Page 169 - Carbonate Facies in Geologic History

156 The Lower Carboniferous Waulsortian Facies

Indell .... _~~ 1_..,)h.401 ..
..
~""rmion Scole
,_. r·'cr .... t
r:-:-1M1IlJtone
L:...:..:.:.:.:Crit
,til ~nolls)

•
til
THORNL.EY

Fig.V-9. Region of "reef knolls" or lime mudstone mounds showing details of two linear
trends near Clitheroe and Bowland in north English basin. Note occurrence of mounds ofT
anticlinal axes but parallel to them. See also Fig. V -3. From Parkinson (1957, Fig. 5), with
permission of American Association of Petroleum Geologists

North American Examples of Waul sort ian Mounds in Mississippian Facies

Despite excellent exposures in North America, regional facies relations of mound-
bearing strata are less clear because of disposition of the outcrops. In the Sacra-
mento Mountains of New Mexico, Mississippian strata (Lake Valley crinoidal
limestones) are exposed along its western scarp in essentially a north-south line
for about 35 km and have been carefully mapped (Pray, 1961; Meyers, 1974). In
the northern part of this narrow belt, mounds rise from a uniform basal limestone
and are surrounded by encrinite (Fig. V-ll). They are numerous, lens-like, and
somewhat irregular, with elongate axes trending north-northwest. More extensive
shelf conditions probably prevailed regionally to the north and east of the present
outcrops, but these cannot be seen and must be inferred from broad, regional
patterns (Fig. V-12).
The southern end of the Sacramento Mountain belt, on the other hand, con-
tains more isolated, larger, and more conical shaped mounds. Large ones, such as
Mule Shoe mound (Pray, 1958), rose more than 100 m from the sea floor (Fig. V-
13). The mound-bearing strata essentially disappear southward along the moun-
tain front. Where Mississippian strata are seen in the next mountains southward
(Franklin and Huecos), early Mississippian strata are thin, or essentially absent,
and a presumed starved basin south of New Mexico (Armstrong, 1962; Wilson,
1969) was filled with Middle Mississippian siliceous platy limestone, the Ranch-
eria Formation.