Thin-section photomicrograph (plane-polarized light) of a near-back-reef grainstone in the
Tansill Formation. The predominant grains again are Mizzia green algae but in this example,
the primary porosity was partially filled with an early diagenetic cement produced in the vadose
zone — note slight corrosion of tops of grains and pendants or microstalactites of calcite cement
below the grains. Subaerial exposure may have occurred on small islands during sedimentation
or in association with a major (early Ochoan) hiatus that follows Tansill deposition. 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

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