285
sediment classification
Secchi disk a white disk of standard size (30 em) used for estimation of the turbidity of the water, which is a function of the transparency. The disk is lowered and the depth at which the disk disappears from the sight of the
observer is the so-called Secchi depth. Comparison with more sophisticated
instruments for measuring light under water delivers empirical formulas to
estimate attenuation coefficients for the visible part of the spectrum from
the Secchi depth. The euphotic zone is roughly three times Secchi depth. Devised
in the 1860s by the Italian astronomer Angelo Secchi while he worked in the
Mediterranean aboard the papal vessel Immacolata Concezione. Its strength
is its simplicity and the possibility to compare data collected with the same
apparatus for over more than a century. Although the method is subjective
it can give a reliable estimate, if used with care. In extremely transparent
waters such as occur in mid-ocean or in the Antarctic, depths down to
almost 80 m can be attained, be it with disks of a larger diameter.
secondary production -7production.
secondary wave -7S-wave.
sediment particulate solid material accumulated by natural processes.
sedimentary structures structures in sedimentary rocks resulting from depositional, deformational, and/ or diagenetic processes. Structures may be formed
either simultanously with deposition (primary sedimentary structures) or
subsequently (secondary sedimentary structures). A large part of the vocabulary of sedimentary structures refers to the external forms and internal
structure of beds of sediments (-7cross-bedding and -7graded bedding), markings
on bedding planes (-7ichnofossil), and penecontemporaneous (at or shortly
after deposition) deformation of bedding. Bed forms depend on particle size
and current velocity. Generally speaking, tranquil flow of water produces
small ripples and megaripples (more than 60 em in length), while rapid flow
produces plane beds and antidunes. Often the distribution of bed forms is
selective, so that we can distinguish sedimentary environments, such as
coastal, deltaic, mudflat, slope and deep-sea environments, each having its
own characteristic configuration of bed forms. Wave ripples, for example, are
restricted to shallow water environments (less than 60 m and usually from 0
to 20 m water depth), while contourites are found on the slope and abyssal plain.
(Figure see p. 286)
sediment classification three major types can be distinguished: (a) lithogenous
sediments: detrital sediments produced by desintegration of pre-existing rocks
and of volcanic ejecta. Nomenclature based on grain size; additional qualifiers
are derived from the lithologic components (terrigenous, bioclastic, calcareous, volcanogenic, etc.) and from the structure and color of the deposits.
sediment classification
Secchi disk a white disk of standard size (30 em) used for estimation of the turbidity of the water, which is a function of the transparency. The disk is lowered and the depth at which the disk disappears from the sight of the
observer is the so-called Secchi depth. Comparison with more sophisticated
instruments for measuring light under water delivers empirical formulas to
estimate attenuation coefficients for the visible part of the spectrum from
the Secchi depth. The euphotic zone is roughly three times Secchi depth. Devised
in the 1860s by the Italian astronomer Angelo Secchi while he worked in the
Mediterranean aboard the papal vessel Immacolata Concezione. Its strength
is its simplicity and the possibility to compare data collected with the same
apparatus for over more than a century. Although the method is subjective
it can give a reliable estimate, if used with care. In extremely transparent
waters such as occur in mid-ocean or in the Antarctic, depths down to
almost 80 m can be attained, be it with disks of a larger diameter.
secondary production -7production.
secondary wave -7S-wave.
sediment particulate solid material accumulated by natural processes.
sedimentary structures structures in sedimentary rocks resulting from depositional, deformational, and/ or diagenetic processes. Structures may be formed
either simultanously with deposition (primary sedimentary structures) or
subsequently (secondary sedimentary structures). A large part of the vocabulary of sedimentary structures refers to the external forms and internal
structure of beds of sediments (-7cross-bedding and -7graded bedding), markings
on bedding planes (-7ichnofossil), and penecontemporaneous (at or shortly
after deposition) deformation of bedding. Bed forms depend on particle size
and current velocity. Generally speaking, tranquil flow of water produces
small ripples and megaripples (more than 60 em in length), while rapid flow
produces plane beds and antidunes. Often the distribution of bed forms is
selective, so that we can distinguish sedimentary environments, such as
coastal, deltaic, mudflat, slope and deep-sea environments, each having its
own characteristic configuration of bed forms. Wave ripples, for example, are
restricted to shallow water environments (less than 60 m and usually from 0
to 20 m water depth), while contourites are found on the slope and abyssal plain.
(Figure see p. 286)
sediment classification three major types can be distinguished: (a) lithogenous
sediments: detrital sediments produced by desintegration of pre-existing rocks
and of volcanic ejecta. Nomenclature based on grain size; additional qualifiers
are derived from the lithologic components (terrigenous, bioclastic, calcareous, volcanogenic, etc.) and from the structure and color of the deposits.