摘要:

Surficial sediments rich in apatite pellets were recovered from an 80‐m‐deep area that runs parallel to the eastern coast of Vizcaino Bay, Baja California. This area is subject to intense seasonal upwelling, the sediments presenting elevated phosphate (P2O5), organic carbon (Corg), and carbonate concentrations. The pellets are moderately well sorted, concentrated mainly in the 3ø size class within a poorly sorted sediment matrix. Abundant nodular apatite and phosphatized bone fragments were found in only one of the pellet‐bearing samples. This sample has a P2O5concentration of over 20%, the ≥ — 2.5ø to 0.5ø grain size classes alone being formed of up to 32% P2O5. The high proportion of fragmented nodules and the presence of volcanic rock pebbles indicate that at least part of this deposit is allochthonous. The apatite pellets have a flat to concave‐downward heavy rare earth (HREE) shale normalized pattern and, except for La, are depleted in light rare earth elements (LREE). The close resemblance between the HREE patterns and the relatively high La concentration in the pellets of Vizcaino Bay, and the onland phosphorites of the southern Baja California Peninsula, suggest similar depositional histories for these deposits. No significant Ce anomalies were observed, but a negative Eu deviation is common in all of the pellet‐bearing sediments. The depletion of LREE in the pellets of Vizcaino Bay may indicate the preferential removal of these elements by weathering processes.

ISSN:1064-119X    

DOI:10.1080/10641199809379954

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Recent research efforts have involved the development of computer programs and quantitative techniques designed specifically to facilitate the reduction and interpretation of large geochemical data sets acquired during marine mineral exploration surveys. The purpose of this study is to examine the applicability of these same techniques in developing meaningful interpretations of geoenvironmental data.

ISSN:1064-119X    

DOI:10.1080/10641199809379955

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Study of bathymetric data for the distal Bengal Fan reveals the presence of positive topographic features resembling seamounts. These features exhibit a relief of about 800 m above the surrounding seafloor at 4,400 m and are associated with large‐amplitude magnetic and gravity anomalies. Magnetic model studies suggest that one of the seamounts evolved along with the oceanic crust represented by the magnetic isochron A32 (∼ 72 My), while the other seamount was emplaced over the Cretaceous Quiet Zone Crust with reversed polarity. The seamounts studied provide an environment for possible locations of polymetallic encrustations. Morphology of the seamounts depends on several factors, including physical and chemical composition of the magma, eruption style, sediment thickness, maturity of underlying crust, and time of origin. Studying the seamounts together with integrated geophysical and physical data gave useful indications of their evolution and the existence of possible mineral deposits.

ISSN:1064-119X    

DOI:10.1080/10641199809379956

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The British Geological Survey (BGS) has completed a geological survey of the UK Offshore Continental Shelf and Slope and has published geophysical and geological maps for the area at 1:250,000 scale together with a set of regional reports. The requirements of acquisition, storage, and manipulation of the offshore data collection for map making are considered. Geophysical techniques, seabed coring equipment, wireline coring equipment, and station‐keeping procedures have been developed and proven, and now enjoy international application. To store this information BGS has created, and continues to maintain, a sample and core archive, an analog record archive, and an interactive computer database. These validated datasets, fronted by computerized indices, assist rapid access to stored information and facilitate reinterpretation and integration with other research data—a feature which is especially important for present‐day multidisciplinary projects. Current work is extending the offshore mapping into UK‐designated frontier areas in the northeast Atlantic Ocean, where the water depths can exceed 2,000 m. International collaboration with other surveys and industry has also posed new challenges, particularly with regard to shallow stratigraphic drilling techniques and environmental survey, for which the huge dataset amassed during the regional geological survey is now of importance for the provision of baseline information.

ISSN:1064-119X    

DOI:10.1080/10641199809379957

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Researchers at the University of Hawai'i at Manoa have been working for the past several years to develop the necessary techniques for finding and quantitatively characterizing offshore unconsolidated carbonate deposits with potential for beach nourishment and use in construction aggregates for tropical island communities. This article examines particular results of this research, with special attention given to the area offshore from Waikiki Beach. Acoustic surveying, water‐jet probing to measure the thickness of unconsolidated material and three different sampling methods were used in this study. Two separate seismic systems were used for the subbottom profiling survey, a Datasonics Bubble‐Pulser® system and a broad‐band, frequency‐modulated ("chirp") prototype system.

ISSN:1064-119X    

DOI:10.1080/10641199809379958

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:1064-119X    

DOI:10.1080/10641199809379953

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor