Thin-section photomicrograph (cross-polarized light) of a near-back-reef
grainstone in the Tansill
Formation. The predominant grains are Mizzia green algae (some heavily encrusted by foraminifers
and blue-green algae). A very large percentage of the primary porosity was obliterated by
penecontemporaneous marine cementation (note the cloudy, fibrous to bladed crusts). The very
near-back-reef facies, like the reef itself, typically underwent intense marine cementation.
Sample from Walnut Canyon (New Mexico Highway 7), less than 1 km west of the canyon mouth,
Carlsbad Caverns National Park, Eddy Co., NM. Long axis of photo = 6 mm.
© Peter A. Scholle, 1999