Page 429 - Carbonate Facies in Geologic History

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Plate IV. Reef Flank and Reef Boundstone of Virgilian
(Late Pennsylvanian)

(A) Standard microfacies 5 is bioclastic, lithoclastic packstone composed of de-
bris on the mound slope. Sample DC-88 is from an off-reef position at the eastern
base of the lower mound at the mouth of Dry Canyon, section 29, Sacramento
Mountains, New Mexico (see Frontispiece) and consists of rotted debris of algal
plates, tubular foraminifera, and Tubiphytes (lower left corner of photo). The
depositional environment and interpretation of this Late Pennsylvanian sediment
is very similar to that of ARP shown on Plate I. The mixture of ill-sorted, partly
worn and partly angular bioclasts and lithoclasts is typical of reef flank deposits,
facies P-7, Chapter VII. Thin section, x 15
(B) Encrusting bindstone, standard microfacies 7. Sample consists of altered
encrusting codiacean? algal laminae with masses of dark, microporous, tubular
calcitornellid foraminifera. Cores of Middle Pennsylvanian mounds in the Para-
dox basin, Utah contain organic structures similar in configuration to the
coarsely crystalline laminae shown here from Virgil ian strata. The former have a
cortical tubular structure much like that of codiacean algae. This type of bound-
stone caps phylloid algal micrite mounds located on the gently sloping outer
margin of the narrow shelf on the west side of the Sacramento Mountains. Sample
ART is from the top of the western (left) side of the main mound, north wall of
Dry Canyon (see Frontispiece). See also tubular foraminiferal bindstone,
Plate XX. See description in Chapter VI. Thin section, x 15