All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
2144.
Integrated Paleoseismic Chronology of the Last Glacial Lake Lisan: From Lake Margin Seismites to Deep-Lake Mass Transport Deposits
Journal of Geophysical Research: Solid Earth,
123
(4)
2806 – 2824
2018
2143.
[English]
Sampling bias of fracture orientation: Tests using data from the kimama borehole, Snake River Plain, Idaho, USA
Publisher
American Rock Mechanics Association (ARMA)
2018
Department of Physics, UWI, Trinidad and Tobago; Inst. for Geophysical Research, Dept. of Physics, University of Alberta, Edmonton, AB T6G 2E1, Canada; Earth, Atmospheric, and Planetary Sciences Department, Purdue University, West Lafayette, IN, United States2142.
[English]
Krafla magma testbed: Understanding and using the magma-hydrothermal connection
Volume 42
,
Page 2396 – 2405
Publisher
Geothermal Resources Council
2018
ISBN:
0934412235
2141.
[English]
Krafla magma testbed (KMT): Engineering challenges of drilling into magma and extracting its energy
Volume 42
,
Page 2422 – 2434
Publisher
Geothermal Resources Council
2018
ISBN:
0934412235
2140.
Improving geothermal economics by utilizing supercritical and superhot systems to produce flexible and integrated combinations of electricity, hydrogen, and minerals
Volume 42
,
Page 1914 – 1927
2018
2139.
Ultra-high temperature drilling fluid technology of well Songke-2
钻井液与完井液,
35
(2)
29-34
2018
ISSN: 10015620
Publisher: 钻井液与完井液
Abstract: ▾ The well Songke-2 is a high temperature deep scientific exploration well deployed in the Songliao Basin, its purpose is to penetrate the Cretaceous formations to obtain the records of basal continental deposit. The bottom hole temperature has been predicted to be over 220 ℃. Measures for preventing borehole wall collapse are especially important in drilling the fourth and fifth intervals since borehole wall collapse has occurred previously in drilling the interbedded mudstone and sandstone in the Shahezi formation, and the broken tuff, mudstone and coal seam in the Huoshiling formation, which were to be penetrated by the fourth and fifth intervals of the well. Continuous coring was to be conducted in the fourth and fifth intervals, and frequent tripping of drill string gave a big challenge to borehole wall stabilization because of long time contact of the open hole with drilling fluid. The adoption of different drilling techniques in turn gave a challenge to drilling fluid. A high temperature polymer drilling fluid has been formulated to deal with these challenges. The composition of the drilling fluid is as follows: 1.0% bentonite + 2% attapulgite +0.2%KOH +(0.5%-1.0%) high MW filter loss reducer +1% moderate MW filter loss reducer + 2.5% filming agent + (2%-4%)SMC +2%FT +3%KCl + 2%NaCOOH +3% white oil. At the beginning of the fourth interval, the mud left over from the third interval was evaluated and converted for re-use in the fourth interval based on large amount of pilot tests. In the fifth interval, the property of the mud was greatly modified because of the needs for dealing with downhole troubles. When the downhole troubles were resolved, the mud property was gradually adjusted to a stable state. In field application the mud property was adjusted at all times in accordance with the requirements of drilling operations. The mud had good rheology at high temperatures and good high temperature stability. High temperature resistance of the mud formulation was 240 ℃ based on laboratory test. The mud property was still satisfactory even after hot rolling for 72 ℃, providing strong technical support for the success of drilling operation. The drilling fluid technology used in drilling the well Songke-2 is of guiding significance in improving job quality of drilling and reducing exploration cost. © 2018, The Editorial Board of Drilling Fluid & Completion Fluid. All right reserved.
2138.
Transmission electron microscopy of impact-generated platinum group element alloys from Barberton spherule layers: New clues to their formation
Meteoritics and Planetary Science,
53
(7)
1516 – 1536
2018
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ The oldest known large bolide impacts onto Earth are represented by approximately 3.47–3.2 Ga old Archean spherule layers of the Barberton Greenstone Belt (BGB) in South Africa and the Pilbara craton in West Australia. These layers were recognized as impact deposits by their excessively high platinum group element (PGE) contents that are indicative of an extraterrestrial component. This was followed by measurements of extraterrestrial Cr isotopic ratios, in some cases. Recently, the extraterrestrial PGE signature in Archean spherule layers from the BGB was localized and positively associated with the presence of submicrometer PGE alloy micronuggets associated with Ni,Cr-rich spinel. The actual formation of these platinum group mineral (PGM) phases has, however, not yet been resolved. Primary meteoritic particles from the impacting body, the products of impact melting, or condensation from impact vapor plumes have all been proposed as possible genetic process. Resolving this requires detailed microanalytical investigation of the internal microchemical and microstructural compositions, textural characteristics, and crystallographic relationships between the different phases. Here, we report the results of a first transmission electron microscopy (TEM) study of six such PGE microparticles enclosed in Ni-Cr spinel or occurring in groundmass of Barberton spherule layers from the BARB5 ICDP drill core and from the CT3 exploration core. Results include a variety of chemical and structural PGM compositions that are difficult to explain by a single process, leading to the conclusion that several processes may have been involved in the formation of PGMs in Archean spherule layers from the BGB. There is evidence supporting formation of these PGMs by exsolution from the spinel host phase, precipitation from a melt phase, and condensation from a gas phase (of the impact vapor plume). © The Meteoritical Society, 2018.
2137.
Towards an understanding of climate proxy formation in the Chew Bahir basin, southern Ethiopian Rift
Palaeogeography, Palaeoclimatology, Palaeoecology,
501111-123
2018
ISSN: 00310182
Publisher: Elsevier B.V.
Keywords:▾
alkalinity; authigenic mineral; catchment; clay mineral; climate variation; concentration (composition); evaporation; illitization; lacustrine deposit; mineral alteration; paleoclimate; potassium; precipitation (climatology); proxy climate record; salinity; wetting-drying cycle; Younger Dryas; zeolite, East African Rift; Ethiopian Rift
Abstract: ▾ Deciphering paleoclimate from lake sediments is a challenge due to the complex relationship between climate parameters and sediment composition. Here we show the links between potassium (K) concentrations in the sediments of the Chew Bahir basin in the Southern Ethiopian Rift and fluctuations in the catchment precipitation/evaporation balance. Our micro-X-ray fluorescence and X-ray diffraction results suggest that the most likely process linking climate with potassium concentrations is the authigenic illitization of smectites during episodes of higher alkalinity and salinity in the closed-basin lake, due to a drier climate. Whole-rock and clay size fraction analyses suggest that illitization of the Chew Bahir clay minerals with increasing evaporation is enhanced by octahedral Al-to-Mg substitution in the clay minerals, with the resulting layer charge increase facilitating potassium-fixation. Linking mineralogy with geochemistry shows the links between hydroclimatic control, process and formation of the Chew Bahir K patterns, in the context of well-known and widely documented eastern African climate fluctuations over the last 45,000 years. These results indicate characteristic mineral alteration patterns associated with orbitally controlled wet-dry cycles such as the African Humid Period (~15–5 ka) or high-latitude controlled climate events such as the Younger Dryas (~12.8–11.6 ka) chronozone. Determining the impact of authigenic mineral alteration on the Chew Bahir records enables the interpretation of the previously established μXRF-derived aridity proxy K and provides a better paleohydrological understanding of complex climate proxy formation. © 2018
2136.
Topographic control on shallow fault structure and strain partitioning near Whataroa, New Zealand demonstrates weak Alpine Fault
New Zealand Journal of Geology and Geophysics,
61
(1)
1-8
2018
ISSN: 00288306
Publisher: Taylor and Francis Asia Pacific
Keywords:▾
bedrock; fault; mechanical property; numerical model; plate boundary; strain partitioning; strength; stress field; tectonics; topographic effect, Alpine Fault Zone; New Zealand; South Island; West Coast [South Island]; Whataroa
Abstract: ▾ It is notoriously difficult to characterise the strength and stress states of major plate boundaries. By taking advantage of the well-constrained stress contribution of topography adjacent to a segmented section of the Alpine Fault, New Zealand, we have identified a mechanical mix that produces the distinct fault segmentation pattern seen in field observations. Slope-generated shear and normal stresses rotate the principal stresses relative to the regional tectonically derived stress state and under certain strength states influence the displacement pattern. Three-dimensional models show that the scale and form of the near-surface partitioning depend on both topographic relief and local fault strength relative to the bedrock. The models suggest the Alpine Fault is weak to moderately weak relative to the bedrock and is a single structure to within c. 500 m of the surface, above which segmentation occurs. Adjacent to the Alpine Fault, the stress state is highly variable. The intermediate principal stress, σ2, is rotated from tectonically dominated, near-vertical beneath ridges to near-horizontal beneath large valleys. Individual segments along the Alpine Fault dominated by strike-slip faulting, oblique thrusting or thrusting, can be identified by extracting the topographic contribution to the stress state from numerical models. © 2017 The Royal Society of New Zealand.
2135.
Three novel species of bacillariophyta (Diatoms) in the genera surirella and thalassiosira from pleistocene paleolake lorenyang (~2-1.6 ma) turkana basin, Kenya
Phytotaxa,
371
(3)
230 – 240
2018
ISSN: 11793155
Publisher: Magnolia Press
Abstract: ▾ Three novel species of Bacillariophyta (diatom) are described from the sediments of Paleolake Lorenyang, a large lake that existed in the Turkana Basin, Kenya during the Gelasian age of the Pleistocene Epoch. Sediment cores extracted as part of the Hominin Sites and Paleolakes Drilling Project (HSPDP) were sampled to provide a diatom-based paleoecological record of Paleolake Lorenyang. Preliminary results of the paleoecological analysis unearthed three novel species of diatoms belonging to Surirella and Thalassiosira in the Natoo Member of the Nachukui Formation. Comparisons of Surirella from Paleolake Lorenyang are made to previous reports of Surirella from modern lakes in East Africa and comparisons of Thalassiosira species from the paleolake are made to modern and fossil species reported from East Africa. This is a first report of diatoms in the Natoo Member, which has previously been described as a floodplain deposit, and thus provides evidence of the last occurrence of Paleolake Lorenyang within the Turkana Basin. Herein we describe a new species of Surirella and two Thalassiosira with remarks on morphology and evolution of East African Surirella and Thalassiosira. © 2018 Magnolia Press.
2134.
The world’s largest late to post-archaean asteroid impact structures
Modern Approaches in Solid Earth Sciences,
1461-78
2018
Abstract: ▾ As distinct from small to medium-size impact events, large asteroid impacts producing explosions more powerful than 107 TNT-equivalent, represented by craters and rebound domes larger than about 100 km in diameter have major consequences including the triggering of major seismic events, tsunami events and extinction episodes. Such events are manifested by the Archaean ~3.25–3.24 Ga impact cluster and associated transformation from greenstone-granite terrains to semi-continental assemblages (Glikson AY, Vickers J, Earth Planet Sci Lett 241:11–20, 2006). These impact events are considered in Chap. 6. The oldest identified mega-impact is the ~3 Ga Maniitsoq structure in southwest Greenland, while younger mega-impact structures >100 km in diameter include the Vredefort and Sudbury structures. Phanerozoic mega-impacts include the Woodleigh impact structure, Warburton twin structures, Chicxulub and Popigai structures. The global tectonic consequences of some of these mega-impacts are yet to be elucidated. © 2018, Springer International Publishing AG.
2133.
The world's largest late to post-archaean asteroid impact structures
Modern Approaches in Solid Earth Sciences,
1461-78
2018
Abstract: ▾ As distinct from small to medium-size impact events, large asteroid impacts producing explosions more powerful than 107 TNT-equivalent, represented by craters and rebound domes larger than about 100 km in diameter have major consequences including the triggering of major seismic events, tsunami events and extinction episodes. Such events are manifested by the Archaean ~3.25–3.24 Ga impact cluster and associated transformation from greenstone-granite terrains to semi-continental assemblages (Glikson AY, Vickers J, Earth Planet Sci Lett 241:11–20, 2006). These impact events are considered in Chap. 6. The oldest identified mega-impact is the ~3 Ga Maniitsoq structure in southwest Greenland, while younger mega-impact structures >100 km in diameter include the Vredefort and Sudbury structures. Phanerozoic mega-impacts include the Woodleigh impact structure, Warburton twin structures, Chicxulub and Popigai structures. The global tectonic consequences of some of these mega-impacts are yet to be elucidated. © 2018, Springer International Publishing AG.
2132.
The Lake CHAd Deep DRILLing project (CHADRILL) - targeting ~ 10 million years of environmental and climate change in Africa
Scientific Drilling,
2471 – 78
2018
ISSN: 18168957
Publisher: Copernicus GmbH
Keywords:▾
Biodiversity; Boring; Deposition; Infill drilling; Lakes; Sediments; Water levels; Continuous sequences; Depositional environment; Environmental records; Intertropical convergence zone; Microbial biodiversity; Monsoon circulations; Pleistocene sediments; Subsurface biosphere; Climate change
Abstract: ▾ At present, Lake Chad ( ~13°0 N, ~14° E) is a shallow freshwater lake located in the Sahel/Sahara region of central northern Africa. The lake is primarily fed by the Chari-Logone river system draining a ~600 000 km2 watershed in tropical Africa. Discharge is strongly controlled by the annual passage of the intertropical convergence zone (ITCZ) and monsoon circulation leading to a peak in rainfall during boreal summer. During recent decades, a large number of studies have been carried out in the Lake Chad Basin (LCB). They have mostly focused on a patchwork of exposed lake sediments and outcrops once inhabited by early hominids. A dataset generated from a 673m long geotechnical borehole drilled in 1973, along with outcrop and seismic reflection studies, reveal several hundred metres of Miocene-Pleistocene lacustrine deposits. CHADRILL aims to recover a sedimentary core spanning the Miocene-Pleistocene sediment succession of Lake Chad through deep drilling. This record will provide significant insights into the modulation of orbitally forced changes in northern African hydroclimate under different climate boundary conditions such as high CO2 and absence of Northern Hemisphere ice sheets. These investigations will also help unravel both the age and the origin of the lake and its current desert surrounding. The LCB is very rich in early hominid fossils (Australopithecus bahrelghazali; Sahelanthropus tchadensis) of Late Miocene age. Thus, retrieving a sediment core from this basin will provide the most continuous climatic and environmental record with which to compare hominid migrations across northern Africa and has major implications for understanding human evolution. Furthermore, due to its dramatic and episodically changing water levels and associated depositional modes, Lake Chad's sediments resemble maybe an analogue for lake systems that were once present on Mars. Consequently, the study of the subsurface biosphere contained in these sediments has the potential to shed light on microbial biodiversity present in this type of depositional environment. We propose to drill a total of ~1800m of poorly to semi-consolidated lacustrine, fluvial, and eolian sediments down to bedrock at a single on-shore site close to the shoreline of present-day Lake Chad. We propose to locate our drilling operations on-shore close to the site where the geotechnical Bol borehole (13°280 N, 14°440 E) was drilled in 1973. This is for two main reasons: (1) nowhere else in the Chad Basin do we have such detailed information about the lithologies to be drilled; and (2) the Bol site is close to the depocentre of the Chad Basin and therefore likely to provide the stratigraphically most continuous sequence. © Author(s) 2018.
2131.
Textural changes of graphitic carbon by tectonic and hydrothermal processes in an active plate boundary fault zone, Alpine Fault, New Zealand
Geological Society Special Publication,
453
(1)
205-223
2018
ISSN: 03058719
Publisher: Geological Society of London
DOI:10.1144/SP453.13
Keywords:▾
active fault; carbon; emplacement; fault zone; grain boundary; graphite; mobilization; plate boundary; strain; tectonic setting; texture, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ Graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization. We examine processes of graphitic carbon emplacement and deformation in the active Alpine Fault Zone, New Zealand by analysing samples obtained from Deep Fault Drilling Project (DFDP) boreholes. Optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain. Raman spectroscopy allowed interpretation of the degree of graphite crystallinity, which reflects both thermal and mechanical processes. In the amphibolite-facies Alpine Schist, highly crystalline graphite, indicating peak metamorphic temperatures up to 640°C, occurs mainly on grain boundaries within quartzo-feldspathic domains. The subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions (500-600°C), resulting in clustered (in protomylonites) and foliation-aligned graphite (in mylonites). In cataclasites, derived from the mylonitized schists, graphite is most abundant ( < 50% as opposed to < 10% elsewhere), and has two different habits: inherited mylonitic graphite and less mature patches of potentially hydrothermal graphitic carbon. Tectonic-hydrothermal fluid flow was probably important in graphite deposition throughout the examined rock sequences. The increasing abundance of graphite towards the fault zone core may be a significant source of strain localization, allowing fault weakening. © 2018 The Author(s).
2130.
Rock fluidization during peak-ring formation of large impact structures
Nature,
562
(7728)
511-518
2018
Abstract: ▾ Large meteorite impact structures on the terrestrial bodies of the Solar System contain pronounced topographic rings, which emerged from uplifted target (crustal) rocks within minutes of impact. To flow rapidly over large distances, these target rocks must have weakened drastically, but they subsequently regained sufficient strength to build and sustain topographic rings. The mechanisms of rock deformation that accomplish such extreme change in mechanical behaviour during cratering are largely unknown and have been debated for decades. Recent drilling of the approximately 200-km-diameter Chicxulub impact structure in Mexico has produced a record of brittle and viscous deformation within its peak-ring rocks. Here we show how catastrophic rock weakening upon impact is followed by an increase in rock strength that culminated in the formation of the peak ring during cratering. The observations point to quasi-continuous rock flow and hence acoustic fluidization as the dominant physical process controlling initial cratering, followed by increasingly localized faulting. © 2018, Springer Nature Limited.
2129.
Synoptic-scale control over modern rainfall and flood patterns in the Levant drylands with implications for past climates
Journal of Hydrometeorology,
19
(6)
1077 – 1096
2018
2128.
Synoptic conditions of fine-particle transport to the last interglacial Red Sea-Dead Sea from Nd-Sr compositions of sediment cores
Quaternary Science Reviews,
179123-136
2018
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Binary alloys; Chloride minerals; Climatology; Dust; Floods; Floors; Glacial geology; Isotopes; Lakes; Landforms; Neodymium; Neodymium alloys; Sea level; Seawater; Soils; Storms; Strontium; Strontium alloys; Watersheds, Dead sea; Dust sources; Late quaternary; Levant; Loess; Nd-Sr isotopes; Paleo-climate; Paleo-synoptic; Red sea, Sediments, depocenter; dust; flood; flooding; Heinrich event; hydrological change; isotopic composition; Last Interglacial; loess; marine isotope stage; Mediterranean environment; paleoclimate; particle size; precipitation (climatology); Quaternary; sea level change; sediment core; strontium; strontium isotope; watershed, Dead Sea; Indian Ocean; Levantine Sea; Mediterranean Sea; Red Sea [Indian Ocean]; Sahara
Abstract: ▾ The sediments deposited at the depocenter of the Dead Sea comprise high-resolution archive of hydrological changes in the lake's watershed and record the desert dust transport to the region. This paper reconstructs the dust transport to the region during the termination of glacial Marine Isotope Stage 6 (MIS 6; ∼135–129 ka) and the last interglacial peak period (MIS5e, ∼129–116 ka). We use chemical and Nd and Sr isotope compositions of fine detritus material recovered from sediment core drilled at the deepest floor of the Dead Sea. The data is integrated with data achieved from cores drilled at the floor of the Red Sea, thus, forming a Red Sea-Dead Sea transect extending from the desert belt to the Mediterranean climate zone. The Dead Sea accumulated flood sediments derived from three regional surface cover types: settled desert dust, mountain loess-soils and loess-soils filling valleys in the Dead Sea watershed termed here “Valley Loess”. The Valley Loess shows a distinct 87Sr/86Sr ratio of 0.7081 ± 1, inherited from dissolved detrital calcites that originate from dried waterbodies in the Sahara and are transported with the dust to the entire transect. Our hydro-climate and synoptic conditions reconstruction illustrates the following history: During glacial period MIS6, Mediterranean cyclones governed the transport of Saharan dust and rains to the Dead Sea watershed, driving the development of both mountain soils and Valley Loess. Then, at Heinrich event 11, dry western winds blew Saharan dust over the entire Red Sea - Dead Sea transect marking latitudinal expansion of the desert belt. Later, when global sea-level rose, the Dead Sea watershed went through extreme aridity, the lake retreated, depositing salt and accumulating fine detritus of the Valley Loess. During peak interglacial MIS 5e, enhanced flooding activity flushed the mountain soils and fine detritus from all around the Dead Sea and Red Sea, marking a significant “contraction” of the desert belt. At the end of MIS 5e the effect of the regional precipitation diminished and the Dead Sea and Red Sea areas re-entered sever arid conditions with extensive salt deposition at the Dead Sea. © 2017 Elsevier Ltd
2127.
Study on speed characteristics of hydraulic top drive under fluctuating load
Journal of Petroleum Science and Engineering,
167277-286
2018
ISSN: 09204105
Publisher: Elsevier B.V.
Keywords:▾
Digital storage; Drilling rigs; Drills; Electric power transmission; Hydraulic tools; Oil well drilling; Speed, Continental scientific drillings; Electro-hydraulic proportional control; Fluctuating loads; Main transmission systems; Mechanical structures; Speed characteristics; Theoretical modeling; Variable displacement, Transmissions, acceleration; deep drilling; drilling rig; loading; numerical model; performance assessment; velocity
Abstract: ▾ A hydraulic top drive is a high-power gyrator used in oil or scientific drilling rigs, whose shaft is connected to drill pipe when it drives drilling tools to excavate well. The output speed of top drive determines the speed of drill bit directly. Load acting on the top drive shaft fluctuates randomly, which will cause top drive output speed hard to be in consistent with the setting value. This paper presents a main transmission system of a hydraulic top drive designed for deep continental scientific drilling, which was built with a multi-stage mechanical structure and a closed circuit hydraulic system with variable displacement pumps and motors. Electro-hydraulic proportional control was applied to vary the speed of the hydraulic top drive. A theoretical model is detailed for the hydraulic top drive main transmission system. Among the new techniques proposed in this paper is a simulation model for studying the performance of hydraulic top drive and capturing speed characteristics under fluctuant load. A drilling experiment of the hydraulic top drive was performed on the CRUST-I drilling rig in CCSD-SK-II well site. This paper concludes by comparing the results of the simulation model with theoretical results and drilling experimental data gathered in the hydraulic top drive possessing the same architecture, components, and control methods used within the simulation model. The drilling experiment and the analysis result showed that the hydraulic top drive could meet the requirements of deep continental scientific drilling and that the speed could be output according to the setting speed with very small oscillation. The simulation model can be used for several applications such as hydraulic top drive design and performance analysis of various drilling conditions. © 2018 Elsevier B.V.
2126.
Structural disorder of graphite and implications for graphite thermometry
Solid Earth,
9
(1)
223-231
2018
ISSN: 18699510
Publisher: Copernicus GmbH
Keywords:▾
Calibration; Metamorphic rocks; Statistical mechanics; Thermometers, Active tectonic settings; Carbonaceous materials; Crystalline graphite; Degree of structural order; Irreversible process; Micro-structural observations; Raman microspectroscopy; Structural disorders, Graphite, crystal structure; crystallinity; crystallography; experimental mineralogy; graphite; thermometry
Abstract: ▾ Graphitization, or the progressive maturation of carbonaceous material, is considered an irreversible process. Thus, the degree of graphite crystallinity, or its structural order, has been calibrated as an indicator of the peak metamorphic temperatures experienced by the host rocks. However, discrepancies between temperatures indicated by graphite crystallinity versus other thermometers have been documented in deformed rocks. To examine the possibility of mechanical modifications of graphite structure and the potential impacts on graphite thermometry, we performed laboratory deformation experiments. We sheared highly crystalline graphite powder at normal stresses of 5 and 25 megapascal (MPa) and aseismic velocities of 1, 10 and 100μms1. The degree of structural order both in the starting and resulting materials was analyzed by Raman microspectroscopy. Our results demonstrate structural disorder of graphite, manifested as changes in the Raman spectra. Microstructural observations show that brittle processes caused the documented mechanical modifications of the aggregate graphite crystallinity. We conclude that the calibrated graphite thermometer is ambiguous in active tectonic settings. © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License.
2125.
Spatial patterns of diatom diversity and community structure in ancient Lake Ohrid
Hydrobiologia,
819
(1)
197 – 215
2018
ISSN: 00188158
Publisher: Springer International Publishing
Keywords:▾
Bacillariophyta
Abstract: ▾ The extraordinary diversity in long-lived lakes is largely driven by distinct eco-evolutionary processes. With their unique biota and numerous endemic taxa, these lakes are key settings for fundamental studies related to ecology, diversity, and evolution. Here, we test how the environment shapes diatom diversity and community patterns over space in ancient Lake Ohrid. By applying Bray–Curtis similarity analyses of diatom community data, including widespread and endemic taxa, we identified two major zones: littoral and sublittoral. The latter one is being characterized with higher endemic diversity. The α and β diatom diversity and community distribution in the northern and eastern part of the lake are influenced by the presence of vertical (bathymetrical) and horizontal barriers. The zonation of the diatom communities appears driven by two large-scale factors: (i) water depth, and (ii) water chemistry, primarily, the concentration of total phosphorus, nitrogen ammonia, and conductivity. Both drivers appear to equally influence diatom diversity and community patterns. We present initial data on diatom–environment relations, where the results support earlier ecological studies emphasizing the relevance of ongoing human-induced eutrophication in the northern lake area. This study provides background information on the role of the environment in structuring contemporary diatom diversity. However, future research needs to focus on the biotic component including species competition in order to reveal the mechanisms driving spatial community dynamics in Lake Ohrid. © 2018, The Author(s).
2124.
Shelf hypoxia in response to global warming after the Cretaceous- Paleogene boundary impact
Geology,
46
(8)
683-686
2018
DOI:10.1130/G45000.1
Abstract: ▾ The Chicxulub asteroid impact at the Cretaceous-Paleogene (K-Pg) boundary resulted in one of the most abrupt global warming events in the past 100 m.y., presenting an analogue to current global warming. Here, we present high-resolution geochemical, micropaleontological, and palynological records of the Brazos-1 (Texas, USA), Stevns Klint (Denmark), and Caravaca (Spain) K-Pg boundary sections to assess the rapid environmental changes during the global warming following the brief K-Pg boundary impact winter. Warming during the first millennia after the impact is associated with hypoxic bottom waters at the studied shelf sites, as indicated by molybdenum enrichments, causing major stress for benthic communities. We attribute this decline in dissolved oxygen to a combination of decreased gas solubility and ocean ventilation resulting from the warming of the sea water, and increased oxygen demand in shelf bottom waters due to increased nutrient inputs and associated high productivity. © 2018 Geological Society of America.
2123.
Serpentinite-Rich Gouge in a Creeping Segment of the Bartlett Springs Fault, Northern California: Comparison With SAFOD and Implications for Seismic Hazard
Tectonics,
37
(12)
4515-4534
2018
ISSN: 02787407
Publisher: Blackwell Publishing Ltd
Keywords:▾
Creep; Kaolinite; Magnesite; Metamorphic rocks; Serpentine; Strike-slip faults, Fault creep; Metasomatic rocks; SAFOD; San Andreas fault; Serpentinite, Structural geology, comparative study; data interpretation; displacement; emplacement; fault gouge; San Andreas Fault; seismic hazard; seismic zone; serpentinite, California; San Andreas; United States
Abstract: ▾ An exposure of a creeping segment of the Bartlett Springs Fault (BSF), part of the San Andreas Fault system in northern California, is a ~1.5-m-wide zone of serpentinite-bearing fault gouge cutting through Late Pleistocene fluvial deposits. The fault gouge consists of porphyroclasts of antigorite serpentinite, talc, chlorite, and tremolite-actinolite, along with some Franciscan metamorphic rocks, in a matrix of the same materials. The Mg-mineral assemblage is stable at temperatures above 250–300 °C. The BSF gouge is interpreted to have been tectonically incorporated into the fault from depths near the base of the seismogenic zone and to have risen buoyantly to the surface where it is now undergoing right-lateral displacement. The ultramafic-rich composition, frictional properties, and inferred mode of emplacement of the BSF serpentinitic gouge correspond to those of the creeping traces of the San Andreas Fault identified in the SAFOD (San Andreas Fault Observatory at Depth) drill hole. This suggests a common origin for creep at both locations. A tectonic model for the source of the ultramafic-rich materials in the BSF is proposed that potentially could explain the distribution of creep throughout the northernmost San Andreas Fault system. Published 2018. This article is a US Government work and is in the public domain in the USA.
2122.
Seismic imaging and attribute analysis of chicxulub crater central sector, Yucatán platform, Gulf of Mexico
Geologica Acta,
16
(2)
215-235
2018
Abstract: ▾ Chicxulub Crater, formed ~66Ma ago by an asteroid impact on the southern Gulf of Mexico, is the best preserved of the three large multi-ring basins in the terrestrial record. The crater structure is characterized by a semi-circular concentric ring pattern, marking the crater basin, peak ring, terrace zone and basement uplift. Analysis of a grid of 19 seismic reflection profiles using seismic attributes, marker horizons, contour surfaces and 3-D views is used to investigate the stratigraphy of the central zone. We used interactive software and routine applications to map the impact breccias, breccia-carbonate contact and post-impact carbonates. Four horizons marked by high-amplitude reflectors representing high-impedance contrasts were identified and laterally correlated in the seismic images. Complex trace attribute analysis was applied for petrophysical characterization. Surface contour maps of base and top of stratigraphic packages were constructed, which mapped the impactites and post-and pre-impact carbonate stratigraphy. Basin floor, marked by the contact between the impact breccias and overlying carbonates is shown by laterally discontinuous high-amplitude reflectors. Discontinuous scattered reflectors interpreted as the upper breccias beneath the crater floor, have an average thickness of ~300msm. The Paleogene sedimentary units are characterized by multiple reflectors with lateral continuity, which contrast with the seismic response of underlying breccias. The basal Paleocene sediments follow the basin floor relief. Upwards in the section, the carbonate strata are characterized by horizontal reflectors, which are interrupted by a regional unconformity. Onlap/downlap packages over the unconformity record a period of sea level change. ©I. Canales-García, J. Urrutia-Fucugauchi, E. Aguayo-Camargo, 2018 CC BY-SA.
2121.
Sediment reflectance spectroscopy as a paleo-hydrological proxy in East Africa
Limnology and Oceanography: Methods,
16
(2)
92-105
2018
ISSN: 15415856
Publisher: Wiley Blackwell
Abstract: ▾ This study presents the merit of visible-spectrum scanning reflectance spectroscopy (VIS-RS) as a rapid technique for determining the concentration of chlorophyll a (Chl a) and its derivatives in lake sediments. In a 25,000-yr sediment record from Lake Challa, in East Africa, we found that VIS-RS values correlate with Chl a concentrations measured by High Performance/Pressure Liquid Chromatography. Observed variation in sedimentary values of RABD660;670 appears linked to proxies of climatic moisture balance as well as to a seismically-derived lake-level reconstruction over this period, indicating that VIS-RS can be used as a proxy for long-term paleo-hydrological change. Changes in the reflectance of Lake Challa sediments are likely related to differences in the preservation/degradation of algal pigments in response to changes in water-column depth and the stability of stratification. The connecting mechanism may be that during lake lowstands, more frequent injection of oxygen to (near-) bottom waters enhance the breakdown of labile organic compounds before permanent burial. We suggest that fast and inexpensive VIS-RS scanning, although less specific than HPLC in quantifying individual pigments, provides accurate data on down-core variations in the concentration of Chl a and its derivatives in lake sediments, hence allows to reconstruct long-term changes in the hydrology of climate-sensitive lakes. The main prerequisite for its successful application is that temporal variation in lake hydrology over the period of interest has not appreciably affected sedimentation dynamics at the core site, since major changes in sediment texture and organic content are likely to create confounding effects in the VIS-RS signature. © 2017 Association for the Sciences of Limnology and Oceanography
2120.
Seasonal and diurnal evaporation from a deep hypersaline lake: The Dead Sea as a case study
Journal of Hydrology,
562155 – 167
2018