The Alden Pyritized Fauna Assemblage

     Perhaps the best known example of such a pyritized fossil assemblage is the so-called "marcasite fauna" first described by Fisher (1951) from the Ledyard Shale (lower Ludlowville Formation, see Stratigraphic Column).  This layer of pyrizied fossils and pyrite concretions is located 27 feet (8.2 m) above the base of the Ledyard Shale at Spring Creek, 0.5 mile (0.8 km) northeast of Alden, Erie County, NY.  The pyritized can be traced westward to Avery Creek, near Buffalo, Erie County, NY, and eastward to East Bethany, Genesee County, NY.

aldenpyr.jpg (19829 bytes)
Pyrite concretions from Spring Creek, Alden, NY
The largest (lower right) is 25 cm in diameter.

     The most immediately obvious feature of this zone is the presence of roughly spherical or somewhat elongated "marcasite" nodules or concretions ranging  in size from 1 to 5 cm in maximum dimension.   The majority of the nodules show irregular crystal forms at the surface suggestive of the cockscomb form of marcasite.  A few nodules exhibit distinctly cubic crytal faces at the surface suggestive of the pyrite form of iron sulfide.  Fisher (1951) considered the nodules to be marcasite, while subsequent studies by Izard and Clemency (1967) using X-ray diffraction analysis concluded only pyrite was present.  These pyrite nodules often contain a fossil as their nucleus, or may have portions of one or more pyritzed brachiopods, pelecypods, or cephalopods protruding from the surface of the nodule.  In the case of elongated fossils such as the orthocone nautiloids, two or more nodules may form along the length of the fossil.

     The fauna of the "marcasite" zone has been described by Fisher (1951) and by Domagala and Selznick (1979).  These authors should be consulted for complete faunal lists.  The pyritized species observed by this writer are listed below:

Pyritized Fossils of the Alden "Marcasite" Zone, Ledyard Shale

Ambocoelia umbonata Conrad Sinochonetes lepidus (Hall)
Mucrospirifer mucronatus (Conrad)
Grammysia arcuata (Conrad) Paleoneilo constricta (Conrad)
Modiella pygmea (Conrad) Paleoneilo filosa Conrad
Nuculites triqueter Conrad Pterochaenia fragilis (Hall)
Nuculoidea corbuliformis (Hall)
Bembexia sulcoemarginata  Hall Paleozygopleura hamiltoniae (Hall)
Bucanella brevilineata Philoxene sp.
Euomphalus disjunctus Hall
Michelinoceras aldenense Tornoceras uniangulare Conrad
Spyroceras sp.
Hyolithes sp.
Greenops boothi (Green) Phacops rana (Green)

(It should be noted that additional, non-pyritized, fossils species are also found in the "Marcasite" zone.)


Domagala, M.A. and Selznick, M.R. (1979)  Paleontology and Stratigraphy of the Ledyard Shale (Middle Devonian) at Spring Creek, Alden, New York.   Rochester Academy of Science Mineral Section, Special Publication No. 1

Fisher, D.W. (1951)  Marcasite Fauna in the Ludlowville Formation of Western New York.  J. Paleontology  25, 365-371.

Izard, J.E. and Clemency, C.V. (1967) X-ray Study of the Sedimentary Pyrite of Western New York.  J. Sed. Petrol. 37, 221-239.

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Page last revised Feb. 4, 2009