Anatomy of an Early Devonian Carbonate Buildup, Central New York

On a global basis, carbonate buildups of Early Devonian age are little known compared to examples from Silurian and later Devonian time, and they may be rare in occurrence. Study of the Knoxboro buildup (a patch reef) and related buildups of the Deansboro Member of the Coeymans Formation (Lower Devonian) from central New York has provided insight into the style and development of buildups of this age. The Knoxboro buildup formed on an open marine carbonate platform, and it exhibits three distinct vertical stages of sedimentologic and biologic development. Stage I--Initial Colonization and Substrate Stabilization--is recognized by the growth of moderately large favositid tabulate corals on a crinoidal calcarenite substrate. Most tabulates are preserved in growth position. Stage II--Growth to Mean Wave Base--is characterized primarily by beds of micrite and biomicrite-biomicrudite with in situ colonies of dendroid Favosites and Tryplasma corals. These beds form the "core" of the buildup. Channels, mostly filled with crinoidal debris, cut into beds formed during Stage II. Stage III--Diversification--is marked by beds of crinoidal debris which blanket the biomicrite core. Planar tabulate (favositid) corals and stromatoporoids (the latter often encrusting the former) are conspicuous in these uppermost beds. Localized occurrences of articulated crinoid columnals represent crinoid patches that occupied somewhat protected locations in the buildup area. Faunal diversity reaches a maximum in these beds, although diversity appears to be no greater than that of equivalent "non-buildup" facies of the Deansboro Member. This tabulate and colonial rugose coral buildup is transitional in both form and faunal composition between North American midcontinent Silurian buildups and later buildups of Middle Devonian age.