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Plate X. Ooid Grainstones, Oolite, Standard Microfacies 15

(A) Over-packed oolite with both superficially coated grains and well-formed
ooids. Packing, to the extent of fitted and planar contacts between the grains, is
probably the result of early solution. The grains are evenly lined with a fine druse
interpreted as probable marine cement. Such history indicates deposition and
lithification in and out of the marine environment on shoals. The presence of
foraminifera and coated bivalve or brachiopod fragments indicates possibly open
marine circulation. Sample is from the Upper Jurassic Arab C Formation in
Qatar Petroleum Company, Fuweirat well, 5230ft depth, northeast coast of Qa-
tar, Arabia. Peel, x 18
(B) Normally packed oolite with mostly well-formed, multiple-coated, spheri-
cal grains. The nuclei are composed of echinodermal, foraminiferal, and mollus-
can fragments. Shoal deposition is indicated in open marine water. Today such
well-formed ooids are found mainly in tidal bars. Higher magnification shows
that the cement between grains is a mosaic of blocky calcite and perhaps is late
diagenetic, possibly from meteoric water in the phreatic zone. The sample is from
the Late Jurassic Smackover Formation from a Skelly Oil Company well in
northeast Texas at 8813-8834ft.See Fig.X-ll for comparable facies in another
well. Thin section, x 16