Page 173 - Carbonate Facies in Geologic History

160 The Lower Carboniferous Waulsortian Facies

BIOHERM STRUCTURE - LAKE VALLEY FORMATION
SAN ANDRES CANYON
SAN ANDRES MOUNTAI NS

Current direction -

Fig. V -13. Early Mississippian (Lake Valley Group) in San Andres Mountains, New Mexico
showing relationship of Waulsortian mound to surrounding strata. From Laudon and
Bowsher (1941, Fig. 29), courtesy of Geological Society of America

There are subtle, but real facies changes across the positive block which have
been worked out by Smith from study of the Lodgepole cyclic sediments extend-
ing across it (Chapter X). The lowest of these cycles embraces the Paine Member
of the Lodgepole, a thin and rhythmically bedded argillaceous, siliceous, lime
mudstone and wackestone with bryozoans and crinoid fragments (termed "deeper
water limestone" by Wilson, 1969). Waulsortian type mounds of moderate size
exist in the Paine Member and have been investigated by Cotter (1965) in the Big
Snowy Mountains and by Stone (1971) in the Bridger Range, as well as by Smith
(1972).
Cotter described the buildups in the Big Snowy Mountains as follows: there
are three individual accumulations in the Paine Member in West Swimming
Woman Canyon, each about 300 m long and about 70 m high. No oriented trends
of the buildups can be ascertained from their outcrops.
The intermound rock is dark argillaceous, cherty, horizontally bedded lime-
stone. The bodies themselves are massive but show vague compositional (mainly
textural) layering. The sediment is all wackestone. On an average the rock is 60%
micrite and 25% crinoid ossicles and fenestrate bryozoans (about half and halt).
Less than 5% of other types of bioclasts occur. Around 10-15% consists of sparry
caicite, including somewhat irregular stromatactoid structure. The fauna of the
banks is somewhat different and more varied than that from the more common
basinal Lodgepole. In addition to crinoids, fenestrates, and brachiopods, many
mollusk, including nautiloids, occur along with trilobites, caicispheres, ostracods,
foraminifera and the solitary coral Amplexus and colonial Syringopora. No cal-
careous algae have been reported.