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101.
The British Tertiary igneous province: palaeomagnetism of the dyke swarm along the Sleat coast of Skye 总被引:1,自引:0,他引:1
Summary. A palaeomagnetic investigation has been made of a swarm of more than 400 dykes along the south coast of Skye, Scotland, by the Sound of Sleat.
Seven red lamprophyre dykes have palaeomagnetic directions inconsistent with Tertiary age, and not inconsistent with their previously held Caledonian age. The remaining 409 dykes have palaeomagnetic directions that are consistent with a Lower Tertiary age. We present evidence suggesting that the Tertiary dykes might have been emplaced during a short time, over which the geomagnetic polarity occupied as few as three polarity intervals (NRN or RNR).
Certain 'intermediate' directions of magnetization have also been found, and are presented here. 相似文献
Seven red lamprophyre dykes have palaeomagnetic directions inconsistent with Tertiary age, and not inconsistent with their previously held Caledonian age. The remaining 409 dykes have palaeomagnetic directions that are consistent with a Lower Tertiary age. We present evidence suggesting that the Tertiary dykes might have been emplaced during a short time, over which the geomagnetic polarity occupied as few as three polarity intervals (NRN or RNR).
Certain 'intermediate' directions of magnetization have also been found, and are presented here. 相似文献
102.
103.
J. Grabowski L. Krzemiski P. Nescieruk E. Starnawska 《Geophysical Journal International》2006,166(3):1077-1094
Results of palaeomagnetic investigations of the Lower Cretaceous teschenitic rocks in the Silesian unit of the Outer Western Carpathians in Poland bring evidence for pre-folding magnetization of these rocks. The mixed-polarity component reveals inclinations, between 56° and 69°, which might be either of Cretaceous or Tertiary age. Apparently positive results of fold and contact tests in some localities and presence of pyrhotite in the contact aureole suggest that magnetization is primary, although a Neogene or earlier remagnetization cannot be totally excluded since inclination-only test between localities gives 'syn-folding' results. Higher palaeoinclinations (66°–69°) correlate with a younger variety of teschenitic rocks dated for 122–120 Ma, while lower inclinations (56°–60°) with an older variety (138–133 Ma). This would support relatively high palaeolatitudes for the southern margin of the Eurasian plate in the late part of the Early Cretaceous and relatively quick northward drift of the plate in this epoch, together with the Silesian basin at its southern margin. Declinations are similar to the Cretaceous–Tertiary palaeodeclinations of stable Europe in the eastern part of the studied area but rotated ca. 14°–70° counter-clockwise in the western part. This indicates, together with older results from Czech and Slovakian sectors of the Silesian unit, a change in the rotation pattern from counter-clockwise to clockwise at the meridian of 19°E. The rotations took place before the final collision of the Outer Carpathians nappe stack with the European foreland. 相似文献
104.
A. Carraro P. Fabbri A. Giaretta L. Peruzzo F. Tateo F. Tellini 《Environmental Earth Sciences》2013,70(7):3067-3084
A pilot area within the Venetian Plain was selected to assess the arsenic (As) contamination of groundwater. The area represents a typical residential, industrial and agricultural organization representative of most western countries, and is also devoid of lithologies with high or anomalous As content. Hydrogeological and chemical data have been collected, the latter spatialized by a geostatistical approach. The unconfined aquifer reservoir varies from a predominantly gravel composition in the north to a sandy and silt–clay composition further south, including peat layers. The hydrochemical features of the waters are rather homogeneous, featuring low mineral content and a Ca-bicarbonate signature. In contrast, the redox state is highly variable; oxidizing conditions are predominant in the northern and coarse parts of the aquifer, whereas reducing potentials prevail in the southern and silt–clay parts. Several well waters contain arsenic in excess of drinkable limits (=10 ppb), and most of these wells are located in the southern area. A large portion of the studied area has a high probability of containing non-potable water (up to 150 ppb As). Remarkably, As “hot spots” (As > 300 ppb, up to 431 ppb) were identified at the transition from gravel to silt–clay sediments. No industrial or agricultural source of As has been found. 相似文献
105.
Mohammed Abdul Rasheed M. Lakshmi P. L. S. Rao D. J. Patil A. M. Dayal V. Sudarshan 《Natural Resources Research》2012,21(4):427-441
Mesozoic sediments are source rocks for nearly half the world’s hydrocarbon reserves. Hence, there is great interest in the oil industry to know the trap and sub-trappean sediment thickness and their extent in the trap covered regions of Jamnagar study area. The microbial prospecting method is applied in the Jamnagar sub-basin, Gujarat for evaluating the prospects for hydrocarbon exploration by investigating the anomalous abundance of n-pentane- and n-hexane-oxidizing bacteria of this area. A total of 150 near-surface soil samples were collected in Jamnagar sub-basin, Gujarat for the evaluation of hydrocarbon resource potential of the basin. In this study, bacterial counts for n-pentane-utilizing bacteria range between 1.09 × 102 and 9.89 × 105 cfu/g and n-hexane-utilizing bacteria range between 1.09 × 102 and 9.29 × 105 cfu/g. The adsorbed hydrocarbon gases consisting of ethane plus hydrocarbons (ΣC2+) of 1–977 ppb and n-pentane (nC5) of 1–23 ppb. The integrated geomicrobial and adsorbed soil gas studies showed the anomalous hydrocarbon zones nearby Khandera, Haripur, and Laloi areas which could probably aid to assess the true potential of the basin. Integrated geophysical studies have shown that Jamnagar sub-basin of Saurashtra has significant sediment thickness below the Deccan Traps and can be considered for future hydrocarbon exploration. 相似文献
106.
Thomas Stephens Daniel Atkin Paul Augustinus Philip Shane Andrew Lorrey Alayne Street-Perrott Andreas Nilsson Ian Snowball 《Journal of Paleolimnology》2012,48(4):785-800
We present the first continuous paleolimnological reconstruction from the North Island of New Zealand (37°S) that spans the last 48.2?cal kyr. A tephra- and radiocarbon-based chronology was developed to infer the timing of marked paleolimnological changes in Lake Pupuke, Auckland, New Zealand, identified using sedimentology, magnetic susceptibility, grain size and geochemistry (carbon, nitrogen and sulphur concentrations and fluxes, carbon and nitrogen stable isotopes). Variable erosional influx, biomass and benthic REDOX conditions are linked to changing effective precipitation and seasonality within three inferred broad intervals of climatic change: (1) the Last Glacial Coldest Phase (LGCP) of reduced effective precipitation and cooler temperatures, from 28.8 to 18.0?cal kyr BP, (2) the Last Glacial Interglacial Transition (LGIT) of increasing effective precipitation and warmer conditions, from 18.0 to 10.2?cal?kyr?BP, and (3) a Holocene interval of high effective precipitation, beginning with a warm period of limited seasonality from 10.2?cal?kyr?BP and followed by increasing seasonality from 7.6?cal?kyr?BP. The LGCP and LGIT also contain millennial-scale climate events, including the coldest inferred glacial conditions during the LGCP from 27.8 to 26.0 and 22.0?C19.0?cal?kyr?BP, and a climate reversal in the LGIT associated with lower lake level, from 14.5 to 13.8?cal?kyr?BP, coeval with the Antarctic Cold Reversal. The onset of seasonal thermal stratification occurred at 5.7?cal?kyr?BP and was linked to natural eutrophication of Lake Pupuke, which produced enhanced organic sedimentation. 相似文献
107.
108.
PEI Xiandeng KONG Lingwang ZHU Yuanhong HUANG Hao 《地球空间信息科学学报》2005,8(4):306-310
IntroductionIn color reproduction and communication, met-amer exists inherently when the conventionalcondition matching used. Therefore , the colordifference introduced makes the accuracy of colorrepresentation be lowered.In order to eli minatemetamer CIE developed the scheme so-calledspectra matching in Publication 15 .2 and speci-fied that using band-pass filters with 5 nminter-val to sample and then reconstruct the originalcolor signal ,thus the color difference will disap-pear[1].Spectra… 相似文献
109.
Graça Cabeçadas M. José Brogueira M. Gelena Cavaco Célia Gonçalves 《Journal of Oceanography》2010,66(2):201-210
Although the circulation of intermediate water masses in the eastern North Atlantic remains poorly defined, the presence of
fresher intermediate waters, the Sub-Artic (SAIW) and the Antarctic Intermediate Water (AAIW), as well the saline intermediate
Mediterranean Water (MW), has been tracked using biogeochemical properties. Here we assess the hydrographic and chemical structures
of intermediate waters along the western Portuguese margin by examining the vertical distributions and property-property plots
of chemical tracers (oxygen and nutrients). AAIW was traced by low oxygen and high nutrients, while SAIW was recognized by
low nutrients. The Mediterranean Water (MW) undercurrent is shown to spread towards the eastern flank of Gorringe bank. Concurrently,
the fresher waters gained salt by direct incorporation of MW, while this water was enriched in nutrients on its way northward
and westward owing, to a great extent, to the entrainment of an AAIW branch. The distributions of nutrients and apparent oxygen
utilization are discussed in terms of regional ocean circulation. Our analysis suggests a circulation pattern of the various
intermediate waters along the western Portuguese margin: MW extends all over the area, but its presence is more pronounced
around cape St. Vincent; SAIW apparently moves southward, reaching the Gorringe bank region, and AAIW flows northward along
the coast and around the bank. 相似文献
110.
Subsidence of organic soils in the Sacramento-San Joaquin Delta threatens sustainability of the California (USA) water supply system and agriculture. Land-surface elevation data were collected to assess present-day subsidence rates and evaluate rice as a land use for subsidence mitigation. To depict Delta-wide present-day rates of subsidence, the previously developed SUBCALC model was refined and calibrated using recent data for CO2 emissions and land-surface elevation changes measured at extensometers. Land-surface elevation change data were evaluated relative to indirect estimates of subsidence and accretion using carbon and nitrogen flux data for rice cultivation. Extensometer and leveling data demonstrate seasonal variations in land-surface elevations associated with groundwater-level fluctuations and inelastic subsidence rates of 0.5–0.8 cm yr–1. Calibration of the SUBCALC model indicated accuracy of ±0.10 cm yr–1 where depth to groundwater, soil organic matter content and temperature are known. Regional estimates of subsidence range from <0.3 to >1.8 cm yr–1. The primary uncertainty is the distribution of soil organic matter content which results in spatial averaging in the mapping of subsidence rates. Analysis of leveling and extensometer data in rice fields resulted in an estimated accretion rate of 0.02–0.8 cm yr–1. These values generally agreed with indirect estimates based on carbon fluxes and nitrogen mineralization, thus preliminarily demonstrating that rice will stop or greatly reduce subsidence. Areas below elevations of –2 m are candidate areas for implementation of mitigation measures such as rice because there is active subsidence occurring at rates greater than 0.4 cm yr–1. 相似文献