vertical inclines, flat-banded tufa reflects precipitation on a gentle slope, and wedge-shaped tufa formed where more rapid downslope calcite precipitation caused a progressive decrease in slope. The tufa contains stromatolitic facies (including streamer, porous laminar, dense laminar) and nonstromatolitic facies (bedded, crenulated) that reflect variations in the biology, water temperature, and style of flow of different parts of the spring flow path.
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de Wet, Carol B., Andrew P. de Wet, Linda Godfrey, Elizabeth Driscoll, Samuel Patzkowsky, Chi Xu, Sophia Gigliotti, and Melina Feitl. "Pliocene short-term climate changes preserved in continental shallow lacustrine-palustrine carbonates: Western Opache Formation, Atacama Desert, Chile." GSA Bulletin 132, no. 9-10 (December 23, 2019): 1795–816. http://dx.doi.org/10.1130/b35227.1.
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Abstract Multiple climate proxies indicate episodic changes in moisture levels within an ∼1 Ma duration (early–mid Pliocene) interval. Limestones within the Opache Formation, Calama Basin, Atacama Desert region, Chile, contain evidence for wetter and drier periods on short time scales. Proxies include carbonate lithological changes, paleontology (stromatolites, oncolites, gastropods, ostracods and diatoms), O and C stable isotopes, geochemistry, and mineralogical changes (aragonite, calcite, Mg-calcite, dolomite and gypsum) throughout a 30 m stratigraphic section. Stromatolite fossil cyanobacteria dark and light laminations and mesohaline to hypersaline diatom species suggest Pliocene annual seasonality. Short-term changes between wetter and drier conditions indicate that at least this part of the Atacama region was experiencing relatively rapid early–mid Pliocene climate instability. The predominance of limestone in the Opache Formation, in contrast to the 1500 m of Oligocene-Miocene siliciclastic conglomerates and sandstones, interpreted as arid climate alluvium, that underlie it, indicates a shift from arid or hyperarid climate to a semi-arid climate. Semi-arid conditions promoted limestone deposition in a shallow lacustrine-palustrine environment. In this setting, events such as storms with associated surface water flow, erosion, siliciclastic sand, gravel, and intraclast deposition, coupled with significant biological activity, represent sedimentation during more humid periods in a shallow lacustrine depositional environment. In contrast, limestone characterized by mudcracks, Navicula diatoms, and vadose syndepositional cementation, reflect periods of enhanced evaporation, water shallowing, and episodic desiccation, characteristic of a palustrine depositional system. These facies shifts, in conjunction with geochemical and isotopic proxy evidence, yield a sedimentary record of wetter and drier climate shifts.
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Xia, J., D. R. Engstrom, and E. Ito. "Geochemistry of ostracode calcite: Part 2. The effects of water chemistry and seasonal temperature variation on Candona rawsoni." Geochimica et Cosmochimica Acta 61, no. 2 (January 1997): 383–91. http://dx.doi.org/10.1016/s0016-7037(96)00354-7.
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Menking, Kirsten M. "Decadal to millennial-scale solar forcing of Last Glacial Maximum climate in the Estancia Basin of Central New Mexico." Quaternary Research 83, no. 3 (May 2015): 545–54. http://dx.doi.org/10.1016/j.yqres.2015.02.002.
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Lacustrine sediments from the Estancia Basin of central New Mexico reveal decadal to millennial oscillations in the volume of Lake Estancia during Last Glacial Maximum (LGM) time. LGM sediments consist of authigenic carbonates, detrital clastics delivered to the lake in stream flow pulses, and evaporites that precipitated in mudflats exposed during lake lowstands and were subsequently blown into the lake. Variations in sediment mineralogy thus reflect changes in hydrologic balance and were quantified using Rietveld analysis of X-ray diffraction traces. Radiocarbon dates on ostracode valve calcite allowed the construction of mineralogical time series for the interval ~ 23,600 to ~ 18,300 ka, which were subjected to spectral analysis using REDFIT (Schulz and Mudelsee, 2002). Dominant periods of ~ 900, ~ 375, and ~ 265 yr are similar to cycles in Holocene 14C production reported for a variety of tree ring records, suggesting that the Lake Estancia sediments record variations in solar activity during LGM time. A prominent spectral peak with a period of ~ 88 yr appears to reflect the solar Gleissberg cycle and may help, along with the ~ 265 yr cycle, to explain an ongoing mystery about how Lake Estancia was able to undergo abrupt expansions without overflowing its drainage basin.
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Grizelj, Anita, Monika Milošević, Koraljka Bakrač, Ines Galović, Tomislav Kurečić, Valentina Hajek-Tadesse, Radovan Avanić, et al. "Paleoecological and sedimentological characterisation of Middle Miocene sediments from the Hrvatska Kostajnica area (Croatia)." Geologia Croatica 73, no. 3 (October 26, 2020): 153–75. http://dx.doi.org/10.4154/gc.2020.15.
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The Miocene deposits of the Hrvatska Kostajnica (KOS-I) area belong to the south-western marginal part of the Pannonian Basin System (PBS). Investigation of the lithostratigraphical column included: mineralogical, geochemical, sedimentological and integrated palaeontological (calcareous nannofossil, foraminifers, ostracodes, palynomorphs) analyses. Badenian and Sarmatian sediments of this column were deposited in a marine offshore environment with local input of terrigenous material represented by marls and silty marls. Based on palaeontological data, the recorded palaeoclimate was subtropical in the late Badenian changing to a warm temperate climate of the early Sarmatian. Marly sediments predominantly consist of carbonate (calcite and aragonite) and clay minerals, while quartz and plagioclase are less abundant. Most samples contain a small amount of zeolite minerals from the clinoptilolite/heulandite series. Among the clay minerals, smectite and illite/muscovite are the most abundant. Based on provenance analyses we concluded that the Badenian-Sarmatian marls were predominantly formed by the weathering of acidic (Si-rich) source rock derived material from the neighbouring Inner Dinarides.
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Al Balushi, Said A. K., and Joe H. S. Macquaker. "Sedimentological evidence for bottom-water oxygenation during deposition of the Natih-B Member intrashelf-basinal sediments: Upper Cretaceous carbonate source rock, Natih Formation, North Sultanate of Oman." GeoArabia 16, no. 2 (April 1, 2011): 47–84. http://dx.doi.org/10.2113/geoarabia160247.
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ABSTRACT Geologists have commonly argued that the deposition of the excellent carbonate source rock (up to 13.7% total organic carbon) in the Upper Cretaceous Natih-B Member intrashelf basin (water depth circa 50 m) was mainly controlled by the presence of bottom-water “anoxia” in the basin centre. Some authors have even linked the formation of the Natih-B organic-carbon-rich sediments to the global development of “oceanic anoxia” that occurred a number of times during the Late Cretaceous. Recent research, however, suggests that the mechanisms that underpin organic-carbon enrichment in intrashelf-basinal settings are complicated and, instead, controlled by the complex interplay of variations in primary production of organic carbon, clastic dilution, bottom-water anoxia, early diagenesis and optimising rates of sediment accumulation, and are not necessarily related to global-forcing mechanisms. In this study, the requirement for persistent bottom-water anoxic conditions for the preservation of organic matter in this setting is assessed, evidence for oxic/dysoxic bottom-water conditions during deposition of the Natih-B organic-carbon-rich sediments is presented, and alternative models to explain organic-matter enrichment are considered. Natih-B sediments (collected both spatially and temporally from both core and exposures in North Oman) have been investigated using a combination of optical and electron-optical (backscattered electron imagery) techniques, which provide additional data to those gathered by traditional field and geochemical methods. Natih-B lithofacies alternate between two main types: organic-carbon-rich carbonate mudstones and calcite-cement-rich wackestones. The organic-rich mudstones are typically fine grained, dark grey, exhibit remnant parallel lamina, and are partially burrowed. These units commonly contain planktonic foraminifera, coccoliths and organic matter (average about 5.4%, up to 13.7% total organic carbon). In addition, in-place bivalves (including thick-shelled oysters and flattened pectens) are present. The calcite-cement-rich wackestones are lighter in colour and extensively bioturbated (in most cases < 1.5% total organic carbon). This lithofacies comprises a mix of reworked skeletal fragments (including bivalves, gastropods, echinoderms, brachiopods and corals), ostracods, calcispheres, and both benthic and planktonic foraminifera that are pervasively cemented by calcite. Given the above observations, bottom waters during deposition of the Natih-B intrashelf-basinal sediments must have contained at least some oxygen, and it is unlikely that they were persistently “anoxic”. Instead, it is likely that short-term enhanced organic productivity, rapid delivery of organic components to the sediment/water interface, optimal rates of sediment accumulation and episodic burial were the fundamental parameters that controlled organic-carbon production and preservation. Organic-matter enrichment was, therefore, not restricted to anoxic depositional environments, and exploration strategies within intrashelf-basinal settings need to be expanded beyond times when basinal anoxia is thought to have existed.
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Chafetz, Henry S., and Sean A. Guidry. "Deposition and diagenesis of Mammoth Hot Springs travertine, Yellowstone National Park, Wyoming, U.S.A." Canadian Journal of Earth Sciences 40, no. 11 (November 1, 2003): 1515–29. http://dx.doi.org/10.1139/e03-051.
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Strata forming a 113 m long core through Mammoth Hot Springs record the Holocene evolution of this travertine accumulation from deposition as part of a lacustrine to a terraced mound environment. The deposit is readily divided into four intervals: 11367 m, carbonate-cemented volcaniclastic with intercalated layers of travertine; 6760 m, moderately pure travertine with some volcaniclastics; 6050 m, carbonate-cemented volcaniclastic-rich interval; and 500 m, essentially pure travertine. Lithologic composition, sedimentary structures, and the rare ostracode fossils indicate that the lower 67 m predominantly accumulated in a lacustrine environment, whereas the upper 40 m are terraced mound deposits. All of the travertine is calcite, some after aragonite. Layers of shrubs, oncoids, and peloids, all bacterial in origin, form the dominant allochems within the travertine. Stable isotopic carbon and oxygen values (n = 128) are strongly positively correlated and decrease up-core ~4 and 8, respectively, reflecting a change in depositional environment from lacustrine to terraced mound upsection. Other stable isotopic trends indicate a pronounced difference between travertine allochems and immediately adjacent spar, e.g., spar averages 0.9 and 0.6, respectively, lower than immediately adjacent shrubs (n = 7 pairs). This difference is interpreted to reflect degassing and evaporation in the surface waters prior to precipitation of the allochems. The trends in stable isotopic values provide valuable corroborative data with regard to the depositional environment and diagenesis of the travertine.
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Aheen O. Abdullah and Sardar M. Balaky. "Stratigraphy and Mineralogy of Balambo Formation (Aptian - Cenomanian) near Chomabrok village, Imbrication Zone, Iraqi Kurdistan Region." Tikrit Journal of Pure Science 27, no. 5 (November 28, 2022): 57–67. http://dx.doi.org/10.25130/tjps.v27i5.18.
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The stratigraphy and mineralogy of Balambo Formation (Aptian - Cenomanian) in exposed surface section near Chomabrok village in the Imbrication zone, northeastern Iraq is studied. The Formation is 450 meters thick and consists of thin to medium to thick bedded yellowish-brown, and black to dark gray limestones, marly limestones, with thin- medium bedded, grayish - black marl and shale, with thin bands of black cherts and abundant nodules and lenses. From the field observations and petrographic studies, the formation mainly made from two main lithofacies types; marly limestone-marl lithofacies and cherty limestone lithofacies. The petrographic study of carbonate rocks deepened on 79 thin sections and demonstrated that the carbonates of Balambo Formation composed of micrite ground mass with abundant skeletal grains; planktonic and some benthic foraminifera, radiolaria, calcisphere, ostracods, pelecypods, larva-ammonoids, small-brachiopods, sponge spicules, echinoid spines, and bioclasts. Non-skeletal grains include peloids only. Using extraction method and according to an assessment of foraminiferal assemblages and based on the defined planktonic foraminifera the assigned age of Balambo Formation in the studied section is Aptian to Cenomanian as upper Balambo age. The results of X-ray diffraction (XRD) analysis for bulk mineralogy of selected shale and marl samples suggested the presence of phyllosilicate with abundant calcite, common quartz, and moderate Fluorapatite with minor dolomite content. Illite is the dominant clay mineral in the Balambo Formation and indicates a hot, arid climate during most of the Cretaceous period in the Imbrication zone, Northeastern Iraq.
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Wansard, Guy. "La géochimie des éléments en traces dans la calcite des ostracodes: Principes, limites et perspectives de la méthode pour une reconstitution quantifiée des paléoenvironnements." Geobios 32, no. 6 (January 1999): 928–33. http://dx.doi.org/10.1016/s0016-6995(99)80876-6.
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Kiessling, W., R. Scasso, M. Aberhan, L. Ruiz, and S. Weidemeyer. "A Maastrichtian microbial reef and associated limestones in the Roca Formation of Patagonia (Neuquén Province, Argentina)." Fossil Record 9, no. 2 (August 1, 2006): 183–97. http://dx.doi.org/10.1002/mmng.200600007.
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Abstract. We describe a small microbial reef and associated limestones occurring in a Maastrichtian transgressive succession of mixed carbonate-siliciclastic lithologies at Sierra Huantraico near Chos Malal (Neuquén, Argentina). Strontium isotope data suggest that the reef is of earliest Maastrichtian age. The small reef (0.8 m thick, 2 m wide) is mostly composed of peloidal bindstone, dense stromatolite-cement crusts and thrombolite. Except for some ostracods, no metazoan fossils were found in the reef structure, although the majority of peloids are fecal pellets, probably of larger crustaceans. Small foraminifers with calcite tests and probable green algae have also been noted. Sedimentological data and fossils within and immediately above the reef suggest that the reef was formed in a transgressive systems tract under freshwater to brackish-water conditions. Limestones above the reef are serpulid-bryozoan packstones and intraclast-ooid grainstones. These limestones yield a mixture of typical non-tropical (common serpulids and bryozoans) and typical tropical aspects (common dasycladaceans and ooids). This mosaic is explained by salinity fluctuations, which in our case dominate over temperature in determining the grain associations. Wir beschreiben ein kleines mikrobielles Riff, das in der Sierra Hunatraico (Neuquén, Argentinien) in einer transgressiven, gemischt siliziklastisch-kalkigen Abfolge gefunden wurde. Nach Strontiumisotopen-Datierung ist das Riff in das unterste Maastrichtium zu stellen. Das kleine Riff (0,8 m Mächtigkeit, 2 m Breite) besteht überwiegend aus peloidalem Bindstone, dichten Stromatolith-Zement-Krusten und Thrombolith. Mit Ausnahme von Ostrakoden konnten keine Metazoen in der Riffstruktur nachgewiesen werden, obwohl die Mehrzahl der Peloide als Kotpillen zu interpretieren sind, die vermutlich auf größere Krebse zurückgehen. Kleine Foraminiferen und mögliche Grünalgen sind die einzigen zusätzlich nachweisbaren Eukaryoten. Die Fossilien im Riff und in den überlagernden Kalken sprechen für ein Riffwachstum unter transgressiven aber hyposalinen Bedingungen. Die Kalke über dem Riff tragen ein gemischtes paläoklimatisches Signal, das sowohl typisch nicht-tropische als auch typisch tropische Komponenten beinhaltet. Dieses Mosaik ist möglicherweise durch die starken Salinitätsschwankungen erklärbar und erfordert ein Überdenken der bisherigen Modelle zur klimatischen Steuerung der Karbonatsedimentation. doi:10.1002/mmng.200600007
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Sampaio, Lorena Da Fonseca, Patrick Führ Dal’ Bó, Giorgio Basilici, and Thiago Da Silva Marinho. "Interpretação paleoambiental dos calcretes da Formação Marília na região de Uberaba (MG)." Geologia USP. Série Científica 17, no. 2 (August 1, 2017): 193. http://dx.doi.org/10.11606/issn.2316-9095.v17-423.
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Calcretes são acumulações secundárias de carbonato de cálcio continentais formadas próximo à superfície como resultado de processos pedogenéticos e diagenéticos, produzindo grande variedade de morfologias e texturas. Na Formação Marília (Cretáceo Superior da Bacia Bauru) na região de Uberaba (MG), os calcretes têm sido estudados por seu significado paleoclimático e paleoambiental. Contudo, sua origem e relações entre processos de sedimentação, pedogênese e eodiagênese carecem de estudos detalhados. Em campo, foram distintas quatro morfologias de calcretes no Membro Ponte Alta (nodular, brechoso, venular e maciço) e três no Membro Serra da Galga (nodular, laminar e hardpan). Os calcretes do Membro Ponte Alta são formados por processos palustres e/ou diagenéticos freáticos, marcados pela presença de micrita com feições de exposição subaérea, ostracodes, biválvios e carófitas, e por intensa cimentação espática e neomorfismo. No Membro Serra da Galga, calcretes nodulares e laminares são caracterizados por associação de microfeições pedogênicas e biogênicas, tais como tramas cristalíticas, rizotúbulos, Microcodium e esferulitos, embora cimentação por calcita espática diagenética ocorra pontualmente. Os calcretes tipo hardpan ocorrem no topo de perfis de paleossolos e possuem origem poligenética, com sobreposição de feições palustres e diagenéticas. Na Formação Marília, a formação de calcretes está relacionada à emergência ou ao rebaixamento de águas subterrâneas sobressaturadas em carbonato de cálcio em sedimentos ou perfis de solo. A predominância de feições diagenéticas freáticas e palustres no Membro Ponte Alta sugere condições climáticas semiáridas com períodos de maior pluviosidade e/ou aumento das taxas de subsidência durante sua deposição.
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Daux, Valérie, Alain Foucault, Frédéric Melieres, and Mélanie Turpin. "Sapropel-like Pliocene sediments of Sicily deposited under oxygenated bottom water." Bulletin de la Société Géologique de France 177, no. 2 (March 1, 2006): 79–88. http://dx.doi.org/10.2113/gssgfbull.177.2.79.
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Abstract The Pliocene Punta Piccola series, deposited on the Sicily sill at 100–400 m depths, consists of alternating whitish hemipelagic marl and carbonate-poor, organic-carbon-richer, brownish dark marl. The rhythmic bedding is interpreted to result from the precession driven alternation of more or less humid periods. In the present study, we compare the mineralogical and geochemical composition (isotope ratios of oxygen and carbon; Ca, Mn, Mg, Sr, and Fe concentrations) of the carbonate fractions of the whitish marl to those of the dark layers to evaluate the environmental changes that likely produced these alternations. High Mn concentrations in the dark layers, and the occurrence of pseudo-kutnahorite (Mn-Ca mixed carbonate), bioturbation, ostracodes, and benthic foraminifera favour the hypothesis of the dark-layer deposition taking place under oxygen-bearing bottom waters. The original value of the concentration of the organic carbon in the dark layers of Punta Piccola, estimated from the δ13C measured in the carbonate fraction, was higher than the post-diagenetic one. It may have reached 7% in the dark layer 107, which was therefore a true sapropel at the time of deposition. This result indicates that anoxic conditions are not a prerequisite for sapropelic sediment formation. However, the pristine concentration of the organic carbon in the dark layers at Punta Piccola is lower than those of coeval sapropels cored in the nearby deep settings, which were deposited under an anoxic water column. This difference may result from the effect of water column anoxia on the organic carbon content. Diagenetic reactions took place in the dark layers through the oxidation of large amounts of organic matter. The dissolution of primary calcium carbonates (biogenic in origin) and the reduction of Fe and Mn oxyhydroxides led the interstitial solutions to be supersaturated towards Mn-rich calcite and/or pseudo-kutnahorite. The secondary carbonates are Mg-enriched and Sr and Fe-depleted. The negative shifts of the δ18O signal in the carbonates of the dark layers of Punta Piccola are consistent with an increased river discharge in the Mediterranean at the time of deposition.
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Parameswari, E., V. Davamani, R. Kalaiarasi, T. Ilakiya, and S. Arulmani. "Utilization of Ostracods (Crustacea) as Bioindicator for Environmental Pollutants." International Research Journal of Pure and Applied Chemistry, June 1, 2020, 73–93. http://dx.doi.org/10.9734/irjpac/2020/v21i730182.
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Ecosystem undergoes drastic changes due to the anthropogenic activities. As a consequence of industrial development, increasing population growth and modernized agricultural practices water resources like limnetic zone and marine areas have undergone eutrophication. This resulted in the decline in population of phytoplankton and zooplankton. Hence, it is an urgent need to monitor the quality of the environment. Several organisms are used as biomonitors. Among them, Ostracodes (Seed Shrimps) which belong to Crustacean group are very sensitive to those changes in the environment and useful in predicting the paleo environmental conditions. Ostracodes are bivalve arthropods which are enclosed in a carapace made of low magnesium calcite. These species are occurring for about 450 million years dates back to ordovician which are known for their easier fossilization. The development of Ostracodes is influenced by the physic - chemical properties of waters such as Salinity, temperature, pH, Dissolved oxygen, bottom grain sizes and sedimentation rates. In addition to diversity and abundance of population, morphological and geochemical changes can also be detected in the Ostracod carapace (shell) which serves as a tracer of the water quality. These details are basis for utilizing Ostracods as paleoenvironmental (paleoclimatic, paleosalinity, paleooceanographic) reconstruction, ecotoxicity monitoring, biostratigraphic indicator. Moreover, these microcrustaceans showed similar or higher sensitivity to herbicides, pesticides, oil spills or heavy metals pollution other than traditional groups like copepods, protozoan, rotifers, cladocerans which are used to test the human impacts on ecosystem. These meiofaunas are highly adaptable to waters containing organic and inorganic contaminants generated by catastrophic activities by human beings in the surroundings.
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Börner, Nicole, Klaus Peter Jochum, Marleen Stuhr, Michelle Abstein, Birgit Plessen, Peter Frenzel, Junbo Wang, Liping Zhu, and Antje Schwalb. "Late Quaternary changes in moisture availability and weathering intensity on the central Tibetan Plateau indicated by chemical signatures of ostracod shells." Frontiers in Earth Science 10 (July 26, 2022). http://dx.doi.org/10.3389/feart.2022.826143.
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High-resolution multi-proxy records from two lakes on the southern Tibetan Plateau, Nam Co and Tangra Yumco, are used to infer long-term variations in the Asian monsoon system with a novel set of ostracod shell chemistry proxies. We track the moisture evolution since the Last Glacial Maximum using the trace element, rare earth element (REE) and stable isotope composition of ostracod shells. The sediment records covering the past 18.8 cal. ka BP and 17.4 cal. ka BP, respectively, demonstrate the suitability of REEs as indicators of weathering intensity and thus hydrological changes and moisture sources in the catchment. In Nam Co, high concentrations of light REEs between 14 and 13 cal. ka BP suggest an increased drainage from the glaciated Nyainqêngtanglha Mountains in the south, pointing to meltwater input. REEs in ostracod shells therefore provide additional information on water sources critical for the interpretation of stable isotope records. Mg/Ca, Sr/Ca, and Ba/Ca ratios reflect salinity and thus changes in effective moisture. Asynchronous behavior of Mg/Ca, Sr/Ca, and Ba/Ca ratios are controlled by changes in dominance of precipitating carbonate minerals in the lake. Synchronous behavior reflects calcite precipitation, indicating low-Mg/Ca warm-wet conditions. Constantly low Sr/Ca ratios reflect aragonite precipitation, indicating high-Mg dry conditions. Increased Sr/Ca and Ba/Ca relative to Mg/Ca ratios show monohydrocalcite precipitation, indicating high-Mg/Ca cold-dry conditions. Furthermore, Fe/Ca, Mn/Ca and U/Ca ratios in ostracods reflect changes in oxygen saturation in lake bottom waters controlled by lake level and microbial activity. The paleoclimate histories reconstructed from Nam Co and Tangra Yumco show high similarity throughout the late Quaternary. We identified two major dry periods, corresponding to Heinrich 1 and the Younger Dryas, followed by strengthening in Indian summer monsoon precipitation. The early Holocene is characterized by a moisture maximum, reflecting abundant water supply by a strong ISM. A time-delayed shift to dry conditions occurred at 2.6 cal. ka BP at Tangra Yumco, and at 2 cal. ka BP at Nam Co, resulting in decreasing lake levels, caused by weakened monsoon intensity due to a southeastward migration of the ISM-Westerly boundary with an estimated velocity of approximately 600 m per year.
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McCormack, Jeremy, and Ola Kwiecien. "Coeval primary and diagenetic carbonates in lacustrine sediments challenge palaeoclimate interpretations." Scientific Reports 11, no. 1 (April 12, 2021). http://dx.doi.org/10.1038/s41598-021-86872-1.
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AbstractLakes are sensitive to climate change and their sediments play a pivotal role as environmental recorders. The oxygen and carbon isotope composition (δ18O and δ13C) of carbonates from alkaline lakes is featured in numerous studies attempting a quantitative reconstruction of rainfall, temperature and precipitation-evaporation changes. An often-overlooked challenge consists in the mineralogically mixed nature of carbonates themselves. We document a large variability of carbonate components and their respective distinct δ18O and δ13C values from sediments of Lake Van (Turkey) covering the last 150 kyr. The carbonate inventory consists of primary (1) inorganic calcite and aragonite precipitating in the surface-water, (2) biogenic calcite ostracod valves; and post-depositional phases: (3) dolomite forming in the sediment, and previously overlooked, (4) aragonite encrustations formed rapidly around decaying organic matter. We find a systematic relation between the lithology and the dominant deep-water carbonate phase formed recurrently under specific hydrological conditions. The presence of the different carbonates is never mutually exclusive, and the isotopic composition of each phase forms a distinctive cluster characteristic for the depth and timing of their formation. Our findings stretch the envelope of mechanisms forming lacustrine carbonates and highlight the urge to identify and separate carbonate components prior to geochemical analyses.
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Wrozyna, Claudia, Juliane Meyer, Martin Dietzel, and Werner E. Piller. "Neotropical ostracode oxygen and carbon isotope signatures: implications for calcification conditions." Biogeochemistry, March 29, 2022. http://dx.doi.org/10.1007/s10533-022-00917-9.
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AbstractCalcitic valves of non-marine ostracodes are important geochemical archives. Investigations of the relationship between the ranges of oxygen and carbon isotope values of modern ostracode populations and their host water provide important information on local or regional conditions and influences. Here we present the first δ18Oostracode and δ13C of the freshwater ostracode species Cytheridella ilosvayi along with the isotopic composition of the waters in which the ostracodes calcified, δDwater, δ18Owater, δ13CDIC values—covering a large geographical range (Florida to Brazil). With this data we extended a newly developed approach based on the estimation of δ18O values of monthly equilibrium calcites as references for the interpretation of δ18Oostracode values. The expected apparent oxygen isotope fractionation between CaCO3 and H2O is correlated with temperature with smaller values occurring at higher temperatures as valid at isotope equilibrium (δ18Ocalcite_eq). Uncertainties about the expected equilibrium calcites derive from incomplete knowledge of high-frequency variations of the water bodies caused by interplay of mixing, evaporation, and temperature. Coincidence between δ18Oostracode and δ18Ocalcite_eq is restricted to few months indicating a seasonal calcification of Cytheridella. There is a characteristic pattern in its difference between mean δ18Oostracode and δ18Ocalcite_eq which implies that Cytheridella provides a synchronous life cycle in its geographical range with two calcification periods in spring (May, June) and autumn (October). This ubiquitous life cycle of Cytheridella in the entire study area is considered to be phylogenetically inherited. It might have originally been adapted to environmental conditions but has been conserved during the migration and radiation of the group over the Neotropical realm.
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Al-Khafaji, Sattar Jabar, and Maher Mandeel Mahdi. "Geochemical, Mineralogical and Biological study of Holocene deposits in Almuthana province, southern Iraq." Iraqi Journal of Science, July 17, 2019, 1521–29. http://dx.doi.org/10.24996/ijs.2019.60.7.12.
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Fifteen samples were collected from recent sediments grouping at 80 km east Samawa City, southern Iraq. Three selected samples for grain size analysis and twelve samples for chemical and biofacies analysis. Grain size analysis indicated that the sediment is mainly composed of the silt and clay with a small amount of sand. Most of the samples considered to be as clayey silt. The dominated non clay minerals are Quartz, Calcite, and Dolomite, while the clay minerals are composed of mixed Montmorillonite- Chlorite, Palygorskite, Illite and Kaolinite. Chemical analysis showed that all samples have high concentrations of SiO2 and CaO in comparison with Al2O3, MgO, Fe2O3, K2O and N2O. The identified faunas consist of a number of groups such as Mollusca, Ostracoda and Charophyta, all diagnosed genera indicated of fresh water environments. The results from all collected data are indicated that the sediments belong to flood plain deposits which deposited in fluviatile environments.
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Suárez-Ibarra, Jaime Y., Cristiane F. Frozza, Pâmela L. Palhano, Sandro M. Petró, Manuel F. G. Weinkauf, and Maria A. G. Pivel. "Calcium Carbonate Dissolution Triggered by High Productivity During the Last Glacial–Interglacial Interval in the Deep Western South Atlantic." Frontiers in Earth Science 10 (March 23, 2022). http://dx.doi.org/10.3389/feart.2022.830984.
Full textAbstract:
Studies reconstructing surface paleoproductivity and benthic environmental conditions allow us to measure the effectiveness of the biological pump, an important mechanism in the global climate system. In order to assess surface productivity changes and their effect on the seafloor, we studied the sediment core SAT-048A, spanning 43–5 ka, recovered from the continental slope (1,542 m water depth) of the southernmost Brazilian continental margin, deep western South Atlantic. We assessed the sea surface productivity, the organic matter flux to the seafloor, and calcite dissolution effects, based on micropaleontological (benthic and planktonic foraminifers, ostracods), geochemical (benthic δ13C isotopes), and sedimentological data (carbonate and bulk sand content). Superimposed on the induced changes related to the last glacial–interglacial transition, the reconstruction indicates a significant and positive correlation between the paleoproductivity proxies and the summer insolation. From the reconstructed data, it was possible to identify high (low) surface productivity, high (low) organic matter flux to the seafloor, and high (low) dissolution rates of planktonic Foraminifera tests during the glacial (postglacial). Furthermore, within the glacial, enhanced productivity was associated with higher insolation values, explained by increased northeasterly summer winds that promoted meandering and upwelling of the nutrient-rich South Atlantic Central Water. Statistical analyses support the idea that productivity is the main cause for seafloor calcium carbonate dissolution, as opposed to changes in the Atlantic Meridional Overturning Circulation (at least for the 25–4 ka period). Further efforts must be invested in the comprehension and quantification of the total organic matter and biogenic carbonate burial during time intervals with an enhanced biological pump, aiming to better understand their individual roles.