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grain size distribution
glauconite clay mineral, a green illite that can be formed by authigenesis in marine
sediments. Because both Fe2+ and Fe3+ occur simultaneously, the mineral is
formed in microenvironments which are alternately reducing and oxidizing,
e.g., within the tests of Foraminifera.
globigerina ooze ~Foraminifera.
Gnathostomulida (jaw worms) small phylum of microscopic, free-living marine
worms. The simple hermaphrodite animals have a specialized pharynx with a
pair of jaws, the body is covered with cilia, and the head may have some pairs
of sensory bristles. There is no anus. They live interstitially in sandy sediments.
Feeding by grazing the surface of sand grains.
gonad organ producing gametes (reproductive cells: eggs and sperms).
Gondwana the late Mesozoic continent that split into present-day South America,
Africa, Australia, India, and Antarctica. ~continental displacement and ~Pangea.
gonoduct tube through which the mature germ cells pass to the exterior.
Gorgonacea ~Octocorallia.
grab ocean-bottom sampler that consists of segments which drive into the sediment, enclose and retain a sample. The Van Veen grab is made up of two
opposed, pivoting, hemicylindrical buckets that shut by rotation on a hinge
when the sampler is pulled up. A fair-sized grab can bring up approximately 1 m3 of material. ~bottom samplers.
graded bedding beds of sediment in which relatively coarse material is concentrated at the base and finer material at the top. They may form when the
velocity of the prevailing current oscillates (each level will then be well sorted), or by emplacement by a single short-lived flow with declining velocity,
such as a turbidity current.
grain flow ~sediment-gravity flow.
grain size size of sediment particles; constitutes the main characteristic used for
classifying lithogenous sediments. One can distinguish: clay - smaller than 2
flm; silt - between 2 and 64 flm; sand - between 64 flm and 2 mm; granules -
between 2 and 4 mm; gravel pebbles - between 4 mm and 6 cm; cobbles -
between 6 and 25 cm; and boulders -larger than 25 cm. ~grain-size distribution.
grain-size distribution percentage (by weight or count) of particles of each grainsize fraction. The grain-size distribution is a measure of the energy of the
grain size distribution
glauconite clay mineral, a green illite that can be formed by authigenesis in marine
sediments. Because both Fe2+ and Fe3+ occur simultaneously, the mineral is
formed in microenvironments which are alternately reducing and oxidizing,
e.g., within the tests of Foraminifera.
globigerina ooze ~Foraminifera.
Gnathostomulida (jaw worms) small phylum of microscopic, free-living marine
worms. The simple hermaphrodite animals have a specialized pharynx with a
pair of jaws, the body is covered with cilia, and the head may have some pairs
of sensory bristles. There is no anus. They live interstitially in sandy sediments.
Feeding by grazing the surface of sand grains.
gonad organ producing gametes (reproductive cells: eggs and sperms).
Gondwana the late Mesozoic continent that split into present-day South America,
Africa, Australia, India, and Antarctica. ~continental displacement and ~Pangea.
gonoduct tube through which the mature germ cells pass to the exterior.
Gorgonacea ~Octocorallia.
grab ocean-bottom sampler that consists of segments which drive into the sediment, enclose and retain a sample. The Van Veen grab is made up of two
opposed, pivoting, hemicylindrical buckets that shut by rotation on a hinge
when the sampler is pulled up. A fair-sized grab can bring up approximately 1 m3 of material. ~bottom samplers.
graded bedding beds of sediment in which relatively coarse material is concentrated at the base and finer material at the top. They may form when the
velocity of the prevailing current oscillates (each level will then be well sorted), or by emplacement by a single short-lived flow with declining velocity,
such as a turbidity current.
grain flow ~sediment-gravity flow.
grain size size of sediment particles; constitutes the main characteristic used for
classifying lithogenous sediments. One can distinguish: clay - smaller than 2
flm; silt - between 2 and 64 flm; sand - between 64 flm and 2 mm; granules -
between 2 and 4 mm; gravel pebbles - between 4 mm and 6 cm; cobbles -
between 6 and 25 cm; and boulders -larger than 25 cm. ~grain-size distribution.
grain-size distribution percentage (by weight or count) of particles of each grainsize fraction. The grain-size distribution is a measure of the energy of the