Marginal lagoon carbonate deposition in the Crown Point Formation (Ordovician) of New York

F.O. Meyer

University of Michigan, Ann Arbor, Michigan, 48109

Two non-reefal Crown Point carbonate facies exposed in a 10m thick section along I-87 at the type locality (Chazy, New York) of the formation were deposited just above and below sea-level. Minor fluctuations in sea level shifted depositional regimes laterally causing abrupt lateral and vertical lithologic changes. At Chazy, near-shore subtidal deposits occur between low-supratidal carbonates. The low-supratidal facies are characterized by sparsely fossiliferous, pelletal, dolomitic, mudcracked, discontinuously bedded, nodular wackestones. Desiccation and rare spar-filled shrinkage cracks indicate periods of subaerial exposure. Wackestone nodules, surrounded by dolomite, represent mud-polygons modified by burrowers and weathering. Dolomitization was penecontemporaneous and is inferred to have been similar to the formation of modern dolomite in Florida. The neat-shore subtidal facies is a thin to medium bedded, skeletal, bioturbated, intraclastic, pelletal packstone, containing abundant Maclurites and some stromatoporoid encrustations. Stromatoporoids require continuous marine submergence. The stratigraphic juxtaposition of subtidal carbonates and deposits that clearly indicate periods of subaerial exposure suggests subtidal deposition occurred in a shallow near-shore environment.

These facies occupy about the same stratigraphic position in the Crown Point Formation, as do several nearby stromatoporoid reefs. While the reefs formed offshore barriers, these carbonates were deposited along the margins of a shallow protected lagoon.

Meyer, F. O., 1977, Marginal lagoon carbonate deposition in the Crown Point Formation (Ordovician) of New York: Geological Society of America, Abstracts with Programs, v. 9, p. 302.