NORTHERN APPALACHIAN ACCRETION OF AVALONIA: EVIDENCE FROM CHEMOSTRATIGRAPHY AND K/AR DATING OF ILLITIZATION IN THE SILURIAN ARISAIG GROUP, NOVA SCOTIA

The Arisaig Basin in Nova Scotia, Canada provides a nearly continuous history of the Silurian period—the period in which the microcontinent Avalonia accreted onto Laurentia. The basin's dynamic depositional settings during this period makes it an ideal setting to examine the nature and the timing of the closure of the Iapetus Ocean and the formation of the northern Appalachians. Here we report the chemostratigraphy of the Arisaig Group, a series of shales interbedded with K-bentonites. The trace and major element geochemistry of this group provides considerable insight into the oceanographic and geological processes that were active in the ocean basin during closure. In particular, trends in concentrations of U, Mo, V, and other elements are indicative of regional shifts in ocean redox state, which can serve as a proxy for ocean circulation and regional tectonic activity. We constrain the timing of basin closure by determining the date of illitization of a series of K-bentonites in the Arisaig Group through K-Ar dating. In combination with trace element analysis and traditional sedimentological methods, these data provide considerable insight into the closure of the Iapetus Ocean and accretion of Avalonia.