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Paleotopography and Substrate Lithology as Controls on Initiation of Waulsortian Reef Growth: Examples from Sacramento Mountains, New Mexico

Wayne M. Ahr, W. M. Blount (FOOTNOTE *), P. G. George, E. D. Morey

Frameless mud mounds, usually called Waulsortian reefs, are common in Osagean and Kinderhookian rocks of North America and western Europe. Spectacular Waulsortian reefs crop out in the Sacramento Mountains of New Mexico along 10 mi of continuous exposure, where detailed petrographic studies and field measurements of the strata between the top of the Devonian and the base of the reefs reveal: (1) down-to-the-southwest paleoslope on an uneven, gently dipping ramp; (2) widespread deposition of skeletal packstones and siliciclastics to the northeast; (3) patchy, local thicks of skeletal packstones surrounded by shaly wackestones to the southwest; (4) relict highs on the Devonian surface beneath the skeletal packstone "pods"; (5) clusters of sheetlike reefs weakly associated w th paleotopography in the northern outcrops; and (6) large, domelike individual reefs strongly associated with depositional topography and skeletal packstone/grainstone substrates in the southern outcrops. The pre-reef strata do not exhibit abrupt changes in thickness or lithology to indicate a break in regional slope, and the reefs are not aligned with patterns in thickness or facies that would distinguish shelf-edge environments from lagoonal environments. Like their European counterparts, the Osagean reefs in the Sacramento Mountains grew on a

FOOTNOTE *. Denotes speaker other than senior author.

ramp where the nonreef facies were grainy updip and muddy downdip, and reef anatomy varied from sheetlike updip to domelike downdip. The association between paleotopography, substrate lithology, and the initiation of Waulsortian reef growth provides new information about regional depositional patterns in the Early Mississippian.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.