Ten carbonate lithofacies are recognized in the Lower Ordovician (Canadian) Great Meadows and Fort Ann Formations in eastern New York and adjacent southwestern Vermont. These lithofacies developed on a shallow shelf adjacent to the deeper proto-Atlantic Ocean on the east, and were deposited within the tidally influenced zone along the margin (pericontinental zone) of a craton-wide epeiric sea.

Shelf sedimentation involved the formation of a widespread carbonate tidal-flat complex, and was succeeded temporally by a lithofacies mosaic which reflected the balance between the laterally discontinuous progradation of low-energy carbonate tidal flats and algal shoals, and the patchy submergence by quiet-water, fossiliferous subtidal limestones. Shelf-marginal lithofacies appear to have consisted of high-energy oolite shoals which persisted throughout early Canadian time.

Periodic circulation restriction between inner-shelf and open-ocean waters by marginal shoals and areal restriction of shallow subtidal environments by extensive prograding tidal flats affected salinity fluctuations within shelf waters, from normal to hypersaline conditions. Widespread intertidal environments at times isolated local evaporite-depositing salinas on desiccated tidal flats.