Phosphatic Oolitic Sand Photomicrographs

In a Texas natural gas well, in a condensed section of the Austin Chalk, we noted calcium phosphate oolites with nuclei containing planktic foraminifera, quartz grains, and rock fragments in an argillaceous, fine-medium grain, siliciclastic sandstone. Note the partially crushed, outer layers of some of the oolites indicating compaction, and the terrigenous clay (dark brown layer) in the third and fourth photomicrographs.

Phosphatic oolite with nuclei of sand grains in an argillaceous, siliciclastic sandstone (under plane polarized light) (PPL).
Phosphatic oolite with rock fragment nuclei in an argillaceous, siliciclastic sandstone (under crossed nicols with gypsum plate) (UXN w/GP).
Phosphatic oolitic siliciclastic sandstone, with grainstone fabric. Note the oolite with the planktic foram nuclei and crushed outer layers of oolites indicating compaction (PPL).
Same as previous photomicrograph, but under crossed nicols with gypsum plate. Note the crushed outer layers of the oolites indicating compaction (UXN w/GP).
Phosphatic oolites with nuclei of quartz sand grains. Note the medium-coarse grain phosphatic oolites and quartz sand with the quartz silt & very fine grain quartz sand having an argillaceous packstone fabric (UXN w/GP).
Medium-coarse grain phosphatic oolites with silt-very fine-medium grain quartz sand with an argillaceous packstone fabric (UXN w/GP).

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