Page 57 - Atlas of Sedimentary Rocks Under The Microscope

Carbonate rocks 118, 119, 120
B i o c l a sts

Calcispheres and Worm Tubes

Worm tubes

Although rarely abundant, calcareous worm tubes are
widespread in shallow marine and freshwater limestones.
118 shows a bioclastic limestone with a large fragment
comprising numerous worm tubes, seen in cross-section.
Most of the tubes are filled with micrite. The associated
fauna include a bryozoan (top centre}, molluscan casts
(top right}, an echinoderm fragment (top right) and
brachiopods (bottom). The sediment is cemented by blue.
stained f e rroan calcite. 1 1 9 shows sections through the
coiled calcareous worm tube Spirorbis. Sparry calcite
ce ment fills the chambers and the surrounding sediment is
micrite with a few thin-valved ostracods (e.g. upper left).

118: Swined lhin seclion, In f erior Oolite, M id d l e Jurassir.
1-ecklwmplon Hill, Glouceslershire, England; magnific ·
tlliOII X 13, PPL.
119: Uns1t1ined lhin section, Ardwick Limestone. U p p e r
Carbonif e rous, Manches1er, England; magnifica/ion x /7,
PPL.
Worm wbes are also shown in 214 and 215.

Calcispheres

Calcispheres arc small hollow spherical bodies of calcite,
usually with a micritic wall. They are particularly com·
mon in Upper Palaeozoic limestones and may be the
calcified reproductive parts of dasycladaccan algae. 120
) deep, red-brown-stained walls - associated with micrite·
shows numerous calcispheres - the circular objects l\1th
walled cndothyracid f o raminifera and a f o liated brachio­
pod shell which extends right across the field of view.

111
120: Swined ace/ate peel, Woo Dale Limes/one, Loll'lt
Carboni ferous, Long Dale, Derbyshire, England; magnific· I
ation x21, PPL.
/I Of/
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