308 Upper Silurian (Pridoli) Stromatoporoidea of New York

Stromatoporoids are a major component of the faunas of the Upper Silurian (Pridoli) rocks in New York. They are found in the Wilbur, Glasco, and Cobleskill Members of the Rondout Formation.

Eleven species are described. Three, Stomatopora clarkei Parks, Parallelostroma constellatum (Hall), and Denstroma tenuissimum (Parks) have previously been described from the Cobleskill Member. Stictostroma pseudoconvictum, n. sp., Plectostroma micum (Bogoyablenskaya), Stromatopora bekkeri Nestor, Stromatopora eoconcentrica, n. sp.,  Parallelostoma typicum (Rosen), Parallelostroma kaugatomicum (Riabinin), Parallelostroma rondoutense, n. sp. and Densastroma pexisum (Yavorsky) are reported here for the first time.

Stromatoporoid faunas from the Rondout Formation are typical of the Upper Silurian. Some of these species reflect relationships with taxa from earlier or later ages.

A study of the stratigraphy and paleoecology of the Rondout Formation stromatoporoids indicates that they lived in shallow water near the shore of the Appalachian Basin. Information from the lithofacies and stromatoporoid biofacies gives a more precise indication of the depositional environments. The presence of dolomite is indicative of intertidal or supratidal conditions, except where it was transported as a coastal silty dolomite facies. Silicified stromatoporoids represent an early stage of diagenesis in shallow or supratidal areas. Fossiliferous limestones indicate deeper water, farther from shore. Subspherical stromatoporoid-dominated biostromes resulted from carbonate bank development in the surf zone.

The Wilbur Member in eastern New York, consisting predominantly of fossiliferous limestone, resulted from deeper conditions than the correlative Cobleskill Member in central and western New York, which contains both limestone and dolomite. A biostrome in the Cobleskill Member in the Cayuga Lake area also resulted from shallower conditions. The same relationship exists between the younger Glasco Member (fossiliferous limestone) in the east, and the correlative Chrysler Member (barren dolomite) in the central and western part of the state. Within the Cobleskill Member, the increase in dolomite to the west, the biostrome in Cayuga Lake area, and the silicified stromatoporoids to the west, all indicated shallower conditions in the western part of New York than in the central part.

Wilbur-Cobleskill deposition took place in deeper water than did Glasco-Chrysler deposition. Fossiliferous limestone and dolomite of the Cobleskill Member were succeeded by the barren dolomite of the Chrysler Member. Just as the biostrome in the Cobleskill Member indicates shallower conditions than in the Wilbur Member, biostromes in the Glasco Member are a result of shallower conditions than in the earlier Wilbur Member. 

Year published: 1980