All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1644.
Pliocene to Pleistocene climate and environmental history of Lake El'gygytgyn, Far East Russian Arctic, based on high-resolution inorganic geochemistry data
Climate of the Past,
10
(4)
1381-1399
2014
ISSN: 18149324
Publisher: Copernicus GmbH
Abstract: ▾ The 3.6 Ma sediment record of Lake El'gygytgyn/NE Russia, Far East Russian Arctic, represents the longest continuous climate archive of the terrestrial Arctic. Its elemental composition as determined by X-ray fluorescence scanning exhibits significant changes since the mid-Pliocene caused by climate-driven variations in primary production, postdepositional diagenetic processes, and lake circulation as well as weathering processes in its catchment. <br><br> During the mid-to late Pliocene, warmer and wetter climatic conditions are reflected by elevated Si/Ti ratios, indicating enhanced diatom production in the lake. Prior to 3.3 Ma, this signal is overprinted by intensified detrital input from the catchment, visible in maxima of clastic-related proxies, such as K. In addition, calcite formation in the early lake history points to enhanced Ca flux into the lake caused by intensified weathering in the catchment. A lack of calcite deposition after ca. 3.3 Ma is linked to the development of permafrost in the region triggered by cooling in the mid-Pliocene. After ca. 3.0 Ma the elemental data suggest a gradual transition to Pleistocene-style glacial-interglacial cyclicity. In the early Pleistocene, the cyclicity was first dominated by variations on the 41 kyr obliquity band but experienced a change to a 100 kyr eccentricity dominance during the middle Pleistocene transition (MPT) at ca. 1.2-0.6 Ma. This clearly demonstrates the sensitivity of the Lake El'gygytgyn record to orbital forcing. A successive decrease of the baseline levels of the redox-sensitive Mn/Fe ratio and magnetic susceptibility between 2.3 and 1.8 Ma reflects an overall change in the bottom-water oxygenation due to an intensified occurrence of pervasive glacial episodes in the early Pleistocene. The coincidence with major changes in the North Pacific and Bering Sea paleoceanography at ca. 1.8 Ma implies that the change in lake hydrology was caused by a regional cooling in the North Pacific and the western Beringian landmass and/or changes in the continentality. Further increases in total organic carbon and total nitrogen content after ca. 1.6 Ma are attributed to reduced organic matter decay in the sediment during prolonged anoxic periods. This points to more extensive periods of perennial ice coverage, and thus, to a progressive shifts towards more intense peak glacial periods. In the course of the Pleistocene glacial-interglacial sequence eight so-called "super-interglacials" occur. Their exceptionally warm conditions are reflected by extreme Si/Ti peaks accompanied by lows in Ti, K, and Fe, thus indicating extraordinary high lake productivity. © 2014 Author(s).
1643.
Recent anthropogenic impact in ancient Lake Ohrid (Macedonia/Albania): a palaeolimnological approach
Journal of Paleolimnology,
52
(3)
139 – 154
2014
ISSN: 09212728
Publisher: Kluwer Academic Publishers
Abstract: ▾ Ancient lakes, which are important centres of biodiversity and endemism, are threatened by a wide variety of human impacts. To assess environmental impact on ancient Lake Ohrid we have taken short sediment cores from two contrasting site locations, comprising a site of urban pollution and an apparently pristine area. Recent impacts on water quality and ecology were assessed using sediment, geochemical, ostracode, and diatom data derived from analysis of two 210Pb-dated sediment cores spanning the period from 1918 to 2009. According to the index of geoaccumulation, sediments were often moderately contaminated with As. Fe and Ni concentrations often exceeded reported maximum limits above which harmful effects on sediment-dwelling organisms are expected. Productivity in the (pristine) south-eastern part of Lake Ohrid (Sveti Naum) is generally lower than in the north, probably due to the strong influence of spring discharge. Low ostracode and diatom concentrations, low abundance of the epilimnetic diatom Cyclotellaocellata, and low values of TOC and TIC indicate a lower productivity from the early 1920s to the late 1980s. Since the mid 1970s, increased relative abundance of C. ocellata and increasing diatom concentration indicate increasing productivity in the south-eastern part. Rising numbers of ostracode valves and higher TIC and TOC contents in both sediment cores indicate an increase in productivity during the late 1980s. A slight increase in productivity near Sveti Naum continued from the early 1990s until 2009, witnessed by rising TC, TIC, and TOC content and a generally high number of ostracode valves and ostracode diversity. The area near the City of Struga (site of urban pollution) is also characterized by rising TOC and TIC contents and, furthermore, by increasing Cu, Fe, Pb, and Zn concentrations since the early 1990s. The recent reduction in the number of ostracode valves and ostracode diversity is probably caused by a higher heavy metal load into the lake. This suggests that living conditions for the endemic species in Lake Ohrid have become less favourable in the northern part of the lake, which might threaten the unique flora and fauna of Lake Ohrid. © 2014, Springer Science+Business Media Dordrecht.
1642.
Post-rift geodynamics of the Songliao Basin, NE China: Origin and significance of T11 (Coniacian) unconformity
Tectonophysics,
6341-18
2014
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Deposition; Geodynamics; Lakes; Petroleum reservoirs; Structural geology; Tectonics; Volcanoes, Basin inversions; Northeast Asia; Post-rift; Songliao basin; Unconformity, Petroleum reservoir engineering, Coniacian; depositional environment; depositional sequence; geodynamics; lacustrine deposit; paleoenvironment; plate tectonics; rifting; sedimentary basin; tectonic reconstruction; unconformity, China; Songliao Basin, Ostracoda
Abstract: ▾ The T11 unconformity lies between the Qingshankou and Yaojia Formations in the post-rifting sequence of the Cretaceous Songliao Basin, NE China. It is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage. We present the interpretations from new seismic surveys and cored sections of the Cretaceous Continental Scientific Drilling borehole (CCSD-SK-1) in order to resolve the nature and origin of T11 unconformity. The T11 is often a low-angle unconformity with underlying Qingshankou Formation having been deformed and eroded prior to deposition of the Yaojia Formation. In the post-rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment, documented by reddening of the lacustrine mudstone, extinction of the ostracod assemblages and a great increase of coarse detrital inputs. The sharp change of depositional environment, the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities, all happened simultaneously, immediately before the development of T11 unconformity, indicating a significant regional compressional uplift event in the basin. The timing of the T11 unconformity formation is within the interval 88-86.2. Ma. Correlations with coeval unconformities in other Cretaceous sedimentary basins in eastern Asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the Eurasian and Paleo-Pacific plates that culminated at 88-87. Ma. During this short interval the northeast Asian margin, in eastern China, South Korea, Japan and Russian Far East experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction. The post-rift basin tectonic inversion occurred during T11 (Coniacian) time; thereafter the basin again evolved in an extension regime. Two subsidence phases in post-rift history took place as the direct consequence of Coniacian compression peak, which defined the distribution of oil sources and reservoirs. © 2014 Elsevier B.V.
1641.
Potential influence of sulphur bacteria on Palaeoproterozoic phosphogenesis
Nature Geoscience,
7
(1)
20-24
2014
ISSN: 17520894DOI:10.1038/ngeo2005
Abstract: ▾ All known forms of life require phosphorus, and biological processes strongly influence the global phosphorus cycle. Although the record of life on Earth extends back to 3.8 billion years ago and the advent of biological phosphate processing can be tracked to at least 3.5 billion years ago, the earliest known P-rich deposits appeared only 2 billion years ago. The onset of P deposition has been attributed to the rise of atmospheric oxygen 2.4-2.3 billion years ago and the related profound biogeochemical shifts, which increased the riverine input of phosphate to the ocean and boosted biological productivity and phosphogenesis. However, the P-rich deposits post-date the rise of oxygen by about 300 million years. Here we use microfabric, trace element and carbon isotope analyses to assess the environmental setting and redox conditions of the 2-billion-year-old P-rich deposits of the vent-or seep-influenced Zaonega Formation, northwest Russia. We identify phosphatized microorganism fossils that resemble modern methanotrophic archaea and sulphur-oxidizing bacteria, analogous to organisms found in modern seep settings and upwelling zones with a sharp redoxcline. We therefore propose that the P-rich deposits in the Zaonega Formation were formed by phosphogenesis mediated by sulphur bacteria, similar to modern sites, and by the precipitation of calcium phosphate minerals on microbial templates during early diagenesis. © 2014 Macmillan Publishers Limited.
1640.
Preparation for drilling well IDDP-2 at Reykjanes
Geothermics,
49119-126
2014
ISSN: 0375-6505Keywords:▾
Supercritical fluids, Iceland Deep Drilling Project, IDDP-2 well at Reykjanes, Black smoker analog
Abstract: ▾ Preparation has begun for drilling the second deep IDDP well into the saline Reykjanes high-temperature field in SW-Iceland. The site selection for the IDDP-2 drillhole is under review and the prime candidate is essentially the same as the 1st priority site suggested for the Reykjanes field in 2003. More recent drillhole data and new MT surveys have amplified the justification for selecting that site. Deep drilling to 4–5km depth is an important part of the HS Orka exploration strategy for enhanced power production, either by direct use of high energy steam, or by attempting to enhance the field performance by re-injecting geothermal fluid deep into very hot rocks. Pending on several decisions and development in Iceland, outside the control of the IDDP energy consortium, the IDDP-2 well might possibly be drilled to 4–5km depth as early as 2014.
1639.
Probing reservoir-triggered earthquakes in Koyna, India, through scientific deep drilling
Scientific Drilling,
185-9
2014
ISSN: 18168957
Publisher: Copernicus GmbH
Keywords:▾
Drilling; Energy resources, Continental scientific drillings; Course of action; Deep drilling; Detailed planning; Near fields; Salient features; Scientific deep-drilling; Triggered Earthquakes, Earthquakes
Abstract: ▾ We report here the salient features of the recently concluded International Continental Scientific Drilling Program (ICDP) workshop in Koyna, India. This workshop was a sequel to the earlier held ICDP workshop in Hyderabad and Koyna in 2011. A total of 49 experts (37 from India and 12 from 8 other countries) spent 3 days reviewing the work carried out during the last 3 years based on the recommendations of the 2011 workshop and suggesting the future course of action, including detailed planning for a full deep drilling proposal in Koyna, India. It was unanimously concluded that Koyna is one of the best sites anywhere in the world to investigate genesis of triggered earthquakes from near-field observations. A broad framework of the activities for the next phase leading to deep drilling has been worked out.
1638.
Quaternary forest associations in lowland tropical West Africa
Quaternary Science Reviews,
847 – 25
2014
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Forestry; Isotopes; Lakes; Plants; Pollen; Ashanti; Georgia; Ghana; Lake Bosumtwi; Savannah; United States; West Africa; Amaranthaceae; Caryophyllaceae; Celtis; Cyperaceae; Macaranga; Moraceae; Poaceae; Trema; Uapaca; Isotopes; Lakes; Vegetation; Assemblage composition; Ghana; Interglacial periods; Marine Isotope Stage 7; Pollen; Quaternary; Terrestrial pollen records; West Africa; forest; fossil record; global climate; Holocene; interglacial; marine isotope stage; pollen; Quaternary; savanna; vegetation; Forestry
Abstract: ▾ Terrestrial fossil pollen records are frequently used to reveal the response of vegetation to changes in both regional and global climate. Here we present a fossil pollen record from sediment cores extracted from Lake Bosumtwi (West Africa). This record covers the last c. 520 thousand years (ka) and represents the longest terrestrial pollen record from Africa published to date. The fossil pollen assemblages reveal dynamic vegetation change which can be broadly characterized as indicative of shifts between savannah and forest. Savannah formations are heavily dominated by grass (Poaceae) pollen (>55%) typically associated with Cyperaceae, Chenopodiaceae-Amaranthaceae and Caryophyllaceae. Forest formations are palynologically more diverse than the savannah, with the key taxa occurring in multiple forest zones being Moraceae, Celtis, Uapaca, Macaranga and Trema. The fossil pollen data indicate that over the last c. 520ka the vegetation of lowland tropical West Africa has mainly been savannah; however six periods of forest expansion are evident which most likely correspond to global interglacial periods. A comparison of the forest assemblage composition within each interglacial suggests that the Holocene (11-0ka) forest occurred under the wettest climate, while the forest which occurred at the time of Marine Isotope Stage 7 probably occurred under the driest climate. © 2013 The Authors.
1637.
Resolution of non-double-couple components in the seismic moment tensor using regional networks-i: A synthetic case study
Geophysical Journal International,
196
(3)
1869-1877
2014
ISSN: 0956540XAbstract: ▾ We perform a detailed synthetic study on the resolution of non-double-couple (non-DC) components in the seismic moment tensors from short-period data observed at regional networks designed typically for monitoring aftershock sequences of large earthquakes. In addition, we test two different inversion approaches-a linear full moment tensor inversion and a nonlinear moment tensor inversion constrained to a shear-tensile source model. The inversions are applied to synthetic first-motion P- and S-wave amplitudes, which mimic seismic observations of aftershocks of the 1999 Mw = 7.4 Izmit earthquake in northwestern Turkey adopting a shear-tensile source model. To analyse the resolution capability for the obtained non-DC components inverted, we contaminate synthetic amplitudes with random noise and incorporate realistic uncertainties in the velocity model as well as in the hypocentre locations. We find that the constrained moment tensor inversion yields significantly smaller errors in the non-DC components than the full moment tensor inversion. In particular, the errors in the compensated linear vector dipole (CLVD) component are reduced if the constrained inversion is applied. Furthermore, we show that including the S-wave amplitudes in addition to P-wave amplitudes into the inversion helps to obtain reliable non-DC components. For the studied station configurations, the resolution remains limited due to the lack of stations with epicentral distances less than 15 km. Assuming realistic noise in waveform data and uncertainties in the velocity model, the errors in the non-DC components are as high as ±15 per cent for the isotropic and CLVD components, respectively, thus being non-negligible in most applications. However, the orientation of P- and T-axes is well determined even when errors in the modelling procedure are high. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.
1636.
Paleoenvironmental conditions define current sustainability of microbial populations in Laguna Potrok Aike sediments, Argentina
Aquatic Sciences,
76
(1)
101 – 114
2014
1635.
Magnetic fabrics in deformed metaperidotites of the Outokumpu Deep Drill Core, Finland: Implications for a major crustal shear zone
Tectonophysics,
629224 – 237
2014
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Finland; Outokumpu; Pohjois-Karjala; Deformation; Drills; Ferrimagnetism; Horizontal wells; Infill drilling; Iron ores; Magnetic anisotropy; Magnetic susceptibility; Magnetite; Paramagnetism; Core drilling; Magnetism; Tectonics; Borehole measurements; Deep drilling; Ferrimagnetic minerals; Finland; Magnetic anomalies; Magnetic fabrics; Magnetic foliation; Outokumpu area; High-strain zones; Magnetic minerals; crustal structure; deformation; magnetic anisotropy; magnetic anomaly; magnetic fabric; magnetic mineral; magnetic susceptibility; peridotite; shear zone; deep drilling; geomagnetism; petrofabric; tectonic setting; Core drilling; Magnetic anisotropy
Abstract: ▾ The Outokumpu (OKU) assemblage was studied in drill cores from the 2516m deep OKU Deep Drill Hole, Finland, and we observed that the strongest magnetic anomalies found in borehole measurements are related to three ferrimagnetic metaperidotite units with magnetic susceptibilities of up to 93×10-3SI separated by paramagnetic rock units. The main ferrimagnetic minerals are magnetite and minor pyrrhotite. Magnetic fabric studies were done in order to examine deformation within the OKU assemblage during the collisional deformation event 1.9Ga ago. Well-defined magnetic axes (kmax, kmin) and nearly horizontal magnetic foliation subparallel to the macroscopic foliation occur at the top and the bottom of the OKU formation. Low- and high-field AMS measurements showed that ferri- and paramagnetic subfabrics are coaxial. Paramagnetic units intercalated between the ferrimagnetic units show mostly triaxial magnetic fabrics, and low degrees of magnetic anisotropy values (P'<1.3) with a high variation of the shape factor (T) from prolate to oblate shapes. P' of the ferrimagnetic metaperidotite is high and range between 1.3 and 3.6 and T tends to more oblate shapes (T>0). Ferrimagnetic unit 2 shows the highest magnetic susceptibility and P' up to 5.6, which is related to a high amount of magnetite and pyrrhotite mostly concentrated in huge aggregates and veins. Alignment of magnetic minerals parallel with the structural foliation and the high P' values in the ferrimagnetic metaperidotite indicate that magnetic fabric was acquired in a high strain zone. The magnetic fabrics represent shear zone (SC) fabrics, which have been formed during early obduction-related deformation of the Svecofennian orogeny. The stacked sequence of the ferri- and paramagnetic metaperidotite bodies can be interpreted as a thrust system with an imbricate fan, in which three individual listric thrust sheets occur. This interpretation is in accordance with previous tectonic models of the Outokumpu area. © 2014 Elsevier B.V.
1634.
Origin and palaeoenvironmental significance of C25 and C27 n-alk-1-enes in a 25,000-year lake-sedimentary record from equatorial East Africa
Geochimica et Cosmochimica Acta,
14589-102
2014
ISSN: 00167037
Publisher: Elsevier Ltd
Keywords:▾
accumulation rate; alkene; climate variation; cyanobacterium; geological record; green alga; lacustrine deposit; Last Glacial Maximum; monsoon; paleoclimate; paleoenvironment; solar radiation; suspended particulate matter, Kilimanjaro [Kilimanjaro (RGA)]; Kilimanjaro [Tanzania]; Lake Challa; Tanzania
Abstract: ▾ We studied the distribution of long-chain alkenes (n-C23 to n-C31) in well-dated sediments from Lake Challa, a deep crater lake near Mt. Kilimanjaro in equatorial East Africa, to reveal signatures of palaeo-environmental and palaeo-climatic changes affecting the production of these compounds during the last 25kyr. The apolar fractions of organic sediment extracts dated to the last 16kyr showed an unusual dominance of δ13C-depleted n-C25:1 and n-C27:1 alk-1-enes. These alkenes were not detected in soil and litter from near the shoreline and from the inner rim of the crater, pointing to an autochthonous, aquatic source. Analysis of suspended particulate matter indicated that the n-alk-1-enes are produced in the well-oxygenated upper 30m of the water column, indicating a phytoplanktonic origin. Sedimenting particles collected monthly from December 2006 to November 2007 showed increased fluxes of n-alk-1-enes following the locally prominent short rain season in November-December. Green algae and/or cyanobacteria were identified as candidate sources of these alkenes. Production of the n-C25:1 and n-C27:1 alkenes in Lake Challa was much reduced during the Last Glacial Maximum and early late-glacial period, suggesting a temperature or CO2 effect on habitat suitability. We explored the potential of n-alk-1-ene accumulation rates, and of a derived Alkene Index [n-C27:1]/([n-C25:1]+[n-C27:1]), to record longer-term climatic changes. The Alkene Index record of Lake Challa over the past 25kyr shows clear periodicity with a dominant frequency of ~2.3kyr, potentially indicative of monsoon variability directly or indirectly forced by variation in solar radiation. © 2014 Elsevier Ltd.
1633.
Modelling of temperature conditions near the bottom of well IDDP-1 in Krafla, Northeast Iceland
Geothermics,
4949-57
2014
ISSN: 0375-6505Keywords:▾
Geothermal, Krafla, IDDP-1, Magma intrusion, Temperature conditions, Modelling, Superheated steam
Abstract: ▾ The transient temperature conditions near the bottom of well IDDP-1 in Krafla, which was drilled into a magma intrusion, have been simulated by some simple models of: (i) evolution of temperature conditions at the magma intrusion, (ii) cooling of the producing zone, a permeable layer above the intrusion, due to circulation losses during drilling and subsequent injection, (iii) reheating of the permeable layer after drilling and (iv) temperature evolution during the early phases of discharge testing in 2010. The modelling is not definitive, and does not consider later, more long-term flow testing (2011–2012), because the necessary down-hole data are lacking. However, results indicate that the evolution of the temperature conditions can be explained by these models. If the magma was emplaced during the most recent Krafla volcanic episode 25–35 years ago, the intrusion must have a thickness of at least 50–100m. The effective thickness of the permeable layer is estimated to be about 45m and its equilibrium temperature to be 390–400°C. No direct contact of the fluid with the magma is needed to explain the superheated steam discharged by the well. The situation near the bottom of the well clearly warrants further study, both through more advanced modelling and input of further data. The IDDP-1 well had to be quenched in July 2012. Whether it can maintain in the long-term the high energy output (15–40MWe), achieved during discharge testing, depends on sufficient recharge and efficient heat-exchange, if it can be rehabilitated. Carefully executed reinjection may be the solution if long-term recharge is not sufficient.
1632.
Rock-magnetic signature of precipitation and extreme runoff events in south-eastern Patagonia since 51,200calBP from the sediments of Laguna Potrok Aike
Quaternary Science Reviews,
98110 – 125
2014
Keywords:▾
Argentina; Laguna Potrok Aike; Patagonia; Santa Cruz [Argentina]; Catchments; Demagnetization; Deposits; Geomagnetism; Iron; Lakes; Magnetization; Runoff; Sedimentology; Sediments; Stratigraphy; Lacustrine sediments; Laguna potrok aike; Mass movement; Paleo-environment; Rock magnetism; facies; geochronology; hematite; isotherm; lacustrine deposit; last glaciation; magnetization; paleoenvironment; precipitation (climatology); runoff; sedimentary sequence; sulfide; Sedimentary rocks
Abstract: ▾ A 106-m long sediment sequence from the maar lake Laguna Potrok Aike in southern Patagonia was recovered in the framework of the International Continental Scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO). About half of the sedimentary sequence is composed of mass movement deposits (MMDs) and the event-corrected record reaches back to 51,200calBP. Here we present a high-resolution rock-magnetic study revealing two sedimentary facies associated with MMDs and characterized by two different types of spurious gyroremanent magnetization (GRM) acquired during static alternating field demagnetization. The first rock-magnetic signature is detected in MMDs composed of reworked sand and tephra material. The signature consists of GRM acquired during demagnetization of the natural remanent magnetization (NRM) and other rock-magnetic properties typical of iron sulfides such as greigite. We interpret these intervals as authigenic formation of iron sulfides in suboxic conditions within the MMD. The second rock-magnetic signature consists of a series of 10 short intervals located on the top of MMDs characterized by GRM acquisition during demagnetization of the isothermal remanent magnetization (IRM). Based on geological, limnological, stratigraphic and climatic evidence these layers are interpreted as reflecting pedogenic hematite and/or goethite brought to the lake by runoff events related to precipitation and permafrost melt. The pedogenic iron minerals mobilized from the catchment most likely settled out of suspension on top of MMDs after a rapid remobilization event. The series of runoff events corresponds to periods of increased lacustrine productivity in Laguna Potrok Aike and are coeval within the limit of the chronology to warm periods of the Last Glacial as recorded in Antarctica, the deglaciation in the mid-latitudes of the Southern Hemisphere and enhanced precipitation during the Early Holocene in southeastern Patagonia. © 2014 Elsevier Ltd.
1631.
Lithology of the long sediment record recovered by the ICDP Dead Sea Deep Drilling Project (DSDDP)
Quaternary Science Reviews,
102149-165
2014
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Glacial geology; Infill drilling; Lakes; Lithology; Magnetic susceptibility; Salinity measurement; Sea level; Sedimentology; Stratigraphy, Deep drilling; Hypersaline lakes; Laminated sediments; Paleoclimates; Sediment facies, Sediments, deep drilling; depositional sequence; facies; Holocene; hypersaline environment; lithology; magnetic susceptibility; ocean basin; outcrop; paleoclimate; paleoenvironment; sediment core; sedimentation; sequence stratigraphy; water depth, Dead Sea
Abstract: ▾ The sedimentary sections that were deposited from the Holocene Dead Sea and its Pleistocene precursors are excellent archives of the climatic, environmental and seismic history of the Levant region. Yet, most of the previous work has been carried out on sequences of lacustrine sediments exposed at the margins of the present-day Dead Sea, which were deposited only when the lake surface level rose above these terraces (e.g. during the Last Glacial period) and typically are discontinuous due to major lake level variations in the past. Continuous sedimentation can only be expected in the deepest part of the basin and, therefore, a deep drilling has been accomplished in the northern basin of the Dead Sea during winter of 2010-2011 within the Dead Sea Deep Drilling Project (DSDDP) in the framework of the ICDP program. Approximately 720m ofsediment cores have been retrieved from two deep and several short boreholes. The longest profile (5017-1), revealed at a water depth of ~300m, reaches 455m below the lake floor (blf, i.e. to ~1175m below global mean sea level) and comprises approximately the last 220-240ka. The record covers the upper part of the Amora (penultimate glacial), the Last Interglacial Samra,the Last Glacial Lisan and the Holocene Ze'elim Formations and, therewith, two entire glacial-interglacial cycles. Thereby, for the first time, consecutive sediments deposited during the MIS 6/5, 5/4 and 2/1 transitions were recovered from the Dead Sea basin, which are not represented in sediments outcropping on the present-day lake shores. In this paper, we present essential lithological data including continuous magnetic susceptibility and geochemical scanning data and the basic stratigraphy including first chronological data of the long profile (5017-1) from the deep basin. The results presented here (a) focus on the correlation of the deep basin deposits with main on-shore stratigraphic units, thus providing a unique comprehensive stratigraphic framework for regional paleoenvironmental reconstruction, and (b) highlight the outstanding potential of the Dead Sea deep sedimentary archive to record hydrological changes during interglacial, glacial and transitional intervals. © 2014 Elsevier Ltd.
1630.
Long-term freshening of the Dead Sea brine revealed by porewater Cl- and δO18 in ICDP Dead Sea deep-drill
Earth and Planetary Science Letters,
40094-101
2014
ISSN: 0012821X
Publisher: Elsevier
Keywords:▾
Calcium; Chlorine; Chlorine compounds; Evaporation; Glacial geology; Gypsum; Isotopes; Lakes; Mixing; Oxygen; Paleolimnology; Shock tubes; Turbulent flow, Chloride; Dead sea; Oxygen isotopes; Pore brine profiles; Quarter-nary, Brines, brine; Chinese Continental Scientific Drilling Project; chloride; isotopic composition; oxygen isotope; paleolimnology; Quaternary, Dead Sea
Abstract: ▾ The geological evolution of the unique Dead Sea Ca-chloride brine has been the focus of many research efforts for several decades. These studies relied on the information obtained from sedimentary exposures of the marginal terraces of the modern Dead Sea, mostly documenting the history of the surface lake brine during its high stands periods. The present study is the first attempt to establish the history of the deepest part of the lake by direct measurements of the chemical and isotopic composition of pore-fluids that were extracted from cores drilled during 2011 by ICDP in the deep basin of the Dead Sea at water depth of 300 m. The vertical profiles of chloride (Cl-) and oxygen isotopes (δO18) in pore brines reveal a substantial decrease in the salinity of the hyper-saline lake during the last glacial and particularly during MIS2 (~31-17 kaBP). The Cl- concentration of the deep brine in the lake decreased gradually, reaching a minimum of less than 2/3 of its present value while the δO18 increased to maximum of ~7‰ (3‰ higher than today). The low Cl- indicates significant dilution of the bottom water mass (hypolimnion) of Lake Lisan (the last glacial predecessor of the modern Dead Sea) during its highest stand period. Beforehand, during the interglacial and later during the post-glacial and the Holocene the Cl- concentrations and δO18 values were similar to those of the modern Dead Sea. The slow dilution of the deep Ca-chloride brine was caused probably by continuous turbulent mixing of the hypolimnion with the less saline high δO18 epilimnetic brine, across the epilimnion/hypolimnion interface (EHI). While the increase in δO18 during the salinity decrease of Lake Lisan is a result of "normal" evaporation of the less saline epilimnetic brine, the post-glacial δO18 decrease (contemporaneous with salinity increase) is attributed to the "reversed" behavior of δO18 during evaporation of high salinity brine. During the long freshening period the hypolimnion was enriched with dissolved sulfate supplied by the freshwater and transported by the turbulent mixing across the EHI until reaching gypsum saturation that commenced massive gypsum deposition at the end of this period, when full overturn took place. © 2014 Elsevier B.V.
1629.
Magnetic susceptibility logging of Chicxulub proximal impact breccias in the Santa Elena borehole: Implications for emplacement mode
Studia Geophysica et Geodaetica,
58
(1)
100-120
2014
Abstract: ▾ Magnetic susceptibility logging is used to study the impact breccias in the Chicxulub crater. The basic premise is that the high contrasts in magnetic properties can be used to characterize the breccias. The Santa Elena borehole was drilled 110 km radial distance from crater center and sampled a 172 m thick sequence of impact breccias, between 332 and 504 m depth. Breccia units are distinguished from differences in composition, size, and relative contents of clasts, type of matrix and textural and lithological assemblages, which can be resolved in the susceptibility logs. The whole-core log shows characteristic variation patterns with high, intermediate and low susceptibilities. High resolution logging of matrix and clasts records the heterogeneous nature of impactites, with higher variability at smaller spatial scales. Measurements confirm that diamagnetic susceptibilities characterize the carbonate clasts, high susceptibilities the basement granitic clasts and intermediate values the silicate melt-rich and silicate-poor matrix. Intermediate variable susceptibilities characterize breccias rich in melt particles. Correlation of matrix and clast logs with whole-core log shows that signal is controlled by the matrix. Logs for clast shows a discrete distribution with peaks of intermediate to high values, which correlate with large clast distributions. The ejecta blanket includes the fallback suevites rich in silicate melt particles and shocked minerals, the high temperature vapor deposits from ejecta curtain collapse and high velocity basal flows, and the carbonate rich deposits from lateral basal flows and secondary cratering. Late fallback suevites record minor turbulent conditions resulting from progressive cooling of the ejecta plume. © 2013 Institute of Geophysics of the ASCR, v.v.i.
1628.
Magnetostratigraphy of sediments from Lake El'gygytgyn ICDP Site 5011-1: paleomagnetic age constraints for the longest paleoclimate record from the continental Arctic
Climate of the Past,
10
(2)
623-642
2014
ISSN: 18149324
Publisher: European Geosciences Union
Keywords:▾
climate variation; crater; deposition; lacustrine deposit; lamination; magnetite; magnetostratigraphy; mass movement; paleoclimate; paleomagnetism; Pliocene; proxy climate record; remanent magnetization; scanning electron microscopy; sediment core, Arctic; Chukchi; Elgygytgyn Lake; Russian Far East; Russian Federation
Abstract: ▾ Paleomagnetic measurements were performed on sediments drilled from ICDP Site 5011-1 in Lake El'gygytgyn (67°30' N, 172°05' E) located in Far East Russian Arctic. The lake partly fills a crater formed by a meteorite impact 3.58 ± 0.04 Ma ago. Sediments from three parallel cores (5011-1A, 5011-1B and 5011-1C), recovered from the middle part of the lake, yield a total of 355 m of sediment. Sediments are characterized by a variable lithology, where intervals of homogenous and laminated sediments alternate, and mass movement deposits occur frequently along the sediment profile. Mineral magnetic investigation made on sediments enclosed in core catchers suggests that magnetic carrier in these sediments is partly maghemitized Ti-rich pseudo-single domain magnetite. Its detrital origin can be shown by mineral magnetic measurements and SEM-EDS analyses performed on mini-sized cylindrical rock samples, polished rock sections and creek sediments. The intensity of the natural remanent magnetization in the sediments is high with a range from about 1 to 1000 mA mg-1. Most of the sediments carry a stable magnetization interpreted as primary depositional remanent magnetization. Characteristic inclination data show alternating intervals of steep positive and negative inclinations that are used to assign magnetic polarity to the lake sediment profile. This is a rather straightforward procedure owing to the mainly high quality of data. The Matuyama/Gauss (M/G) (2.608 Ma) and Brunhes/Matuyama (B/M) (0.780 Ma) reversals were recognized in the sediments. The Mammoth and Kaena reversed subchrons were identified during the Gauss chron, and the Olduvai and Jaramillo normal subchrons as well as the Réunion and Cobb Mountain cryptochrons were identified during the Matuyama chron. Sediments also provide a record of the Olduvai precursor and Intra-Jaramillo geomagnetic excursions. Sediment deposition rate is highest at the base of the sequence laid down in the early Gauss chron, when the deposition rate is approximately 44 cm kyr-1. Sediment deposition decelerates upcore and it is an order of magnitude lower during the Brunhes chron in comparison with the early Gauss chron. Decrease in sediment deposition in the late Pliocene probably relates to atmospheric and oceanic reorganization heralding the onset of Quaternary climate change. The high-quality magnetostratigraphy reconstructed from Lake El'gygytgyn sediments provides 12 first-order tie points to pin down the age of the longest paleoclimate record from the continental Arctic. © 2014 Author (s).
1627.
Modeling submarine landslide-generated waves in lake Ohrid, Macedonia/Albania
Advances in Natural and Technological Hazards Research,
37497 – 506
2014
ISSN: 18789897
Publisher: Springer Netherlands
Abstract: ▾ We study potential tsunami hazards associated with submarine landslides in Lake Ohrid, Macedonia/Albania. The transboundary Lake Ohrid located on the Balkan Peninsula shared by Macedonia and Albania is considered to be the oldestcontinuously existing lake in Europe (2–5 Ma), though the age and the origin are not completely unraveled to date. Previous studies by means of hydroacoustic methods have shown that the western margin of Lake Ohrid has a long history of mass wasting. Based on seismic data, slide deposits are found in different stratigraphic levels as well as on the lake floor where they have affected a large area. This study is focused on the well-studied Udenisht Slide Complex covering an area of 27 km2 within the southwestern part of Lake Ohrid. The Udenisht slide is by far the largest mass movement with an average thickness of 30–40 m and an estimated volume of about 0.11 km3. It is therefore well within the limits of submarine landslides that are known to be capable of triggering tsunamis. Using numerical modeling, the propagation of a landslide-generated tsunami with an initial wave height of more than 5 m has been calculated. Run-up heights estimated for coastal communities around the lake are moderate in the north (2–3 m) can reach up to 10 m directly at the site where the slide initiated. This study is a first generation of landslide tsunami hazard assessment for Lake Ohrid and further detailed modeling is recommended for the region. © Springer International Publishing Switzerland 2014.
1626.
Modern seasonality in Lake Challa (Kenya/Tanzania) and its sedimentary documentation in recent lake sediments
Limnology and Oceanography,
59
(5)
1621-1636
2014
Abstract: ▾ From November 2006 to January 2010, a sediment trap that was cleared monthly was deployed in Lake Challa, a deep stratified freshwater lake on the eastern slope of Mt. Kilimanjaro in southern Kenya. Geochemical data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to characterize the effect of single parameters on productivity and sedimentation processes in the crater basin. During the southern hemisphere summer (November—March), when the water temperature is high and the lake is biologically productive (nondiatom algae), calcite predominated in the sediment trap samples. During the “long rain” season (March—May) a small amount of organic matter and lithogenic material caused by rainfall appeared. This was followed by the cool and windy months of the southern hemisphere winter (June—October) when diatoms were the main component, indicating a diatom bloom initiated by improvement of nutrient availability related to upwelling processes. The sediment trap data support the hypothesis that the light—dark lamination couplets, which are abundant in Lake Challa cores, reflect seasonal delivery to the sediments of diatom-rich particulates during the windy months and diatom-poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Niño—Southern Oscillation (ENSO)-related rainfall and drought cycles, exert a strong influence on the magnitude and geochemical composition of particle export to the hypolimnion of Lake Challa.
1625.
Observations of the genus Cyclotella (Kützing) Brébisson in ancient lakes Ohrid and Prespa and a description of two new species c. paraocellata sp. nov. and C. prespanensis sp. nov
Nova Hedwigia,
98
(3-4)
313 – 340
2014
ISSN: 00295035
Publisher: Gebruder Borntraeger Verlagsbuchhandlung
Abstract: ▾ Several taxa from the genus Cyclotella observed in two ancient sister lakes, Prespa and Ohrid were studied and compared to the regionally common species Cyclotella ocellata. Two new species are described from Lake Prespa and additionally Cyclotella thienemannii var. minuscula from Lake Ohrid is formally transferred to Cyclotella minuscula (Jurilj) Cvetkoska stat. nov. Cyclotella paraocellata sp. nov. is compared to C. ocellata and is characterized by a large morphological variability in the fossil and recent diatom assemblages. Cyclotella prespanensis sp. nov. is described and distinguished as a separate taxon by its valve size range, colliculate central area, stria density and number and position of marginal fultoportulae and rimoportulae. The investigation reveals C. ocellata and C. minuscula as the only taxa of the genus Cyclotella present in fossil and contemporary diatom assemblages from both Lake Ohrid and Lake Prespa. © 2014 J. Cramer in Gebr. Borntraeger Verlagsbuchhandlung, Stuttgart. Germany.
1624.
More than one million years of history in Lake Ohrid cores
Eos,
95
(3)
25 – 26
2014
ISSN: 00963941
Publisher: American Geophysical Union
Keywords:▾
Lake Ohrid; climate variation; core analysis; deep drilling; lacustrine deposit; natural hazard; paleoclimate; paleolimnology; paleontology; stratigraphic correlation; Earth
Abstract: ▾ Continental scientific drilling is an important tool for exploring natural and anthropogenic processes on Earth. In past decades the results obtained from lake drilling projects contributed significantly to a better understanding of short-term and long-term climate change and natural hazards. ©2014. American Geophysical Union. All Rights Reserved.
1623.
Morphology and ultrastructure of Hippodonta qinghainensis sp. Nov. (bacillariophyceae), a new diatom from lake Qinghai, China
Phytotaxa,
186
(2)
061 – 074
2014
ISSN: 11793155
Publisher: Magnolia Press
Keywords:▾
Bacillariophyceae; Bacillariophyta; Hippodonta
Abstract: ▾ A new medium-sized species of Hippodonta (Bacillariophyceae) is described from Lake Qinghai, China. The morphology and ultrastructure of Hippodonta qinghainensis sp. nov. are described using light and scanning electron microscopy. This new species is compared with similar species of Hippodonta using conventional and geometric morphometric analyses. Hippodonta qinghainensis can be separated from the other species of Hippodonta by a unique combination of characters that include an elliptic-lanceolate to rhombic-lanceolate valve shape, non protracted apices, the absence of fascia, relatively coarse, uniseriate striae and the presence of two rows of lineolae around the valves apices. © 2014 Magnolia Press.
1622.
New isotopic and geochemical data from the Palaeoproterozoic Pechenga Greenstone Belt, NW Russia: Implication for basin development and duration of the volcanism
Precambrian Research,
24551--65
2014
1621.
New proposed drilling at Surtsey Volcano, Iceland: SUSTAIN workshop; Heimaey Island, Iceland, 30 September to 4 October 2014
Eos (United States),
95
(51)
488
2014
ISSN: 00963941
Publisher: Blackwell Publishing Ltd
Keywords:▾
colonization; conference proceeding; drilling; hydrothermal alteration; microbial activity; mineral; pyroclastic deposit; rift zone; tephra; volcanic eruption; volcanism; World Heritage Site, Iceland; Surtsey
Abstract: ▾ Surtsey, an isolated oceanic island and a World Heritage Site of the United Nations Educational, Scientific and Cultural Organization, is a uniquely well-documented natural laboratory for investigating processes of rift zone volcanism, hydrothermal alteration of basaltic tephra, and biological colonization and succession in surface and subsurface pyroclastic deposits. Deposits from Surtsey's eruptions from 1963 to 1967 were first explored via a 181-meter hole drilled in 1979 by the U.S. Geological Survey and Icelandic Museum of Natural History. © 2014. American Geophysical Union. All Rights Reserved.
1620.
Noble gas residence times of saline waters within crystalline bedrock, Outokumpu Deep Drill Hole, Finland
Geochimica et Cosmochimica Acta,
145159 – 174
2014
ISSN: 00167037
Publisher: Elsevier Ltd
Keywords:▾
Baltic Shield; East European Craton; Finland; Outokumpu; Pohjois-Karjala; bedrock; carbon dioxide; diffusion; groundwater; hydrochemistry; hydrogen; isotopic composition; noble gas; residence time
Abstract: ▾ Noble gas residence times of saline groundwaters from the 2516m deep Outokumpu Deep Drill Hole, located within the Precambrian crystalline bedrock of the Fennoscandian Shield in Finland, are presented. The accumulation of radiogenic (4He, 40Ar) and nucleogenic (21Ne) noble gas isotopes in situ together with the effects of diffusion are considered. Fluid samples were collected from depths between 180 and 2480m below surface, allowing us to compare the modelled values with the measured concentrations along a vertical depth profile. The results show that while the concentrations in the upper part are likely affected by diffusion, there is no indication of diffusive loss at or below 500m depth. Furthermore, no mantle derived gases were found unequivocally. Previous studies have shown that distinct vertical variation occurs both in geochemistry and microbial community structuring along the drill hole, indicating stagnant waters with no significant exchange of fluids between different fracture systems or with surface waters. Therefore in situ accumulation is the most plausible model for the determination of noble gas residence times. The results show that the saline groundwaters in Outokumpu are remarkably old, with most of the samples indicating residence times between ~20 and 50Ma. Although being first order approximations, the ages of the fluids clearly indicate that their formation must predate more recent events, such as Quaternary glaciations. Isolation within the crust since the Eocene-Miocene epochs has also direct implications to the deep biosphere found at Outokumpu. These ecosystems must have been isolated for a long time and thus very likely rely on energy and carbon sources such as H2 and CO2 from groundwater and adjacent bedrock rather than from the ground surface. © 2014 Elsevier Ltd.