Page 69 - Atlas of Sedimentary Rocks Under The Microscope

Carbonate rocks 148, 149, 150
L i m e stone
s
c l as i f i c ati o n
(continued)

148 :.hows a wackestone. The grains are bioclasts. mainly
echinoderm plates with some bryozoans (e.g. lower left
part). These grains arc supported by a matrix of car­
bonate mud in which many small particles are visible at
this magnification.
149 shows a mudstone, being a matrix-supported
limestone with less than 10% allochems. In this case the
allochems arc microfossils f o raminifera and calcite casts
of radiolaria. The sediment is cut by thin veins of pale
.
blue-stained f e rroan calcite. This sample is a fo s siliferous
micrite according to Folk's classification.
A boundstone is a limestone in which sediment is
bound together by organisms, such as occurs in many
reef's. Textures are often more clearly visible at hand­
specimen scale. ISO shows a thin section of a reef
limestone comprising growths of a number of problema­
tic organisms (probably algae or foraminif e ra) which
have encrusted one another while incorporating fine­
grained sediment into the rock framework.

148: Stained t1cetate peel, Wenlock Limestone, Silurian
Shropshire, England; magn(fication x II, P PL.
149: Stained thin section. Upper Crewceous, Pindos Zone,
Greece; magnification x 43. PPL.
150: Stained thin section, Red Hill Oolite, Lower Carbon­
iferous, Elliscales Quarry, Dalton-in-F u rne.s·s, Cumbria,
England; magnification x 12, P PL.
Other wackestones are shown (Folk classification in
brackets), in 105 (biomicrite) and 156 (biomicrite).

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