Page 161 - Carbonate Facies in Geologic History

Chapter V

The Lower Carboniferous Waulsortian Facies

Massive lime mudstone containing scattered crinoid and bryozoan fragments and
forming lens-like buildups and mounds, constitutes a distinctive and ubiquitous
facies in Lower Carboniferous (Tournaisian-Visean) strata throughout the north-
ern hemisphere. The rock of such buildups takes the name Waulsortian, from a
village in the Dinant basin, south of Namur in Belgium. Mounds and massive
sheet limestone of the same age and type are well known in Pembroke, Derby-
shire, and the Pennines of England and in Ireland; they also occur in central
France. In the regional paleotectonic patterns of all these areas, the Waulsortian
mounds and lenses appear chiefly as an intermediate (shelf margin) facies between
geosynclinal basins and shelf deposits which were formed in conditions of open
marine circulation (Fig. V-I).
Similar facies are known in the Osagian Series (early Mississippian) of North
America. Micritic mounds, surrounded by halos of crinoids, occur in the Big
Snowy Mountains, west of the apex of the Central Montana high, in the Bridger
Range of Montana (Cotter, 1965; Smith, 1972), in the Boone Formation of north-
eastern Oklahoma around the Ozark dome (Harbaugh, 1957; Troell, 1962), and
in the subsurface of north central Texas. This latter area has an arcuate belt
stretching from Comanche to Montague counties and includes circular masses as

North EngliJh baJin
FigJ V.3,8,9

Fig. V -1. Early Carboniferous (Mississippian) facies in western Europe showing limestone
shelves bordering Hercynian uplifts (dotted pattern). Culm facies is argillaceous, black sili-
ceous limestone and siltstone in intervening basins