TOURNAISIAN CONODONTS AND MISSING BIOZONES AT REGIONAL UNCONFORMITIES, WESTERN MONTANA

New collections of conodonts from Devonian-Mississippian lag deposits in southwestern and south-central Montana are helping to refine the age relationships of sequence boundaries in the Sappington-Bakken-Lodgepole-Cottonwood Canyon system. Conodonts from several locations are compared and contrasted. Conodonts are the principal correlative tool for this time period. Some new localities have similar age relationships with missing biozones across sequence boundaries and show the duration of these erosional and/or non-depositional events. It appears that durations of unconformities may be variable, although the lowest Tournaisian S. sulcata, S. duplicata and most if not all of the S. sandbergi conodont zones are missing. The Siphonodella lineage is currently under review to better delineate the Devonian-Carboniferous boundary; many Siphonodella species and other conodont elements are found in these lag deposits. The S. isosticha zone has been found at one location, with four biozones missing. However, it appears that some conodonts from these missing zones are found mixed in other lag deposits from the region. Comparison of conodonts from multiple locations provides better age constraints on unconformities and clarifies the stratigraphy in the region.