Page 164 - Carbonate Facies in Geologic History

Relation of Waulsortian Facies to Regional Paleostructure 151

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10' g' S' ~~ 6'
51.'
oJii .~
...
I o Longford
~
~thlone o Mullingor

53°

i=Leinster

: massif

52°
10 20 30 1.0 50 miles
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20 /.0 60 SOkm

S' 7' 6'

Fig. V -4. Isopach of the Waulsortian mudbank complex in southern Ireland. Thicknesses in
feet. Land areas lined. From Lees (1961, Fig. 3)

The massive, type Waulsortian facies encompasses late Tournaisian to early
Visean stages and locally varies greatly in thickness (more than 100 min 11/2 km),
indicating mound-like forms. Facies change is very rapid from the massive Waul-
sortian into lithoclastic talus and crinoidal limestone, particularly south of an
irregular main belt of mounds trending east from Avesnes in France (Fig. V-2).
They separate a shallow lagoon in the Namur-Dinant basins to the north, from a
deeper trough which extends southward and includes the geosynclinal Culm
facies. The Ardennes, a questionable land mass to the south, complicates the
paleogeography. Intermound and off-mound strata consist normally of dark cri-
noidal wackestone-packstone (Yvoir limestone) with chert and are overlain by
light-colored, more micritic and less crinoidallimestone (Leffe Formation). The
facies transition into the massive Waulsortian strata is highly dolomitized. The
uppermost beds of the lagoon, behind the mounds, are of early Visean age and
overlap the mound topography. They are black, laminated, thin-bedded peloidal-
foraminiferal wackestone and mudstones with some packstones; they represent