A GRENVILLIAN PROVENANCE FOR MIDDLE CAMBRIAN CARBONATE STORM DEPOSIT ZIRCONS, STISSING FORMATION, SOUTHEASTERN NEW YORK

Approximately 560 zircons were collected and dated by the LA-ICPMS U-Pb method from seven closely spaced storm beds in a single exposure of carbonate rocks within the Cambro-Ordovician Wappinger Group, Dutchess County, New York. The beds were mapped as part of the Pine Plains Formation, but are now assigned to the Stissing Formation by the presence of the Middle Cambrian organic microfossils, Adara undulata and Archeodiscina umbonulata volkova. This Series 3, Stage 5 age is corroborated by the presence of Echinoderm ossicles, sponge spicules and a lack of archeocyanthans in thin sections of patch reefs from the outcrop. All seven storm beds gave essentially similar age patterns. All zircons are older than 950 Ma indicating a lack of input from rift related igneous activity and Ordovician volcanic arcs. The majority fall into the 1.3 – 1.0 Ga (Grenvillian) age range. The next largest distribution is in the 1.50 – 1.30 Ga age range. There is a small representation of zircons in the age range from 1.8 – 1.6 Ga and 2.7 – 2.5 Ga. These ages suggest affinities to the Grenville Orogen and may have been derived from an emergent Hudson Highlands or possibly an exotic terrain such as Amazonia.