ND TDM MODEL AGES OF UPPER AND MIDDLE DEVONIAN AND SHALES OF WESTERN AND CENTRAL NEW YORK

Representative samples of nineteen Upper and Middle Devonian shales from the Appalachian Basin of western and central New York yield model ages (T_DM) ranging from 1504-1825 Ma. One sample, the Upper Devonian Ellicott shale, yields a T_DM of 2219 Ma. Two samples of Middlesex shale yield T_DM values of 1624 and 1825 Ma, while two Gowanda shales yield 1519 and 1782 Ma, demonstrating variability within individual units. There is little systematic variation based on relative stratigraphic position or geographic location. REE totals varied from 102-255 ppm, with a general increase towards the top of the stratigraphic section. Neodymium concentrations ranged from 22.2-50.4 ppm while Sm ranged from 4.12-9.22 ppm. ¹⁴⁷ Sm/¹⁴⁴Nd ratios range from 0.1048-0.1275, similar to average shales (0.10-0.12), and argue against strong diagenetic effects. Most shales show a near linear relationship when ¹⁴⁷ Sm/¹⁴⁴Nd is plotted against T_DM, except for the Union Springs member of the Marcellus shale, the Ellicott shale, and the Penn Yan shale. Only shales of the West Falls Group (Angola, Rhinestreet, and Nunda shales) plot in a tight cluster on the ¹⁴⁷ Sm/¹⁴⁴Nd vs. T_DM plot. La/Sm ratios ranged from 4.1-6.7; only the Sonyea Group showed considerable scatter and has outliers on the La/Sm vs. ƐNd(0) plot. Dy/Yb ratios ranged from 1.5-2.3; outliers on the Dy/Yb vs. ƐNd(0) plot include the Ellicott and Union Springs shales. Epsilon Nd T_CHUR range from -5.04 (Union Springs) to -14.56 (Ellicott). However, the rest of the shales plot within a very restricted range between -8.83 to -7.50. Initial ¹⁴³Nd/¹⁴⁴Nd ratios vary from 0.511403 (Ellicott Shale) -0.511824 (Union Springs shale) however, all others, expect the Penn Yan shale (0.511684), fall between 0.511739-0.511764. Major and trace element geochemical analyses indicate most of the outliers on the plots discussed above have unique features. For example, the Ellicott shale, has the least TOT/C (0.09%), while the Union Springs member of the Marcellus Shale has non-detectable concentrations of S (<0.02%). The results indicate a fairly uniform provenance for the Upper and Middle Devonian shales with the possible exception of perturbations during the deposition of the Union Springs, Penn Yan, and Ellicott shales.