Page 2 - Carbonate Facies in Geologic History

Upper Pennsylvanian section on the north wnll of Dry Canyon III the Sacramento Mountains.
6 km northeast of Alamogordo. New Mexico. The bot 10m of the creek is about the base of Missourian
beds. The base of Virgilan strata is about the base of the pronounced biohermallevel. The
well-marked dark thin bed below the main bioherm is composed of peloidal grainstone. forescl-
bedded to Ihc left (west into the Oro GrandI! basin). The bioherms are algal plate mud mounds
and aredevcloped at a very gl!ntJe shelf margin and on the west nank of a Pennsylvanian
anticline whose axis lay to the right edge of the photo. The axis is cut transversely by the canyon.
The t .... o mounds at the wcst end are micritic cores wnh abundant algal phlles. The main
mound is composed chieny offoreset·bcdded, detrita\. bioclastic nanking strata derived from
organisms growing 011 mounds exposed on the soulh side of the clmyon from where the picture
was taken. The ledges above the main mound level are principally limestones capping sedimentary
shelfcyclcs described 011 Figs. VI·7, VI-I2, VII-8. The cycles grade a few kilometers
east to red beds and conglomerates of the Pennsylvanian upland.