CORRELATION OF SYNTHETIC GAMMA RAY PROFILES FROM OUTCROPS OF THE NEW SCOTLAND FORMATION, HELDERBERG GROUP (LOCHKOVIAN) AT CHERRY VALLEY AND SCHOHARIE, NEW YORK
These two stratigraphic sections were measured, described, and gamma ray measurements were made at half-meter intervals through the New Scotland Fm. at CV and 37 m of the uppermost Kalkberg, New Scotland and most of the Becraft Fm. on I-88. The Gamma Surveyor Vario, a 2048 channel gamma-ray spectrometer was used to measure K (%), U (ppm) and Th (ppm), which then were converted to API units to create synthetic gamma ray logs.
The gamma ray log of the New Scotland Fm. at CV shows greater radioactivity (average 10 API units higher) with greater enrichment of U and Th than the I-88 outcrop. We interpret the Th data as indicating that CV received greater siliciclastic input and occupied a more proximal position than the I-88 section. This is supported by the presence of rounded quartz silt present in thin sections from the CV section.
The highest API peak at CV corresponds to the Judds Falls Bentonite (a.k.a. “Kalkberg” bentonite; H1-1 of Husson et al. 2015). The highest API peak at I-88 occurs in a tephra bed ~ 8 m above the contact with the Kalkberg Fm. (H2-4 of Husson et al. 2015). The shapes of the gamma ray curves suggest that these maxima do not correlate. Rather, the Judds Falls Bentonite correlates with a tephra bed approximately 2 m above the Kalkberg - New Scotland contact (H2-2 of Husson et al. 2015).
Small scale (2-8 m) cycles within the New Scotland are characterized by abrupt shifts to high radioactivity at the base which then decline upward. These cycles likely reflect onsets of dysoxia followed by a gradual increase in oxygenation. Preliminary data on vertical variations in macrofauna lend further support to the interpretation that these oxygenation cycles represent small scale (5th or 6th order) eustatic cycles.