TY - JOUR A1 - Deino, A. L. A1 - Dommain, René A1 - Keller, C. B. A1 - Potts, R. A1 - Behrensmeyer, A. K. A1 - Beverly, E. J. A1 - King, J. A1 - Heil, C. W. A1 - Stockhecke, M. A1 - Brown, E. T. A1 - Moerman, J. A1 - deMenocal, P. A1 - Deocampo, D. A1 - Garcin, Yannick A1 - Levin, N. E. A1 - Lupien, R. A1 - Owen, R. B. A1 - Rabideaux, N. A1 - Russell, J. M. A1 - Scott, J. A1 - Riedl, S. A1 - Brady, K. A1 - Bright, J. A1 - Clark, J. B. A1 - Cohen, A. A1 - Faith, J. T. A1 - Noren, A. A1 - Muiruri, V. A1 - Renaut, R. A1 - Rucina, S. A1 - Uno, K. T1 - Chronostratigraphic model of a high-resolution drill core record of the past million years from the Koora Basin, south Kenya Rift: Overcoming the difficulties of variable sedimentation rate and hiatuses JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - The Olorgesailie Drilling Project and the related Hominin Sites and Paleolakes Drilling Project in East Africa were initiated to test hypotheses and models linking environmental change to hominin evolution by drilling lake basin sediments adjacent to important archeological and paleoanthropological sites. Drill core OL012-1A recovered 139 m of sedimentary and volcaniclastic strata from the Koora paleolake basin, southern Kenya Rift, providing the opportunity to compare paleoenvironmental influences over the past million years with the parallel record exposed at the nearby Olorgesailie archeological site. To refine our ability to link core-to-outcrop paleoenvironmental records, we institute here a methodological framework for deriving a robust age model for the complex lithostratigraphy of OL012-1A. Firstly, chronostratigraphic control points for the core were established based on 4 Ar/39Ar ages from intercalated tephra deposits and a basal trachyte flow, as well as the stratigraphic position of the Brunhes-Matuyama geomagnetic reversal. This dataset was combined with the position and duration of paleosols, and analyzed using a new Bayesian algorithm for high-resolution age-depth modeling of hiatus-bearing stratigraphic sections. This model addresses three important aspects relevant to highly dynamic, nonlinear depositional environments: 1) correcting for variable rates of deposition, 2) accommodating hiatuses, and 3) quantifying realistic age uncertainty with centimetric resolution. Our method is applicable to typical depositional systems in extensional rifts as well as to drill cores from other dynamic terrestrial or aquatic environments. We use the core age model and lithostratigraphy to examine the inter connectivity of the Koora Basin to adjacent areas and sources of volcanism. (C) 2019 Elsevier Ltd. All rights reserved. KW - Pleistocene KW - Paleolimnology KW - East Africa KW - Sedimentology KW - Radiogenic isotopes KW - Bayesian modeling KW - paleosol KW - Tephrostratigraphy KW - Magnetostratigraphy KW - Kenya Rift Y1 - 2019 U6 - https://doi.org/10.1016/j.quascirev.2019.05.009 SN - 0277-3791 VL - 215 SP - 213 EP - 231 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Deino, Alan L. A1 - Sier, Mark Jan A1 - Garello, Dominique A1 - Keller, B. A1 - Kingston, John A1 - Scott, Jennifer J. A1 - Dupont-Nivet, Guillaume A1 - Cohen, Andrew T1 - Chronostratigraphy of the Baringo-Tugen-Barsemoi (HSPDP-BTB13-1A) core-Ar-40/Ar-39 dating, magnetostratigraphy, tephrostratigraphy, sequence stratigraphy and Bayesian age modeling JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - The Baringo-Tugen-Barsemoi 2013 drillcore (BTB13), acquired as part of the Hominin Sites and Paleolakes Drilling Project, recovered 228 m of fluviolacustrine sedimentary rocks and tuffs spanning a similar to 3.29-2.56 Ma interval of the highly fossiliferous and hominin-bearing Chemeron Formation, Tugen Hills, Kenya. Here we present a Bayesian stratigraphic age model for the core employing chronostratigraphic control points derived from Ar-40/Ar-39 dating of tuffs from core and outcrop, Ar-40/Ar-39 age calibration of related outcrop diatomaceous units, and core magnetostratigraphy. The age model reveals three main intervals with distinct sediment accumulation rates: an early rapid phase from 3.2 to 2.9 Ma; a relatively slow phase from 2.9 to 2.7 Ma; and the highest rate of accumulation from 2.7 to 2.6 Ma. The intervals of rapid accumulation correspond to periods of high Earth orbital eccentricity, whereas the slow accumulation interval corresponds to low eccentricity at 2.9-2.7 Ma, suggesting that astronomically mediated climate processes may be responsible for the observed changes in sediment accumulation rate. Lacustrine transgression-regression events, as delineated using sequence stratigraphy, dominantly operate on precession scale, particularly within the high eccentricity periods. A set of erosively based fluvial conglomerates correspond to the 2.9-2.7 Ma interval, which could be related to either the depositional response to low eccentricity or to the development of unconformities due to local tectonic activity. Age calibration of core magnetic susceptibility and gamma density logs indicates a close temporal correspondence between a shift from high- to low-frequency signal variability at similar to 3 Ma, approximately coincident the end of the mid-Piacenzian Warm Period, and the beginning of the cooling of world climate leading to the initiation of Northern Hemispheric glaciation c. 2.7 Ma. BTB13 and the Baringo Basin records may thus provide evidence of a connection between high-latitude glaciation and equatorial terrestrial climate toward the end of the Pliocene. KW - Chemeron Formation KW - Pliocene KW - Eccentricity KW - Precession KW - Paleoclimate KW - Paleolimnology Y1 - 2019 U6 - https://doi.org/10.1016/j.palaeo.2019.109258 SN - 0031-0182 SN - 1872-616X VL - 532 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Lev, L. A1 - Almogi-Labin, Ahuva A1 - Mischke, Steffen A1 - Ito, E. A1 - Ben-Avraham, Zvi A1 - Stein, M. T1 - Paleohydrology of Lake Kinneret during the Heinrich event H2 JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - During the last glacial period lake Kinneret (the Sea of Galilee) fluctuated between high and low water levels reflecting the hydrological conditions of the lake watershed. Here, we focus on the hydrology of the lake after its retreat from the last glacial MIS2 (similar to 27-25 ka BP) highest stand of similar to 170 m below mean sea level (m bsl) to the low stand of similar to 214 m bsl at similar to 24-21 ka BP. The limnological-hydrological history of this time interval is recovered from trench and borehole that were dug and drilled in the southwestern shore of the lake at Ohalo-II archeological site. Cyprideis torosa (Ostracoda) recovered from the trench yielded elemental, Sr-87/Sr-86 and delta O-18 isotope data that provide information on the shore environment during the low stand period. The Sr-87/Sr-86 and Sr/Ca ratios in the ostracods, varying between similar to 0.70789 and similar to 0.70815 and 0.0017 and 0.0030, respectively indicate contributions of waters from the last glacial lake and regional runoff. The increase in the Sr-87/Sr-86 ratios reflects the decreasing effect of the last glacial Lake Kinneret waters and enhanced contribution of local runoff that washed down dried mountain soils that were previously developed during the wet and vegetated glacial. The lake retreat at similar to 24 ka BP coincided with the Heinrich event H2 at the northern Atlantic. H2 was expressed by severe aridity in Lake Kinneret-Dead Sea watershed. The limnological-hydrological change at post H2 was accompanied by 2% decrease in the delta O-18 value from -2% to -4% reflecting the change in the composition of the east Mediterranean rain sources. The last glacial lake Sr-87/Sr-86 ratio is similar to the Tiberias Spa saline waters and distinctly different from the modern Lake Kinneret fresh waters: Sr-87/Sr-86 similar to 0.70785 compared to similar to 0.70760, respectively. This difference is explained by enhanced contribution of Ca-chloride brines with high Sr-87/Sr-86 values to the last glacial lake and reduced Jordan River contribution due to cold freezing conditions at its headwaters, while the modern Lake Kinneret is more affected by low Sr-87/Sr-86 freshwater from the Jordan watershed. KW - Ostracods KW - Lake Kinneret KW - Paleolimnology KW - Paleohydrology KW - Sr-87/Sr-86 KW - delta O-18 Y1 - 2014 U6 - https://doi.org/10.1016/j.palaeo.2014.01.005 SN - 0031-0182 SN - 1872-616X VL - 396 SP - 183 EP - 193 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Wang, Yongbo A1 - Liu, Xingqi A1 - Mischke, Steffen A1 - Herzschuh, Ulrike T1 - Environmental constraints on lake sediment mineral compositions from the Tibetan Plateau and implications for paleoenvironment reconstruction JF - Journal of paleolimnolog N2 - Inorganic minerals form a major component of lacustrine sediments and have the potential to reveal detailed information on previous climatic and hydrological conditions. The ability to extract such information however, has been restricted by a limited understanding of the relationships between minerals and the environment. In an attempt to fill in this gap in our knowledge, 146 surface sediment samples have been investigated from 146 lakes on the Tibetan Plateau. The mineral compositions derived from these samples by X-Ray Diffraction (XRD) were used to examine the relationships between mineral compositions and the environmental variables determined for each site. Statistical techniques including Multivariate regression trees (MRT) and Redundancy Analysis (RDA), based on the mineral spectra and environmental variables, reveal that the electrical conductivity (EC) and Mg/Ca ratios of lake water are the most important controls on the composition of endogenic minerals. No endogenic minerals precipitate under hyper-fresh water conditions (EC lower than 0.13 mS/cm), with calcite commonly forming in water with EC values above 0.13 mS/cm. Between EC values of 0.13 and 26 mS/cm the mineral composition of lake sediments can be explained in terms of variations in the Mg/Ca ratio: calcite dominates at Mg/Ca ratios of less than 33, whereas aragonite commonly forms when the ratio is greater than 33. Where EC values are between 26 and 39 mS/cm, monohydrocalcite precipitates together with calcite and aragonite; above 39 mS/cm, gypsum and halite commonly form. Information on the local geological strata indicates that allogenic (detrital) mineral compositions are primarily influenced by the bedrock compositions within the catchment area. By applying these relationships to the late glacial and Holocene mineral record from Chaka Salt Lake, five lake stages have been identified and their associated EC conditions inferred. The lake evolved from a freshwater lake during the late glacial (before 11.4 cal. ka BP) represented by the lowest EC values (< 0.13 mS/cm), to a saline lake with EC values slightly higher than 39 mS/cm during the early and mid Holocene (ca. 11.4-5.3 cal. ka BP), and finally to a salt lake (after 5.3 cal. ka BP). These results illustrate the utility of our mineral-environmental model for the quantitative reconstruction of past environmental conditions from lake sediment records. KW - Mineral composition KW - XRD KW - Multivariate regression trees KW - Electrical conductivity KW - Paleolimnology KW - Tibetan Plateau Y1 - 2012 U6 - https://doi.org/10.1007/s10933-011-9549-2 SN - 0921-2728 VL - 47 IS - 1 SP - 71 EP - 85 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Opitz, Stephan A1 - Wünnemann, Bernd A1 - Aichner, Bernhard A1 - Dietze, Elisabeth A1 - Hartmann, Kai A1 - Herzschuh, Ulrike A1 - IJmker, Janneke A1 - Lehmkuhl, Frank A1 - Li, Shijie A1 - Mischke, Steffen A1 - Plotzki, Anna A1 - Stauch, Georg A1 - Diekmann, Bernhard T1 - Late Glacial and Holocene development of Lake Donggi Cona, north-eastern Tibetan Plateau, inferred from sedimentological analysis JF - Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences N2 - Sediments of Lake Donggi Cona on the northeastern Tibetan Plateau were studied to infer changes in the lacustrine depositional environment, related to climatic and non-climatic changes during the last 19 kyr. The lake today fills a 30x8 km big and 95 m deep tectonic basin, associated with the Kunlun Fault. The study was conducted on a sediment-core transect through the lake basin, in order to gain a complete picture of spatio-temporal environmental change. The recovered sediments are partly finely laminated and are composed of calcareous muds with variable amounts of carbonate micrite, organic matter, detrital silt and clay. On the basis of sedimentological, geochemical, and mineralogical data up to five lithological units (LU) can be distinguished that document distinct stages in the development of the lake system. The onset of the lowermost LU with lacustrine muds above basal sands indicates that lake level was at least 39 m below the present level and started to rise after 19 ka, possibly in response to regional deglaciation. At this time, the lacustrine environment was characterized by detrital sediment influx and the deposition of siliciclastic sediment. In two sediment cores, upward grain-size coarsening documents a lake-level fall after 13 cal ka BP, possibly associated with the late-glacial Younger Dryas stadial. From 11.5 to 4.3 cal ka BP, grain-size fining in sediment cores from the profundal coring sites and the onset of lacustrine deposition at a litoral core site (2 m water depth) in a recent marginal bay of Donggi Cona document lake-level rise during the early to mid-Holocene to at least modern level. In addition, high biological productivity and pronounced precipitation of carbonate micrites are consistent with warm and moist climate conditions related to an enhanced influence of summer monsoon. At 4.3 cal ka BP the lake system shifted from an aragonite- to a calcite-dominated system, indicating a change towards a fully open hydrological lake system. The younger clay-rich sediments are moreover non-laminated and lack any diagenetic sulphides, pointing to fully ventilated conditions, and the prevailing absence of lake stratification. This turning point in lake history could imply either a threshold response to insolation-forced climate cooling or a response to a non-climatic trigger, such as an erosional event or a tectonic pulse that induced a strong earthquake, which is difficult to decide from our data base. KW - China KW - Monsoon KW - Paleolimnology KW - Multi-site study KW - Aragonite KW - XRF KW - XRD KW - Sedimentology Y1 - 2012 U6 - https://doi.org/10.1016/j.palaeo.2012.04.013 SN - 0031-0182 VL - 337 IS - 23 SP - 159 EP - 176 PB - Elsevier CY - Amsterdam ER - TY - THES A1 - Hultzsch, Nadja T1 - Lakustrine Sedimente als Archive des spätquartären Umweltwandels in der Amery-Oase, Ostantarktis T1 - The Late Quaternary climatic and environmental history of Amery Oasis, East Antarctica N2 - Im Rahmen einer deutsch-australischen Forschungskooperation erfolgte im Südsommer 2001/2002 eine Expedition in die Amery-Oase (70°50’S, 68°00’E), die im Einzugsgebiet des Lambert-Gletscher/Amery-Schelfeis-Systems, dem größten ostantarktischen Eis-Drainagesystem, liegt. Von deutscher Seite wurden im Zuge der Geländekampagne erstmals lakustrine Sedimentsequenzen gewonnen, um die bislang wenig erforschte spätquartäre Klima- und Umweltgeschichte dieser rund 1800 km2 großen eisfreien Region zu rekonstruieren. Die drei untersuchten Glazialseen Beaver, Radok und Terrasovoje unterscheiden sich sowohl deutlich in ihrer Größe, Bathymetrie und den hydrologischen Merkmalen sowie in ihren Sedimentabfolgen. Einen Schwerpunkte dieser Doktorarbeit bildet die Rekonstruktion der Sedimentationsprozesse und des Ablagerungsmilieus sowie Untersuchungen zur Herkunft des detritischen Sedimentmaterials in den Seebecken. Der methodische Ansatz verfolgt die Charakterisierung der klastischen Sedimentfazies an Hand lithologisch-granulometrischer Merkmale sowie mineralogisch-geochemischer Analysen der Sedimentherkunft. Ein weiterer Schwerpunkt ist die Rekonstruktion der holozänen biogen gesteuerten Ablagerungsbedingungen im Terrasovoje-See, die Rückschlüsse auf den kurzfristigen postglazialen Klima- und Umweltwandel in der Amery-Oase gestattet. Dabei wurden mikrofazielle Untersuchungsmethoden und hochauflösende Elementscannermessungen angewandt. Die klastische Sedimentherkunft in den drei Seen unterscheidet sich räumlich deutlich voneinander und spiegelt den komplexen geologischen Aufbau der Amery-Oase wider. Als Sedimentquellen konnten präkambrische Metamorphite, permotriassische Sedimentgesteine und tertiäre Lockersedimente identifiziert werden. Die Varibilität der Herkunftssignale ist zeitlich weniger deutlich als räumlich ausgeprägt und deutet auf relativ konstante Liefergebiete in den einzelnen Seen hin. Das glaziolakustrine Ablagerungsmilieu der drei untersuchten Seen zeigt klare räumliche und zeitliche Unterschiede. In allen drei Seen setzen sich die älteren Sedimente aus grobkörnigem, häufig diamiktischem Material zusammen, während die jüngeren Sedimente aus feinkörnigen Laminiten bestehen. Die lithofazielle Zweiteilung in den Sedimentabfolgen deutet auf einen Rückzug der Gletscher und/oder einen Anstieg der Wassertiefen im Übergang von den grobkörnigen zu den feinkörnigen Ablagerungseinheiten hin. Die oberen feinkörnigen Kernabschnitte spiegeln in allen drei Seen die postglaziale lakustrine Sedimentation wider. Im Beaver-See wird die postglaziale Fazies durch laminierte klastische Stillwassersedimente repräsentiert, im Radok-See durch Turbiditsequenzen und im Terrasovoje-See durch Algenlaminite. Abgesehen vom Terrasovoje-See ist die zeitliche Einordnung der Fazieswechsel auf Grund mangelnder Altersinformationen schwer erfassbar. Im Terrasovoje-See setzte die postglaziale Sedimentation um rund 12,4 cal. ka ein. Somit weisen die darunterliegenden glazigenen Klastika mindestens ein spätpleistozänes Alter auf. Die sedimentologischen Eigenschaften, Änderungen der Sedimentationsraten und organogene Zusammensetzung der postglazialen Biogenlaminite des Terrasovoje-Sees deuten auf Variationen der paläolimnologischen Bedingungen hinsichtlich Eisbedeckung, biologischer Produktivität, Wasserstand, Redoxbedingungen und Salinität hin, die mit regionalen holozänen Klimaänderungen in Verbindung gebracht werden können. Weitere Anhaltspunkte ergeben sich aus der Zusammensetzung und den Mächtigkeitsvariationen der Laminae, die generell aus Wechsellagerungen von Cyanobakterienmatten mit feinklastischen Lagen bestehen. Lagenzählungen der Laminae belegen Änderungen des Ablagerungsmilieus auf subdekadischen Zeitskalen, wobei zeitweilige jährliche Signale nicht ausgeschlossen werden können. Unter Berücksichtigung aller faziellen Indikatoren lässt sich aus der Sedimentabfolge des Terrasovoje-Sees ein frühholozänes Klimaoptimum zwischen 9 und 7 cal. ka sowie weitere Wärmephasen zwischen 3,2 und 2,3 cal. ka sowie 1,5 und 1,0 cal. ka ableiten. Im Vergleich mit Eiskernarchiven und anderen Seesedimentabfolgen aus ostantarktischen Oasen zeigt sich, dass das Auftreten postglazialer Warmphasen nicht allenorts einem allgemein gültigen räumlich-zeitlichen Muster folgt. Die Ursachen hierfür liegen vermutlich in den lokalen geographischen Gegebenheiten. Es lässt sich daraus schliessen, dass die bisher vorliegenden Klimarekonstruktionen eher das Lokalklima an einem Untersuchungsstandort als das Großklima der Ostantarktis reflektieren. Daraus ergibt sich die Notwendigkeit weiterer Untersuchungen von antarktischen Klimaarchiven und Untersuchungsstandorten, um örtliche von überregionalen Klimasignalen besser unterscheiden zu können. N2 - In the scope of a German-Australian research cooperation field work was conducted in the Amery Oasis (70°50’S, 68°00’E), situated in the Lambert Glacier/Amery Ice Shelf region, the largest East Antarctic ice drainage system. The German part comprised the retrieval of lacustrine sediment cores for the reconstruction of the late Quaternary development of the palaeoenvironment in the 1800 km2 large ice-free region. The three studied glacial lakes Beaver, Radok, and Terrasovoje reveal marked differences in size, hydrology and their sedimentary inventory. The goals of this thesis were to infer the onset of depostion in the lacustrine basins and to characterize changes in the depositional environment in the course of glacial retreat and the postglacial climate development. The methodic approach followed the recognition of sedimentary facies variability and sediment sources by means of facies analysis and mineralogical-geochemical provenance analysis. Another aspect was the high-resolution reconstruction of postglacial biogenic sedimentary modes in Lake Terrasovoje that provide insights into the short-term Holocene palaeo-climatic and palaeoenvironmental development. The origin of siliciclastics shows marked spatial differences between the lakes, reflecting the complex geological setting of the Amery Oasis. The main detrital sources comprise crystalline rocks of the East Antarctic craton, Permotriassic and Tertiary sedimentary rocks. The temporal variability of sediment provenance is less developed than the spatial pattern, pointing to relatively constant sediment sources through time in the respective lakes. The glaciolacustrine depositional environment of the three lakes shows clear spatial and temporal contrasts. In all lakes, the older sediments are composed of coarse, partly diamictic lithologies, while the younger materials consist of fine-grained laminites. The twofold lithofacial pattern is related to regional glacial retreat at the boundary between both sedimentary units that reduced direct glacigenic sediment input. In the epishelf Lake Beaver, in addition, the effect of postglacial sea-level rise led also to the rise of lake level and shifted the study site towards a more distal position from the shore, away from the influence of coarse clastic sediment input. The upper sedimentary units of the three lakes are dominated by fine-grained sediments, which only occasionally include ice-rafted dropstones. The postglacial sediments comprise clastic stillwater laminites at Lake Beaver, finely laminated turbidites in Lake Radok, and algal laminites in Lake Terrasovoje. Apart from Lake Terrasovoje the timing of the lithological change is hard to determine, because of missing age constraints. At Lake Terrasovoje, the postglacial sequence started at approximately 12.4 cal. ka BP, suggesting an late Pleistocene age for the underlying glacial sediments. Sedimentological features, changes in sedimentation rates, and the compositional variability of the organic-rich postglacial laminites in Lake Terrasovoje point to variations in the palaeolimnic environment in terms of ice cover, biological productivity, lake level, redox conditions, and salinity that can be related to the regional Holocene climate history. Further evidence arises from the structure, composition, and thickness variations of the laminae, which basically consist of alternations of algal mats (cyanobacteria) and fine-clastic layers. The counting of laminae couplets reveal changes in the depositional enviroment at sub-decadal time scales that partly might include annual layering. Under the consideration of all sedimentological facies indicators, the postglacial laminite sequence of Lake Terrasovoje documents an early Holocene climate optimum between 9 and 7 cal. ka as well as two warm spells between 3.2 and 2.3 cal. ka and 1.5 and 1.0 cal. ka, respectively. In comparison with ice-core records and lake records from other East Antarctic ice-free regions, it becomes evident that the appearence of warm episodes does not follow a consistent spatial-temporal pattern. Common trends comprise the existence of an early Holocene climate optimum, as seen in the ice-core records and in the Amery Oasis, and several warm episodes in the middle to late Holocene that are often time-transgressive. The cause of this inconsistent pattern probably can be explained by local boundary conditions that affect the study sites, such as topography, maritime influences and the distance to glacial ice. Therefore, many climate reconstructions basically document local climate rather than overregional Antarctic climate. In conclusion, there is need for ongoing palaeoclimatic studies in East Antarctica and the establishment of a dense network of study sites to distinguish and validate local from overregional palaeoclimatic fingerprints. KW - Antarktis KW - Sedimentologie KW - Limnologie KW - Geochemie KW - Mineralogie KW - Amery-Oase KW - Ostantarktis KW - Spätquartär KW - Paläolimnologie KW - Amery Oasis KW - East Antarctica KW - Late Quaternary KW - Paleolimnology Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-7980 ER -