Palynomorphs from the Silurian medina group (lower llandovery) of the Niagara Gorge, Lewiston, New York, U.S.A.

Abstract

The Lower Silurian Medina Group from the Niagara Gorge at Lewiston, New York, contains one of the oldest known Llandovery palynomorph assemblages in North America. Age determinations using conodonts and brachiopods from the basal units of the overlying Clinton Group suggest that the Medina Group may be correlative with the Rhuddanian Stage of the Llandovery. A brief review of North American Lower Silurian series nomenclature is presented to place the Medina Group in a regional stratigraphic context. Previous recommendations that North American series nomenclature be replaced by the standard British Llandovery stages are followed.

Well‐preserved acritarchs, chitinozoans, and spore‐like micro‐fossils have been recovered and described from the Whirlpool Sandstone, Power Glen Formation, and Grimsby Sandstone. Forty palynomorph species were recognized. Four new species and one new combination of acritarchs are proposed: Cymatiosphaera densisepta n. sp., Eupoikilofusa? rhomba n. sp., Micrhystridium? polorum n. sp., Retisphaeridium? fragile n. sp., and Moyeria cabotti n. comb. et emend.

In addition to previously described spore‐like microfossils, two new genera, Strophomorpha and Vermiculatisphaera, and four new species are proposed: Nodospora retimembrana n. sp., Rugosphaera? cerebra n. sp., Strophomorpha ovata n. sp., and Vermiculatisphaera obscura n. sp.

The Whirlpool Sandstone and lower part of the Power Glen Formation are dominated by spore‐like microfossils, whereas the upper part of the Power Glen and lower part of the Grimsby contain predominantly acritarchs. The palynomorphs recovered from these Lower Silurian near‐shore facies appear to have been controlled by the depositional setting and are compared to other Lower Silurian palynomorph assemblages from North America and Britain.