14-3 Correlating the Eifelian/Givetian stage boundary (Middle Devonian) across the Appalachian Basin using conodonts and magnetic susceptibility data from the Marcellus subgroup (New York) and Delaware Formation (Ohio)

Abstract:

Chronostratigraphic correlation of the mid-Eifelian through lowest Givetian stages has been problematic in the Marcellus subgroup (proximal Appalachian Basin) and the approximately coeval uppermost Columbus through Delaware formations (distal Appalachian Basin), in large part because of limited conodont data. Of the seven conodont zones comprising this interval, only the costatus and kockelianus zones have been identified within the Marcellus subgroup in previous studies. Similarly, only the costatus, australis, and eiflius zones have been recognized in past studies of the uppermost Columbus through Delaware formations. No conodonts indicative of the lowest Givetian hemiansatus Zone have been recovered in either unit, but macropaleontological evidence indicates that the Eifelian/Givetian boundary occurs within the East Berne Member of the Oatka Creek Formation of the Marcellus subgroup. Furthermore, the limited conodont data makes identifying the stratigraphic position of the globally recognized Kačák Bioevent (ensensis Zone, latest Eifelian) difficult in the Appalachian Basin.     

To improve chronostratigraphic correlation between the proximal and distal basin and better constrain the position of the Eifelian/Givetian boundary, we collected additional conodont samples and developed magnetic susceptibility curves (δMS) from the Marcellus subgroup and upper Columbus through Delaware formations. These new conodont data allow for the recognition of the Eifelian pseudofoliatus Zone in the uppermost Columbus and lower Delaware formations, and the ensensis Zone in the upper Delaware Formation and the Cherry Valley Member of the Oatka Creek Formation. No hemiansatus Zone conodonts were recovered. Sharply rising δMS values from the top of the Cherry Valley through lower East Berne members, and within much of the upper Delaware Formation, are similar to those that occur within the ensensis Zone at the Givetian GSSP and which coincide with the global Upper Kačák Bioevent. As at the Givetian GSSP, we place the Eifelian/Givetian boundary at a negative δMS deflection just above this initial rise. In Ohio, this deflection occurs just above the highest occurrence of the conodont Icriodus stelcki, which does not extend into the Givetian. Combined, the new conodont and δMS data from New York and Ohio improve chronostratigraphic correlation of the mid-Eifelian through lowest Givetian strata of the Appalachian Basin and constrain the position of strata correlating to the Kačák Bioevent.

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