Authors / CoAuthors
Marshall, J.F.
Abstract
Sands are predominant over the entire continental shelf, and mud is absent or only a minor component of the sediments. The amount of gravel, largely biogenic, is high in some places, but it has a scattered distribution. The amount of carbonate on the outer shelf is relatively low as a result of the formation of authigenic minerals. The amount and type of carbonate material have a substantial bearing on the grainsize and sorting of the sediments. The terrigenous component of the sediments is dominated by quartz, and there are usually only minor amounts of feldspar and rock fragments. Four typesof quartz grains have been identified on the basis of roundness, sorting, and grainsize. These quartz types are believed to be related to various sources including beach and fluvial deposits. Skeletal carbonate components include mainly foraminifera, molluscs, Bryozoa, echinoderms, and calcareous red algae. Intraclasts with either micrite or sparite cement are common and various types of carbonate cements have developed, predominantly within the chambers of organisms. Authigenic components of the shelf sediments consist of glauconite, goethite, and apatite. These are most abundant on the outer shelf, especially between 29° and 32°S. Goethite and glauconite most commonly fill the chambers of organisms, especially foraminifera, and apatite is present within the matrix of nodules and boulders of cemented nodules. Most of the sediments on the shelf are considered to be relict.Sediments were analysed for iron, arsenic, phosphorus, and titanium. High iron values, up to 25 percent F e 2 O s , are present on the outer shelf between 29° and 32°S.These high values are related to sediments which have high concentrations of goethite and glauconite. High arsenic values (up to 390 ppm As) are associated with these sediments, and also with the phosporites. Phosphorus values of about 6-10 percent P 2 0 5 characterise nodules from the same area. Most titanium values are less than 0.5percent TiOo. Factor analysis indicates a good correlation between Fe, As, and P 2 0 5 . The iron-rich sediments on the outer shelf are considered to have formed by the oxidation of glauconite, resulting in the formation of hydrated iron oxides. Arsenic and to some extent phosphorus have been adsorbed onto the hydrated iron oxides. The phosporites are considered to have formed in two stages: (1) direct precipitation of carbonate- apatite between mineral grains, and (2) subsequent replacement of micritic carbonate.
Product Type
document
eCat Id
56
Contact for the resource
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
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- GA PublicationBulletin
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- AU-NSWAU-QLD
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_External
Publication Date
1980-01-01T00:00:00
Creation Date
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unknown
Topic Category
geoscientificInformation
Series Information
Bulletin 207
Lineage
Unknown
Parent Information
Extents
[-32.0, -25.0, 152.0, 156.0]
Reference System
Spatial Resolution
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Associations
Source Information
Source data not available.