The 1‐million‐year‐old quartz assemblage from Pont‐de‐Lavaud (Centre,France) in the European context          下载免费PDF全文

Jackie Despriée  Marie‐Hélène Moncel  Marta Arzarello  Gilles Courcimault  Pierre Voinchet  Jean‐Jacques Bahain  Christophe Falguères 《第四纪科学杂志》2018,33(6):639-661

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A SIMS zircon age for a biostratigraphically dated Upper Viséan (Asbian) bentonite in the Central-European Variscides (Bardo Unit,Polish Sudetes)   总被引：1，自引：1，他引：0  

Ryszard Kryza  Jolanta Muszer  Joanna Haydukiewicz  Czesław August  Marta Jurasik  Nickolay Rodionov 《International Journal of Earth Sciences》2011,100(6):1227-1235

A Lower Carboniferous platform sedimentary sequence (the Paprotnia Beds) in the Bardo Unit of the central Sudetes (NE part of the Bohemian Massif, SW Poland) is biostratigraphically well dated, based on rich macro- and micro-fossil evidence, as Late Viséan (late Asbian, crenistria, Go III α zone). The beds contain several bentonite layers, one of which was dated using the U–Pb SHRIMP method on volcanic zircons and yielded an age of 334 ± 3 Ma. This date fits well to the recently established chronostratigraphic limits of the Viséan, and is consistent with the newest isotopic age constraints of 336.5–332 Ma for the Asbian boundaries.  相似文献   

Spatial variation patterns of subtidal seaweed assemblages along a subtropical oceanic archipelago: Thermal gradient vs herbivore pressure     

Carlos Sangil  Marta Sansón 《Estuarine, Coastal and Shelf Science》2011,94(4):322-333

The structure and composition of subtidal rocky seaweed assemblages were studied at 69 sites on the Canary Islands (northeastern Atlantic). This group of islands are situated at the southern boundary of the warm temperate region and adjacent to the cold waters from the northwest African coastal upwelling, which creates a difference of almost 2 °C in surface seawater temperature from the eastern to the western islands. This thermal variation allows an examination of the transition between the warm temperate and the tropical regions along this longitudinal gradient together with the hypothesised Fucales-dominated assemblages towards the eastern islands in contrast to the Dictyotales-dominated assemblages towards the western ones. Environmental and biological parameters were considered in order to investigate which were the main factors explaining spatial variation along the gradient in a multi-scaled approach. Although seventy-nine macroalgae were identified, 87.63% of the total mean cover was due to six taxa (Lobophora variegata, nongeniculate corallines, Canistrocarpus cervicornis, Jania adhaerens, Cystoseira abies-marina and Pseudolithoderma adriaticum). At a large scale, sea urchin density explained the highest variation in seaweed assemblages (26.94%), and its pattern of distribution across the islands. The expected pattern of distribution according to the upwelling distance only occurred in restricted areas of the Canarian Archipelago in absence of herbivore pressure and habitat degradation. Spatial variations within islands (medium scale) were mainly related to wave exposure, while at a small scale these were mostly due to the degree of sedimentation.  相似文献   

Soil Iodine Determination in Deccan Syneclise,India: Implications for Near Surface Geochemical Hydrocarbon Prospecting     

Devleena Mani  T. Satish Kumar  M. A. Rasheed  D. J. Patil  A. M. Dayal  T. Gnaneshwar Rao  V. Balaram 《Natural Resources Research》2011,20(1):75-88

The association of iodine with organic matter in sedimentary basins is well documented. High iodine concentration in soils overlying oil and gas fields and areas with hydrocarbon microseepage has been observed and used as a geochemical exploratory tool for hydrocarbons in a few studies. In this study, we measure iodine concentration in soil samples collected from parts of Deccan Syneclise in the west central India to investigate its potential application as a geochemical indicator for hydrocarbons. The Deccan Syneclise consists of rifted depositional sites with Gondwana–Mesozoic sediments up to 3.5 km concealed under the Deccan Traps and is considered prospective for hydrocarbons. The concentration of iodine in soil samples is determined using ICP-MS and the values range between 1.1 and 19.3 ppm. High iodine values are characteristic of the northern part of the sampled region. The total organic carbon (TOC) content of the soil samples range between 0.1 and 1.3%. The TOC correlates poorly with the soil iodine (r ² < 1), indicating a lack of association of iodine with the surficial organic matter and the possibility of interaction between the seeping hydrocarbons and soil iodine. Further, the distribution pattern of iodine compares well with two surface geochemical indicators: the adsorbed light gaseous hydrocarbons (methane through butane) and the propane-oxidizing bacterial populations in the soil. The integration of geochemical observations show the occurrence of elevated values in the northern part of the study area, which is also coincident with the presence of exposed dyke swarms that probably serve as conduits for hydrocarbon microseepage. The corroboration of iodine with existing geological, geophysical, and geochemical data suggests its efficacy as one of the potential tool in surface geochemical exploration of hydrocarbons. Our study supports Deccan Syneclise to be promising in terms of its hydrocarbon prospects.  相似文献   

Stable carbon isotope geochemistry of adsorbed alkane gases in near-surface soils of the Saurashtra Basin,India     

Devleena Mani  D.J. Patil  A.M. Dayal 《Chemical Geology》2011,280(1-2):144-153

The stable carbon isotopic compositions of light hydrocarbon gases adsorbed in near-surface soil and sediments from the Saurashtra basin were characterized for their origin and maturity. Saurashtra is considered geologically prospective for oil and gas reserves; however, a major part of the basin is covered by the Deccan Traps, hindering the exploration of Mesozoic hydrocarbon targets. Surface geochemical prospecting, based on micro-seepage of hydrocarbons from subsurface accumulations, could be advantageous in such areas. In light of this, 150 soil samples were collected from the northwestern part of Saurashtra, around the Jamnagar area, where a thick sedimentary sequence of about 2–3 km exists under 1–1.5 km of Deccan basalt. The concentration of acid desorbed alkane gases from soil samples was found to vary (in ppb) as: methane (C₁) = 3–518; ethane (C₂) = 0–430; propane (C₃) = 0–331; i-butane (iC₄) = 0–297; n-butane (nC₄) = 2–116; i-pentane (iC₅) = 0–31 and n-pentane (nC₅) = 0–23, respectively.Fifteen samples with high concentrations of alkane gases were measured for their δ¹³C₁; δ¹³C₂ and δ¹³C₃ compositions using gas chromatography–combustion-isotope ratio mass spectrometry (GC–C-IRMS). The values for methane varied from ? 27 to ? 45.4‰, ethane from ? 20.9 to ? 27.6‰, and propane from ? 20.4 to ? 29.1‰ versus the Vienna PeeDee Belemnite (VPDB). The carbon isotope ratio distribution pattern represents isotopic characteristics pertaining to hydrocarbon gases derived from thermogenic sources. Comparisons of carbon isotopic signatures and compositional variations with the standard carbon isotopic models suggest that hydrocarbon gases found in the shallow depths of the study area are not of bacterial origin but are formed thermally from deeply buried organic matter, likely to be mainly a terrestrial source rock with a partial contribution from a marine source. These gases may have migrated to the near-surface environment, where they represent an admixture of thermally generated hydrocarbon gases from mixed sources and maturity. The maturity scale (δ¹³C versus Log Ro %) applied to the surface sediment samples of the Jamnagar area indicated the source material to be capable of generating oil and gas. The detection of thermogenic alkane gases in near-surface sediments offers the possibility of hydrocarbons at depth in Saurashtra.  相似文献   

A reinterpretation of two chertbreccias from the Proterozoic basins of India     

Vivek S. Kale  Shilpa Patil Pillai 《Journal of the Geological Society of India》2011,78(5):429-445

Several horizons of a unique lithotype called “chertbreccia” are interbedded within the Proterozoic platform sediments of the Peninsular India. These cherty rocks with brecciated texture appearing as blocky masses were earlier diversely interpreted as being products of disparate processes such as fault-zone breccias, collapse breccias, and so on. Two of these horizons, one from the Kaladgi Basin (Dharwar Craton) and the other from the Dhar Forest Inlier of the Vindhyanchal Basin (Bundelkhand — Aravalli Craton) are compared in context of their geological setting, field relations and petrological constitution. A model of the mode of development of these peculiar rocks is reconstructed, taking into account their characters and limitations of previous interpretations. They are interpreted as transported debris deposits of syntectonogenic material released during the episodic activity of the growth faults of the Kaladgi and Vindhyanchal Basins that was diagenetically silicified.  相似文献   

The status of measurement of the Mediterranean mean dynamic topography by geodetic techniques   总被引：1，自引：1，他引：0  

Philip L. Woodworth  Médéric Gravelle  Marta Marcos  Guy Wöppelmann  Chris W. Hughes 《Journal of Geodesy》2015,89(8):811-827

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Climatic vs. tectonic signals in a continental extensional basin (Teruel,NE Spain) from stable isotope (δ18O) and sequence stratigraphical evolution     

Lope Ezquerro  Aránzazu Luzón  Marta Navarro  Carlos L. Liesa  José L. Simón 《地学学报》2014,26(5):337-346

Alluvial fans and shallow carbonate lakes interfered in the Teruel half‐graben during the Late Miocene–Pliocene. Tectonic influence is recorded in alluvial and lacustrine–palustrine successions, with long‐term climate changes being recorded in detail in the isotopic signatures of carbonates. Episodes of tectonic activity induced alluvial fan progradation and lake retraction in the whole basin. Three lacustrine stages have been identified, which support the idea that climate also exerted an important control on sedimentation. The transition between stages 1 and 2 occurred during a tectonically calm episode due to an increase in aridity in the Early Turolian; small fans with source areas next to the lake margin prograded, inducing lake‐shore retraction. The transition from stage 2 to 3 was caused by the superimposition of increasing tectonic activity and aridity effects. Our study demonstrates that discrimination of allogenic factors controlling sedimentation in continental closed basins is possible using sequence stratigraphy in combination with other techniques such as geochemistry of carbonates.  相似文献   

Experimental validation of seismic retrofit solutions for URM chimneys     

Marta Giaretton  Jason M. Ingham  Dmytro Dizhur 《Bulletin of Earthquake Engineering》2018,16(1):295-313

Clay-brick unreinforced masonry (URM) chimneys are a common architectural feature of vintage domestic and commercial URM and timber-framed buildings widely encountered worldwide. URM chimneys include a cantilevered appendage above the roofline that during earthquakes-induced shaking is susceptible to significant damage and collapse, which can result in fatalities, injuries, and property damage. To mitigate this risk, many vintage URM chimneys are removed, braced, or eventually replaced with modern alternatives. The earthquake performance of 15,400 URM chimneys damaged during the 2010/2011 Canterbury earthquake sequence was investigated using a photographic database and insurance claims data. The widespread damage and failure of a large proportion of retrofitted chimneys was the impetus for an experimental shake-table testing campaign that was undertaken to assess the performance of five prototypical URM chimneys in their as-built and retrofitted conditions. Cost-effective retrofit techniques with low aesthetic impact, including the use of near surface mounted carbon-fibre reinforced polymer strips and post-tensioning, were investigated. Tested chimneys were constructed to replicate the most commonly encountered geometric characteristics and construction details collected during an in-field pilot survey of 351 undamaged vintage URM chimneys.  相似文献   

Mediterranean Sea response to climate change in an ensemble of twenty first century scenarios     

Fanny Adloff  Samuel Somot  Florence Sevault  Gabriel Jordà  Roland Aznar  Michel Déqué  Marine Herrmann  Marta Marcos  Clotilde Dubois  Elena Padorno  Enrique Alvarez-Fanjul  Damià Gomis 《Climate Dynamics》2015,45(9-10):2775-2802

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