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871.
Dr. Thomas Mathai K. N. Rajarama Satish Kumar M. Suresh Chandran M. R. Asoka Kumar 《Marine Georesources & Geotechnology》2013,31(2):180-193
Offshore geotechnical surveys form part of an integrated investigation to rejuvenate a decrepit minor port at Badagara, Kerala on the southwestern coast of India. The sediments typify a fluvio-marine milieu ranging from silty clay, sand, silty sand, sandy silt and clayey silt. Geotechnical and sedimentological studies of shallow cores reveal the geotechnical aspects besides the depositional history of the sediments. Downcore geotechnical variations and regressive coefficients based on their inter-relationships highlight diverse factorial inferences. X-Ray Diffraction data indicate the prominent clay type. A comparative evaluation of the geotechnical characteristics of clayey sediments off Badagara, with similar studies along various sectors of the Kerala coast, both on land as well as in the near shore, is broadly attempted. Geotechnical studies carried out earlier on the uplifted Cochin marine clays provide comparative data for evaluating the possible variations between present day marine clayey sediments occurring along the Kerala coast and uplifted marine clays which, besides their gross variations in levels with respect to the present sea-level, also obviously relate to a much older depositional environment and provenance during probable Holocene times. 相似文献
872.
Susana Bolhão Muiños James R. Hein Martin Frank José Hipólito Monteiro Luís Gaspar Tracey Conrad 《Marine Georesources & Geotechnology》2013,31(1):40-70
Eighteen deep-sea ferromanganese crusts (Fe-Mn crusts) from 10 seamounts in the northeast Atlantic were studied. Samples were recovered from water depths of ~1,200 to ~4,600 m from seamounts near Madeira, the Canary and Azores islands, and one sample from the western Mediterranean Sea. The mineralogical and chemical compositions of the samples indicate that the crusts are typical continental margin, hydrogenetic Fe-Mn crusts. The Fe-Mn crusts exhibit a Co + Cu + Ni maximum of 0.96 wt%. Platinum-group element contents analyzed for five samples showed Pt contents from 153 to 512 ppb. The resource potential of Fe-Mn crusts within and adjacent to the Portuguese Exclusive Economic Zone (EEZ) is evaluated to be comparable to that of crusts in the central Pacific, indicating that these Atlantic deposits may be an important future resource. 相似文献
873.
The Håkon Mosby Mud Volcano (HMMV) is a seafloor mud volcano, having a 1-km-diameter circular shape and a relief of 8–10?m. HMMV is located within a slide scar on the Bjørnøya glacial submarine fan on the SW Barents Sea slope, and is underlain by a >6-km-thick Cenozoic sequence. Multichannel seismic data reveal a 1- to 2-km-wide disturbed zone, which extends to a depth of >3?km below the HMMV. We relate the zone to the presence of free gas. The seismic data are compatible with an intrasedimentary sourced mud volcano related to the glacial sedimentation history and mass movements. 相似文献
874.
Acoustic reflection signatures of four hydro-carbon seeps were classified using near-bottom 25-kHz echosounder profiles.
Echo patterns were compared with ground-truth data obtained by submersible observations and shallow coring. Six echo types
were distinguished: strong reflections from (1) exposed or (2) buried hard substrates, such as authigenic carbonate or gas
hydrate; acoustic scattering in (3) unlayered or (4) layered sediments owing to gas, shells, or disseminated carbonates; (5) attenuation
caused by gas; and (6) undisturbed sediments. Echo type distributions suggest that high spatial variability indicates a younger,
vigorous seep, whereas extensive hard substrate implies an older, encrusted seep.
Received: 29 May 1998 / Revision received: 7 October 1998 相似文献
875.
We examine results from a cruise in May 1997. CTD casts to near the bottom were made south of the Aleutian Islands, across Amchitka Pass, and north of the islands. We computed a westward geostrophic speed of 123 cm s–1 at 173.5°W in the Alaskan Stream. The computed volume transport there, referred to the bottom, was 25×106m3s–1. On other similar sections, transports were 8–15 × 106 m3s–1. Various complex variations in geopotential height along the Stream apparently altered the cross-stream gradients, and hence the transports. Rotational tendencies were also present. Northward inflow through Amchitka Pass was quite strong (6 × 106 m3s–1). Data north of the islands supported the existence of a zero-velocity reference level of variable depth. 相似文献
876.
Scanning and transmission electron microscopic analyses of shale samples from offshore Louisiana, USA, Gulf of Mexico, reveal
the relationship between mineralogical and microfabric changes during burial diagenesis. The local geopressured zone begins
at 2200-m depth. Above that depth the shales are smectite-rich, generally lack particle orientation, and contain appreciable
pores. Below the 2200-m depth, the shales become more illite-rich with increasing burial, more crystalline, and less porous.
Microfabric changes are mainly caused by compaction during burial diagenesis; mineralogical changes (smectite-to-illite) and
crystal growth also play an important role in fabric alteration during deep burial diagenesis.
Received: 12 May 1998 / Revision received: 14 July 1998 相似文献
877.
The Cenozoic shelf margin of the Amazon Mouth Basin is characterized by a thick prograding prism of siliciclastic sediments.
This prism, composed mainly of Upper Miocene and younger sediments, overlies a Lower Tertiary carbonate shelf. Two tectonic–sedimentary
models for the area were developed with the aid of new deep-reflection seismic data. Gravitational tectonics dominate the
regional geological framework. Tensional stresses are created near the shelf margin, and compressional features dominate at
the base of the slope. The morphology of this compressional zone is closely associated with the St. Paul Fracture Zone and
the boundary between continental and oceanic crusts.
Received: 20 August 1996 / Revision received: 11 June 1998 相似文献
878.
Cessation of the Norwegian drift net fishery: changes observed in Norwegian and Russian populations of Atlantic salmon 总被引:1,自引:2,他引:1
879.
The morphology, swimming behaviour, settlement preferences and behaviour of five species of Demospongiae are described. The sponges, Haliclona sp., Microciona coccinea, Ophlitaspongia seriata, Mycale macilenta, and Halichondria moorei, are all common in the intertidal region in the north of New Zealand. The view is put forward that larval behaviour must be interpreted in terms of the known ecological situation of the adult sponge. 相似文献
880.
A. M. R. Burnet 《新西兰海洋与淡水研究杂志》2013,47(1):55-62
Brown trout Salmo trutta Linn, were marked with individual tags and recaptured throughout a year in two small Canterbury streams. The growth recorded showed a marked seasonal variation which differed in pattern in the two streams. There was a considerable difference in the growth rate between the two populations and fish transferred from the slow‐growth stream to the faster‐growth stream showed an immediate response to the change. 相似文献