All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
744.
Session 15. The Evolution of the Biogeochemical Cycling of Phosphorus and Other Bioessential Elements
Astrobiology,
8
(2)
356--361
2008
743.
Water content and dry bulk density of piston core CON01-603-2 from CONTINENT Ridge
742.
SHRIMP U–Pb dating, trace elements and the Lu–Hf isotope system of coesite-bearing zircon from amphibolite in the SW Sulu UHP terrane, eastern China
Geochimica et Cosmochimica Acta,
72
(12)
2973-3000
2008
ISSN: 0016-7037Abstract: ▾ In this study, we link mineral inclusion data, trace element analyses, U–Pb age and Hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi-stage metamorphic evolution of amphibolites from the Sulu ultrahigh-pressure (UHP) terrane, eastern China. Zircon grains separated from amphibolites from the CCSD-MH drill hole (G12) and Niushan outcrop (G13) were subdivided into two main types based on cathodoluminescence (CL) and Laser Raman spectroscopy: big dusty zircons with inherited cores and UHP metamorphic rims and small clear zircons. Weakly zoned, grey-white luminescent inherited cores preserve mineral inclusions of Cpx+Pl+Ap±Qtz indicative of a mafic igneous protolith. Dark grey luminescent overgrowth rims contain the coesite eclogite-facies mineral inclusion assemblage Coe+Grt+Omp+Phe+Ap, and formed at T=732–839°C and P=3.0–4.0GPa. In contrast, white luminescent small clear zircons preserve mineral inclusions formed during retrograde HP quartz eclogite to LP amphibolite-facies metamorphism (T=612–698°C and P=0.70–1.05GPa). Inherited zircons from both samples yield SHRIMP 206Pb/238U ages of 695–520Ma with an upper intercept age of 800±31Ma. The UHP rims yield consistent Triassic ages around 236–225 and 239–225Ma for G12 and G13 with weighted means of 229±3 and 231±3Ma, respectively. Small clear zircons from both samples give 206Pb/238U ages around 219–210Ma with a weighted mean of 214±3Ma, interpreted as the age of retrograde quartz eclogite-facies metamorphism. Matrix amphibole from both samples indicate Ar–Ar ages of 209±0.7 and 207±0.7Ma, respectively, probably dating late amphibolite-facies retrogression. The data suggest subduction of Neoproterozoic mafic igneous rocks to UHP conditions in Middle Triassic (∼230Ma) times and subsequent exhumation to an early HP (∼214Ma) and a late LP stage (∼208Ma) over a period of ∼16 and 6Myr, respectively. Thus, early exhumation from a mantle depth of 120–100km to about 60km occurred at an average rate of 0.3cm/y, while subsequent exhumation to a middle crustal level took place at approximately 0.54cm/y. These exhumation rates are considerably slower than those obtained for UHP rocks in the Dora Maira and Kokchetav massifs (2–3cm/y). Based on similar P–T estimates and trace element and Hf isotope compositions, Sulu amphibolites can be identified as retrograde UHP eclogites. The εHf(800) of +8 implies a significant input from the depleted mantle to the Sulu–Dabie terrane during the middle Neoproterozoic. Overgrown rims are characterized by a distinct trace element composition with low Lu/Hf and Th/U and significantly higher 176Hf/177Hf ratios than inherited cores, consistent with formation during/after garnet (re-)crystallization and fractionation of the Lu–Hf system during UHP metamorphism. The combined dataset suggests homogenization of the 176Hf/177Hf ratio within the metamorphic mineral assemblage and during protolith formation. Observed variations are explained by mixing of material from both domains during laser ablation, e.g., due to partial recrystallization of inherited cores.
741.
The potential of Lake Ohrid for long-term palaeoenvironmental reconstructions
Palaeogeography, Palaeoclimatology, Palaeoecology,
259
(2-3)
341 – 356
2008
ISSN: 00310182
Publisher: Elsevier B.V.
Keywords:▾
Albania; Eurasia; Europe; Lake Ohrid; Macedonia [Southern Europe]; Southern Europe; Bacillariophyta; biogeochemistry; bioturbation; chronology; comparative study; core analysis; grain size; lacustrine deposit; mass movement; paleoenvironment; physical property; reconstruction; sedimentation rate; seismic survey; tectonics; Tertiary
Abstract: ▾ Lake Ohrid, at the Macedonian/Albanian border, was likely tectonically formed during the Tertiary and therefore is one of the oldest lakes in Europe. However, only a few studies exist concerning the potential of Lake Ohrid sediments for long-term palaeoenvironmental reconstructions within the scope of future potential deep-drilling campaigns. Therefore, as a first step, a transect of short surface sediment cores was investigated for chronology, physical properties, grain size, and biogeochemistry. The results were compared with information derived from a shallow hydro-acoustic seismic survey. The investigations indicate a rather uniform and bioturbated sedimentation in the central part of the lake basin with mean sedimentation rates of ca. 0.5-1 mm/year. The sediment composition is dominated by authigenetic carbonates. Diatom frustules or fragments form the major part of biogenic matter deposits, as indicated by the relatively high contents of biogenic opal and low contents of total organic carbon and total nitrogen. The shallow hydro-acoustic seismic survey indicates that horizons of sediment redeposition occur sporadically. Towards the shore of the lake, the sedimentation rate increases and sedimentation is increasingly influenced by local inflows or mass-movement processes triggered by tectonic activities. Thus Lake Ohrid has a high potential for palaeoenvironmental reconstructions on a multi-decadal scale and provides additional information concerning tectonic activity in the region. © 2007 Elsevier B.V. All rights reserved.
740.
[English]
Formation evaluation of gas hydrate bearing sediments
Publisher
Society of Petrophysicists and Well-Log Analysts (SPWLA)
2008
Department of Geology, University of Leicester, Leicester, LE1 7RH, United Kingdom; British Geological Survey, Keyworth, Nottinghamshire, NG12 5GG, United Kingdom; RWE Dea AG, Hamburg, 22297, Germany739.
[English]
Constraining the far-field in situ stress state near a deep south african gold mine
Volume 46
,
Page 555 – 567
2008
Shell International Exploration and Production, Inc., Houston, TX, United States; Stanford University, Stanford, CA, United States; University of Oklahoma, Norman, OK, United StatesKeywords:▾
African gold mine; Borehole images; Boundary elements; Far-field; Far-field stress; Fault slip; Forward modeling; Induced stress; Insitu stress; Mining excavation; Natural earthquake; Principal stress; Seismic event; State of stress; Stress field; Stress state; Virgin state, Earthquakes; Gold; Gold mines; Mines; Rock mechanics; Rocks; Stresses, Mining
738.
737.
Yellowstone plume-continental lithosphere interaction beneath the Snake River Plain
Geology,
36
(1)
51-54
2008
ISSN: 00917613Keywords:▾
Lithosphere; Mantle plume; Volcanic activity, Basalt; Geochemistry; Isotopes; Tectonics; Volcanoes, Volcanic rocks, basalt; continental lithosphere; isotopic composition; lead isotope; mantle plume; mantle source; neodymium isotope; strontium isotope, Idaho; North America; Snake River Plain; United States
Abstract: ▾ The Snake River Plain represents 17 m.y. of volcanic activity that took place as the North American continent migrated over a relatively fixed magma source, or hotspot. The identification of a clear seismic image of a plume beneath Yellowstone is compelling evidence that the Miocene to recent volcanism associated with the Columbia Plateau, Oregon High Lava Plains, Snake River Plain, Northern Nevada Rift and Yellowstone Plateau represents a single magmatic system related to a mantle plume. A remaining enigma is, why do radiogenic isotope signatures from basalts erupted over the Mesozoic-Paleozoic accreted terrains suggest a plume source while basalts erupted across the Proterozoic-Archean craton margin indicate an ancient subcontinental mantle lithosphere source? We show that ancient cratonic lithosphere like that of the Wyoming province superimposes its inherent isotopic composition on sublithospheric plume and/or asthenospheric melts. The results show that Yellowstone plume could have a radiogenic isotope composition similar to the mantle source of the early Columbia River Basalt Group and that the plume source composition has persisted to the present day. © 2008 The Geological Society of America.
736.
Wellbore-stability study for the SAFOD borehole through the San Andreas Fault
SPE Drilling and Completion,
23
(4)
394-408
2008
ISSN: 10646671
Publisher: Society of Petroleum Engineers
Keywords:▾
Acoustic logging; Boring; Finite element method; Logging while drilling; Strike-slip faults, A-stable; California; Fault creep; Fluid penetration; Logging while drilling; Microearthquakes; Mud weights; San Andreas fault; Wellbore; Wellbore stability studies, Boreholes, borehole geophysics; borehole stability; creep; drilling; drilling fluid; finite element method; microearthquake; numerical model; San Andreas Fault, California; North America; Parkfield; United States
Abstract: ▾ This paper presents a wellbore-stability study of the San Andreas Fault Observatory at Depth (SAFOD) research borehole located near Parkfield, California, USA. In the summer of 2005, the SAFOD borehole was drilled successfully through the active trace of the San Andreas Fault (SAF) in an area characterized by fault creep and frequent microearthquakes. In this study, we report how the analysis of wellbore failures in the upper part of the hole, geophysical logs, and a model for stress gradients in the vicinity of the fault were used to estimate the mud weights required to drill through the fault successfully. Because logging-while-drilling (LWD) acoustic caliper data and real-time hole-volume calculations both showed that relatively little failure occurred while drilling through the SAF, the predicted mud weight was successful in drilling a stable borehole. However, a six-arm caliper log, run after drilling was completed, indicates that there was deterioration of the borehole with time, which appears to be caused by fluid penetration around the borehole. The LWD-resistivity measurements show that essentially no fluid penetration occurred as the hole was being drilled. Because of this, the mud weight used was capable of maintaining a stable wellbore. However, the resistivity data obtained after drilling show appreciable fluid penetration with time, thus negating the effectiveness of the mud weight and leading to time-dependent wellbore failure. Using finite-element modeling (FEM), we show that mud penetration into the fractured medium around the borehole causes failure with time. Copyright © 2008 Society of Petroleum Engineers.
735.
Well site selecting, core profile characteristics and distribution of the special lithology in CCSD-SK II
Acta Geologica Sinica (English Edition),
82
(5)
669 – 675
2008
ISSN: 10009515
Publisher: Science Press
Abstract: ▾ CCSD-SK II is one of the two drilling wells of the Cretaceous Scientific Drilling Project in Songliao Basin. It is located at limb section of the nose-like structure in the Gulong sag of the central depression, north of Songliao Basin. Based on the detailed description on the cores from the second member bottom of Nenjiang Formation to the third member top of Quantou Formation in CCSD-SK II, the core profile was established, and five common lithology (mudstone, silty mudstone, mudy siltstone, siltstone and sandstone) and eight special lithology (dolomite, volcanic ash, oil shale, lime mudstone, marlite, recrystalline limestone, ostracode clastic limestone and ostracode limestone) were identified. 172 layers of special lithology in CCSD-SK II were recognized with a total thickness of 14. 516m. They are distributed mainly in the Qingshankou Formation, the second and third member of Yaojia Formation and Nenjiang Formation. The detailed description of the cores and identification on special lithology are the base for the next studies.
734.
Water content and dry bulk density of pilot core to CON01-603-2, PANGAEA
733.
Viscosity of andesite melts and its implication for magma mixing prior to Unzen 1991-1995 eruption
Journal of Volcanology and Geothermal Research,
175
(1-2)
208-217
2008
ISSN: 03770273Keywords:▾
Igneous rocks; Iron; Mixing; Viscometers; Viscosity, andesite melt; dissolved water; magma mixing; redox state of iron; Unzen, Hydrodynamics, andesite; magma chamber; redox conditions; rhyolite; viscosity; volcanic eruption; water content, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano
Abstract: ▾ The viscosity of an iron-bearing melt with composition similar to Unzen andesite was determined experimentally in the high (109-1010.5 Pa s) and low (5-1000 Pa s) viscosity range using a parallel plate viscometer and the falling sphere method, respectively. Falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 K and 200 to 2000 MPa. Creep experiments were performed in the temperature range of 747-845 K at 300 MPa. The water content of the melt varies from nominally dry to 6.2 wt.% H2O. The Fe2+/Fetot ratio was determined for each sample in the quenched glass using a colorimetric method. Pressure has minor influence on the viscosity compared with the effect of temperature, water content (main compositional parameter controlling the viscosity) or with the Fe2+/Fetot ratio (especially important at low water content of the melt). Based on our new viscosity data and literature data with measured Fe2+/Fetot ratio we propose a new empirical equation to estimate the viscosity η (in Pa s) of andesitic melts as a function of temperature T (in K), water content w (in wt.%) and Fe2+/Fetot ratio. The derived relationship reproduces the experimental data (87 in total) in the viscosity range from 100.5 to 1013 Pa s with a 1σ standard deviation of 0.17 log units. However, application of this calculation model is limited to Fe2+/Fetot Fetot > 0.3 and to temperatures above Tg. Moreover, in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements. The viscosity data are used to interpret mixing processes in the Unzen magma chamber prior to 1991-1995 eruption. We demonstrate that the viscosities of the rhyolite and andesite melts from the two end-member magmas are nearly identical prior and during mixing, enabling efficient magma mixing. © 2008 Elsevier B.V. All rights reserved.
732.
Using open hole and cased-hole resistivity logs to monitor gas hydrate dissociation during a thermal test in the mallik 5L-38 research well, Mackenzie Delta, Canada
Petrophysics,
49
(3)
285-294
2008
ISSN: 15299074Abstract: ▾ Gas hydrates, which are naturally occurring ice-like combinations of gas and water, have the potential to provide vast amounts of natural gas from the world's oceans and polar regions. However, producing gas economically from hydrates entails major technical challenges. Proposed recovery methods such as dissociating or melting gas hydrates by heating or depressurization are currently being tested. One such test was conducted in northern Canada by the partners in the Mallik 2002 Gas Hydrate Production Research Well Program. This paper describes how resistivity logs were used to determine the size of the annular region of gas hydrate dissociation that occurred around the wellbore during the thermal test in the Mallik 5L-38 well. An open-hole logging suite, run prior to the thermal test, included array induction, array laterolog, nuclear magnetic resonance and 1.1-GHz electromagnetic propagation logs. The reservoir saturation tool was run both before and after the thermal test to monitor formation changes. A cased-hole formation resistivity log was run after the test.Baseline resistivity values in each formation layer (Rt) were established from the deep laterolog data. The resistivity in the region of gas hydrate dissociation near the wellbore (Rxo) was determined from electromagnetic propagation and reservoir saturation tool measurements. The radius of hydrate dissociation as a function of depth was then determined by means of iterative forward modeling of cased-hole formation resistivity tool response. The solution was obtained by varying the modeled dissociation radius until the modeled log overlaid the field log. Pretest gas hydrate production computer simulations had predicted that dissociation would take place at a uniform radius over the 13-ft test interval. However, the post-test resistivity modeling showed that this was not the case. The resistivity-derived dissociation radius was greatest near the outlet of the pipe that circulated hot water in the wellbore, where the highest temperatures were recorded. The radius was smallest near the center of the test interval, where a conglomerate section with low values of porosity and permeability inhibited dissociation. The free gas volume calculated from the resistivity-derived dissociation radii yielded a value within 20 per cent of surface gauge measurements. These results show that the inversion of resistivity measurements holds promise for use in future gas hydrate monitoring. © 2008 Society of Petrophysicists and Well Log Analysts. All rights reserved.
731.
Three-dimensional seismic attenuation structure around the SAFOD site, Parkfield, California
Bulletin of the Seismological Society of America,
98
(6)
2934-2947
2008
ISSN: 00371106Keywords:▾
Alternating methods; California; Cenozoic; Earthquake datum; Event locations; Fault zones; Fluid pathways; Low velocities; Portable arrays; Q-values; Salinian basements; San andreas faults; Seismic attenuations; Seismic networks; Seismogenic zones; Site response; Source parameters; Three-dimensional (3D), Buildings; Crack closure; Earthquakes; Fluids; Sedimentology; Tectonics; Three dimensional, Sedimentary rocks, data inversion; fault zone; P-wave; S-wave; San Andreas Fault; seismic attenuation; seismic data; seismic source; three-dimensional modeling, California; North America; Parkfield; United States
Abstract: ▾ We present models of the three-dimensional (3D) seismic attenuation structure, both Q p and Q s for a 16 km 2 area centered on the San Andreas Fault Observatory at Depth (SAFOD). The P- and S-wave t*-values used in the inversion were determined from local earthquake data recorded by seismic network and portable array stations within the Parkfield region by inverting arrival spectra for source parameters, t* and site response. Two techniques for determining the site response, the joint and alternating methods, were compared and it was found that the alternating method significantly underestimated site response variations. The t*-values were inverted to obtain 3D frequency-independent Q p and Q s models using 3D V p and V s models and associated event locations. A shallow low-Q area (Q p and Q s about 50-75) on the southwest edge of both models is attributed to the low-velocity Cenozoic sedimentary rocks that overlie the Salinian basement rock. A high-Q feature (Q p and Q s about 250 to 300) abuts this area and is interpreted as the Salinian basement. Adjacent to the San Andreas fault (SAF) trace, on its southwest side, there is a low-Q feature (Q p and Q s about 50-80) attributed to a wedge of sedimentary rocks; uniformly low Q p- and Q s-values suggest that the wedge is fluid rich. A low-Q basin feature (Q p and Q's about 50-75) on the northeast side of the SAF is interpreted as a fluid rich zone. Beneath this area there is a high-Q feature (Q p and Q s about 220-300), which may be caused by crack closure due to increased pressure with depth in the rocks of the Franciscan formation. Given these high Q-values, it seems unlikely that this area acts as a fluid pathway for fluids entering the fault zone from the east into the seismogenic zone of the SAF.
730.
The neglected side of speciation in ancient lakes: Phylogeography of an inconspicuous mollusc taxon in lakes Ohrid and Prespa
Hydrobiologia,
615
(1)
141 – 156
2008
ISSN: 15735117Keywords:▾
Eurasia; Europe; Lake Mikri Prespa; Lake Ohrid; Southern Europe; Bivalvia; Mollusca; Pisidium; Pisum sativum; Sphaeriidae (bivalves); Biodiversity; Electric network analysis; Graph theory; Network protocols; Sensor networks; endemic species; fauna; lake; mollusc; morphometry; phylogenetics; phylogeography; speciation (biology); taxonomy; Ancient lakes; Cryptic speciation; Morphometrics; Phylogenetics; Pisidium; Pisidium edlaueri; Pisidium maasseni; Lakes
Abstract: ▾ The morphologically remarkable endemic fauna within ancient lakes has received much attention in the literature. More inconspicuous taxa, however, often lack detailed molecular and morphometrical examination, although their proportion of the endemic fauna of an ancient lake must not be underestimated. Consequently, a better understanding of evolutionary patterns and processes within these lakes requires more knowledge about the often-neglected inconspicuous taxa. In the present study, we focus on the notoriously cryptic pea clam genus Pisidium (Bivalvia: Sphaeriidae). Though the genus is widely distributed, most endemic species are reported only from ancient lakes, including the European ancient sister lake system of Ohrid and Prespa on the Balkan Peninsula. Here we test for the first time hypotheses on the evolution of the endemic pea clams in this European biodiversity hotspot by molecular means. Combining a broad 16S phylogeny (comprising most European pea clam species), network analyses and morphometrical analyses, we found interesting biogeographical patterns and provide evidence for cryptic species in both lakes. Furthermore, we confirmed the proposed sister-species relationship of the endemics P. edlaueri in Lake Ohrid and P. maasseni in Lake Prespa, and we suggest scenarios of the endemic pea clam evolution within both lakes. The patterns of speciation found in the genus Pisidium are compared to patterns in morphologically distinct molluscan groups in lakes Ohrid und Prespa. © 2008 Springer Science+Business Media B.V.
729.
Signature of long supercycles in the Pleistocene history of Asian limnic systems
Journal of Paleolimnology,
40
(1)
445 – 452
2008
ISSN: 09212728Keywords:▾
Asia; Eurasia; Far East; Hvsgol Aymag; Lake Baikal; Lake Khubsugul; Mongolia; Russian Federation; biodiversity; biota; carbon isotope; eccentricity; glacial-interglacial cycle; paleolimnology; periodicity; Pleistocene; sediment chemistry; water budget
Abstract: ▾ The analysis of sediment chemistry and biota in drill cores from Lake Khubsugul in Mongolia (KDP-01) and Lake Baikal in Siberia (BDP-96/1), two great Eurasian freshwater lakes, detected prominent climate and biological events at 460-420 and 670 kyrs BP in addition to the orbital cycles of precession, tilt and eccentricity. The revealed long-term events were associated with notable changes in biodiversity and geography/landscapes, mainly in water budgets and weathering patterns. The span between 460-420 and 670 kyrs BP was the time when the climate and geographic conditions differed from those before and after these events. The corresponding 33-24 m (670-460 kyr) interval of the Khubsugul core lacked the usual signature of the Milankovitch glacial/interglacial cycles. Events of approximately these ages were found in some other continental ecosystems and in oceanic δ13C records. The two events may mark the phases of a 300-500-kyr long supercycle (or megastadial) in the evolution of continental ecosystems. Among other causes (e.g., regional tectonic events), this periodicity, being globally correlated, may be associated with the 400-kyr cycle of the Earth's orbital eccentricity. © 2007 Springer Science+Business Media B.V.
728.
The last 40 ka tephrostratigraphic record of Lake Ohrid, Albania and Macedonia: a very distal archive for ash dispersal from Italian volcanoes
Journal of Volcanology and Geothermal Research,
177
(1)
71 – 80
2008
ISSN: 03770273Keywords:▾
Albania; Eurasia; Europe; Macedonia [Southern Europe]; Mediterranean Sea; Southern Europe; Backpropagation; Landforms; Magnetic materials; Magnetic properties; Magnetic susceptibility; Minerals; Sedimentation; Sedimentology; Volcanoes; biostratigraphy; dispersion; explosive volcanism; magnetic susceptibility; tephra; tephrochronology; trachyte; volcanic ash; volcanic eruption; volcanology; Albania/Macedonia; Italian volcanoes; Lake Ohrid; tephrochronology; tephrostratigraphy; Lakes
Abstract: ▾ A 1075 cm long core (Lz1120) was recovered in the south-eastern part of the Lake Ohrid (Republics of Macedonia and Albania) and sampled for identification of tephra layers. Magnetic susceptibility investigations show rather high magnetic values throughout the core, with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment. Naked-eye inspection of the core allowed us to identify of two tephra layers, at 896-897 cm and 1070-1075 cm. Laboratory inspection of the grain-size fraction > 125 μm allowed for the identification of a third cryptotephra at 310-315 cm. Major element analyses on glass shards of the tephra layers at 896-897 cm and 1070-1075 cm show a trachytic composition, and indicate a correlation with the regionally dispersed Y-3 and Y-5 tephra layers, dated at ca 30 and 39 cal ka BP. The cryptotephra at 310-315 cm has a mugearitic-benmoreitic composition, and was correlated with the FL eruption of Mt. Etna, dated at 3370 ± 70 cal yr BP. These ages are in agreement with five 14C AMS measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core. The recognition of distal tephra from Italian volcanoes allows us to link the Lake Ohrid succession to other archives located in the Mediterranean area and in eastern Europe. The benmoreitic-mugearitic tephra layer at 310-315 cm is the first recognition in the Balkan area of a distal ash deposit from a mid-intensity explosive eruption of Mt. Etna, as far as 600 km from the source. © 2007 Elsevier B.V. All rights reserved.
727.
The forming mechanism of Dolostone of Nengjiang Formation in Songliao Basin - Example from CCSD-SK II
Acta Geologica Sinica (English Edition),
82
(1)
48 – 54
2008
ISSN: 10009515
Publisher: Science Press
Abstract: ▾ The CCSD-SK is the first scientific drilling well of whole core Cretaceous rocks in the continent of China, which is composed of two drilling wells: CCSD-SK I in the north and CCSD-SK II in the south. Totally, 62 layers of bedded and ellipsoidal dolostone were identified in the Nenjiang Formation during the description of CCSD-SK II. Dolostone nodular occurs as lens in the vertical section, and interior of the nodular is characterized by foliation which converges at both lateral edges. Under microscopic observation, dolostone is grey in the core and bright at the rim, and marl has been replaced, locally forming "leopard spot" dolomite. All these features indicate that dolomite of the Nengjiang Formation was the product of lacustrine facies limestone during penecontemporaneous replacement. The forming mechanism of dolostone of the Nenjiang Formation was that under the setting of the marine transgression of Late Cretaceous in the Songliao Basin, marls brought by turbidity flow and extinction of ostracoda began to deposit during the replacement, thus forming the dolostone.
726.
The formation of biogeochemical laminations in Lake Bosumtwi, Ghana, and their usefulness as indicators of past environmental changes
Journal of Paleolimnology,
40
(1)
339 – 355
2008
ISSN: 09212728Keywords:▾
Africa; Ashanti; Ghana; Lake Bosumtwi; Sub-Saharan Africa; West Africa; biogeochemistry; collagen; comparative study; crater lake; environmental indicator; lacustrine deposit; lamination; lead isotope; paleoenvironment; precipitation assessment; radiocarbon dating; reconstruction; stratigraphy; varve
Abstract: ▾ The sediments from Lake Bosumtwi, Ghana contain a unique record of fine-scale (mm to sub-mm) laminations, which will provide a valuable annual chronometer for reconstructing paleoenvironmental changes in West Africa covering much of the last 1 Ma. Comparisons of laminae counts to independent 210Pb dates and the rise in anthropogenic "bomb" radiocarbon support the interpretation of the laminations in the uppermost sediments as registering annual events. Radiocarbon dates on in-situ fish-bone collagen are in agreement with varve counts, further supporting the annual nature of our varve chronology. Over the instrumental period (1925-1999), dark-varve thickness measurements are correlated with local rainfall (r = 0.54) and appear able to resolve decadal-scale changes in precipitation. The relationship between varve thickness and rainfall provides support for our interpretation that dark-colored varve thickness records catchment runoff during the rainy season rather than dust flux during the dry season. Dark laminae alternate with organic and carbonate-rich light laminae formed during the fall period of enhanced productivity. Downcore, varves undergo significant microstratigraphic and geochemical variations, but retain the same pattern of alternating clastic and organic-rich laminae, providing support that the laminae may represent annual time markers for reconstructions of the deeper part of the record. © 2007 Springer Science+Business Media B.V.
725.
Testing two contrasting evolutionary patterns in ancient lakes: Species flock versus species scatter in valvatid gastropods of Lake Ohrid
Hydrobiologia,
615
(1)
169 – 179
2008
ISSN: 15735117Keywords:▾
Eurasia; Europe; Lake Mikri Prespa; Lake Ohrid; Southern Europe; Gastropoda; Invertebrata; Valvata; Valvatida; Digital signal processing; Shells (structures); evolutionary biology; freshwater ecosystem; gastropod; lake; phylogenetics; species flock; taxonomy; Ancient lake species flock; Ancient lake species scatter; Ancient lakes; Lake Ohrid; Lake Prespa; Valvata; Lakes
Abstract: ▾ Ancient lakes have long been recognized as "hot spots of evolution" and "evolutionary theatres" and they have significantly contributed to a better understanding of speciation and radiation processes in space and time. Yet, phylogenetic relationships of many ancient lake taxa, particularly invertebrate groups, are still unresolved. Also, the lack of robust morphological, anatomical, and phylogeographical data has largely prevented a rigorous testing of evolutionary hypotheses. For the freshwater gastropod genus Valvata-a group with a high degree of endemism in several ancient lakes-different evolutionary scenarios are suggested for different ancient lakes. Lake Baikal, for example, is inhabited by several endemic Valvata taxa that presumably do not form a monophyletic group. For such an evolutionary pattern, the term ancient lake species scatter is introduced here. In contrast, for the Balkan Lake Ohrid, workers previously suggested the presence of a monophyletic group of endemic Valvata species, that is, an ancient lake species flock. Sequence data of the mitochondrial cytochrome oxidase c subunit I gene (COI) from worldwide taxa, with a strong emphasis on Balkan species, are here used to test whether the putative Ohrid Valvata endemics represent an ancient lake species flock and to study patterns of speciation both on the Ohrid and the Balkan scale. The study reveals three distinct clades of endemic Valvata in Lake Ohrid. Monophyly of these taxa, however, is rejected, and they therefore do not represent an ancient lake species flock, but rather an ancient lake species scatter. Also, in contrast to many other gastropod groups in Lake Ohrid, the valvatids apparently did not radiate. Many Valvata taxa in ancient lakes are characterized by enhanced levels of shell complexity. However, it remains unclear whether these patterns are associated with ancient lake environments per se. It is here suggested that similarities in shell structure between North American and Balkan taxa might simply be due to convergent evolution. © 2008 Springer Science+Business Media B.V.
724.
Temperature variations at Lake Qinghai on decadal scales and the possible relation to solar activities
Journal of Atmospheric and Solar-Terrestrial Physics,
70
(1)
138 – 144
2008
ISSN: 13646826Keywords:▾
Atmospheric composition; Carbonates; Meteorology; Solar energy; Decadal scales; Solar activity; Sunspot; Temperature variation; Atmospheric temperature
Abstract: ▾ Temperature variations at Lake Qinghai, northeastern Qinghai-Tibet plateau, were reconstructed based on four high-resolution temperature indicators of the δ18O and the δ13C of the bulk carbonate, total carbonate content, and the detrended δ15N of the organic matter. There are four obvious cold intervals during the past 600 years at Lake Qinghai, namely 1430-1470, 1650-1715, 1770-1820, and 1920-1940, synchronous with those recorded in tree rings at the northeast Qinghai-Tibet plateau. The intervals of 1430-1470, 1650-1715, and 1770-1820 are consistent with the three coldest intervals of the Little Ice Age. These obvious cold intervals are also synchronous with the minimums of the sunspot numbers during the past 600 years, suggesting that solar activities may dominate temperature variations on decadal scales at the northeastern Qinghai-Tibet plateau. © 2007 Elsevier Ltd. All rights reserved.
723.
Temperature memory gauge survey and estimation of formation temperature of the USDP-4 conduit hole at Unzen Volcano, Japan
Journal of Volcanology and Geothermal Research,
175
(1-2)
20-27
2008
ISSN: 03770273Keywords:▾
Drilling; Estimation; Gages; Geothermal energy; Geothermal fields; Surveys; Volcanoes, Bore hole; borehole temperature; Drilling operations; Energy potential; formation temperature; Geothermal systems; High-temperature environments; Measured depth; Rotary drilling; temperature memory gauge; temperature simulation; temperature survey; volcanic conduit; Volcanic eruptions, Boreholes, borehole logging; drilling; gauge; geothermal system; magma; temperature profile; volcanic eruption, Asia; Eurasia; Far East; Japan; Kyushu; Nagasaki [Kyushu]; Unzen Volcano
Abstract: ▾ The Unzen Scientific Drilling Project was initiated in 1999 to investigate a magma conduit that had recently fed a volcanic eruption. The conduit hole, USDP-4, was drilled to 810 m in 2003. In 2004, the hole was extended with intention of reaching the conduit at a drilled depth of about 2000 m. This objective was achieved, and the final measured depth of USDP-4 was 1995.75 m. A new temperature memory gauge for rotary drilling application was designed and developed for the project in order to measure borehole temperatures as often as possible in the expected high temperature environment near the conduit. Temperature ratings of the tool are up to 250 °C with dewar. A total of 10 surveys were conducted at depths of 1555-1995.75 m. This tool was used in six surveys, and borehole temperature data was successfully obtained from all surveys. Based on the measured temperatures, it is apparent that the thermal energy potential of the conduit regime (i.e. thermal supply from conduit) is not large compared to that of most known geothermal systems. Formation temperatures along the conduit hole were estimated from measured temperatures by using a borehole temperature simulator, which we developed and subsequently modified. According to the simulation, the maximum in the formation temperature profile is located at a depth of about 1970 m, and its temperature was about 170 °C before the drilling operation started. This maximum approximately coincides with the center of the conduit, but is surprisingly low for a system that ceased eruption only 9 years before the temperature survey. © 2008 Elsevier B.V.
722.
Surge deposit misidentification at Spor Mountain, Utah and elsewhere: A cautionary message for Mars
Journal of Volcanology and Geothermal Research,
177
(4)
755-759
2008
Abstract: ▾ Before base surges were described in association with nuclear blasts and explosive volcanic eruptions (especially, the 1980 eruption of Mount St. Helens, Washington), laminar and cross-bedded volcanogenic surge deposits were commonly misinterpreted as being of fluvial or aeolian origin. One well-documented example involves the "water-laid tuffs" in and near the Spor Mountain beryllium mine, Utah; other examples abound. In light of how frequently volcanogenic surge deposits have been misinterpreted on Earth, extreme caution is urged for Mars studies. Contrary to what has been claimed, the markedly cross-bedded, salty deposits at Meridiani Planum on Mars need not have been formed by a combination of aeolian and aqueous processes, and their contained hematitic spherules need not have formed as aqueous concretions. Given the lack of indications of volcanism in the vicinity, and the planet-wide abundance of impact craters, deposition by surges associated with distant impact targets consisting of brine-soaked, locally sulfidic regolith is a reasonable explanation for all features observed, especially if diagenesis and weathering are considered. The uniformly sized and shaped, Ni-enriched blue-gray hematitic spherules would then be some type of vapor condensation spherules (including accretionary lapilli). A similar interpretation is possible for deposits in the Home Plate area, Gusev Crater. Unlike on the dry and atmosphereless Moon, salty impact surge deposits containing spherules should be common, and well-preserved, on Mars. © 2008 Elsevier B.V.
721.
Summary on China Cretaceous Scientific Drilling Engineering in Well-1 of Songliao Scientific Drilling (in Chinese with English abstract);中国白垩纪科学钻探松科一井(主井)钻探工程概要
Exploration Engineering,
31-4
2008
720.
Studies of the working mechanism of cuttings suspension of drilling fluid in the main hole of well Songke-1
Drilling Fluid and Completion Fluid,
25
(3)
4–6+83
2008