The North Evans Limestone
The North Evans Limestone (NELs) is a thin (2-18 cm thick) limestone layer that occurs over a restricted area of central Erie County, NY, extending from Smoke Creek southwest to 18 Mile Creek. Accessible exposures are found at 18 Mile Creek (especially Grabau's sections 1 and 2) near North Evans, NY, and at the former Penn Dixie Quarry at Hamburg, NY (now operated by the Hamburg Natural History Society as a paleontological and outdoor educational center). Both the 18 Mile Creek and Penn Dixie sites have recently been reviewed (Over et al., 1999; Bastedo, 1999). The NELs is considered a member of the Genesee Formation of the Seneca Group of the Upper Devonian. It rests unconformably on the top of the Windom Shale Member of the Moscow Formation, Hamilton Group, of the Middle Devonian. The Genundewa Ls. of the Genesee Formation lies above the NELs. The Genundewa Ls. may be separated locally from the NELs by thin sheets of dark shale which may represent remnants of the Geneseo and Penn Yan Shale members of the Genesee. However, the NELs is often in direct contact with the Genundewa Ls.
The NELs (Rickard, 1964) was originally described as the "Conodont Bed" of the Genundewa by Hinde (1879). As the name suggests, it is notable for the heavy concentration of conodonts, small tooth-like, phosphatic structures that until recently were of uncertain affinity. However, recent finds of conodont animals with soft parts preserved indicate that the conodont animals were primitive chordates, and possible vertebrates (see Donaghue et al., 1998, for a discussion). The conodonts of the NELs have been extensively described by Bryant (1921). In addition to the conodonts, the NELs also contains many fish teeth and scales, the bony plates of placoderms, quartz grains, and hiatal concretions and clasts.
Bryant (1921) suggested that the NELs represents a sandbar deposit. Brett and Baird (1982) have demonstrated that the NELs represents a lag deposit consisting of material accumulated by the shoaling and subsequent submarine erosion and winnowing of the sediments that elsewhere became the upper portions of the Windom Shale, the Geneseo Shale, and the Penn Yan Shale. This origin through condensation explains the finding in the NELs of conodonts of three or four subzones (Huddle, 1981), the presence of rounded pebbles and grains of bone (K.A. Wilson, unpublished observations), and clasts and glauconite-coated hiatal concretions.
The conodont and fish remains in the NELs are phosphatic, rendering them less susceptible than the carbonate matrix to the action of weak acids. The fossils are readily recovered by dissolution of the rock with 10 or 15% acetic acid, followed by washing, sieving, and drying. Most of these remains require magnification for study, placing them in the "microfossil" category.
Fossils of the North Evans Limestone:
Other Fish Teeth
Fish Scales and Denticles
Large Placoderm Bony Plates
Bastedo, J.C. (1999) Penn Dixie Paleontological and Outdoor Education Center: Visit to a Classic Geological and Outdoor Education Center. New York State Geological Association 71st Annual Meeting Field Trip Guidebook, SUNY-Fredonia, Oct. 1-3, 1999. Sun. A1-Sun. A19.
Brett, C.E., and Baird, G.C. (1982) Upper Moscow-Genesee Stratigraphic Relationships in Western NY: Evidence for Regional Erosive Beveling in the Late Middle Devonian. New York State Geological Association 54st Annual Meeting Field Trip Guidebook, Buffalo, NY, Oct. 8-9, 1999. Pages 19-63.
Bryant, W.L. (1921) The Genesee Conodonts. Bull. Buffalo Soc. Nat. Sci. 13, 1-59.
Donoghue, P.C.J., Purnell, M.A., and Aldridge, R.J. (1998) Conodont Anatomy, Chordate Phylogeny and Vertebrate Classification. Lethaia 35, 211-219.
Hinde, G.V. (1879) On Conodonts from the Chazy and Cincinnati Group of the Cambro-Silurian and from the Hamilton and Genesee Shale Divisions of the Devonian in Canada and the United States. Geol. Soc. Quart. J. 35, 351-369.
Huddle, J.W. (1981) Conodonts from the Genesee Formation in Western New York. US Geol. Survey Prof. Paper 1032-B, 66 Pages.
Over, D.J., Baird, G.C, and Kirchgasser, W.T. (1999) Frasnian (lower Upper Devonian) Geology of Western New York as Seen along Eighteen Mile Creek and Route 20A: Submarine Discontinuities, Gravity Flows, and Mass Extinction. NYSGA 71st Annual Meeting Field Trip Guidebook, SUNY Fredonia, October 1-3, 1999. Sun. B8-Sun. B16.
Rickard, L.V. (1964) Correlation of the Devonian Rocks in New York State. NYS Mus. Sci. Serv. Map and Chart Series No. 15.
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Page last revised Feb. 4, 2009