Paper No. 1
Presentation Time: 9:00 AM
CONODONT BIOSTRATIGRAPHY OF THE ROCKDALE RUN FORMATION, PINESBURG STATION DOLOMITE, ST. PAUL GROUP, AND CHAMBERSBURG FORMATION (MIDDLE TO LOWER UPPER ORDOVICIAN) NEAR CLEAR SPRING, MARYLAND
There is an extensive and apparently uninterrupted succession of Middle through lower Upper Ordovician (middle Whiterockian - lower Mohawkian, upper Dapingian – Sandbian) rocks exposed along I-70 west of Clear Spring, Maryland that allows for detailed sampling of carbonate rocks for conodonts. The units studied are the Rockdale Run Formation, Pinesburg Station Dolomite, St. Paul Group and Chambersburg Formation. Conodonts recovered from the upper 45m of the Rockdale Run Formation include Neomultiostodus compressus, Chosodina rigbyi, Drepanoistodus sp. cf. D. angulensis, Walliserodus? sp., Pteracontiodus? sp., Multiostodus subdentatus, Leptochirognathus sp., and Paraprioniodus sp. cf. P. neocostatus. This fauna is consistent with assignment to the N. compressus/T. clypeus to H. holodentata Zones of the upper Dapingian to lower Darriwilian. The uppermost 20 m of the 155 m-thick Pinesburg Station has a conodont fauna of Plectodina? sp., Phragmodus sp., Leptochirognathus sp., Leptochirognathus quadratus, Belodina sp., Panderodus sp. and Parapanderodus sp. aff. P. striatus. This fauna is consistent with assignment to the P. polonicus – C. sweeti Zones of the Darriwilian. Conodonts are more abundant in the St. Paul Group than in the Pinesburg Station and consist of Erismodus sp. Curtognathus sp., Plectodina sp., Plectodina joachimensis, Apteracontiodus? sp., Pteracontiodus? sp., Drepanodus sp., Drepanoistodus sp., Phragmodus sp. and Rhipidognathus sp. This fauna is consistent with assignment to the P. polonicus – C. Sweeti Zones of the Darriwilian to the lowermost Sandbian. Baltoniodus gerdae is present in the lower part of the Chambersburg Formation, indicating that it is within the B. gerdae Subzone of the lower Sandbian. This conodont biostratigraphy provides a foundation for correlation of the Clear Spring carbonate succession and a foundation onto which chemostratigraphy can be interpreted.