All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1194.
SAFOD Phase III Core sampling and data management at the Gulf Coast repository
Scientific Drilling
(1)
48-50
2011
ISSN: 18168957
Publisher: Copernicus GmbH
1193.
Postglacial fault drilling in Northern Europe: Workshop in Skokloster, Sweden
Scientific Drilling
(1)
56-59
2011
ISSN: 181689571192.
Physical properties of the Yaxcopoil-1 deep drill core, Chicxulub impact structure, Mexico
Meteoritics and Planetary Science,
46
(11)
1640-1652
2011
Abstract: ▾ The Chicxulub structure in Mexico, one of the largest impact structures on Earth, was formed 65Ma by a hypervelocity impact that led to the large mass extinction at the K-Pg boundary. The Chicxulub impact structure is well preserved, but is buried beneath a sequence of carbonate sediments and, thus, requires drilling to obtain subsurface information. The Chicxulub Scientific Drilling Program was carried out at Hacienda Yaxcopoil in the framework of the International Continental Scientific Drilling Program in 2001-2002. The structure was cored from 404m down to 1511m, through three intervals: 794m of postimpact Tertiary sediments, a 100m thick impactite sequence, and 616m of preimpact Cretaceous rocks thought to represent a suite of megablocks. Physical property investigations show that the various lithologies, including the impactite units and the K-Pg boundary layer, can be characterized by their physical properties, which depend on either changes in fabric or on mineralogical variations. The magnetic properties show mostly dia- or paramagnetic behavior, with the exception of the impactite units that indicate the presence of ferromagnetic, probably hydrothermally deposited magnetite and pyrrhotite. The magnetic fraction contributes mainly to enhanced magnetization in the impactite lithologies and, in this way, to the observed magnetic anomalies. The shape and orientation of the magnetic grains are varied and reflect inhomogeneous fabric development and the influence of impact-related redeposition and hydrothermal activity. The Chicxulub impact occurred at the time of the reverse polarity geomagnetic chron 29R, and this finding is consistent with the age of the K-Pg boundary. © The Meteoritical Society, 2011.
1191.
Petrophysical properties of the Outokumpu Deep Drill Core and the surrounding bedrock
Special Paper of the Geological Survey of Finland,
2011
(51)
63 – 82
2011
ISSN: 07828535ISBN:
978-952217152-8
Abstract: ▾ Petrophysical laboratory measurements of the Outokumpu Deep Drill Core were carried out in 2005-2008 at the Geophysical Laboratory of the Geological Survey of Finland (GTK). This report describes the pre-processing and measurement procedures and summarizes the measurement results of a total of 1992 samples taken at one-metre intervals along the drill core, representing depths from 55.5 m to 2503.9 m. The determined parameters were density and porosity, magnetic susceptibility and the intensity of remanent magnetization, electrical properties (resistivity and chargeability), P-wave velocity and thermal conductivity. The samples represented different rock types, and their petrophysical parameters showed typical values reflecting the mineralogical variation in the rocks. Generally weak magnetic properties characterize both the drill core samples and the outcropping bedrock (magnetic susceptibilities mainly ≤ 1000 × 10-6 SI). The only magnetically anomalous rocks are serpentinites and other altered ophiolitederived rocks of the Outokumpu assemblage, with susceptibilities of the order of ≥ 10 000 × 10-6 SI. No clear systematic effect of depth along the drill core on density or susceptibility can be observed. P-wave velocity and specific resistivity tend to decrease with depth. The porosity of mica schists increases with depth, but the drill core bulk densities do not change. Microfracturing due to pressure release possibly explains part of this effect. However, the grain densities of mica schists tend to increase with depth. Compared with surface densities, the densities of different rock types in the core are ca. 40 kg/m3 higher than the densities of corresponding rock types exposed around the drilling site (< 100 km). The magnetic properties of different rock types are of about the same intensity. Only black schists on the surface are more highly magnetic than those from the core, suggesting differences in monoclinic / hexagonal pyrrhotite contents.
1190.
Petrology of the dril hole R2500 at Outokumpu, Eastern Finland - The deepest dril hole ever driled in Finland
Special Paper of the Geological Survey of Finland,
2011
(51)
17 – 46
2011
ISSN: 07828535ISBN:
978-952217152-8
Abstract: ▾ Deep reflection seismic measurements in 2002 across the Outokumpu region revealed numerous reflectors, some of which related to mafic rock assemblages or to rocks that otherwise showed impedance contrasts with their surroundings. Two shallow reflective zones were later targeted for drilling in order to test interpretations of the seismic data. The immediate proximity of the famous Outokumpu ore belt naturally provided an additional incentive for drilling, which was undertaken by NEDRA, a state owned Russian drilling contractor. The Outokumpu region is located within the Paleoproterozoic Karelian schist belt close to the boundary between the Neoarchaean craton in the east and the Paleoproterozoic Svecofennian island arc complex in the west. The Karelian schist belt is divided into the lower Sariolan and Jatulian (2.5-2.1 Ga, mainly autochthonous), and the upper Kalevian (2.1-1.9 Ga) units. The deep drill hole R2500 is located in the allochthonous upper part of the latter unit. The uppermost 2 km of the drill hole consists mainly of mica schist with minor biotite gneiss, chlorite-sericite schist, black schist and hornblende-epidote schist intercalations. Within the interval ca. 1300-1500 m, the mica schist formation encloses a previously unknown assemblage of Outokumpu-type rocks. From ca. 1650 m downwards mica schist is intruded by pegmatitic granitoids, which in turn dominate from ca. 2000 m downwards. The chemical index of alteration (CIA) of the mica schists and biotite gneisses (50.3-65.2) indicates weak to moderate weathering of their source rocks. The lower CIA values of the mica schists probably reflect rapid and subsequent erosion, transportation and re-deposition from large deltas. On the other hand the higher CIA value of the biotite gneisses is a consequence of mineralogy, because it was originally fine-grained shale rich in clay minerals. Chlorite-sericite schist closely resembles mica schist chemically, while the hornblende-epidote schist differs in containing distinctly more CaO and less Na2O and K2O. Black schists are divided into two main types: "ordinary" black schist and calcareous black schist. The latter type is rich in tremolite and differs chemically mainly in containing less SiO2 and more CaO and MgO. Rocks of the Outokumpu assemblage consist of lithologically diverse rock types ranging from monomineralic serpentinites to various diopside- and/or tremolite-bearing skarns and quartz rocks. A few narrow and strongly schistose mafic dykes, which have been altered to chlorite schists, crosscut skarn. Primarily the Outokumpu-type rock assemblages represent fragments of mantle peridotites affected by hydrothermal and metasomatic alteration. For this reason serpentinites, skarns and quartz rocks usually have trace element concentrations very similar to pyrolite. Although pegmatitic granitoids show significant variations in the modal composition, they are always very leucocratic (M=0.2-4). Chemically all pegmatite types display peraluminous affinities (A/CNK = 1.02-2.08). On A/CNK versus SiO2 and Na 2O versus K2O diagrams pegmatites fall into both S-type or I-type categories.
1189.
Permafrost-associated natural gas hydrate occurrences on the Alaska North Slope
Marine and Petroleum Geology,
28
(2)
279-294
2011
ISSN: 02648172Keywords:▾
Alaska; Coring; Exploration; Petroleum systems; Resources; Seismic analysis, Energy resources; Gases; Hydration; Natural gas; Natural gas deposits; Natural gas well completion; Natural gas well drilling; Offshore oil wells; Permafrost; Petroleum deposits; Petroleum prospecting; Production; Rating; Resource valuation; Seismology; Stratigraphy, Gas hydrates, core logging; drilling; gas hydrate; gas production; hydrocarbon exploration; hydrocarbon generation; hydrocarbon resource; hydrocarbon technology; natural gas; permafrost, Alaska; North Slope; United States
Abstract: ▾ In the 1960s Russian scientists made what was then a bold assertion that gas hydrates should occur in abundance in nature. Since this early start, the scientific foundation has been built for the realization that gas hydrates are a global phenomenon, occurring in permafrost regions of the arctic and in deep water portions of most continental margins worldwide. In 1995, the U.S. Geological Survey made the first systematic assessment of the in-place natural gas hydrate resources of the United States. That study suggested that the amount of gas in the gas hydrate accumulations of northern Alaska probably exceeds the volume of known conventional gas resources on the North Slope. Researchers have long speculated that gas hydrates could eventually become a producible energy resource, yet technical and economic hurdles have historically made gas hydrate development a distant goal. This view began to change in recent years with the realization that this unconventional resource could be developed with existing conventional oil and gas production technology. One of the most significant developments was the completion of the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope, which along with the Mallik project in Canada, have for the first time allowed the rational assessment of gas hydrate production technology and concepts. Almost 40 years of gas hydrate research in northern Alaska has confirmed the occurrence of at least two large gas hydrate accumulations on the North Slope. We have also seen in Alaska the first ever assessment of how much gas could be technically recovered from gas hydrates. However, significant technical concerns need to be further resolved in order to assess the ultimate impact of gas hydrate energy resource development in northern Alaska. © 2009 Elsevier Ltd.
1188.
Patterns of seismic swarm activity in the Corinth Rift in 2000-2005
Izvestiya, Physics of the Solid Earth,
47
(7)
610 – 622
2011
ISSN: 10693513Abstract: ▾ Based on the data of the detailed earthquake catalog provided on the website of the Corinth Rift Laboratory, zones of swarm activity are revealed and the variations in the statistical parameters of seismic swarms that occurred in the western part of the Gulf of Corinth are calculated. The preliminary analysis of the catalogue is carried out; the magnitude of completeness and the accuracy of the location of the earth-quake are estimated; the changes in these parameters associated with the development of the observational network are assessed. The b-value (b-values) and the cluster dimension of the set of hypocenters are estimated, and time variations in these parameters in the course of the evolution of swarm activity are revealed. The style of changes in the parameters characterizing the seismic regime during intervals of swarm activity indicates that the process of failure exhibits scale redistribution over the course of time, changing from upscaling (progression from smaller to larger scales) at the stage of increasing seismicity to downscaling (progression from larger to lower scales) at the stage of decay. These particular features of enhancement and reduction of swarm seismicity are qualitatively similar to the scenarios of source preparation and aftershock relaxation of strong earthquakes. The pattern of variations of the swarm seismicity studied is similar to those identified in the previous laboratory and field modeling of various transient modes of seismicity. This fact confirms the relevancy of the retrieved results and conclusions based on the laboratory studies of transient modes, and suggests that the latter have a universal governing mechanism. © 2011 Pleiades Publishing, Ltd.
1187.
Palynological record from a composite core through Late Cretaceous-early Paleocene deposits in the Songliao Basin, Northeast China and its biostratigraphic implications
Cretaceous Research,
32
(1)
1-12
2011
ISSN: 01956671Keywords:▾
biostratigraphy; biozonation; chronostratigraphy; Cretaceous; Paleocene; palynology; palynomorph; taxonomy; Tertiary, China; Songliao Basin, Coniacian
Abstract: ▾ Two boreholes drilled approximately 75 km apart in the Songliao Basin, Northeast China, have together provided a composite core that represents an almost continuous section through Late Cretaceous-early Paleocene deposits. Eight biozones have been established for this succession of seven formations based on occurrences and associations of biostratigraphically significant palynomorph genera. Seven of these suggest that there was more or less continuous deposition from the late Turonian to the early Paleocene, with the eighth encompassing a Miocene formation that overlies the succession unconformably. This zonation provides a new chronostratigraphic framework for the Late Cretaceous deposits of the Songliao Basin. The ages of most of the formations involved differ from those determined previously. One of the sedimentary units, the Mingshui Formation, includes the Cretaceous/Paleogene boundary, which seems to be indicated by an apparent " mass extinction" of palynomorph taxa, a comparatively rare occurrence outside North America. The upper Quantou Formation, the lowest unit in the succession, is dated as late Turonian-Coniacian, which is much younger than previously thought. The same applies to the overlying Qingshankou and Yaojia formations, and also to the other three (Nenjiang, Sifangtai and Mingshui) but to a lesser extent, in the conformable succession. The Early/Late Cretaceous boundary must now be located probably below the Quantou Formation, either between it and the underlying Denglouku Formation or within the latter. © 2010 Elsevier Ltd.
1186.
Paleosecular variation and paleointensity records for the last millennium from southern South America (Laguna Potrok Aike, Santa Cruz, Argentina)
Physics of the Earth and Planetary Interiors,
184
(1-2)
41 – 50
2011
Keywords:▾
Argentina; Laguna Potrok Aike; Santa Cruz [Argentina]; Iron ores; Lithology; Stratigraphy; ICDP; Paleointensity; Paleosecular variations; PASADO; Southern Hemisphere; core analysis; geochronology; Holocene; magnetic intensity; magnetic survey; paleomagnetism; secular variation; sediment core; Southern Hemisphere; stratigraphic correlation; Minerals
Abstract: ▾ High-resolution paleo- and rock magnetic studies were performed on a group of four sediment cores from Laguna Potrok Aike (Santa Cruz, Argentina) representing the time period AD 1300-2000. The rock magnetic analyses show that the main magnetic mineral is (titano)magnetite with a concentration between 0.01 and 0.08%, and a grain size of 4-15 μm. This study is helpful in order to complete the paleosecular variation (PSV) and paleointensity type curves for South America which do not have a detailed record for the last millennium. The comparison with the study carried out for Lake El Trébol shows a very good agreement, supporting that PSV records of south-western Argentina can be developed into a stratigraphic correlation tool on a regional scale. © 2010 Elsevier B.V.
1185.
Modification of the magnetic mineralogy in basalts due to fluid-rock interactions in a high-temperature geothermal system (Krafla, Iceland)
Geophysical Journal International,
186
(1)
155-174
2011
ISSN: 0956540XKeywords:▾
Acidic conditions; Backscatter electron microscopy; Drill core; Ferrimagnetic minerals; Fluid-rock interaction; Geothermal areas; Geothermal systems; Grain shapes; High temperature; Hydrothermal activity; Hydrothermal alterations; Hydrothermal system; Icelands; Krafla caldera; Latter mechanism; Low-temperature oxidation; Magnetic anomalies; Magnetic mineralogy; Magnetic minerals; Magnetization loss; Microscopic methods; Mineral assemblage; Nano-porous; Natural remanent magnetization; Oceanic crust; Oxidizing conditions; Rock magnetic properties; Spinel lattices; Thermomagnetic analysis; Titanomagnetites; Two-stage transformations; Vacancy concentration; Volcanic islands, Basalt; Clay minerals; Concentration (process); Core drilling; Crystallography; Dissolution; Drills; Electron probe microanalysis; Geothermal fields; Lithology; Magnetic susceptibility; Magnetization; Mineralogy; Natural resources management; Oxide minerals; Paramagnetism; Petrography; Rocks; Silicates; Textures; Titanium; X ray diffraction; X ray diffraction analysis, Geomagnetism, basalt; caldera; chlorite; dissolution; geomagnetism; geothermal system; high temperature; hydrothermal activity; hydrothermal alteration; hydrothermal system; magnetic anomaly; magnetic susceptibility; magnetization; mineralogy; natural remanent magnetization; oceanic crust; oxidation; petrology; pyrite; smectite; volcanic island, Iceland; Krafla
Abstract: ▾ Active high-temperature (>150 °C) geothermal areas like the Krafla caldera, NE-Iceland, often show distinct magnetic lows in aeromagnetic anomaly maps suggesting a destruction of magnetic minerals by hydrothermal activity. The main alteration processes in such an environment are low-temperature oxidation (<350 °C, maghemitization) and fluid-rock interactions. We investigated the rock magnetic properties [natural remanent magnetization (NRM) magnetic susceptibility and their temperature and field variation] and the mineralogy, using X-ray diffraction, microscopic methods and electron microprobe analyses, of two drill cores (KH1 and KH3) from the rim of the Krafla caldera. The drill cores have distinctly lower NRM values (average <3 A m-1) compared to younger surface basalts (average 20 A m-1) along with a large variation in magnetic susceptibility (1.3 × 10-7- 4.9 × 10-5 m3 kg-1). The secondary mineral assemblage (sulphides, sphene, rutile and chlorite) indicates an alteration within the chlorite-smectite zone for both cores without depth zoning. Optical miscroscopy in combination with the Bitter technique and backscatter electron microscopy along with the thermomagnetic analyses allow distinguishing two different magnetomineralogical groups of titanomaghemite: (1) titanomaghemite with intermediate titanium concentration and probably high vacancy concentration, and (2) titanomaghemite with low titanium concentration and low vacancy concentration. The mineral assemblages, textures and magnetic properties deduced from the mentioned magnetic measurements indicate two-stage transformation mechanism: (1) Dissolution of titanium at low pH under oxidizing conditions. The ulvöspinel component of titanomagnetite and ilmenite forms rutile or sphene, and Fe2 + migrates out of the spinel lattice forming titanomaghemite. (2) Formation of pyrite and dissolution of remaining titanomaghemite under reducing and acidic conditions. The latter mechanism produces ghost textures (all titanomaghemite is transformed and only their former grain shapes are preserved), with only paramagnetic minerals left and ferrimagnetic minerals nearly dissolved. This mechanism could explain the significant magnetization loss, which is seen in many local magnetic anomaly lows within the oceanic crust and volcanic islands like Iceland or Hawaii. The production of nanoporous textures in titanomaghemites is suggested as a mechanism for the enhancement of the magnetic susceptibility values related to the hydrothermal alteration of Krafla. © 2011 The Authors. Geophysical Journal International © 2011 RAS.
1184.
Paleomagnetism of impact breccias from the Chicxulub crater - Implications for ejecta emplacement and hydrothermal processes
Physics of the Earth and Planetary Interiors,
186
(3-4)
154-171
2011
Abstract: ▾ Results of a paleomagnetic study of 89 samples from impact breccias from the Chicxulub crater are presented and used to investigate on ejecta emplacement, hydrothermal and alteration processes. The impactite sequence sampled in cores from Yaxcopoil-1 borehole is ∼100. m thick and formed by six subunits characterized by petrographic, scan images, geochemical and textural analyses, which point to different emplacement modes. Impact occurred within reverse polarity chron C29r; therefore, magnetization acquired at crater formation and shortly thereafter will present reverse polarity, which is supported by paleomagnetic measurements on melt samples from Yucatan-6 borehole. Results after step-wise thermal and alternating field demagnetization document a pattern of 23 upward and 29 downward inclinations at Yaxcopoil-1 around -33° and 38°, respectively. Measurements of magnetic hysteresis and variation of low-field susceptibility with temperature suggest low-Ti titanomagnetites and magnetite as main magnetic carriers. Petrographic observations indicate the presence of fine-grained magnetite, hematite and Fe-oxyhydroxides, related to hydrothermal alteration processes. Curie points are in the range of 520-580 °C. The wide range of unblocking temperature spectra points to variable grain sizes of a magnetic phase that unblocks around 580 °C. Hysteresis ratio plots indicate most samples fall in the pseudo-single domain field. In some samples, wasp-waist constrained hysteresis loops suggest magnetite and hematite. Analyses of vector plots and coercivity and unblocking temperature spectra do not show apparent differences within and between subunits. Subunits are characterized by distinct textural and compositional differences in size, type and relative abundance of clasts and melt-rich or carbonate-rich matrix types. Bulk properties vary with composition and clast contents, particularly within the Middle Suevite and Brecciated Melt Rock subunits that show higher values, while low values characterize the Lower Suevite carbonate-rich with rare basement clasts subunit. Magnetization acquisition mechanisms are discussed, with reference to impactite characteristics, and may relate to remagnetization from hydrothermal and post-impact alteration processes. © 2011 Elsevier B.V.
1183.
Neon identifies two billion year old fluid component in Kaapvaal Craton
Chemical Geology,
283
(3-4)
287-296
2011
ISSN: 00092541Keywords:▾
Abiogenic; Abiogenic origin; Archaean; Archean; Chemolithotrophs; Crustal fluid; Crystalline basement; Deep fluids; Deep fractures; Deep gold mines; Deep groundwaters; Dissolved gas; Endmembers; Fluid components; Fluid geochemistry; Fluid inclusion; Formation water; Fracture systems; Fracture water; High concentration; High salinity; Higher hydrocarbons; Hydro-carbon gas; Hydrothermal fluids; Isotopic analysis; Isotopic characteristics; Isotopic signatures; Key objective; Maintenance levels; Metamorphic fluids; Microbial communities; Microbial eco system; Neon isotopes; Noble gas; South Africa; Subsurface microbiology; Sulphate reducing bacteria; Time-scales; Water rock interactions; Water-rock reactions, Analytical geochemistry; Biodiversity; Biospherics; Ecosystems; Fluids; Fluorine; Fracture; Gallium; Gas fuel analysis; Gold mines; Groundwater; Groundwater geochemistry; Helium; Hydrocarbons; Inert gases; Isotopes; Methanogens; Microbiology; Mineralogy; Rock products; Saline water; Weathering, Neon, concentration (composition); isotopic composition; methanogenesis; microbial community; neon; noble gas; water chemistry; water-rock interaction, South Africa; Witwatersrand
Abstract: ▾ The deep gold mines of the Witwatersrand Basin, South Africa have gained recent attention not only because of investigations of the deep fracture water and associated CH4- and H2-rich gases found there, but because of recent reports of deep microbial communities persisting to depths of almost 3km - an exotic outpost of the Earth's deep biosphere. While shallower fluids in the basin (to approximately 1km) were found to contain abundant populations of methanogens and sulphate-reducing bacteria, the deepest, oldest, most saline fracture waters in the basin hosted hitherto unrecognised low biomass and low biodiversity chemoautotrophic ecosystems independent from the photosphere. Shallow and deep fluids also show distinct differences in gas and fluid geochemistry. Paleometeoric waters are dominated by hydrocarbon gases with compositional and isotopic characteristics consistent with production by methanogens utilising the CO2 reduction pathway. In contrast the deepest, most saline fracture waters contain gases that are dominated by high concentrations of H2 gas, and CH4 and higher hydrocarbon gases with isotopic signatures attributed to abiogenic processes of water-rock reaction. The high salinities (up to hundreds of g/L), highly altered δ18O and δ2H signatures, and both 36Cl and measurements of co-occurring nucleogenic noble gases for these fracture waters are consistent with extensive water-rock interaction over geologically long time scales in these high rock/water ratio environments. While the ultimate origin of these fluids has been attributed alternately to saline waters that penetrated the crystalline basement, formation water, or hydrothermal fluids in some cases, their δ18O and δ2H isotopic signatures have typically been so profoundly overprinted by the effects of long-term water-rock interaction that, for the most saline end-members, little evidence of their primary composition remains. The key objective of the present study is to further investigate the origin of these fluids by integrating for the first time detailed neon isotope analyses on the dissolved gases. Helium isotopic analysis confirmed that there is no significant mantle-derived component associated with these fluids and gases. Neon isotope results show distinct differences in neon composition that correspond to the different fluid geochemical end-members previously identified. Typical crustal neon signatures (type A) are identified in the paleometeoric waters populated with abundant methanogens. In contrast, the deep more saline fracture waters contain an enriched nucleogenic neon signature unlike any previously reported in crustal fluids. These samples show the highest 21Ne/22Ne ratios (0.160±0.003) ever reported in groundwater. Fluid inclusions in these rocks yield even higher 21Ne/22Ne ratios between 0.219 and 0.515, consistent with an extrapolated 21Ne/22Ne value of 3.3±0.2 at 20Ne/22Ne=0. We show that this enriched nucleogenic neon end-member represents a fluid component that was produced in the fluorine-depleted Archaean formations and trapped in fluid inclusions ≥2Ga ago. The observation of enriched nucleogenic neon signatures in deep fracture water implies the release of this billion year old neon component from the fluid inclusions and its accumulation in exceptionally isolated fracture water systems. The observed association of this Archean neon signature with H2-hydrocarbon-rich geogases of proposed abiogenic origin dissolved in the same deep groundwater suggests that the fracture systems have also allowed for the accumulation of various products of water-rock reactions throughout geologic times. One of these fracture systems contained the deepest characterised microbial ecosystems on earth - chemolithotrophs eking out an existence at maintenance levels independent from sunlight. Consequently, the enriched nucleogenic neon isotope signature may indicate regions in the Archaean crust where investigations of the deep biosphere might be focused. © 2011 Elsevier B.V.
1182.
Scientific drilling in the Great Rift Valley: The 2005 Lake Malawi Scientific Drilling Project - An overview of the past 145,000years of climate variability in Southern Hemisphere East Africa
Palaeogeography, Palaeoclimatology, Palaeoecology,
303
(1-4)
3-19
2011
ISSN: 00310182Keywords:▾
climate variation; lake level; Last Glacial Maximum; marine record; paleobiology; paleoclimate; rift zone; Southern Hemisphere; thermohaline circulation; tropical region, East African Lakes; Kenya; Lake Malawi; Rift Valley, Homo sapiens
Abstract: ▾ The recovery of detailed and continuous paleoclimate records from the interior of the African continent has long been of interest for understanding climate dynamics of the tropics, and also for constraining the environmental backdrop to the evolution and spread of early Homo sapiens. In 2005 an international team of scientists collected a series of scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from interior East Africa. The paleoclimate records, which include lithostratigraphic, geochemical, geophysical and paleobiological observations documented in this special issue of Palaeo3, indicate an interval of high-amplitude climate variability between 145,000 and ~60,000years ago, when several severe arid intervals reduced Lake Malawi's volume by more than 95%. These intervals of pronounced tropical African aridity in the early Late Pleistocene around Lake Malawi were much more severe than the Last Glacial Maximum (LGM), a well-documented period of drought in equatorial and Northern Hemisphere tropical east Africa. After 70,000years ago climate shifted to more humid conditions and lake levels rose. During this latter interval however, wind patterns shifted rapidly, and perhaps synchronously with high-latitude shifts and changes in thermohaline circulation. This transition to wetter, more stable conditions coincided with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa. © 2010 Elsevier B.V.
1181.
Metamorphism as a function of depth in metasedimentary rocks of the Outokumpu Deep Drill Hole
Special Paper of the Geological Survey of Finland,
2011
(51)
47 – 62
2011
ISSN: 07828535ISBN:
978-952217152-8
Abstract: ▾ Metamorphic mineral assemblages and mineral compositions were investigated in metasediments of the Outokumpu drill hole from the surface to 2.5 km depth in order to determine the Proterozoic geothermal gradient. The common mineral assemblage of the mica gneisses is biotite-plagioclase-quartz±muscovite. Finegrained garnet and Al silicates (sillimanite, kyanite, andalusite) are locally found, whereas staurolite is rare. Small abundances of leucosome indicating the onset of partial melting are present, especially in the lower parts of the hole, which also show some grain-size coarsening. The Fe and Mg distribution coefficient (KD) between coexisting garnet and biotite increases slightly from the surface to the deeper levels, indicating increasing temperature. The garnet-biotite thermometer shows a slight increase in temperatures from c. 605-610 °C near the surface to c. 620-630 °C at 1200-1500 m depth, indicating an average gradient of 19 °C/km, but the result is within the error limits of the thermometer (±15 °C). Temperatures calculated using Thermocalc software are several tens of degrees higher. Metamorphic pressures calculated using the garnet-biotite-plagioclase- quartz and garnet-muscoviteplagioclase- quartz barometers and the Thermocalc average PT method are in the range from c. 4-9 kbars. Pressures given by fluid inclusion barometry are 2-5 kbars. Geobarometry does not indicate systematic changes as a function of the depth. A clockwise PT path, where pressure increased to 8-9 kbars and was followed by decompression down to the andalusite field, explains the observed mineral assemblages and thermobarometric results.
1180.
Microbiological sampling and analysis of the Outokumpu Deep Drill Hole biosphere in 2007-2009
Special Paper of the Geological Survey of Finland,
2011
(51)
199 – 206
2011
ISSN: 07828535ISBN:
978-952217152-8
Abstract: ▾ Three sampling campaigns were performed during the years 2007-2009 to develop microbiological sampling techniques and to study the deep biosphere in the Outokumpu Deep Drill Hole R2500, drilled into a Palaeoproterozoic sequence of rocks consisting of metasediments, ophiolite-derived altered ultramafic rocks and pegmatitic granite. The results revealed the presence of microbial communities in the saline fluids sampled from the open borehole and fracture systems in the low-porosity crystalline bedrock in Outokumpu. According to the microbiological analyses, the microbial cell density varies from 105 cells ml-1 at the surface to 103 ml-1 at 2350 m depth. The composition of microbial communities in the borehole was found to vary with sampling depth, and the changes appear to be connected to both geological and geochemical factors as well as to fracture zones in the bedrock. Sulphate reducing bacteria and methanogenic archaea are present throughout the borehole water column.
1179.
Millennial-scale Arctic climate change of the last 3.6 million years: Scientific drilling at Lake El'gygytgyn, Northeast Russia
Oceanography,
24
(3)
80-81
2011
ISSN: 104282751178.
Monthly monitoring of gas and isotope compositions in the free gas phase at degassing locations close to the Nový Kostel focal zone in the western Eger Rifţ Czech Republic
Chemical Geology,
290
(3-4)
163 – 176
2011
ISSN: 00092541Keywords:▾
Bohemia; Cheb Basin; Czech Republic; Germany; Karlovarsky; Vogtland; Carbon dioxide; Degassing; Earthquakes; Gases; Geochemistry; Geologic models; Helium; Isotopes; Magnetic leakage; He ratios; Cenozoic; Earthquake swarms; Magma intrusion; ; carbon dioxide; Cenozoic; degassing; earthquake swarm; focal mechanism; gas; helium isotope; igneous intrusion; isotopic composition; isotopic ratio; lithospheric structure; magma; mantle chemistry; rift zone; Focusing
Abstract: ▾ We report new data on gas and isotope compositions of mantle-derived exhalations from five locations in the Vogtland (Germany)/NW Bohemia (Czech Republic) area, close to the Nový Kostel focal zone, recorded by monthly sampling of gases over a three year period. This region is the locus typicus for the term "earthquake swarm"; since 1985/86 the largest numbers of earthquake swarms in the Vogtland/NW Bohemia have occurred in the Nový Kostel focal zone. Mantle-derived degassing has been studied at four locations within the Cheb Basin degassing centre, and at the Wettinquelle spring to the north on the edge of the Cheb Basin. The Bublák and U Mostku locations are on the Počatky Plesná Fault Zone (PPZ) while the Kopanina and Dolni Častkov locations are on the Mariánské Lázně Fault (MLF). The mantle-derived helium content at locations along the PPZ covers the range of the sub-continental lithospheric mantle (SCLM). Along the MLF the 3He/4He ratios are with up to 5.4Ra a little bit lower as at the PPZ locations. The CO2/3He ratios point to a predominantly magmatic source. Depending on the magnitude of gas flux the monthly sampling results indicated various major influences on the fluid signatures at the monitored locations due to seasonal cycles based on the different strong influence of CO2/water interaction. Micro-seismicity occurred repeatedly during the monitoring period and seismically triggered geochemical anomalies were repeatedly observed at the locations close to the focal zone. The 3He/4He ratios drop from 5.9Ra (mean) up to 5.6Ra at Bublák and from 5.6Ra up to 5.3Ra at U Mostku. A decrease in 3He/4He ratios was observed prior to seismic events due to stress accumulation before rupturing, and also after the events due to the release of crustal-derived components within the area of the focal zone. Due to the higher 'helium baseline content' of the Kopanina gas the 3He/4He ratios decreased there only from 4.6 to 4.5Ra. At the Wettinquelle, the most distant from the focal zone, the 3He/4He ratios ranged between 2.3 and 2.5Ra altogether. Superimposed to the seismically induced anomalies a clear three month-lasting increase of mantle-derived helium was observed at the locations on the PPZ. The 3He/4He ratios increased to 6.3Ra at Bublák and to 6.0Ra at U Mostku. An increase in the 3He/4He ratios was also noted at Kopanina (to 4.7Ra) and Dolni Častkov (to 5.4Ra), interpreted as indicating an ascent of less degassed magma (dyke intrusions) from the deeper lithospheric mantle reservoir. Superimposed geochemical effects initiated by the temporal and spatial evolution of a hidden magmatic-driven geodynamic process have therefore been observed in a continental rift system for the first time. © 2011 Elsevier B.V.
1177.
Nanoscale porosity in SAFOD core samples (San Andreas Fault)
Earth and Planetary Science Letters,
301
(1-2)
179-189
2011
ISSN: 0012821XKeywords:▾
Fault rock; Permeability; SAFOD; San Andreas Fault; TEM, Core samples; Fluids; Ion beams; Mercury (metal); Porosity; Quartz; Rocks; Shear strength; Silicate minerals; Tectonics; Transmission electron microscopy, Structural geology, cataclasite; fault zone; feldspar; fluid pressure; hydrothermal fluid; permeability; porosity; quartz; San Andreas Fault; shear strength; transmission electron microscopy
Abstract: ▾ With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured core samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1-5%) is comparable to the connected fault rock porosity (2.8-6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10-21-10-19 m2 and 10-17 m2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radius>200nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radius<50nm) are typically observed in the extremely fine-grained matrix (grain size<1>m). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength of the fault. © 2010 Elsevier B.V.
1176.
New progress of integrated chronostratigraphy of the Cretaceous in Songliao Basin
Journal of Stratigraphy,
35
(3)
250-257
2011
1175.
P- and S-wave velocities of rocks from the upper 1.5 km crustal section sampled by the Outokumpu Deep Driling Project, Finland
Special Paper of the Geological Survey of Finland,
2011
(51)
95 – 104
2011
ISSN: 07828535ISBN:
978-952217152-8
Abstract: ▾ Longitudinal (VP) and shear wave (Vs) velocities of the upper 1.5 km of the Outokumpu Deep Drill Core were measured using a novel ultrasonic instrument. The aim of the laboratory tests was to determine the seismic velocities of rocks as a function of pressure and temperature and to identify parameters that influence these velocities. The velocities differed significantly throughout the core due to variations in mineralogical composition, lithology, fracturing and anisotropy. Notably, even a minor increase in pressure dramatically increased the VP and VS due to microcrack closure. When the pores and microcracks were closed by pressurization, the highest velocities in the upper schist series (33-1314 m) and the ophiolitic series (1314-1515 m) were met within chlorite-sericite schists (VP 5704 m/s, VS 3495 at 30 MPa) and diopside-tremolite skarns (VP 6572 m/s, VS 3752 m/s at 30 MPa), respectively. This new velocity data could improve the interpretation of crustal models by providing constraints on seismic velocities as well as estimates of the seismic impedances and Poisson's ratios in various rock types in the area of the Outokumpu Deep Drill Core.
1174.
Numerical study of gas evolution and transport behaviours in natural gas-hydrate reservoirs
Journal of Canadian Petroleum Technology,
50
(1)
70-88
2011
ISSN: 00219487
Publisher: Society of Petroleum Engineers (SPE)
Keywords:▾
Bubbles (in fluids); Gas hydrates; Gas oils; Gases; Hydration; Kinetics; Natural gas; Natural gasoline plants; Petroleum reservoirs; Transport properties, Critical gas saturation; Gas hydrate reservoir; Hydrate dissociation; Natural gas hydrate reservoir; Natural gas recoveries; Numerical simulators; Relative permeability curves; Reservoir simulation, Natural gas fields
Abstract: ▾ Gas hydrates are a potentially vast untapped source of natural gas. Recent numerical and field studies suggest the Mallik gas-hydrate field in Canada's Mackenzie Delta may represent a technically producible and potentially economically viable reservoir of natural gas. Our initial reservoir simulations using a kinetic reaction approach indicate that gas evolution and transport within porous geologic reservoirs have a significant effect on fluid production characteristics, while field and laboratory data suggest that significant amounts of evolved gas can be trapped for some time within the reservoir, depending on the field operation. In this work, we invoke modelling concepts extensively employed in quantifying gas ex-solution from viscous oils to further assess the kinetic behaviour of gas-hydrate ex-solution through depressurization. Here, the gas bubbles can be categorized into three groups with explicit transport behaviour: small bubbles (water phase), large bubbles (immobile) and connected bubbles (or free gas). These concepts allow the development of a new set of kinetic reactions for hydrate dissociation: one representing the (possibly delayed) conversion of hydrate into water and dispersed gas bubble phases, and one representing the evolution from dispersed bubbles to connected bubbles. These reactions can effectively capture the nonequilibrium fluidflow behaviour observed in field production tests. For modelling of the transport phenomenon, we assumed two explicit mobility formulations: (1) trapped bubbles (no mobility) and a flowing water phase and (2) large connected gas bubbles and flowing water (with relative mobility). Relative mobility can be estimated by using traditional gridblock-relative permeability curves. We then develop a simple mechanistic gas bubble trapping tool as a function of the capillary number, which can easily be incorporated into our numerical simulator. This entrapment of the nonwetting gas-phase results in higher values of critical gas saturation. Two case studies based on alternative representations of a Mallik-like gas-hydrate reservoir demonstrate that significant errors can result in reservoir modelling if these fluid transport phenomena are not adequately represented in numerical simulations. Aspects of the model developed here have been applied to history matching and prediction of natural gas recovery from a clastic, sand-dominated reservoir at the Mallik site.
1173.
Occurrence and distribution of series long-chain alkyl naphthalenes in Late Cretaceous sedimentary rocks of the Songliao Basin, China
Geochemical Journal,
45
(2)
125-135
2011
ISSN: 00167002
Publisher: The Physiological Society of Japan
Keywords:▾
anoxic conditions; biomarker; Cretaceous; hydrocarbon resource; naphthalene; sedimentary rock; source rock; thermal maturity; total organic carbon, China; Songliao Basin, Embryophyta
Abstract: ▾ A pair of series straight long-chain 2- and 1-alkyl naphthalenes (aNs) with alkyl chain carbon number up to 30 was detected in late Cretaceous sedimentary source rocks of the onshore Songliao Basin, NE China. Their sedimentary profile was shown to correlate positively with the relative abundances of several higher plant biomarkers including iP-iHMN and phenanthrene and weakly inversely with the relative abundance of alkylbenzenes. In contrast, the aNs distribution shows no relationship with hydrocarbon maturity indicators. The TOC, δ13C profile and other molecular features (e.g., CPI, OEP, Pr/Ph, Ga/C31H) were consistent with transgressive/regressive water cycles of the palaeo-lake of Songliao Basin. Decreasing Pr/Ph values in the upper horizon indicative of increasingly anoxic conditions. The distinctive occurrence and distribution of the long-chain aN compounds on the profile of the SK-1 borehole may imply some unique source inputs under particular lacustrine environmental conditions. Copyright © 2011 by The Geochemical Society of Japan.
1172.
Optimum design and application of balling-preventing bit
Coal Geology & Exploration,
39
(1)
71-73
2011
1171.
Organic geochemical records from Lake Malawi (East Africa) of the last 700years, part II: Biomarker evidence for recent changes in primary productivity
Palaeogeography, Palaeoclimatology, Palaeoecology,
303
(1-4)
140-154
2011
ISSN: 00310182Keywords:▾
accumulation rate; biomarker; ciliate; climate variation; deforestation; dinoflagellate; geochemical method; paleoclimate; phytoplankton; primary production; proxy climate record; sediment core; soil erosion; spectral analysis; tropical region, East Africa; East African Lakes; Lake Malawi, Bacillariophyta; Ciliophora; Coniferophyta; Dinophyceae
Abstract: ▾ Relatively few well-dated and high-resolution paleoclimate records of the past few centuries presently exist from tropical East Africa. Here, we examine the bulk and molecular geochemical records of two varved sediment cores from Lake Malawi, which together provide a continuous record of environmental variability in East Africa of the last 730years. We observe a number of changes in the aquatic ecosystem of Lake Malawi, which are likely attributed to both natural climatic forcing and anthropogenic activities. Biomarkers of dinoflagellates (dinosterol) and bacterivorous ciliates (tetrahymanol) display increased accumulation rates from ~1900AD to the present, while a simultaneous decrease in accumulation rates of diatom biomarkers (isololiolide/loliolide) is observed. Increased accumulation rates of retene, a compound derived from conifers, are also noted since ~1930AD and likely reflect increased soil erosion due to deforestation of the Lake Malawi watershed. Spectral analysis of the high-resolution TOC record indicates a periodicity of 204years, similar to the 206year cycle noted in 14C and 10Be records, suggesting a link between East African climate and solar forcing. © 2010 Elsevier B.V.
1170.
Organic geochemical records of environmental variability in Lake Malawi during the last 700 years, Part I: The TEX86 temperature record
Palaeogeography, Palaeoclimatology, Palaeoecology,
303
(1-4)
133-139
2011
ISSN: 00310182Keywords:▾
geochemical method; paleoclimate; paleotemperature; primary production; prokaryote; proxy climate record; surface temperature; surface water; water temperature, East African Lakes; Lake Malawi, Archaea
Abstract: ▾ We have applied the TEX86 paleothermometer to produce a surface water temperature record for Lake Malawi spanning the past 700years. Over much of the record temperature fluctuates from ~24-27°C with a mean of ~25°C; however, there has been a substantial increase in temperature of ~2.0°C during the past ~ 100years. The TEX86 temperature record reveals a strong similarity to the instrumental record; both records demonstrate warming (~0.7-1.4°C) over the past ~50years as well as a cooling anomaly around 1959. Comparison of the TEX86 temperature record with the proxy records of primary productivity suggests that wind induced upwelling and/or precipitation have a strong influence on the surface temperature of Lake Malawi. © 2010 Elsevier B.V.