All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1844.
Special Collection: Rates and depths of magma ascent on earth: Degassing of hydrous trachytic campi flegrei and phonolitic vesuvius melts: Experimental limitations and chances to study homogeneous bubble nucleation
American Mineralogist,
101
(4)
859 – 875
2016
ISSN: 0003004X
Publisher: Walter de Gruyter GmbH
Keywords:▾
Campania [Italy]; Campi Flegrei; Italy; Napoli [Campania]; Vesuvius; Coalescence; Crystallization; Cylinders (shapes); Degassing; Nucleation; Porosity; Silicates; Supersaturation; Surface tension; Bubble nucleation; Bubble number densities; Campi Flegrei; Decompression experiments; Magma ascents; bubble; decompression; degassing; magma; melt; volcanic glass; Glass
Abstract: ▾ Melt degassing by bubble nucleation and growth is a driving mechanism of magma ascent. Therefore, decompression experiments with hydrous silicate melts were used to investigate the onset and the dynamics of H2O degassing. Nominally H2O undersaturated trachytic Campi Flegrei and phonolitic Vesuvius melts representative for the magma compositions of the Campi Flegrei volcanic system were decompressed at a super-liquidus temperature of 1050°C from 200 MPa to final pressures (Pfinal) of 100, 75, and 60 MPa using continuous decompression rates of 0.024 and 0.17 MPa/s. Experiments started from either massive glass cylinders or glass powder to demonstrate the infl of the starting material on melt degassing. Glass powder can be used to shorten the equilibration time (teq) prior to decompression for dissolution of H2O in the melt. The decompressed samples were quenched and compared in terms of bubble number density (NV), porosity, and residual H2O content in the melt. Decompression of all glass cylinder samples led to homogeneous bubble nucleation with high NV of ∼105 mm-3. The supersaturation pressures for homogeneous bubble nucleation were estimated to be <76 MPa for the trachytic and <70 MPa for the phonolitic melt. In contrast to glass cylinders, the usage of glass powder equilibrated for 24 h before decompression prevented homogeneous bubble nucleation during decompression. We suggest that trapped air in the powder pore space resulted in the formation of tiny H2O-N2 bubbles throughout the samples prior to decompression. Degassing of these glass powder samples was facilitated by diffusive growth of these pre-existing bubbles and thus did not require signifi H2O supersaturation of the melt. This is evidenced by several orders of magnitude lower NV and lower residual H2O contents at correspondingly higher porosities compared to the glass cylinder samples. However, a signifi extension of teq to 96 h in the glass powder experiments led to degassing results comparable to the glass cylinder samples. This effect is probably due to Ostwald ripening, coalescence, and the ascent of the pre-existing bubbles during the extended teq prior to decompression. The NV of the glass cylinder samples were used to test the applicability of the vesiculation model provided by Toramaru (2006). For the applied decompression rates, the experimental NV are up to 5 orders of magnitude higher than the values predicted by the model. This may be mainly attributed to the usage of the macroscopic surface tension and the total H2O diffusivity in the model to describe the molecular process of bubble nucleation. A signifi increase in modeled NV can be achieved by application of a reduced surface tension in combination with the lower diffusivity of network formers as a limiting parameter for the formation of a bubble nucleus. This study demonstrates that the investigation of homogeneous bubble nucleation necessitates an optimized experimental protocol. We strongly recommend performing experiments with massive glass cylinders as starting material. The timescale of decompression is a limiting parameter and must be short enough to minimize the opportunity for a reduction of NV by bubble coalescence. Considering our comparably high NV, the samples of many previous experimental studies that were used to calibrate models for homogeneous bubble nucleation were probably subject to signifi NV reduction. Newly derived data from optimized experiments will require improved models for homogeneous bubble nucleation during magma ascent. © 2016 by Walter de Gruyter Berlin/Boston.
1843.
Mid-Miocene record of large-scale Snake River-type explosive volcanism and associated subsidence on the Yellowstone hotspot track: The Cassia Formation of Idaho, USA
Bulletin of the Geological Society of America,
128
(7)
1121-1146
2016
ISSN: 00167606
Publisher: Geological Society of America
DOI:10.1130/B31324.1
Keywords:▾
Explosives; Geochronology; Subsidence; Trace elements, Explosive eruption; Explosive volcanism; Miocene topography; North american plates; Snake river plains; Thickness variation; Transport indicators; Yellowstone hotspot, Rivers, explosive volcanism; geochemistry; geochronology; mineralogy; Miocene; paleomagnetism; rhyolite; subsidence; hot spot; ignimbrite; trace element; volcanology, Idaho; Snake River Plain; United States; Wyoming; Yellowstone Caldera
Abstract: ▾ The 1.95-km-thick Cassia Formation, defined in the Cassia Hills at the southern margin of the Snake River Plain, Idaho, consists of 12 refined and newly described rhyolitic members, each with distinctive field, geochemical, mineralogical, geochronological, and paleomagnetic characteristics. It records voluminous high-temperature, Snake River-type explosive eruptions between ca. 11.3 Ma and ca. 8.1 Ma that emplaced intensely welded rheomorphic ignimbrites and associated ash-fall layers. One ignimbrite records the ca. 8.1 Ma Castleford Crossing eruption, which was of supereruption magnitude (~1900 km3). It covers 14,000 km2 and exceeds 1.35 km thickness within a subsided, proximal caldera-like depocenter. Majorand trace-element data define three successive temporal trends toward less-evolved rhyolitic compositions, separated by abrupt returns to more-evolved compositions. These cycles are thought to reflect increasing mantle- derived basaltic intraplating and hybridization of a midcrustal region, coupled with shallower fractionation in upper-crustal magma reservoirs. The onset of each new cycle is thought to record renewed intraplating at an adjacent region of crust, possibly as the North American plate migrated westward over the Yellowstone hotspot. A regional NE-trending monocline, here termed the Cassia monocline, was formed by synvolcanic deformation and subsidence of the intracontinental Snake River basin. Its structural and topographic evolution is reconstructed using thickness variations, offlap relations, and rheomorphic transport indicators in the successive dated ignimbrites. The subsidence is thought to have occurred in response to incremental loading and modification of the crust by the mantle-derived basaltic magmas. During this time, the area also underwent NW-trending faulting related to opening of the western Snake River rift and E-W Basin and Range extension. The large eruptions probably had different source locations, all within the subsiding basin. The proximal Miocene topography was thus in marked contrast to the more elevated present-day Yellowstone plateau. © 2016 Geological Society of America.
1842.
Oxide and diamond nanoparticles modified drilling fluid for deep, complicated drilling conditions
Journal of Nanoscience and Nanotechnology,
16
(12)
13007-13013
2016
ISSN: 15334880
Publisher: American Scientific Publishers
Keywords:▾
Alumina; Aluminum alloys; Aluminum oxide; Diamond drilling; Diamonds; Drill pipe; Drill strings; Drilling fluids; Drills; Friction; Horizontal drilling; Horizontal wells; Silica nanoparticles; Titanium dioxide; Tribology; Wear resistance, Diamond nano-particles; Drilling fluid additives; Lubricating properties; Lubrication devices; Oil-based drilling fluid; Pin on disk; Pin on disk friction; Water-based drilling fluid, Oil well drilling
Abstract: ▾ In the context of well drilling and during the process of drilling down and tripping out of drill string, it is the inevitable contact and friction between drill pipe and casing that causes the wear of the drill pipe and casing tube, especially in the case of drilling deep, ultra-deep, and horizontal wells. Compared with steel drill pipe, the wear of aluminum alloy drill pipe appears to be more serious. Nanoparticles as additives in drilling fluids could potentially reduce mechanical friction, greatly enhancing the lubricating properties of drilling fluids and subsequently reducing the drill pipe and casing materials surface losses. Within this study an attempt has been made to improve the lubricating properties of drilling fluid with regard to deep, complicated drilling conditions by adding oxide nanoparticles to the fluid. Spherical alumina (Al2O3), titania (TiO2), silica (SiO8) and diamond nanoparticles were selected as drilling fluid additives. Effects of different types and concentrations of oxide nanoparticle additives on lubricating properties and friction reduction of drilling fluid have been studied by using an extreme pressure lubrication device and a pin-on-disk tester. In pin-on-disk tests, the pin material was AISI316 steel (casing material) and the disk material was 7075 aluminum alloy (drill pipe material). The pin-on-disk friction and wear tests were carried out under the condition that the pin and disk were immerged in drilling fluid. Results indicated that the lubricating properties of waterbased drilling fluid significantly improved upon adding an appropriate amount of SiO2 nanoparticles, meanwhile TiO2, Al2O3 and diamond nanoparticles had limited effects on the lubricating properties of drilling fluid. The LR (lubricating factor reduce rate) of drilling fluid increased to the maximum value of 16.6% at 0.5 wt% SiO2 nanoparticles addition. The WV (wear volume) of aluminum alloy disc decreased to the minimum value of 0.31 mm3 at 0.4 wt% SiO2 nanoparticles addition. On the basis of the above experimental results, 0.4 wt% SiO2 nanoparticles were added to the oil based drilling fluids used in SK-II well drilling, which is a scientific continental drilling project in the Cretaceous Songliao Basin of northeast China. Results showed that the lubricating coefficient of the drilling fluid was reduced by 20.3%, the friction factor reduction rate was increased by 29.7%, and the aluminum disc wear volume decreased by 26.3%. Copyright © 2016 American Scientific Publishers All rights reserved.
1841.
Microbial sedimentary imprint on the deep Dead Sea sediment
Depositional Record,
2
(1)
118-138
2016
ISSN: 20554877
Publisher: John Wiley and Sons Inc
DOI:10.1002/dep2.16
Abstract: ▾ A study of an International Continental Drilling Program core recovered from the middle of the modern Dead Sea has identified microbial traces within this subsurface hypersaline environment. A comparison with an active microbial mat exhibiting similar evaporative processes characterized iron-sulphur mineralization and exopolymeric substances resulting from microbial activity. Exopolymeric substances were identified in the drilled sediment but unlike other hypersaline environments, it appears that they have a limited effect on the precipitation of calcium carbonate in the sedimentary column. Sulphate reduction, however, plays a role in all types of evaporative facies, leading to the formation of diagenetic iron sulphides in glacial and interglacial intervals. Their synthesis seems to occur under progressive sulphidation that generally stops at greigite because of incomplete sulphate reduction. The latter may be caused by a lack of suitable organic matter in this hypersaline, hence energy-demanding, environment. Pyrite may be found in periods of high lake productivity, when more labile organic matter is available. The carbon and sulphur cycles are thus influenced by microbial activity in the Dead Sea environment and this influence results in diagenetic transformations in the deep sediment. © 2016 The Authors. The Depositional Record published by John Wiley & Sons Ltd on behalf of International Association of Sedimentologists.
1840.
Bimaterial interfaces at the Karadere segment of the North Anatolian Fault, northwestern Turkey
Journal of Geophysical Research: Solid Earth,
121
(2)
931-950
2016
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
fault zone; North Anatolian Fault; P-wave; wave reflection; waveform analysis, Turkey
Abstract: ▾ We image velocity contrast (bimaterial) interfaces along the Karadere Fault of the North Anatolian Fault Zone, toward the eastern part of the 1999 Izmit Mw 7.4 rupture in NW Turkey, using waveforms recorded by a local seismic network. Applying an automatic procedure for identification and picking of fault zone head waves (FZHW) and direct P arrivals, and manually revising the picks through particle motion analysis, we identify two different groups of FZHW as well as fault zone reflected waves (FZRW). The first group of FZHW has a moveout with respect to the direct P arrivals with distance traveled along the fault, indicating a deep bimaterial interface down to the base of the seismogenic crust with an average velocity contrast of ~3.4%. The second group of FZHW has a constant time difference from the direct P arrivals and is associated with a shallow local interface bounding a low-velocity damage zone or basin structure that extends to a depth of 4-5 km. While the first group of FZHW exists on the slower crustal block, the second group of FZHW and the FZRW are present generally on both sides of the fault. These phases add to the richness and complexity of the early P waveforms observed at stations close to a large fault. The relatively low velocity contrast across the Karadere Fault compared to values to the west may have helped stopping the Izmit rupture. ©2016. American Geophysical Union. All Rights Reserved.
1839.
Differential resilience of ancient sister lakes Ohrid and Prespa to environmental disturbances during the Late Pleistocene
Biogeosciences,
13
(4)
1149 – 1161
2016
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
Balkans; Campania [Italy]; Campi Flegrei; Italy; Lake Mikri Prespa; Lake Ohrid; Napoli [Campania]; Bacillariophyta; Campanian; community composition; diatom; ecosystem resilience; environmental disturbance; glacial-interglacial cycle; Heinrich event; paleoclimate; Pleistocene; sediment core; speciation (biology)
Abstract: ▾ Ancient lakes, such as lakes Ohrid and Prespa on the Balkan Peninsula, have become model systems for studying the link between geological and biotic evolution. Recently, the scientific deep-drilling project Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) was initiated to better understand the environmental, climatic, and limnological evolution of the lake. It revealed that Lake Ohrid experienced a number of environmental disturbances during its ca. 2.0 million year long history. These are comprised of disturbances that lasted over longer periods of time ("press events") such as glacial-interglacial cycles and Heinrich events, as well as sudden and short disturbances ("pulse events") like the deposition of landslides, earthquakes, and volcanic ash depositions. The latter includes one of the most severe volcanic episodes during the Late Pleistocene: the eruption of the Campanian Ignimbrite (known as Y-5 marine tephra layer) from the Campi Flegrei caldera, dated to 39.6 ± 0.1 thousand years ago. The event is recorded by the deposition of a ca. 15 cm thick tephra layer in sediment cores of lakes Ohrid (DEEP-5045-1) and Prespa (Co1204). Coincidently, this pulse event is superimposed by the Heinrich H4 event, 40.4-38.4 thousand years ago. In the current paper, diatoms were used as proxies to compare the responses of these lakes to the Y-5 (pulse) and the H4 (press) disturbances. Based on stratigraphically constrained incremental sum of squares cluster (CONISS) and unconstrained Partitioning Around Medoids (PAM) analyses, we found little evidence that diatom community compositions in either lake responded to the H4 event. However, the Y-5 influx caused clear and rapid diatom community changes. After the initial response, community compositions in Lake Ohrid and, to a lesser extent, in Lake Prespa slowly returned to their quasi pre-disturbance state. Moreover, there is no evidence for disturbance-related extinction events. The combined evidence from these findings suggests that lakes Ohrid and Prespa likely did not experience regime shifts. It is therefore concluded that both lakes show resilience to environmental disturbance. However, it seems that Lake Ohrid is more resilient than Lake Prespa, as the recovery of diatom communities is more pronounced and its estimated recovery time is only ca. 1100 years vs. ca. 4000 years in Lake Prespa. The reasons for the differential responses remain largely unknown, but differences in geology, lake age, limnology, and intrinsic parameters of the diatom proxies may play an important role. © Author(s) 2016.
1838.
Design of electro-hydraulic control and auxiliary monitoring system of coring winch for drilling of 6000 m (in Chinese with English abstract);[6000m用取心绞车电液控制及辅助监测系统设计]
Mining & Processing Equipment,
44
(02)
31-34+41
2016
1837.
Description of a new fossil diatom genus, Cribrionella gen. nov. (Bacillariophyta) from quaternary sediments of Lake Ohrid
Phytotaxa,
252
(1)
031 – 042
2016
ISSN: 11793155
Publisher: Magnolia Press
Abstract: ▾ A new diatom genus, Cribrionella gen. nov., is described from Quaternary sediments of Lake Ohrid. Cribrionella comprises distinct morphological features, such as: i) presence of submarginal alveoli followed by regularly or irregularly arranged areolae, ii) cribra on external areolar openings, iii) absence of silicate layers on internal areolar openings, but presence of thick and inwardly raised circumferential silica trabeculae, iv) rimoportulae positioned on costae, and v) absence of central fultoportulae. Detailed light and scanning electron microscope analyses were undertaken and used for comparison to morphologically related genera. The typus generis Cribrionella ohridana is compared to species from its morphologically closest genus Cyclotella sensu stricto (e.g., C. atomus, C. delicatula, C. bifacialis). Cribrionella ohridana has not been reported from the extant diatom flora of Lake Ohrid, nor in the nearby Lake Prespa. The discovery of a new genus in Lake Ohrid confirms again the importance of the lake, not only in light of species richness and endemicity, but also in evolutionary history of the family Stephanodiscaceae. © 2016 Magnolia Press.
1836.
Des-A-lupane in an East African lake sedimentary record as a new proxy for the stable carbon isotopic composition of C3 plants
Organic Geochemistry,
101132-139
2016
ISSN: 01466380
Publisher: Elsevier Ltd
Keywords:▾
Biodegradation; Degradation; Isotopes; Lakes; Sedimentology; Vegetation, Carbon isotopic composition; Des-A-lupane; East Africa; Interglacial transitions; Lacustrine sediments; Microbial degradation; Terrestrial vegetation; Triterpenoids, Paraffins, alkane; angiosperm; C3 plant; C4 plant; carbon isotope; isotopic ratio; lacustrine deposit; leaf; microbial activity; paleoenvironment; paleohydrology; Postglacial; reconstruction; stable isotope; terpene; warming; wax, Kilimanjaro [Tanzania]; Lake Challa; Tanzania, Magnoliophyta
Abstract: ▾ We studied the high-resolution and well-dated 25,000 year sedimentary record of Lake Challa, a deep tropical crater lake in equatorial East Africa, to explore new proxies for paleoenvironmental and paleohydrological change. Sedimentary biomarker analysis revealed the presence of des-A-triterpenoids with oleanane, ursane and lupane carbon skeletons, microbial degradation products of angiosperm plant triterpenoids. Their increased influx from 16,000 years ago corresponds with previously documented changes in the terrestrial vegetation of the Lake Challa basin during postglacial warming, in particular the relative increase in C3/C4 plant ratio inferred from the stable carbon isotopic signature (δ13C) of sedimentary n-alkanes derived from plant leaf waxes. In contrast to this n-alkane δ13C signature, the δ13C of des-A-lupane maintains a constant value of −27.4 ± 1.1‰ across the glacial–interglacial transition. Since des-A-lupane is derived from C3 plants, its δ13C signature is here proposed to represent a novel and independent proxy for the time-variable carbon isotopic composition of local terrestrial C3 plants, which can improve estimates of the C3/C4 plant ratio based on two-end member mixing models of n-alkane δ13C values. © 2016 Elsevier Ltd
1835.
Damaged beyond repair? Characterising the damage zone of a fault late in its interseismic cycle, the Alpine Fault, New Zealand
Journal of Structural Geology,
9076-94
2016
ISSN: 01918141
Publisher: Elsevier Ltd
Keywords:▾
Fracture; Lithology; Seismic waves; Wave propagation, Alpine Faults; Continental scale; Damage zones; DFDP; Fluid-rock interaction; Fracture density; Independent analysis; X-ray computed tomography, Computerized tomography, earthquake damage; fault zone; fracture; lithology; P-wave; plate boundary; slip; wave velocity, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ X-ray computed tomography (CT) scans of drill-core, recovered from the first phase of the Deep Fault Drilling Project (DFDP-1) through New Zealand's Alpine Fault, provide an excellent opportunity to study the damage zone of a plate-bounding continental scale fault, late in its interseismic cycle. Documentation of the intermediate-macro scale damage zone structures observed in the CT images show that there is no increase in the density of these structures towards the fault's principal slip zones (PSZs), at least within the interval sampled, which is 30 m above and below the PSZs. This is in agreement with independent analysis using borehole televiewer data. Instead, we conclude the density of damage zone structures to correspond to lithology. We find that 72% of fractures are fully healed, by a combination of clays, calcite and quartz, with an additional 24% partially healed. This fracture healing is consistent with the Alpine Fault's late interseismic state, and the fact that the interval of damage zone sampled coincides with an alteration zone, an interval of extensive fluid-rock interaction. These fractures do not impose a reduction of P-wave velocity, as measured by wireline methods. Outside the alteration zone there is indirect evidence of less extensive fracture healing. © 2016 Elsevier Ltd
1834.
Crystallization of ikaite and its pseudomorphic transformation into calcite: Raman spectroscopy evidence
Geochimica et Cosmochimica Acta,
175271 – 281
2016
1833.
Constraints on paleofluid sources using the clumped-isotope thermometry of carbonate veins from the SAFOD (San Andreas Fault Observatory at Depth) borehole
Tectonophysics,
690174-189
2016
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Calcite; Carbon; Creep; Deformation; Faulting; Fluids; Isotopes; Observatories; Silicates; Strike-slip faults; Thermometers; Water, Borehole temperature; Calcite veins; Clumped isotopes; Fluid-rock interaction; Isotopic composition; SAFOD; San Andreas fault; Syn-tectonic veins, Flow of fluids, borehole geophysics; calcite; carbonate rock; fault zone; fracture flow; hydrogeology; isotopic composition; meteoric water; San Andreas Fault; vein (geology); water-rock interaction, California; Parkfield; United States
Abstract: ▾ The San Andreas Fault Observatory at Depth (SAFOD), near Parkfield, California, is a borehole drilled through two active deforming zones of the San Andreas fault, the Southwest Deforming Zone (SDZ) and the Central Deforming Zone (CDZ). These zones accommodate displacement by seismic slip and aseismic creep. Elevated fluid pressures and fluid–rock interactions have been proposed to explain the low apparent strength and aseismic creep observed, but the origin of the fluids and existence of high fluid pressures remains uncertain. We use clumped-isotope thermometry and δ18O–δ13C compositions of calcite in veins to constrain the origin of paleofluids and compare these results to the isotopic composition of modern-day pore fluids from the SAFOD borehole and nearby areas. We observe that: (1) calcite vein temperatures vary from 81 to 134 °C, which overlaps the current ambient borehole temperatures of 110–115 °C at sampled depths; (2) vein calcite is not in carbon isotope equilibrium with modern-day pore fluids; (3) the δ18O values of paleofluids close to the SDZ and CDZ, calculated from vein δ18O and temperature data, are not in equilibrium with local modern-day pore waters but approach equilibrium with modern pore waters far from these zones; and (4) syntectonic vein calcite is only in C- and O-isotopic equilibrium with their host rocks within the SDZ and CDZ. Spatial patterns of δ18O and δ13C show little evidence for across-fault fluid-flow. Clumped isotope temperatures are consistent with locally-derived fluid sources, but not with continuous or episodic replenishment of fluids from shallow sedimentary brines or deep fluid sources. Our findings are compatible with flow of meteoric fluids from the southwestern damage zone into the SDZ and CDZ, which would have favored the formation of weak phyllosilicates and contributed to the present day weakness of the two actively deforming zones. © 2016 Elsevier B.V.
1832.
Compositional variation within thick (>10 m) flow units of Mauna Kea Volcano cored by the Hawaii Scientific Drilling Project
Geochimica et Cosmochimica Acta,
185182-197
2016
ISSN: 00167037
Publisher: Elsevier Ltd
Keywords:▾
chemical composition; core analysis; element mobility; enrichment; igneous geochemistry; lava flow; sequence stratigraphy; shield volcano; trace element; volcanic rock, Hawaii [(ISL) Hawaiian Islands]; Hawaii [United States]; Hawaiian Islands; Mauna Kea
Abstract: ▾ Geochemical analyses of stratigraphic sequences of lava flows are necessary to understand how a volcano works. Typically one sample from each lava flow is collected and studied with the assumption that this sample is representative of the flow composition. This assumption may not be valid. The thickness of flows ranges from <1 to >100 m. Geochemical heterogeneity in thin flows may be created by interaction with the surficial environment whereas magmatic processes occurring during emplacement may create geochemical heterogeneities in thick flows. The Hawaii Scientific Drilling Project (HSDP) cored ∼3.3 km of basalt erupted at Mauna Kea Volcano. In order to determine geochemical heterogeneities in a flow, multiple samples from four thick (9.3–98.4 m) HSDP flow units were analyzed for major and trace elements. We found that major element abundances in three submarine flow units are controlled by the varying proportion of olivine, the primary phenocryst phase in these samples. Post-magmatic alteration of a subaerial flow led to loss of SiO2, CaO, Na2O, K2O and P2O5, and as a consequence, contents of immobile elements, such as Fe2O3 and Al2O3, increase. The mobility of SiO2 is important because Mauma Kea shield lavas divide into two groups that differ in SiO2 content. Post-magmatic mobility of SiO2 adds complexity to determining if these groups reflect differences in source or process. The most mobile elements during post-magmatic subaerial and submarine alteration are K and Rb, and Ba, Sr and U were also mobile, but their abundances are not highly correlated with K and Rb. The Ba/Th ratio has been used to document an important role for a plagioclase-rich source component for basalt from the Galapagos, Iceland and Hawaii. Although Ba/Th is anomalously high in Hawaiian basalt, variation in Ba abundance within a single flow shows that it is not a reliable indicator of a deep source component. In contrast, ratios involving elements that are typically immobile, such as La/Nb, La/Th, Nb/Th, Ce/Pb, Sr/Nd, La/Sm, Sm/Yb, Nb/Zr, Nb/Y and La/Yb, are uniform within the units, and they can be used to constrain petrogenetic processes. Nevertheless all elements are mobile under some conditions. For example, a surprising result is that relative to other samples, the uppermost sample collected from subaerial flow Unit 70, less than 1 m below the flow surface, is depleted in P, HREE and Y relative to all other samples from this flow unit. This result is complementary to the P, REE and Y enrichment found in subaerial lava flows from several Hawaiian shields, e.g., Kahoolawe and Koolau Volcanoes. These enrichments require mobilization of REE and followed by deposition a P-rich mineral. © 2016 Elsevier Ltd
1831.
Complexity of diatom response to Lateglacial and Holocene climate and environmental change in ancient, deep and oligotrophic Lake Ohrid (Macedonia and Albania)
Biogeosciences,
13
(4)
1351-1365
2016
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
butterfly; diatom; environmental change; epilimnion; Holocene; late glacial; nutrient availability; oligotrophic environment; paleolimnology; perciform; proxy climate record; water temperature, Albania; Lake Ohrid; Macedonia [Southern Europe], Bacillariophyta; Cyclotella; Cyclotella ocellata; Stephanodiscus
Abstract: ▾ Lake Ohrid (Macedonia and Albania) is a rare example of a deep, ancient Mediterranean lake and is a key site for palaeoclimate research in the northeastern Mediterranean region. This study conducts the analysis of diatoms as a proxy for Lateglacial and Holocene climate and environmental change in Lake Ohrid at a higher resolution than in previous studies. While Lake Ohrid has the potential to be sensitive to water temperature change, the data demonstrate a highly complex diatom response, probably comprising a direct response to temperature-induced lake productivity in some phases and an indirect response to temperaturerelated lake stratification or mixing and epilimnetic nutrient availability in others. The data also demonstrate the possible influence of physical limnological (e.g. the influence of wind stress on stratification or mixing) and chemical processes (e.g. the influence of catchment dynamics on nutrient input) in mediating the complex response of diatoms. During the Lateglacial (ca. 12 300-11 800 cal yr BP), the low-diversity dominance of hypolimnetic Cyclotella fottii indicates low lake productivity, linked to low water temperature. Although the subsequent slight increase in small, epilimnetic C. minuscula during the earliest Holocene (ca. 11 800-10 600 cal yr BP) suggests climate warming and enhanced stratification, diatom concentration remains as low as during the Lateglacial, suggesting that water temperature increase was muted across this major transition. The early Holocene (ca. 10 600-8200 cal yr BP) is characterised by a sustained increase in epilimnetic taxa, with mesotrophic C. ocellata indicating high water-temperature-induced productivity between ca. 10 600-10 200 cal yr BP and between ca. 9500-8200 cal yr BP and with C. minuscula in response to low nutrient availability in the epilimnion between ca. 10 200-9500 cal yr BP. During the middle Holocene (ca. 8200-2600 cal yr BP), when sedimentological and geochemical proxies provide evidence for maximum Holocene water temperature, anomalously low C. ocellata abundance is probably a response to epilimnetic nutrient limitation, almost mimicking the Lateglacial flora apart from the occurrence of mesotrophic Stephanodiscus transylvanicus in the hypolimnion. During the late Holocene (ca. 2600 cal yr BP-present), high abundance and fluctuating composition of epilimnetic taxa are probably a response more to enhanced anthropogenic nutrient input, particularly nitrogen enrichment, than to climate. Overall, the data indicate that previous assumptions concerning the linearity of diatom response in this deep, ancient lake are invalid, and multi-proxy analysis is essential to improve understanding of palaeolimnological dynamics in future research on the long, Quaternary sequence. © Author(s) 2016.
1830.
Coeval ages of Australasian, Central American and Western Canadian tektites reveal multiple impacts 790 ka ago
Geochimica et Cosmochimica Acta,
178307-319
2016
ISSN: 00167037
Publisher: Elsevier Ltd
Keywords:▾
argon-argon dating; impact structure; Quaternary; rare earth element; tektite, Belize [Central America]; Canada
Abstract: ▾ High resolution 40Ar-39Ar step heating dating of australites and indochinites, representing a large area of the Australasian strewn field, and more recently discovered tektite-like glasses from Central America (Belize) and Western Canada, were carried out. Precise plateau ages were obtained in all cases, yielding indistinguishable ages of 789 ± 9 ka for four australites, 783 ± 5 ka for four indochinites, 783 ± 17 ka for one Western Canadian and 769 ± 16 ka for one Belize impact glass. Concerning major elements and REEs, australites and the Western Canadian impact glass are indistinguishable. If the Western Canadian sample was transported by impact ejection and belongs to the Australasian strewn field, this implies extremely far ballistic transport of 9000 km distance, assuming a source crater in southern Asia. The distinct major element and REE composition of the Belize impact glass suggests formation in another separate impact event. We conclude that the Australasian/Western Canadian impact glasses formed 785 ± 7 ka ago in a single event and Belize impact glass in a separate event 769 ± 16 ka ago. The two impact events forming these two strewn fields occurred remarkably closely related in time, i.e., separated by <30 ka. © 2016 Elsevier Ltd.
1829.
Coesite in suevites from the Chesapeake Bay impact structure
Meteoritics and Planetary Science,
51
(5)
946-965
2016
ISSN: 10869379
Publisher: University of Arkansas
Abstract: ▾ The occurrence of coesite in suevites from the Chesapeake Bay impact structure is confirmed within a variety of textural domains in situ by Raman spectroscopy for the first time and in mechanically separated grains by X-ray diffraction. Microtextures of coesite identified in situ investigated under transmitted light and by scanning electron microscope reveal coesite as micrometer-sized grains (1-3 μm) within amorphous silica of impact-melt clasts and as submicrometer-sized grains and polycrystalline aggregates within shocked quartz grains. Coesite-bearing quartz grains are present both idiomorphically with original grain margins intact and as highly strained grains that underwent shock-produced plastic deformation. Coesite commonly occurs in plastically deformed quartz grains within domains that appear brown (toasted) in transmitted light and rarely within quartz of spheroidal texture. The coesite likely developed by a mechanism of solid-state transformation from precursor quartz. Raman spectroscopy also showed a series of unidentified peaks associated with shocked quartz grains that likely represent unidentified silica phases, possibly including a moganite-like phase that has not previously been associated with coesite. © 2016 The Meteoritical Society.
1828.
Changes in repeating earthquake slip behavior following the 2004 Parkfield main shock from waveform empirical Green's functions finite-source inversion
Journal of Geophysical Research: Solid Earth,
121
(3)
1910-1926
2016
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
earthquake magnitude; earthquake prediction; earthquake rupture; fault displacement; Green function; inverse problem; San Andreas Fault; seismograph; stick-slip; stress; wave velocity, California; Parkfield; United States
Abstract: ▾ Finite-source inversions are performed using small earthquake waveforms as empirical Green's functions (eGf) to investigate the rupture process of repeating earthquakes along the San Andreas Fault in Parkfield, California. The eGf waveform inversion method is applied to a repeating Mw 2.1 Parkfield earthquake sequence using three-component velocity waveforms recorded by an array of borehole seismometers. The obtained models show a circular slip distribution with a ~20 m radius, a 3.0-4.2 cm average slip of the main asperity, and peak displacement of 10.6-13.5 cm. The static stress drop distribution shows that the main asperity has a peak stress drop of 69.5-94.7 MPa. The inversion results support an earlier finding by Dreger et al. (2007) that high-strength asperities exist in the rupture areas of the Mw 2.1 events at Parkfield. In addition, notable temporal peak slip and stress drop reduction was observed after the 2004 Parkfield event while the average value remains constant (~12 MPa) over time. These events may represent mechanically strong sections of the fault, surrounded by regions that are undergoing continuous deformation (creep), Given repeated loading of the strong asperities, it would be expected that these similar repeating earthquakes should also have very similar slip distributions since surrounding regions are deforming aseismically. There are small differences in the waveforms of these repeating earthquakes, and this could be because of rupture nucleation points not being in exactly the same location within the region of the fault that is capable of stick-slip behavior. Our result indicates that waveform slip inversion is needed to reveal spatial and temporal variations of the stress drop within the rupture area to improve understanding of fault healing and rupture mechanics. ©2016. American Geophysical Union. All Rights Reserved.
1827.
Changes in dominant moisture sources and the consequences for hydroclimate on the northeastern Tibetan Plateau during the past 32 kyr
Quaternary Science Reviews,
131157-167
2016
ISSN: 02773791
Publisher: Elsevier Ltd
Keywords:▾
Incident solar radiation; Isotopes; Lakes; Moisture; Solar radiation, Holocenes; Hydrogen isotope; Monsoon; Tibetan Plateau; Westerlies; Younger Dryas, Atmospheric thermodynamics, Holocene; hydrogen isotope; moisture content; monsoon; paleoclimate; precipitation (climatology); Quaternary; wax; westerly, China; Qinghai; Qinghai Lake; Qinghai-Xizang Plateau
Abstract: ▾ Lake Qinghai, located on the northeastern Tibetan Plateau north of the modern maximum summer monsoon extent, is well situated to record northward advances of the summer monsoon. Existing paleoclimate records contain conflicting evidence for the timing of summer monsoon advance into this region: an early arrival pre-Younger Dryas or a late arrival at the beginning of the Holocene. A 30-kyr-long leaf wax hydrogen isotope (n-alkanoic acid, δ2Hwax) record from Lake Qinghai helps to address this discrepancy by elucidating changes in the three main moisture sources in this region: southerly (summer monsoon), northwesterly, and local precipitation. Lake Qinghai δ2Hwax indicates that the arid glacial period was dominated by northwesterly moisture. Extremely arid conditions prevailed from 15 to 14 ka, likely because westerly winds were weakening and the summer monsoon had not yet reached this region. This arid period ended by 13.6 ka when small amounts of summer monsoon precipitation reached Lake Qinghai. Summer monsoon moisture subsequently retreated off of the northeastern Tibetan Plateau during the Younger Dryas and re-advanced in the early Holocene. Summer monsoon precipitation decreased progressively throughout the Holocene in response to decreasing summer insolation, and the modern northwesterly- and local-dominated moisture regime was attained ca. 2.6 ka. Lake Qinghai δ2Hwax demonstrates that the summer monsoon extent was dynamic during the past 30 kyr, responding dramatically to insolation and North Atlantic circulation changes. Moreover, Lake Qinghai δ2Hwax demonstrates that local and northwesterly air masses are important moisture sources to the northeastern Tibetan Plateau, and should be considered when reconstructing past hydroclimate in this region. © 2015 Elsevier Ltd.
1826.
Borehole seismic network at Koyna, India
Seismological Research Letters,
87
(3)
661-667
2016
ISSN: 08950695
Publisher: Seismological Society of America
Keywords:▾
Geophysics; Reservoirs (water); Seismic waves; Seismographs; Seismology, Analysis of data; Artificial water; P waves; Seismic activity; Seismic networks; Triggered Earthquakes; West coast, Earthquakes, borehole geophysics; earthquake mechanism; P-wave; reservoir impoundment; reservoir-induced seismicity; seismicity; seismograph; trigger mechanism, India; Koyna Dam; Maharashtra
Abstract: ▾ The Koyna region located near the west coast of India has been continuously having artificial water-reservoir-triggered earthquakes since the impoundment of Koyna Dam in 1962. To improve the accuracy of locations of these triggered earthquakes, a unique network of eight borehole seismometers surrounding the seismicity was designed. Five of these have been installed at depths varying from 1134 to 1522 m, well below the Deccan basalt cover. As it is difficult to install the borehole seismometers with desired orientation of the horizontal components, amplitudes of P waves were used to decipher the true orientations after installation. Analysis of data for the period March-June 2015 demonstrated that there is a remarkable increase in the number of earthquakes located with the help of borehole seismometers. Using the existing network of 21 broadband surface seismometers, 184 earthquakes of ML ≥ 0:5 were located; however, with the borehole seismometers, the number of the located events increased to 888 such events. The data also indicate an increase in seismic activity corresponding to the period of increase in the rate of emptying of the Koyna and Warna reservoirs.
1825.
Assembly processes of gastropod community change with horizontal and vertical zonation in ancient Lake Ohrid: A metacommunity speciation perspective
Biogeosciences,
13
(10)
2901 – 2911
2016
ISSN: 17264170
Publisher: Copernicus GmbH
Keywords:▾
Balkan; Lake Ohrid; Turkmenistan; Gastropoda; assembly rule; biodiversity; biozonation; community dynamics; dispersal; ecozone; evolutionary biology; gastropod; holistic approach; lacustrine environment; relative abundance; speciation (biology); species richness
Abstract: ▾ The Balkan Lake Ohrid is the oldest and most diverse freshwater lacustrine system in Europe. However, it remains unclear whether species community composition, as well as the diversification of its endemic taxa, is mainly driven by dispersal limitation, environmental filtering, or species interaction. This calls for a holistic perspective involving both evolutionary processes and ecological dynamics, as provided by the unifying framework of the "metacommunity speciation model". The current study used the species-rich model taxon Gastropoda to assess how extant communities in Lake Ohrid are structured by performing process-based metacommunity analyses. Specifically, the study aimed (1) to identifying the relative importance of the three community assembly processes and (2) to test whether the importance of these individual processes changes gradually with lake depth or discontinuously with eco-zone shifts. Based on automated eco-zone detection and processspecific simulation steps, we demonstrated that dispersal limitation had the strongest influence on gastropod community composition. However, it was not the exclusive assembly process, but acted together with the other two processes - environmental filtering and species interaction. The relative importance of the community assembly processes varied both with lake depth and eco-zones, though the processes were better predicted by the latter. This suggests that environmental characteristics have a pronounced effect on shaping gastropod communities via assembly processes. Moreover, the study corroborated the high importance of dispersal limitation for both maintaining species richness in Lake Ohrid (through its impact on community composition) and generating endemic biodiversity (via its influence on diversification processes). However, according to the metacommunity speciation model, the inferred importance of environmental filtering and biotic interaction also suggests a small but significant influence of ecological speciation. These findings contribute to the main goal of the Scientific Collaboration on Past Speciation Conditions in Lake Ohrid (SCOPSCO) deep drilling initiative - inferring the drivers of biotic evolution - and might provide an integrative perspective on biological and limnological dynamics in ancient Lake Ohrid. © Author(s) 2016.
1824.
Earthquake impact on iron isotope signatures recorded in mineral spring water
Journal of Geophysical Research: Solid Earth,
121
(12)
8548 – 8568
2016
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
Central Europe; Germany; aquifer; biochemistry; earthquake swarm; iron; isotopic fractionation; spring water; time series analysis
Abstract: ▾ We investigated the iron isotope signatures of dissolved Fe in the water of the Wettinquelle mineral spring (Bad Brambach, Germany) by time series sampling covering seismically active periods related to tectonic activity near the Eger Rift system in central Europe. Our objective was to test whether Fe isotopes trace earthquake-induced abiotic and biotic changes in the fluid/rock interaction of the deep, fissured, granitic aquifer. We found that the dissolved Fe isotope signatures in spring water are distinct from the granitic source signature (δ56Fe = +0.09‰). Particularly, we discovered that water δ56Fe values are remarkably stable (−0.01 ± 0.11‰, 2SD, n = 4) before and during a strong seismic swarm period in 2000 (local magnitudes ML > 3), while O2 and H2 concentrations in water decrease and dissolved Fe content increases. Later, recurring events of lower δ56Fe values down to −0.3‰ are observed in the period from 2001 to 2003 with intermittent seismic events (1 < ML < 3.2). The observations indicate a time lag between tectonic forcing and Fe isotope response. The role of abiotic fluid/rock interaction and Fe-utilizing bacteria identified in the mineral spring water on Fe isotope fractionation is discussed. We explain recurring changes toward isotopically lighter values by a combination of Fe dissolution from deep granite and admixture of isotopically light Fe generated by a complex combination of abiotic and biotic processes operating in the aquifer when disturbed by swarm earthquakes events. We propose a conceptual model scenario of earthquake-triggered changes in biogeochemical processes. ©2016. American Geophysical Union. All Rights Reserved.
1823.
Aptian giant explosive volcanic eruptions in the Songliao Basin and northeast Asia: A possible cause for global climate change and OAE-1a
Cretaceous Research,
6298-108
2016
ISSN: 01956671
Publisher: Academic Press
Keywords:▾
aerosol; anoxic conditions; Aptian; climate change; explosive volcanism; global change; greenhouse gas; isotopic analysis; volcanic ash; volcanic eruption, China; Northeast Asia; Ontong Java Plateau; Pacific Ocean; Songliao Basin
Abstract: ▾ Volcanism is a natural climate force that causes variations in temperatures. The Aptian Oceanic Anoxic Event 1a (OAE-1a) was preceded by a prominent negative C-isotope excursion attributed to major volcanism of the Ontong Java plateau (OJP), which presumably resulted in a pCO2 increase and a climatic change. However, the OJP alone may not adequately explain some important isotopic signatures such as the negative strontium-isotope excursion from 125 Ma to 113 Ma that is recorded in the corresponding marine deposits. We present an independent and hitherto undocumented case, the giant Aptian volcanism in the Songliao Basin and northeast Asia (SB-V) on the Cretaceous active continental margin between the Eurasian and the Pacific plates, which covered an area of ca. 2.3 × 106 km2, nearly matching the simultaneous case of the OJP. Intensive strong, explosive volcanic eruptions of the SB-V occurred at 121-109 Ma and introduced a large volume of fine-grained volcanic ash and degassing volatiles into the atmosphere. The Aptian isotopic ratios (87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb) of marine carbonates from the Mid-Pacific shift in values between their Barremian pre-excursion high values and the negative magmatic values of the SB-V. The transient global cooling at the onset of the OAE-1a coincided with the beginning of the violent acidic eruption of the SB-V (119.9-120.2 Ma). We therefore infer that the SB-V must have played a role in the Aptian global climatic changes and OAE-1a through the heavy fall of volcanic dust and the outgassing of aerosol and greenhouse gases. © 2015 Elsevier Ltd.
1822.
Application of "Crust 1" 10k ultra-deep scientific drilling rig in Songliao Basin Drilling Project (CCSD-SKII)
Journal of Petroleum Science and Engineering,
145222-229
2016
ISSN: 09204105
Publisher: Elsevier B.V.
Keywords:▾
Application programs; Auxiliary equipment; Drilling rigs; Equipment; Hydraulic machinery, Catwalk; Crust 1; Drilling projects; Iron roughneck; Topdrive; Ultra-deep drilling, Drilling equipment, Chinese Continental Scientific Drilling Project; Cretaceous; drilling; drilling rig; hydrocarbon exploration, China; Songliao Basin
Abstract: ▾ This paper presents the earth science program SinoProbe in China, especially the deep continental scientific drilling equipment: "Crust 1" 10k ultra-deep scientific drilling rig and 4 indigenous key equipment: Topdrive system, Pipe handler, Hydraulic catwalk and Iron roughneck. These equipment can save auxiliary time, improve drilling efficiency and reduce labor intensity. Components and technical parameters were also introduced. "Crust 1" was deployed to drill through the Cretaceous continental strata of continental scientific drilling well: Songliao Basin Drilling Project (CCSD-SKII), which is the deepest scientific drilling program in China. Casing program was also introduced in this paper. Automated equipment performs a critical function in CCSD-SKII, the application can provide experience for furthermore scientific drilling program with designed well depth over 10,000 m in China. © 2016 Elsevier B.V..
1821.
Analysis of velocity dispersion using full-waveform multichannel sonic logging data: A case study
Geophysical Prospecting,
64
(4)
1016-1029
2016
ISSN: 00168025
Publisher: Blackwell Publishing Ltd
Keywords:▾
Acoustic logging; Flow of water; Gas hydrates; Gases; Hydration; Physical properties; Seismic waves; Seismology; Velocity; Wave propagation, Critical frequencies; Frequency components; Frequency independent; Geological setting; Laminated sediments; Rock physical properties; Seismic attenuation; Velocity dispersion, Dispersion (waves), data acquisition; gas hydrate; logging (geophysics); P-wave; Q factor; rock property; seismic attenuation; seismic velocity; wave dispersion; waveform analysis, Canada; Mackenzie Delta; Northwest Territories
Abstract: ▾ Seismic attenuation and velocity dispersion are potentially able to reveal the rock physical properties of the subsurface. Conventionally, a frequency-independent quality factor (Q) is measured. This Q is equivalent to the total velocity dispersion in a seismic record and is inadequate for analysing the attenuation mechanism or rock physical properties. Here a new method is proposed to extract the velocity dispersion curves so that more attributes can be obtained from full-waveform multichannel sonic logging data, especially the critical frequency (fc) if it is within the bandwidth of the data. This method first decomposes the seismic data into a series of frequency components, computes the semblance of each frequency component for different velocity values, cross-correlates the semblance matrices of adjacent frequency components to get the velocity gradients, and finally integrates to obtain a velocity dispersion curve. Results of this method are of satisfactory accuracy and robustness. This method is applied to the data acquired in Mallik 5L-38 gas hydrate research well in Mackenzie Delta, Northwest Territories, Canada. The observed P-wave velocity dispersion compares well with the geological setting. In the gas hydrate zone (about 900 m–1100 m), high concentration of gas hydrate causes very strong velocity dispersion and a distinct fc at about 15 kHz, likely due to strong scattering of centimetre-scale inclusions of gas hydrate; concurrently, water flow in connected cracks in some ranges of this zone adds a large part of velocity dispersion and a dimmer fc at about 9.5 kHz. Immediate underneath the gas hydrate zone, abundant free water in weakly laminated sediments causes quite strong velocity dispersion and an fc at about 6.5 kHz. Velocity dispersion is mild and without an obvious fc in sediments above the gas hydrate zone. © 2016 European Association of Geoscientists & Engineers
1820.
Analysis of 6-year fluid electric conductivity logs to evaluate the hydraulic structure of the deep drill hole at Outokumpu, Finland
International Journal of Earth Sciences,
105
(5)
1549 – 1562
2016
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
Finland; Outokumpu; Pohjois-Karjala; borehole logging; deep drilling; diffusion; electrical conductivity; formation water; hydraulic conductivity; hydraulic structure; monitoring; salinity; well logging
Abstract: ▾ Over the last two decades, the flowing fluid electric conductivity (FFEC) logging method has been applied in boreholes in the well-testing mode to evaluate the transmissivity, hydraulic head, and formation water electrical conductivity as a function of depth with a resolution of about 10–20 cm. FFEC profiles along the borehole are obtained under both shut-in and pumping conditions in a logging procedure that lasts only 3 or 4 days. A method for analyzing these FFEC logs has been developed and successfully employed to obtain formation parameters in a number of field studies. The present paper concerns the analysis of a unique set of FFEC logs that were taken from a deep borehole reaching down to 2.5 km at Outokumpu, Finland, over a 6-year time period. The borehole intersects paleoproterozoic metasedimentary, granitoid, and ophiolite-derived rocks. After the well was drilled, completed, and cleaned up, FFEC logs were obtained after 7, 433, 597, 948, and 2036 days. In analyzing these five profiles, we discovered the need to account for salinity diffusion from water in the formation to the borehole. Analysis results include the identification of 15 hydraulically conducting zones along the borehole, the calculation of flow rates associated with these 15 zones, as well as the estimation of the variation of formation water electrical conductivity as a function of depth. The calculated flow rates were used to obtain the tentative hydraulic conductivity values at these 15 depth levels. © 2015, Springer-Verlag Berlin Heidelberg.