CHEMOSTRATIGRAPHIC CORRELATION OF A DARRIWILIAN UNCONFORMITY IN THE APPALACHIAN BASIN

Recent modeling and geochemical studies suggested a protracted (instead of short-lived) glaciation in the Ordovician Period. This hypothesis, however, must be tested with additional sedimentologic and stratigraphic evidence. Previous studies have suggested a possible glacio-eustatic driver for Middle to Late Ordovician unconformities by demonstrating the synchroneity of these unconformities using biostratigraphic correlation. A more precise correlation of these unconformities is hampered by palaeontologic constraints such as the lack of index fossils, faunal provinciality, and temporal uncertainty of biostratigraphic zones. This study aims to address the growing need to provide a chronostratigraphic framework for the Middle to Upper Ordovician unconformities using strontium isotope stratigraphy, which has been proven to be a useful alternative for inter-basinal correlations.

This study focuses on a Darriwilian unconformity in Laurentia that is exposed in two localities: Germany Valley (WV) and Collierstown (VA). The unconformity in both sections is characterized by abrupt facies shift from a fenestral limestone facies (New Market Formation) to a cherty fossiliferous packstone and grainstone facies (Whistle Creek/Lincolnshire Formation). Bulk rock and conodont strontium isotope data (⁸⁷Sr/⁸⁶Sr) from the underlying and overlying strata of the unconformity in both localities show similar values of 0.70840 and 0.70845 suggesting age similarities of the unconformity. Furthermore, the strontium isotope data also suggest that the unconformity can be correlated to other unconformities in different parts of the continent (e.g., Nevada, Oklahoma) with different tectonic settings suggesting a common driver. This finding suggests a glacio-eustasy origin of these unconformities and potentially lends credence to the protracted Ordovician glaciation hypothesis.