All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1119.
Deciphering lake and maar geometries from seismic refraction and reflection surveys in Laguna Potrok Aike (southern Patagonia, Argentina)
Journal of Volcanology and Geothermal Research,
201
(1-4)
357 – 363
2011
Keywords:▾
Argentina; Laguna Potrok Aike; Santa Cruz [Argentina]; Anoxic sediments; Lakes; Lithology; Refraction; Seismic waves; Seismology; Settling tanks; Submarine geophysics; Surveys; Velocity; Explosive volcanism; Maars; PASADO project; Sedimentary basin; South America; drilling; explosive volcanism; lithology; maar; ray tracing; sedimentary basin; seismic reflection; seismic refraction; seismic survey; seismic velocity; volcaniclastic deposit; Sedimentology
Abstract: ▾ Laguna Potrok Aike is a bowl-shaped maar lake in southern Patagonia, Argentina, with a present mean diameter of ~3.5km and a maximum water depth of ~100m. Seismic surveys were carried out between 2003 and 2005 in order to get a deeper knowledge on the lake sediments and the deeper basin geometries. A raytracing model of the Laguna Potrok Aike basin was calculated based on refraction data while sparker data were additionally used to identify the crater-wall discordance and thus the upper outer shape of the maar structure. The combined data sets show a rather steep funnel-shaped structure embedded in the surrounding Santa Cruz Formation that resembles other well-known maar structures. The infill consists of up to 370m lacustrine sediments underlain by probably volcanoclastic sediments of unknown thickness. The lacustrine sediments show a subdivision into two sub-units: (a) the upper with seismic velocities between 1500 and 1800ms-1, interpreted as unconsolidated muds, and (b) the lower with higher seismic velocities of up to 2350ms-1, interpreted as lacustrine sediments intercalated with mass transport deposits of different lithology and/or coarser-grained sediments. The postulated volcanoclastic layer has acoustic velocities of >2400ms-1. The lake sediments were recently drilled within the PASADO project in the framework of the International Continental Scientific Drilling Program (ICDP). Cores penetrated through lacustrine unconsolidated sediments down to a depth of ~100m below lake floor. This minimal thickness for the unconsolidated and low-velocity lithologies is in good agreement with our raytracing model. © 2011 Elsevier B.V.
1118.
Characterization of bacterial diversity to a depth of 1500m in the Outokumpu deep borehole, Fennoscandian Shield
FEMS Microbiology Ecology,
77
(2)
295 – 309
2011
ISSN: 15746941Keywords:▾
Bacteriological Techniques; Biodiversity; Colony Count, Microbial; DNA, Bacterial; Finland; Gene Library; Phylogeny; RNA, Ribosomal, 16S; Sulfur-Reducing Bacteria; Water; Water Microbiology; Baltic Shield; Finland; Ita Suomen; Outokumpu; Bacteria (microorganisms); Comamonadaceae; Desulfotomaculum; Firmicutes; uncultured bacterium; bacterial DNA; RNA 16S; water; aquifer; bacterium; bedrock; borehole; community composition; crystalline rock; dominance; electrokinesis; extremophile; groundwater; microbial community; sampling; species diversity; vertical distribution; article; bacterial count; biodiversity; chemistry; classification; Finland; gene library; genetics; Gram negative anaerobic bacteria; isolation and purification; microbiological examination; microbiology; phylogeny
Abstract: ▾ This paper demonstrates the first microbiological sampling of the Outokumpu deep borehole (2516m deep) aiming at characterizing the bacterial community composition and diversity of sulphate-reducing bacteria (SRB) in Finnish crystalline bedrock aquifers. Sampling was performed using a 1500-m-long pressure-tight tube that provided 15 subsamples, each corresponding to a 100-m section down the borehole. Microbial density measurements, as well as community fingerprinting with 16S rRNA gene-based denaturing gradient gel electrophoresis, demonstrated that microbial communities in the borehole water varied as a function of sampling depth. In the upper part of the borehole, bacteria affiliated to the family Comamonadaceae dominated the bacterial community. Further down the borehole, bacteria affiliated to the class Firmicutes became more prominent and, according to 16S rRNA gene clone libraries, dominated the bacterial community at 1400-1500m. In addition, the largest number of bacterial classes was observed at 1400-1500m. The dsrB genes detected in the upper part of the borehole were more similar to the dsrB genes of cultured SRBs, such as the genus Desulfotomaculum, whereas in the deeper parts of the borehole, the dsrB genes were more closely related to the uncultured bacteria that have been detected earlier in deep earth crust aquifers. FEMS Microbiology Ecology © 2011 Federation of European Microbiological Societies. No claim to original Finnish government works.
1117.
1116.
Deep rock damage in the san andreas fault revealed by P- and S-type fault-zone-guided waves
Geological Society Special Publication,
359
(1)
39-53
2011
ISSN: 03058719DOI:10.1144/SP359.3
Keywords:▾
earthquake; fault slip; fault zone; P-wave; Rayleigh wave; S-wave; seismic wave, California; San Andreas; United States
Abstract: ▾ Damage to fault-zone rocks during fault slip results in the formation of a channel of low seismic-wave velocities. Within such channels guided seismic waves, denoted by F g, can propagate. Here we show with core samples, well logs and F g-waves that such a channel is crossed by the SAFOD (San Andreas Fault Observatory at Depth) borehole at a depth of 2.7 km near Parkfield, California, USA. This laterally extensive channel extends downwards to at least half way through the seismogenic crust, more than about 7 km. The channel supports not only the previously recognized Love-type- (F L) and Rayleigh-type- (F R) guided waves, but also a new fault-guided wave, which we name F Φ. As recorded 2.7 km underground, F Φ is normally dispersed, ends in an Airy phase, and arrives between the P- and S-waves. Modelling shows that F Φ travels as a leaky mode within the core of the fault zone. Combined with the drill core samples, well logs and the two other types of guided waves, F Φ at SAFOD reveals a zone of profound, deep, rock damage. Originating from damage accumulated over the recent history of fault movement, we suggest it is maintained either by fracturing near the slip surface of earthquakes, such as the 1857 Fort Tejon M 7.9, or is an unexplained part of the fault-creep process known to be active at this site. © The Geological Society of London 2011.
1115.
Deep scientific drilling to study reservoir-triggered earthquakes in Koyna, Western India
Scientific Drilling
(12)
53-54
2011
ISSN: 181689571114.
Determination of the optimal sampling interval for cyclostratigraphic analysis by using sampling theorem and accumulation rates
Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences,
36
(1)
12 – 16
2011
1113.
Discovery and focused study of the Chicxulub impact crater
Eos, Transactions American Geophysical Union,
92
(25)
209-210
2011
Keywords:▾
Chicxulub impact crater, history
Abstract: ▾ Three decades ago, a landmark paper by Alvarez et al. [1980] proposed that an asteroid impact 65.5 million years ago was the cause of the mass extinction of about 75% of species, including the dinosaurs, at the boundary between the Cretaceous and Paleogene periods (K-Pg), formerly known as the Cretaceous-Tertiary (K-T) boundary. Alvarez et al. used geochemical studies on carbonate sequences from Italy, Denmark, and New Zealand to study the boundary layer, which was enriched in iridium and other platinum group elements (PGEs) at concentrations well above background levels. They associated these enrichments with the collision of an asteroid that injected large amounts of pulverized debris into the atmosphere, resulting in blockage of solar radiation, global cooling, and a shutdown of photosynthesis.
1112.
Discovery of Late Cretaceous foraminifera in the Songliao Basin: Evidence from SK-1 and implications for identifying seawater incursions
Chinese Science Bulletin,
56
(3)
253 – 256
2011
ISSN: 10016538
Publisher: Science in China Press
Keywords:▾
Coniacian; Foraminifera; Haplophragmoides; Hedbergella; Pullenia
Abstract: ▾ The Songliao Basin is the largest oil-bearing basin in China. In the absence of sufficient evidence, the possibility of seawater incursion(s) into the Songliao Basin remains controversial. Recently, we discovered relatively abundant foraminifera fossils from units 1 and 2 of the Nenjiang Formation of borehole SK-1. Benthic foraminifera (Gavlinella sp., Anomalinoides sp., Pullenia sp., Haplophragmoides sp., Karrorulina hokkaidoana, Clavulinoides sp.), as well as planktonic foraminifera (Archaeoglobigerina blowi, Archaeoglobigerina cretacea and Hedbergella flandrini), were identified. These fossils were widely distributed in the marine Cretaceous. According to the global distribution of the above-mentioned planktonic foraminifera, the age of these fossil bearing strata appears to be Late Coniacian to Santonian. More importantly, these foraminifera provide direct evidence for marine water incursions into the Songliao Basin during deposition of the Lower Nenjiang Formation. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.
1111.
Chemical and isotope compositions of drilling mud gas from the San Andreas Fault Observatory at Depth (SAFOD) boreholes: Implications on gas migration and the permeability structure of the San Andreas Fault
Chemical Geology,
284
(1-2)
148-159
2011
ISSN: 00092541Keywords:▾
A-thermal; Active fault; Carbon isotopes; Continuous flows; Deforming zone; Diffusion loss; Dominant mechanism; Drilling mud; Drilling mud gas; Fault direction; Fault strands; Fluid exchange; Gas accumulation; Gas concentration; Gas migration; Gas monitoring; Helium isotopes; Hydrocarbon generation; Hydrocarbon migration; Isotope compositions; Mantle volatiles; Molecular compositions; Noble gas isotopes; Organic matter; Permeability structure; SAFOD; San Andreas Fault; Shale gas; Source rocks; Spatial variability; Thermal degradations, Boreholes; Boring; Buildings; Drill pipe; Helium; Hydrocarbons; Inert gases; Isotopes; Observatories; Oil well drilling; Petroleum geology; Shale; Tectonics, Gas permeability, active fault; borehole; chemical composition; diffusion; drilling; helium isotope; hydrocarbon migration; isotopic composition; noble gas; organic matter; permeability; San Andreas Fault; spatial distribution
Abstract: ▾ In this contribution we present results from two individual gas monitoring experiments which were conducted during the drilling of the SAFOD (San Andreas Fault Observatory at Depth) boreholes. Gas from circulating drilling mud was monitored during the drilling the SAFOD III side tracks and was later analyzed for δ13C (CH4, C2H6 and C3H8), H/D (CH4) and noble gas isotopes. Furthermore, gas accumulations induced by drill pipe retrieval ("trip gas") from the SAFOD MH and the SAFOD III boreholes were also investigated. The data are interpreted in the context of gas migration processes and the permeability structure of the San Andreas Fault (SAF) around two actively deforming zones at 3194m and 3301m borehole depth. Helium isotope ratios of 0.86 Ra at 3203m and between 0.51 and 0.88 Ra at 3262m (Ra is the atmospheric 3He/4He ratio) indicate an improved flow of mantle volatiles between both fault strands. Much lower values were observed at 3147m (0.26 Ra) and 3312m (0.22 Ra). Hydrocarbon concentrations coincide with the occurrence of shale at ~3150-3200m and below ~3310m depth. The molecular and isotope composition of hydrocarbons and their spatial distributions imply hydrocarbon generation by thermal degradation of organic matter followed by extensive diffusion loss. Carbon isotope data furthermore suggest a thermal maturity of the source rock of approx. 1.4%R0. The concentration of trip gas is generally low in the interval 3100. m-3450. m but exhibits high spatial variability. At 3128. m and 3223. m depth, the trip gas concentrations are as low as in the granite section of the SAFOD Main Hole. Considerable variations of Ra values, trip gas concentrations, and the molecular composition of hydrocarbons when penetrating the active fault strands let us conclude that the permeability of the fault transverse to the fault direction is limited and that the active fault has not been breached over many earthquake cycles such that little or no fluid exchange took place. Diffusion is the dominant mechanism controlling hydrocarbon migration through the fault strands. The elevated Ra values between both fault strands may reflect either episodic or continuous flow of mantle-derived fluids, suggestive of some limited permeability parallel to the fault direction. © 2011 Elsevier B.V.
1110.
Characteristics of elastic properties of the crystalline rock samples from the Outokumpu Deep Drill Hole: Results of Acoustopolariscopic Laboratory measurements
Special Paper of the Geological Survey of Finland,
2011
(51)
207 – 218
2011
ISSN: 07828535ISBN:
978-952217152-8
Abstract: ▾ We present the results of laboratory measurements of the elastic and nonelastic properties of drill core samples from depths of 94-2298 m in the Outokumpu Deep Drill Hole, eastern Finland. A total of 43 cubic rock samples were prepared (30-40 mm side length) and measured with the method of acoustopolariscopy under ambient conditions. In addition, the average velocities were calculated from the modal composition of the rocks. The measurement results provide the complete velocity matrices of the samples with the main components of P-waves as well as S-waves and their anisotropy factors. From the surface down to a depth of ∼1300 m (mostly metasediments), the Outokumpu rocks were found to be strongly anisotropic. The lowest measured anisotropy values were observed in the ∼1300-1600 m depth range (ophiolite-derived altered ultramafic rocks and metasediments). In the lower part of the hole from 1600 m to the hole bottom (metasediments and pegmatitic granite), the velocity anisotropy was variable. The effect of linear acoustic anisotropic absorption (LAAA) is exhibited in samples from the upper and lower sections of the drill hole. We attribute the variations in P- and S-wave velocities and their anisotropies to the variation in rock types and the drilling-induced relaxation of pressure (and to a minor degree temperature), which has resulted in decompaction and the formation of micro-cracks in the drill core. Therefore, a linear decrease in seismic velocities as a function of depth is observed in the laboratory measurements.
1109.
Earthquake Rupture at Focal Depth, Part I: Structure and Rupture of the Pretorius Fault, TauTona Mine, South Africa
Pure and Applied Geophysics,
168
(12)
2395 – 2425
2011
ISSN: 00334553Keywords:▾
Brittle faulting; Deep mines; earthquake mechanics; earthquake rupture zone; Fault reactivation; Fault rock, Earthquakes; Fracture; Rocks; Tectonics, Fault slips, brittle deformation; cataclasite; displacement; earthquake rupture; fault zone; fracture; quartzite; strike-slip fault, South Africa
Abstract: ▾ We analyze the structure of the Archaean Pretorius fault in TauTona mine, South Africa, as well as the rupture-zone that recently reactivated it. The analysis is part of the Natural Earthquake Laboratory in South African Mines (NELSAM) project that utilizes the access to 3. 6 km depth provided by the mining operations. The Pretorius fault is a ~10 km long, oblique-strike-slip fault with displacement of up to 200 m that crosscuts fine to very coarse grain quartzitic rocks in TauTona mine. We identify here three structural zones within the fault-zone: (1) an outer damage zone, ~100 m wide, of brittle deformation manifested by multiple, widely spaced fractures and faults with slip up to 3 m; (2) an inner damage zone, 25-30 m wide, with high density of anastomosing conjugate sets of fault segments and fractures, many of which carry cataclasite zones; and (3) a dominant segment, with a cataclasite zone up to 50 cm thick that accommodated most of the Archaean slip of the Pretorius fault, and is regarded as the 'principal slip zone' (PSZ). This fault-zone structure indicates that during its Archaean activity, the Pretorius fault entered the mature fault stage in which many slip events were localized along a single, PSZ. The mining operations continuously induce earthquakes, including the 2004, M2. 2 event that rejuvenated the Pretorius fault in the NELSAM project area. Our analysis of the M2. 2 rupture-zone shows that (1) slip occurred exclusively along four, pre-existing large, quasi-planer segments of the ancient fault-zone; (2) the slipping segments contain brittle cataclasite zones up to 0. 5 m thick; (3) these segments are not parallel to each other; (4) gouge zones, 1-5 mm thick, composed of white 'rock-flour' formed almost exclusively along the cataclasite-host rock contacts of the slipping segments; (5) locally, new, fresh fractures branched from the slipping segments and propagated in mixed shear-tensile mode; (6) the maximum observed shear displacement is 25 mm in oblique-normal slip. The mechanical analysis of this rupture-zone is presented in Part II (Heesakkers et al., Earthquake Rupture at Focal Depth, Part II: Mechanics of the 2004 M2. 2 Earthquake Along the Pretorius Fault, TauTona mine, South Africa 2011, this volume). © 2011 Springer Basel AG.
1108.
Applications Study of Geo-drilling Technology (in Chinese with English abstract);[地质钻探技术与应用研究]
Acta Geologica Sinica,
85
(11)
1806-1822
2011
1107.
Measurement of 10Be from Lake Malawi (Africa) drill core sediments and implications for geochronology
Palaeogeography, Palaeoclimatology, Palaeoecology,
303
(1-4)
110-119
2011
ISSN: 00310182Keywords:▾
beryllium isotope; cosmogenic radionuclide; geochronology; lacustrine deposit; lake level; marine record; marine sediment; paleoclimate; paleomagnetism; radiocarbon dating; sediment core; sediment transport, East Africa; East African Lakes; Lake Malawi
Abstract: ▾ The cosmogenic radionuclide 10Be was measured from drill core sediments from Lake Malawi in order to help construct a chronology for the study of the tropical paleoclimate in East Africa. Sediment samples were taken every 10m from the core MAL05-1C to 80m in depth and then from that depth in core MAL05-1B to 382m. Sediment samples were then later taken at a higher resolution of every 2m from MAL05-1C. They were then leached to remove the authigenic fraction, the leachate was processed to separate out the beryllium isotopes, and 10Be was measured at the TAMS Facility at the University of Arizona. The 10Be/9Be profile from Lake Malawi sediments is similar to those derived from marine sediment cores for the late Pleistocene, and is consistent with the few radiocarbon and OSL IR measurements made from the same core. Nevertheless, a strong correlation between the stable isotope 9Be and the cosmogenic isotope 10Be suggests that both isotopes have been well mixed before deposition unlike in some marine sediment cores. In addition, the correlation of beryllium isotopes to a proxy of lake level TOC (Total Organic Matter) from Lake Malawi indicates that the concentrations of 10Be in the lake sediments result from the combined effects of global and local climates on lake level, local hydrology, and sediment transport in the Lake Malawi basin rather than as a direct response to its production in the atmosphere modulated by the intensity of the Earth's dipole. Therefore, a direct correlation of the 10Be/9Be to a chronology derived from the paleomagnetic variations measured from marine sediments was not possible. Nevertheless, a comparison of the 10Be/9Be chronology, allowing for decay, at Lake Malawi to that of the global marine paleomagnetic record suggests that the bottom of core MAL05-1B is no more than 750ka in age. © 2010.
1106.
A 370,000-year record of vegetation and fire history around Lake Titicaca (Bolivia/Peru)
Palaeogeography, Palaeoclimatology, Palaeoecology,
305
(1-4)
201 – 214
2011
Keywords:▾
Andes; Bolivia; Lake Titicaca; Peru; Bacillariophyta; charcoal; depositional environment; diatom; fire history; fossil assemblage; glacial-interglacial cycle; interglacial; lacustrine deposit; microfossil; paleoclimate; palynology; vegetation dynamics; vegetation history
Abstract: ▾ Fossil pollen and charcoal analyses of sediments from Lake Titicaca, Peru/Bolivia, provide a record of palaeoclimatic variation spanning four full glacial cycles. Pollen, aquatic microfossils, and charcoal, as well as previously published data including diatom assemblages, carbonate content, and stable carbon isotopic ratios of organic carbon, indicate that interglacials were warm and dry whereas the peaks of glacials were cold and wet. Each of the interglacials documented in the record are somewhat different, with those of MIS 5e and MIS 9 inducing lower lake levels and a drier vegetation signature than those of MIS 7 and 1. The presence of charcoal particles in sediments deposited during previous interglacials provides evidence of the long-term role of fire in shaping Andean ecosystems. © 2011 Elsevier B.V.
1105.
A 500,000-year-long sediment archive drilled in eastern Anatolia
Eos,
92
(51)
477-479
2011
ISSN: 00963941Keywords:▾
lacustrine deposit; marine sediment; Ocean Drilling Program; paleoclimate; reconstruction, Anatolia; Turkey
Abstract: ▾ Sedimentary archives host a wealth of information that can be used to reconstruct paleoclimate as well as the tectonic and volcanic histories of specific regions. Long and continuous archives from the oceans have been collected in thousands of locations by scientific ocean drilling programs over the past 40 years. In contrast, suitable continental archives are rare because terrestrial environments are generally nondepositional and/or subject to erosion. Lake sediments provide ideal drilling targets to overcome this limitation if suitable lakes at key locations have existed continuously for a long time.
1104.
A general viscosity model of Campi Flegrei (Italy) melts
Chemical Geology,
290
(1-2)
50 – 59
2011
ISSN: 00092541Keywords:▾
Campania [Italy]; Campi Flegrei; Italy; Napoli [Campania]; Atmospheric pressure; Atmospheric temperature; Atmospherics; Cylinders (shapes); Reservoirs (water); Spheres; Thermal logging; Viscometers; Water content; Campi Flegrei; Concentric cylinders; Falling sphere; Latites; Micropenetration; Shoshonites; air temperature; atmospheric pressure; caldera; experimental study; hazard assessment; magmatic differentiation; P-T conditions; petrology; shoshonite; viscosity; volcanology; Viscosity
Abstract: ▾ Viscosities of shoshonitic and latitic melts, relevant to the Campi Flegrei caldera magmas, have been experimentally determined at atmospheric pressure and 0.5GPa, temperatures between 840K and 1870K, and H2O contents from 0.02 to 3.30wt.%.The concentric cylinder technique was employed at atmospheric pressure to determine viscosity of nominally anhydrous melts in the viscosity range of 101.5-103Pas. The micropenetration technique was used to determine the viscosity of hydrous and anhydrous melts at atmospheric pressure in the high viscosity range (1010Pas). Falling sphere experiments were performed at 0.5GPa in the low viscosity range (from 100.35 to 102.79Pas) in order to obtain viscosity data of anhydrous and hydrous melts. The combination of data obtained from the three different techniques adopted permits a general description of viscosity as a function of temperature and water content using the following modified VFT equation:logη=-a+bT-c+dT-e·expg·wTwhere η is the viscosity in Pa·s, T the temperature in K, w the H2O content in wt.%, and a, b, c, d, e, and g are the VFT parameters. This model reproduces the experimental data (95 measurements) with a 1σ standard deviation of 0.19 and 0.22 log units for shoshonite and latite, respectively. The proposed model has been applied also to a more evolved composition (trachyte) from the same area in order to create a general model applicable to the whole compositional range of Campi Flegrei products.Moreover, speed data have been used to constrain the ascent velocity of latitic, shoshonitic, and trachytic melts within dikes. Using petrological data and volcanological information (geometrical parameters of the eruptive fissure and depth of magma storage), we estimate a time scale for the ascent of melt from 9. km to 4. km depth (where deep and shallow reservoirs, respectively, are located) in the order of few minutes. Such a rapid ascent should be taken into account for the hazard assessment in the Campi Flegrei area. © 2011 Elsevier B.V.
1103.
A study of rock magnetic properties of serpentinites from the Outokumpu Deep Dril Hole, Finland
Special Paper of the Geological Survey of Finland,
2011
(51)
133 – 150
2011
ISSN: 07828535ISBN:
978-952217152-8
Abstract: ▾ This study examined the rock magnetic properties and magnetic mineralogy of serpentinite, skarn, black schist and mica schist of the Outokumpu (OKU) rock type assemblage, which occur between 1314 and 1515 m in the Outokumpu Deep Drill Hole in Eastern Finland. This depth interval is related to pronounced magnetic anomalies. A banded magnetic anomaly pattern, similar to the one observed in the OKU drill cores, is seen in aeromagnetic surveys for the surface in the vicinity of the OKU borehole. Magnetic logging has revealed that the magnetic anomalies are mostly related to the ferrimagnetic serpentinite units in the OKU assemblage. The serpentinite units show a significant scattering of magnetic susceptibility (κ) from 0.04 to 192.7*10-3 SI and natural remanent magnetization (NRM) from 0.06 to 45.1 A/m, indicating a heterogeneous distribution of ferrimagnetic minerals in the ultramafic rocks. The main magnetic minerals are magnetite and pyrrhotite. Furthermore, variation in the Königsberger ratio (Q) from below 1 up to 16 indicates that some ultramafic rocks in the OKU assemblage are able to carry a remanent magnetization (Q-ratio > 1). The strong scattering of rock magnetic properties is interpreted to reflect a complex geological history of the studied rocks. Magnetite is known to form during the serpentinization of ultramafic rocks on the sea floor or during subduction-related processes. In the OKU assemblage it was partially decomposed during early deformation stages by listwaenite-birbirite-type carbonatequartz alteration. During subsequent events of regional deformation, the magnetic minerals were deformed or some new formation of magnetic minerals occurred.
1102.
Active basins and neotectonics: Morphotectonics of the Lake Ohrid Basin (FYROM and Albania); [Aktive Becken und Neotektonik: Die Morphotektonik des Ohridbeckens (FYROM und Albanien)]
Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften,
162
(2)
217 – 234
2011
ISSN: 18601804Abstract: ▾ The Lake Ohrid Basin in FYROM (Former Yugoslav Republic of Macedonia) and Albania meets all criteria of an active, seismic landscape: linear step-like fault scarps in the landscape and under water within the lake. Post-glacial (or Late Pleistocene) bedrock fault scarps at Lake Ohrid are long-lived expressions of repeated surface faulting in tectonically active regions, where erosion cannot outpace the fault slip. Other morphotectonic features are wind gaps, wineglass-shaped valleys and triangular facets, which are well preserved. Generally, the faults and fault scarps are getting younger towards the basin centre, as depicted on seismic and hydroacoustic profi les. Additionally, mass movement bodies within the lake and also onshore (rockfalls, landslides, sub-aquatic slides, homogenites, turbidites) are likely to have been seismically triggered. These morphotectonic observations are in line with focal mechanisms of earthquakes in the greater Lake Ohrid area. We investigated the neotectonic history and tectonic geomorphology of the Lake Ohrid Basin by means of an integrated multidisciplinary approach, using tectonic geomorphology and a variety of geophysical and remote sensing methods. © 2011 E.
1101.
Aquatic ecosystems of the Yucatán Peninsula (Mexico), Belize, and Guatemala
Hydrobiologia,
661
(1)
407 – 433
2011
ISSN: 00188158
Publisher: Kluwer Academic Publishers
Keywords:▾
Belize [Central America]; Guatemala [Central America]; Mexico [North America]; Yucatan Peninsula; hydraulic conductivity; karst; lake pollution; limnology; morphology; Neotropical Region; physicochemical property; pollution effect; principal component analysis; saline intrusion; surface water; trace element; urban development; water temperature
Abstract: ▾ This study presents limnological and morphological characteristics, physical and chemical properties of waters, and geochemistry of surface sediments for 63 aquatic ecosystems located on the karst Yucatán Peninsula and surrounding areas of Belize and the Guatemalan highlands and eastern lowlands. Our principal goal was to classify the aquatic systems based on their water variables. A principal component analysis (PCA) of the surface water chemistry data showed that a large fraction of the variance (29%) in water chemistry is explained by conductivity and major ion concentrations. The broad conductivity range, from 168 to 55,300 μS cm-1 reflects saline water intrusion affecting coastal aquatic environments, and the steep NW-S precipitation gradient, from ~450 to>3,200 mm year-1. Coastal waterbodies Celestún and Laguna Rosada displayed the highest conductivities. Minimum surface water temperatures of 21.6°C were measured in highland lakes, and warmest temperatures, up to 31.7°C, were recorded in the lowland waterbodies. Most lakes showed thermal stratification during the sampling period, with the exception of some shallow (<10 m) systems. Lakes Chichancanab, Milagros, and Bacalar displayed sulfate-rich waters. Waters of sinkholes had relatively high conductivities (<3,670 μS cm-1) and a broad range of δ18O values (-4.1 to +3.8%). Ca, HCO3, and SO4 dominated the waters of the lowland lakes, whereas Na was the dominant cation in highland lakes. Coastal aquatic ecosystems were dominated by Na and Cl. Cluster analysis based on surface water variables classified aquatic environments of the lowlands and highlands into three groups: (1) lowland lakes, ponds, wetlands, and coastal waterbodies (2) highland lakes, and (3) sinkholes and rivers. A broad trophic state gradient was recorded, ranging from the eutrophic Lake Amatitlán and the Timul sinkhole to oligotrophic Laguna Ayarza, with the highest water transparency (11.4 m). We used major and trace elements in surface sediments to assess pollution of waterbodies. Lakes Amatitlán, Atescatempa, El Rosario, Cayucón, Chacan-Lara, La Misteriosa, rivers Subín and Río Dulce, the wetland Jamolún, and the sinkhole Petén de Monos showed evidence of pollution and urban development. Their surface sediments displayed high concentrations of As, Cu, Fe, Ni, Pb, Se, Zn, and Zr, which suggest moderate to strong pollution. © Springer Science+Business Media B.V. 2010.
1100.
Centimeter-scale sedimentary sequence description of Upper Cretaceous-Lower Paleocene Mingshui Formation: Lithostratigraphy，facies and cyclostratigraphy, based on the scientific drilling (SK1) borehole in the Songliao Basin.
Earth Science Frontiers,
18
(6)
285-328
2011
1099.
Attempt to the Late Cretaceous Ostracod Carapace Stable Isotope Measurement—Case Study on the SK1 Drill Cores
Geoscience,
25
(3)
401
2011
1098.
“Earthtime” Project: Dating Precision and Temporal Resolution in the “Deep Time” Record (in Chinese with English abstract);[“地时”(Earthtime)研究计划:“深时”(Deep Time)记录的定年精度与时间分辨率]
Geosciences,
24
(03)
419-428
2011
1097.
Biogenic silica deposition in Lake Malawi, East Africa over the past 150,000years
Palaeogeography, Palaeoclimatology, Palaeoecology,
303
(1-4)
103-109
2011
ISSN: 00310182Keywords:▾
biogenic deposit; chemical weathering; diatom; drainage basin; ice core; lacustrine deposit; paleoclimate; sediment core; silica; tephra; tropical region, East Africa; East African Lakes; Lake Malawi, Bacillariophyta
Abstract: ▾ We report a 150,000. year record of the abundance of biogenic silica (BSi) in drill cores from the northern and central basins of Lake Malawi. The periods of highest diatom burial at both sites occurred around 65-69 and 51-60. thousand years ago (ka) after the termination of prolonged, intense drought in the region. These peaks are believed to reflect elevated delivery of dissolved silica to the lake due to acceleration of chemical weathering in the drainage basin. The droughts that preceded these BSi depositional episodes occurred at precessional frequency, corresponding to times of minimum austral spring (or summer?) insolation in the region prior to 60. ka. Subsequent arid spells have not been as severe due to the reduced amplitude of precessional forcing as a result of the superimposed effect of eccentricity. However, biogenic silica records do not show significant sensitivity to precessional forcing. The BSi burial flux in the north basin displays strong millennial-scale variability since 50. ka, with peak values occurring during cold times in the Northern Hemisphere, as reflected in the Greenland ice core records. We observe no relationship between BSi and deposition of volcanic tephras in this system. The central basin core also displays millennial-scale variability in BSi abundance during the past 50. ky, of comparable magnitude to that in the north basin, but without systematic correlation to the north basin BSi or Greenland ice core records. In general, we conclude that BSi profiles from the north and (probably) south basins are more readily interpreted in terms of regional climate dynamics than are BSi profiles from more central locations in long, narrow tropical rift lakes. Diatom burial rates are suspected to be too influenced by silica limitations imposed by diatom production and burial in the upwelling systems at either end of these low-latitude lacustrine systems. © 2010 Elsevier B.V.
1096.
Biomarker seasonality study in Lake Van, Turkey
Organic Geochemistry,
42
(11)
1289-1298
2011
ISSN: 01466380Keywords:▾
Archaea; Biomarker flux; Chlorins; Eastern Anatolia; Fucoxanthin; Isoprenoids; Long chain alkenones; Membrane lipids; Organic carbon fluxes; Paleoclimate studies; Particulate materials; Photic zone; Phytoplankton community; Primary productivity; Seasonal changes; Seasonality; Snowmelt runoff; Soda lakes; Strong stratification; Temperature proxy; Temperature range; Total mass; Total mass flux; Water columns, Algae control; Anoxic sediments; Biomarkers; Glycerol; Lipids; Microorganisms; Organic carbon; Phytoplankton; Productivity; Sedimentology, Lakes, biomarker; community structure; isoprenoid; nutrient; organic carbon; paleoclimate; particulate matter; photic zone; phytoplankton; pigment; prokaryote; runoff; seasonality; sediment trap; snowmelt; stratification; temperature profile; water column, Lake Van; Turkey
Abstract: ▾ The endorheic Lake Van in eastern Anatolia (Turkey) is the world's largest soda lake and it is an important site in paleoclimate studies to understand past continental conditions in western Asia. In order to gain further insights into the biomarker signatures in Lake Van's sediments we have analyzed particulate material in sediment traps deployed between August 2006 and July 2007. The biomarkers used were long chain alkenones (LCAs C37-C39, haptophyte lipids), isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs, Archaea membrane lipids) and pigments (chlorins and fucoxanthin). The biomarker fluxes indicate a strong seasonality in export primary productivity and the phytoplankton community structure. The highest total mass and organic carbon fluxes were found in summer, coupled to strong stratification while the lowest mass fluxes occurred in winter at the time of water column mixing. With increasing temperatures in early spring, phytoplankton export productivity grew, coupled with an increase of total mass flux and organic carbon, which might be associated to enhanced nutrient input from snowmelt runoff. The percentage of C37:4 shows some correspondence with observed seasonal changes in Lake Van's stratification structure. We also evaluated the potential applicability of molecular temperature proxies derived from Archaea and haptophyte lipids. The use of the TEX86 proxy was precluded by low GDGT abundances. Estimated LCA temperatures were consistent with temperatures in the photic zone but no seasonality changes were observed despite the wide annual temperature range measured at Lake Van. © 2011 Elsevier Ltd.
1095.
Centimeter-scale sedimentary sequence description of Upper Cretaceous Nenjiang Formation (lower numbers 1&2): Lithostratigraphy, facies and cyclostratigraphy, based on the scientific drilling (SK1) borehole in the Songliao Basin.
Earth Science Frontiers,
18
(6)
195
2011