The Upper Devonian Catskill Magnafacies of New York

ABSTRACT: A unique carbonate bed occurs within the dominantly siliciclastic Catskill Magnafaeies (Upper Devonian) of south-central New York. Associated strata comprise intcrbedded sandstones and mudstones with a variety of burrows, calcareous con-cretions, desiccation cracks, and remains of plants, fish, and the bivalve Archanadon. They are interpreted as the deposits of river channels, crevasse splays, levees, and floodbasins. The 0.4-0.5-m-thick carbonate bed is composed ominantly ofdolomitic mud-stone, containing calcispheres, rare ostracodes, and micron-scale algal filament molds. Laminae are disrupted by vertical and horizontal sheet cracks and burrow tubes which are filled with laminated mudstone, peloids and quartz silt, and spar-mosaic cements. The carbonate bed is interpreted as a freshwater-marsh/shallow-lake deposit, where mud-sized particles originated by precipitation around filaments within cyanobacterial (b ue-green algal) mats. Laminae were deposited mainly from suspension and disrupted by burrowing organisms and periodic desiccation. The Everglades and interior of Andros Island provide modern analogues, the paleoclimatic and paleolatitudinal implications of which are consistent with previous reconstructions of CatskiU deposition under a tropical climate, 200-30 ~from the paleoequator. The carbonate bed probably represents local reduction in siliciclastic deposition rate (associated with river diversion) superimposed upon a regional, increasing deposition rate. There is no evidence of hypersalinity or marine influence