Geoscience Reference
In-Depth Information
pores within the allochem fabric and intercrystal pores
within the cement and allochems.
Limestone is used for building locally and certain
varieties are exported around the world. It has provided
the fabric for some of the most magnificent buildings in
Britain. The more important British limestones will be
discussed below with a selection of limestones from other
countries following.
In northern England, the carboniferous limestone
provides many hard, compact building stones that are
usually cut and polished and sold as panels or tiles. Figure
46
shows 'Swaledale Fossil' limestone that is a pale brown
with many attractive fossils (packed biomicrite). It is used
for mainly decorative flooring and cladding.
The Jurassic System has provided more building
limestone than any other in Britain. Most of the Jurassic
limestones used for building are dominantly oolitic with
variable proportions of shell debris. The Lincolnshire
limestone (Bajocian, Middle Jurassic) has been the source
46
46
'Swaledale Fossil' limestone (Yorkshire, England)
comprising grain-supported fossil allochems (mainly
crinoids) composed of sparry calcite, with a matrix of
micrite; XPT, ×35.
Table 9
Folk (1959, 1962) scheme for classification of limestone
Volumetric allochem
>10% allochems
<10% allochems
composition
Sparry calcite> Micrite> Sparry
1-10% allochems
<1%
Micrite
calcite
allochems
>25% intraclasts
Intrasparite
Intramicrite
Intraclasts
Intraclast-bearing
micrite
>25% ooids
Oosparite
Oomicrite
Ooids
Ooid-bearing
micrite
>3:1
Biosparite
Biomicrite
Bioclasts
Fossilferous
3:1 to
Biopelsparite
Biopelmicrite
micrite
1:3
<1:3
Pelparite
Pelmicrite
Peloids
Peloid-bearing
micrite
