Page 51 - Atlas of Sedimentary Rocks Under The Microscope

Carbonate rocks 101, 102, 103
B i o c l asts

Bryozoans

Bryo�:oans arc widespread in marine limestones and arc
particularly common in Palaeozoic reef complexes. Most
bryo�:oans had calcite hard parts and a laminated wall
structure is preserved.
Among the most characteristic bryozoans are the
frond-like f e nestrate types, examples of which are seen in
tOt. Note the thick wall of laminated calcite surrounding
cement-filled pores (zooccia). Most of the fragments are
tranwcrsc sections but the large piece to the lower left of
centre is a longitudinal section.
102 is a transverse section of a stick-like bryozoan
colony. showing the overall rounded shape of the ·stem'
and of the �:ooecia within. Some of these have been in filled
with fine sediment (upper right of fragment) but most
have a blue-stained, ferroan calcite cement inti II.
In 103. the two circular. concentrically-laminated
grains stained red-brown are brachiopod spines. These
arc encrusted by a bryozoan. Note the thick calcite wall of
the bryo;oan and the pores of different sizes within the
skeleton, filled with pink-stained non-ferroan calcite
cement. Some fr<tgmcnts of fe nestrate bryozoans can be
seen along the left-hand side of the photograph.

/Of· Swined thin section. £yam Limestone. Lower Carho­
ni/ermn. Ricklmt· Quarry. Derbyshire. England: magn(fic­
ation x 16. PPL.
/(}2: Swined thin section. Ouanamane F o rmation. M id d le
.!ura.uic, West e m High Atlas. Morocco: magn(fic­
ation x 27. PPI ..
103: .S 'tained thin section. Red Hill Oolite. £/liscale.l
QuanT. Dalton-in-Fumes.\, Cumbria. England: magni/ic­
utioll x 20. PPL
Or/wr hrl'fl:oons art' sholl'n in 96. 97. 132. 133 and 178.
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