THE POWER OF A PARADIGM: MISIDENTIFICATION AND MISCORRELATION OF THE KALKBERG AND NEW SCOTLAND FORMATIONS (HELDERBERG GROUP, NEW YORK STATE)

Rickard’s (1962) stratigraphic synthesis of the Helderberg Group (Pridoli-Lochkovian) in New York State has guided all subsequent research. To maintain continuity of facies as the lower transgressive sequence transitioned to regression (Becraft Fm.), Rickard inferred a thickened Kalkberg Fm. in the vicinity of Cherry Valley (CV) and a tongue of the Kalkberg that prograded eastward over the New Scotland Fm. Rigid following of this model of diachronous facies has led to misidentification and miscorrelation of some formations, including tephra-bearing strata important in calibration of the Devonian timescale.

Traceable subunits within the Kalkberg Fm. thin westward from the Hudson Valley and lap onto the Punch Kill Unconformity. Only the uppermost Kalkberg subunit is present at CV. Rapid thinning over a short distance indicates that the Kalkberg onlap resulted from tectonically induced subsidence linked to earliest Acadian orogenesis. The relatively thick sequence of strata identified as Kalkberg Fm. at CV is actually the New Scotland Fm. (Ebert et al. 2007). These strata include a U-Pb dated tephra used to estimate the age of the Silurian-Devonian boundary.

Strata formerly described as an upper tongue of the Kalkberg differ lithologically from all subdivisions of that formation. Skeletal packstones to grainstones interbedded with mudstones, shales and siltstones include holdfasts of Aspidocrinus scutelliformis. This unit is a muddy facies of the lower Becraft Fm. now referred to as the Old Stone Fort Mbr. of the Becraft Fm.

Strata that overlie the Deansboro Fm. at Oriskany Falls were referred to the Kalkberg Fm. These strata also differ from Kalkberg lithologies. Preliminary conodont studies indicate a Pragian age for Deansboro Fm. Therefore, these overlying strata (now referred to Buckley Mill Fm.) are also at least Pragian in age, whereas the Kalkberg is Lochkovian.

Failure to recognize the significance of unconformable formational contacts and the shoehorning of disparate units into a Waltherian view of the Helderberg stratigraphy has led to miscorrelation of tephra-bearing strata and necessitated stretching of units by some workers to force isotopic curves to fit a model of diachronous facies. These misidentifications and miscorrelations in New York have hindered correlation within the Appalachian Basin.