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91.
A. García-García T. Tesi D. Orange T. Lorenson S. Miserocchi L. Langone I. Herbert J. Dougherty 《Geo-Marine Letters》2007,27(2-4):143-154
New coring data have been acquired along the western Gulf of Lions showing anomalous concentrations of methane (up to 95,700 ppm) off the Rhône prodelta and the head of the southern canyons Lacaze-Duthiers and Cap de Creus. Sediment cores were acquired with box and kasten cores during 2004–2005 on several EuroSTRATAFORM cruises. Anomalous methane concentrations are discussed and integrated with organic carbon data. Sampled sites include locations where previous surveys identified acoustic anomalies in high-resolution seismic profiles, which may be related to the presence of gas. Interpretation of the collected data has enabled us to discuss the nature of shallow gas along the Gulf of Lions, and its association with recent sedimentary dynamics. The Rhône prodelta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried, effectively removing this organic matter from aerobic oxidation and biological uptake, and leading to the potential for methanogenesis with burial. Away from the flood-related sediments off the Rhône delta, the organic matter is being reworked and remineralized on its way along the western coast of the Gulf of Lions, with the result that the recent deposits in the canyon contain little reactive carbon. In the southernmost canyons, Lacaze-Duthiers and Cap de Creus, the gas analyses show relatively little shallow gas in the core samples. Samples with anomalous gas (up to 5,000 ppm methane) are limited to local areas where the samples also show higher amounts of organic matter. The anomalous samples at the head of the southern canyons may be related to methanogenesis of recent drape or of older sidewall canyon infills. 相似文献
92.
HUANG Xiaohang LAM Patrick P L LIN Xuezheng LIU Chenlin BIAN Ji GAISANO Herbert 《海洋学报(英文版)》2007,26(1):159-164
1 IntroductionSecretion is a basic function of all living organ-isms. In fish, like in mammals, neurotransmitters,hormones, enzymes and other macromolecules aresecreted in several neuronal, neuroendocrine and ex-ocrine organs and tissues located in brain,… 相似文献
93.
The time dependence of the ordering and disordering of Al and Si in sanidine is described within the framework of the kinetic rate laws developed in papers I and II of this series. It was found that the relevant order parameter Q
t is homogeneous and non-conserved. The rate law is:
相似文献
94.
Prasanna Venkatesh Sampath Hua‐Sheng Liao Zachary Kristopher Curtis Matthew E. Herbert Patrick J. Doran Christopher A. May Douglas A. Landis Shu‐Guang Li 《水文研究》2016,30(19):3390-3407
Fens, which are among the most biodiverse of wetland types in the USA, typically occur in glacial landscapes characterized by geo‐morphologic variability at multiple spatial scales. As a result, the hydrologic systems that sustain fens are complex and not well understood. Traditional approaches for characterizing such systems use simplifying assumptions that cannot adequately capture the impact of variability in geology and topography. In this study, a hierarchical, multi‐scale groundwater modelling approach coupled with a geologic model is used to understand the hydrology of a fen in Michigan. This approach uses high‐resolution data to simulate the multi‐scale topographic and hydrologic framework and lithologic data from more than 8500 boreholes in a statewide water well database to capture the complex geology. A hierarchy of dynamically linked models is developed that simulates groundwater flow at all scales of interest and to delineate the areas that contribute groundwater to the fen. The results show the fen receiving groundwater from multiple sources: an adjacent wetland, local recharge, a nearby lake and a regional groundwater mound. Water from the regional mound flows to an intermediate source before reaching the fen, forming a ‘cascading’ connection, while other sources provide water through ‘direct’ connections. The regional mound is also the source of water to other fens, streams and lakes in this area, thus creating a large, interconnected hydrologic system that sustains the entire ecosystem. In order to sustainably manage such systems, conservation efforts must include both site‐based protection and management, as well as regional protection and management of groundwater source areas. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
95.
Herbert E. Huppert 《地球物理与天体物理流体动力学》2013,107(1):317-322
Abstract Some deficiencies in a recent paper by Howard, Malkus and Whitehead are examined. The problem is reformulated in terms of an integro-differential equation, from which both asymptotic and numerical solutions are obtained. 相似文献
96.
Wolf U. REIMOLD Simon P. KELLEY Sarah C. SHERLOCK Herbert HENKEL Christian KOEBERL 《Meteoritics & planetary science》2005,40(4):591-607
Abstract— In earlier studies, the 65‐75 km diameter Siljan impact structure in Sweden has been linked to the Late Devonian mass extinction event. The Siljan impact event has previously been dated by K‐Ar and Ar‐Ar chronology at 342‐368 Ma, with the commonly quoted age being 362.7 ± 2.2 Ma (2 s?, recalculated using currently accepted decay constants). Until recently, the accepted age for the Frasnian/Famennian boundary and associated extinction event was 364 Ma, which is within error limits of this earlier Siljan age. Here we report new Ar‐Ar ages extracted by laser spot and laser step heating techniques for several melt breccia samples from Siljan (interpreted to be impact melt breccia). The analytical results show some scatter, which is greater in samples with more extensive alteration; these samples generally yield younger ages. The two samples with the least alteration yield the most reproducible weighted mean ages: one yielded a laser spot age of 377.2 ± 2.5 Ma (95% confidence limits) and the other yielded both a laser spot age of 376.1 ± 2.8 Ma (95% confidence limits) and a laser stepped heating plateau age over 70.6% 39Ar release of 377.5 ± 2.4 Ma (2 s?). Our conservative estimate for the age of Siljan is 377 ± 2 Ma (95% confidence limits), which is significantly different from both the previously accepted age for the Frasnian/Famennian (F/F) boundary and the previously quoted age of Siljan. However, the age of the F/F boundary has recently been revised to 374.5 ± 2.6 Ma by the International Commission for Stratigraphy, which is, within error, the same as our new age. However, the currently available age data are not proof that there was a connection between the Siljan impact event and the F/F boundary extinction. This new result highlights the dual problems of dating meteorite impacts where fine‐grained melt rocks are often all that can be isotopically dated, and constraining the absolute age of biostratigraphic boundaries, which can only be constrained by age extrapolation. Further work is required to develop and improve the terrestrial impact age record and test whether or not the terrestrial impact flux increased significantly at certain times, perhaps resulting in major extinction events in Earth's biostratigraphic record. 相似文献
97.
98.
Herbert H. B. Lau Richard J. Stancliffe Christopher A. Tout 《Monthly notices of the Royal Astronomical Society》2009,396(2):1046-1057
We investigate the behaviour of asymptotic giant branch (AGB) stars between metallicities Z = 10
99.
100.
The Planar Shape of Rock Joints 总被引:1,自引:1,他引:0
Knowing the planar shape of discontinuities is important when characterizing discontinuities in a rock mass. However, the
real discontinuity shape is rarely known, since the rock mass is usually inaccessible in three dimensions. Information on
discontinuity shape is limited and often open to more than one interpretation. This paper discusses the planar shape of rock
joints, the most common discontinuities in rock. First, a brief literature review about the shape of joints is presented,
including some information on joint-surface morphology, inferences from observed trace lengths on different sampling planes,
information based on experimental studies, and joint shapes assumed by different researchers. This review shows that joints
not affected by adjacent geological structures such as bedding boundaries or pre-existing fractures tend to be elliptical
(or approximately circular but rarely). Joints affected by or intersecting such geological structures tend to be rectangular.
Then, using the general stereological relationship between trace length distributions and joint size distributions developed
by Zhang et al. (Geotechnique 52(6):419–433, 2002) for elliptical joints, the effect of sampling plane orientation on trace lengths is investigated. This study explains why
the average trace lengths of non-equidimensional (elliptical or similar polygonal) joints on two sampling planes can be about
equal and thus the conclusion that rock joints are equidimensional (circular) drawn from the fact that the average trace lengths
on two sampling planes are approximately equal can be wrong. Finally, methods for characterizing the shape and size of joints
(elliptical or rectangular) from trace length data are recommended, and the appropriateness of using elliptical joint shapes
to represent polygonal, especially rectangular, joints is discussed. 相似文献
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