LOWER EIFELIAN (MIDDLE DEVONIAN) DACRYOCONARID BIOSTRATIGRAPHY AND BIOGEOGRAPHY, CENTRAL AND NORTHERN APPALACHIAN BASIN

The Basal Choteč Event (BCE) is a worldwide lower Eifelian environmental perturbation and faunal turnover coincident with the Devonian T-R cycle Ic Transgressive Systems Tract. Its acme at teh cycle Ic maximum flooding is often represented by two black shale/marl beds in proximity to the base of the Polygnathus costatus Zone. The dacryoconarid (dac) fauna of the BCE interval is represented by the Edgecliff and Nedrow members of the Onondaga Formation in the Northern Appalachian Basin (NAB) and the Selinsgrove Member of the Needmore Formatin in the Central Appalachian Basin (CAB). A detailed study of dacs in these units revealed diverse and taxonomically discrete faunas of different origins and histories that populated the two regions of the AB. The BCE daac fauna of the CAB is an incrusion epibole of at least three Old World Eifelian taxa tha is first recorded in the mid Edgecliff-equivalent and last occurs at the top of Nedrow-equivalent strata. This fauna is devoid of endemic CAB Emsian forms and, except for one species that occurs at the top of the Nedrow in NY, did not enter the NAB during the BCE. The NAB fauna, derived from endemic NAB Emsian forms, first appears at the base of the Edgecliff and diversifies upward. This fuana includes six previously undesciribed species most of which last occur in the BCE acme at the top of the Nedrow, whereas the others served as the founders of upper Eifelian and Givetian Hamilton dac faunas. Some of the BCE taxa, such as the new forms Styliolina robusta and Viriatellina exila, may serve as excellent indexes to subsets of the overall event interval.