|Stromatoporoids, like the example shown above from the Cobleskill Limestone of Frontenac Island in Cayuga Lake, are currently interpreted by paleontologists to be a particular type of structure belonging to the Sponge group of animals. These animals were often clustered together, along with corals, to form banks (biostromes) or reefs (bioherms). During the Late Silurian, we find stromatoporoids associated with eurypterid-bearing sequences like the Bertie Group of New York State. In Early Devonian rocks, Erieopterus is found in layers of Manlius Limestone associated with stromatoporoids. In offshore deposits, a pterygotid appears, the successor to Acutiramus cummingsi of the Williamsville Waterlime. The genus Eurypterus, though, is completely replaced by Erieopterus in these Early Devonian deposits.|
|Union Springs, New York is situated on the east side of Cayuga Lake, one of the Finger Lakes. Offshore is Frontenac Island (seen in the photo above) covered by trees, and easily seen from the shoreline at Union Springs. The island is supported by bedrock consisting of a very resistant limestone bed, a stromatoporoid biostrome that occurs in the lower Cobleskill Formation of Late Siiurian age. The north end of the island consists of Bertie dolostone, part of the Williamsville Formation. Eurypterid remains have been found here at the north end but, unfortunately, it is difficult to get at the bedrock. The beds dip beneath the lake waters to reappear on the mainland.|
Stock, C. W., 1979 UPPER SILURIAN (PRIDOLI) STROMATOPOROIDEA OF NEW YORK, Bulletin
of American Paleontology, No. 308, 101 pp.
|ON FRONTENAC ISLAND|
|As we approached the island, the massive bed of stromatoporoidal limestone came into view. About a meter in thickness, the bed dips southward underneath Cayuga Lake. Horn corals and colonial types occur intermingled in this stromatoporoid biostrome within the Cobleskill Limestone. Northward, the limestones give way to the dolomitic Akron Formation. Above photo: Joe La Russa stands next to the massive biostrome. Beneath are transitional beds to the underlying Bertie Formation, the repository of the great eurypterids of western New York. The Bertie beds here have yielded only eurypterid re- mains and cephalopods thus far. The eurypterid may be the easternmost occurrence of Eurypterus lacustris, so common in the Williamsville Formation of western New York and Ontario, Canada.|
BLOCK OF STROMATOPOROIDS (Cobleskill Limestone) with a favositid coral in the middle.
CLICK PHOTO for larger view.
|WHAT ARE STROMATOPOROIDS?|