Small faults and kink bands in the Nankai accretionary complex: Textural observations from Site 808 of ODP Leg 131     

Jonathan C.  Lewis  Tim  Byrne David J.  Prior 《Island Arc》1997,6(2):183-196

Abstract We present backscattered scanning electron microscope and petrographic microscope observations of deformed sediments from Ocean Drilling Program (ODP) Site 808 in order to better understand the dewatering and deformation history of the Nankai accretionary complex. This synthesis of deformation textures has three implications. First, the early structures that dominate the Nankai prism, small faults and kink bands, have very different electron microscope versus optical microscopic expressions. This observation is important to investigations of fine-grained sediment in both stable and active tectonic settings, in part, because these materials have often been studied almost exclusively by electron microscope methods. In sediments of this type, investigators often forego petrographic analysis because of the relative opacity of samples at normal (i.e. 30 pm) thin section thicknesses. Second, the textural observations we have compiled suggest that these deformation structures acted as 'single-event' pathways that contributed to diffusive dewatering of the prism. Third, our observations serve as a reference frame for the early tectonic structures that are important to the dewatering history of a 'sandy' accretionary prism.  相似文献   

Model Simulations in Support of Field Scale Design and Operation of Bioremediation Based on Cometabolic Degradation   总被引：2，自引：0，他引：2  

Margaret M. Lang  Paul V. Roberts  Lewis Semprini 《Ground water》1997,35(4):565-573

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Variations in structures and distributions of C₂₅ highly branched isoprenoid (HBI) alkenes in cultures of the diatom, Haslea ostrearia (Simonsen)     

E. J. Wraige  S. T. Belt  C. A. Lewis  D. A. Cooke  J. -M. Robert  G. Mass  S. J. Rowland 《Organic Geochemistry》1997,27(7-8)

The highly branched isoprenoid (HBI) alkenes of three batch cultures of the diatom Haslea ostrearia have been examined and the occurrence of C₂₅ tri-, tetra- and pentaenes confirmed. Growth of cultures outside at ambient temperature, under natural sunlight, in May (6 days) and June (10 days) 1995 and monitoring of HBI concentrations in samples collected daily and stored frozen, revealed that in May greater concentrations of HBIs (ca 6500 fg cell⁻¹) were produced than in June and at a much earlier stage of growth. Furthermore, in May the HBIs were more unsaturated (predominantly a tetraene rather than a triene). The reasons for these differences are at present unknown and future investigations of the effect of irradiance, temperature, salinity and other environmental variables are required. Such experiments may allow the various HBI distributions in the alga and in sediments to be better understood and, like some other polyunsaturated lipids, HBI alkenes may become useful environmental and palaeoenvironmental indicators. Two previously unreported alkenes, 2,6,10,14-tetramethyl-7-(3-methylpent-4-enyl)pentadec-2,5,9,13-ene (GC retention index, 2201_DB-1) and 2,6,10,14-tetramethyl-7-(3-methylene pent-4-enyl)pentadec-2,5,9,13-ene (GC RI, 2248_DB-1) from a batch culture of Haslea ostrearia grown in October/November 1993 and stored frozen for over a year, have also been isolated and characterised by ¹³C and ¹H NMR, epoxide derivatisation and mass spectrometry. Such structural characterisation studies of HBI alkenes should also aid our understanding of the geochemical fate of these widely distributed hydrocarbons.  相似文献   

THE ADJUSTMENT OF SOME HYDRAULIC VARIABLES AT DISCHARGES LESS THAN ONE CFS*     

Laurence A. Lewis 《The Professional geographer》1966,18(4):230-234

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The Irish Sea cod recovery plan: some lessons learned     

Kelly  Ciaran J.; Codling  Edward A.; Rogan  Emer 《ICES Journal of Marine Science》2006,63(4):600-610

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Longwaves and primary productivity variations in the equatorial pacific at 0°, 140dgW     

D.G. Foley  T.D. Dickey  M.J. Mcphaden  R.R. Bidigare  M.R. Lewis  R.T. Barber  S.T. Lindley  C. Garside  D.V. Manovt  J.D. Mcneil 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)

High temporal resolution measurements of physical and bio-optical variables were made in the upper ocean using a mooring located at 0°, 140°W from 9 February 1992 to 15 March 1993 as part of the equatorial Pacific Ocean (EgPac) study. Chlorophyll and primary productivity time-series records were generated using the mooring data. Primary productivity varied by about 50% around the mean on time scales of weeks and by over a factor of four within our observational period. The mooring observations encompassed both El Niho and cool conditions. Kelvin waves were evident during the El Nifio phase, and tropical instability waves (TIWs) were dominant during the cool phase. The two extreme conditions also were observed concurrently with complementary ship-based measurements. In addition, bio-optical drifters provided simultaneous spatial data concerning net phytoplankton growth rates during passage of a TIW. The collective data sets have been used to examine the causes of the observed variability in phytoplankton biomass and productivity. Our joint results and analyses appear to support the hypothesis that the vertical transport of iron into the upper layer and primary production rates are modulated by variability of the depth of the Equatorial Undercurrent and by equatorial longwaves. In particular, our results are consonant with the suggestion of Barber et al. (1996) that passage of a TIW may be considered to be a natural analog of a small iron enrichment experiment. Predicting primary productivity and, thus, carbon flux in the equatorial Pacific requires continuous, long-term observations of a few physical, biological, and optical properties that can be used to parameterize the biological variability.  相似文献   

3D hydrodynamic modelling of fixed oscillating water column wave power plant by a boundary element methods     

Y. M. C. Delaur  A. Lewis 《Ocean Engineering》2003,30(3):996-330

A three-dimensional (3D) numerical model of fixed Oscillating Water Column system (OWC) is presented and validated. The steady-state potential flow boundary value problem due to regular wave interaction with the OWC is solved by a first order mixed distribution panel method. Ocean response predictions are derived using a deterministic statistical model based on a spectral analysis method. The model validation focusses on diffraction predictions and involves convergence tests and numerical comparisons with independent potential flow computations. Predictions of both regular and irregular wave responses are also compared against experimental results. Sample results including the yearly-averaged power conversion efficiency are presented in the final section to illustrate the method’s suitability to a 3D hydrodynamic design optimisation.  相似文献   

From oblique subduction to intra-continental transpression: Structures of the southern Kermadec-Hikurangi margin from multibeam bathymetry,side-scan sonar and seismic reflection     

Jean-Yves Collot  Jean Delteil  Keith B. Lewis  Bryan Davy  Geoffroy Lamarche  Jean-Christophe Audru  Phil Barnes  Franck Chanier  Eric Chaumillon  Serge Lallemand  Bernard Mercier de Lepinay  Alan Orpin  Bernard Pelletier  Marc Sosson  Bertrand Toussaint  Chris Uruski 《Marine Geophysical Researches》1996,18(2-4):357-381

The southern Kermadec-Hikurangi convergent margin, east of New Zealand, accommodates the oblique subduction of the oceanic Hikurangi Plateau at rates of 4–5 cm/yr. Swath bathymetry and sidescan data, together with seismic reflection and geopotential data obtained during the GEODYNZ-SUD cruise, showed major changes in tectonic style along the margin. The changes reflect the size and abundance of seamounts on the subducting plateau, the presence and thickness of trench-fill turbidites, and the change to increasing obliquity and intracontinental transpression towards the south. In this paper, we provide evidence that faulting with a significant strike-slip component is widespread along the entire 1000 km margin. Subduction of the northeastern scrap of the Hikurangi Plateau is marked by an offset in the Kermadec Trench and adjacent margin, and by a major NW-trending tear fault in the scarp. To the south, the southern Kermadec Trench is devoid of turbidite fill and the adjacent margin is characterized by an up to 1200 m high scarp that locally separates apparent clockwise rotated blocks on the upper slope from strike-slip faults and mass wasting on the lower slope. The northern Hikurangi Trough has at least 1 km of trench-fill but its adjacent margin is characterized by tectonic erosion. The toe of the margin is indented by 10–25 km for more than 200 km, and this is inferred to be the result of repeated impacts of the large seamounts that are abundant on the northern Hikurangi Plateau. The two most recent impacts have left major indentations in the margin. The central Hikurangi margin is characterized by development of a wide accretionary wedge on the lower slope, and by transpression of presubduction passive margin sediments on the upper slope. Shortening across the wedge together with a component of strike-slip motion on the upper slope supports an interpretation of some strain partitioning. The southern Hikurangi margin is a narrow, mainly compressive belt along a very oblique, apparently locked subduction zone.  相似文献   

Instrumental waveform distortion on ocean bottom seismometers     

Brian T. R. Lewis  Jonathan D. Tuthill 《Marine Geophysical Researches》1981,5(1):79-85

Data from the 1978 Lopez Island OBS Intercomparison Experiment and deep sea data from University of Washington OBSs show that there is a considerable amount of waveform distortion resulting from the conversion of horizontal motion into vertical motion, here called cross-coupling distortion. This distortion, which substancially reduces the significance of waveform matching with synthetic seismograms, appears to result from rotation imparted to the OBS package by near-vertically traveling shear energy. The degree of this rotation seems to depend on the instrument surface area above the seafloor and the geometry and surface area of the feet connecting the package to the seafloor. The sensitivity and response of the seismometers within the package to this rotation depends on the precise location of the seismometers with respect to the axis of rotation. The results suggest how to modify OBS designs to minimize these effects.University of Washington Contribution No. 1225.  相似文献   

The principal factors contributing to the flux of salt in a narrow, partially stratified estuary     

R. E. Lewis  J. O. Lewis 《Estuarine, Coastal and Shelf Science》1983,16(6)

Observations of the velocity and salinity structure of the Tees estuary were made at eight stations along the estuary axis between Victoria Bridge and the sea during the summer of 1975. The measurements were made on ten separate tidal periods covering neap and spring tides.The data were collected over a period of relatively low freshwater flows and the residual current was found to have a strong dependence on the Stokes drift. At the upstream stations, the residuals were more than an order of magnitude greater than the currents anticipated from the freshwater discharge. Although the mean stratification decreased as the tidal range increased, the vertical circulation was stronger on spring tides than on neaps. Vertical variations in the amplitude and phase of the tidal current results in a current which strengthens the vertical circulation. However, this effect only made a relatively small contribution to the observed vertical circulation.The relative contribution of the individual salt flux terms to the net upstream transport of salt varies along the estuary. As the estuary narrows, the contribution by the oscillatory terms dominates that from the shear in the steady state flow. Of these oscillatory terms, the correlation of velocity and salinity fluctuations plays a key rôle in the salt transport. The depth mean values make a greater contribution than deviations from the depth mean and the flux due to phase variations over depth is smaller than either of these. Since the Stokes drift is compensated by a down-stream steady state flow, it does not contribute to the tidal mean transport of salt.At the seaward end of the estuary, the salt fluxes due to the steady state vertical shear and the convariance of the tidal fluctuations act in a complementary way to counter the seaward transport of salt by the freshwater flow. With the possible exceptions of the wide or narrow reaches of the Tees, the longitudinal fluxes of salt due to transverse variations in velocity, salinity and depth and turbulent fluctuations are of secondary importance as contributors to the estuary salt budget.On both neap and spring tides, the computed total salt transports at the Newport and Victoria bridges did not match the values required for a salt balance with the corresponding freshwater flows. These fluxes were probably the cause of the observed downstream displacement of the tidal mean salinity distribution between neap and spring tides.  相似文献