This study is based on analysis of 450 large vertical slabs from eight stratigraphic sections in the Black River Group type area, the Black River valley, northwest New York State. The group is underlain by an irregular Precambrian surface, is 90-140 ft thick, and consists of three formations: the basal Pamelia, the Lowville, and the Chaumont. These represent a sequence of six nearshore sedimentologic facies. Superimposed on these are four biogenic sedimentary structure facies, each characterized by particular biogenic structures.

The Pamelia Formation consists of buff, algally laminated, fine-scale-mudcracked, supratidal dolomite characterized by rare vertical burrows like those of the succeeding Lowville Formation, and a sparse euryhaline fauna.

The lower Lowville consists of lithologic types representing two environments: (1) gray, mudcracked, ripple-marked, thin-bedded, intertidal limestone with a euryhaline fauna, and (2) dark gray, thick-bedded, laminated, subtidal limestone containing algally coated grains and a sparse stenohaline fauna. The intertidal Lowville is characterized by permanent, vertical, and U-shaped burrows which today are most common in intertidal environments. Filter feeders usually construct these burrows for protection in environments characterized by stress at the interface. The subtidal part of the lower Lowville Formation is characterized by complex, irregularly oriented, feeding burrows, and large, concentrically laminated burrows. Today these types of burrows are common in quiet subtidal environme ts where deposit feeders dominate.

The upper Lowville Formation represents a wave baffle formed by compound colonies of the spindle-shaped coral Tetradium associated with marginal zones of fallen Tetradium. These rocks are characterized by absence of biogenic structures, probably caused by the mechanical difficulty of burrowing into sediment with such a felted texture.

The Chaumont Formation consists of silt-size debris of a diverse stenohaline biota, and is unbedded because of thorough burrowing. It is characterized by small, horizontal, sediment-filled burrows, which today dominate in level-bottom marine environments where a thin oxidized zone favors deposit feeders which cover broad horizontal areas near the sediment surface. Thus, integration of faunal, sedimentologic, and stratigraphic data with information on recent biogenic structures allows ecologic interpretation of Ordovician structures.

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