The Mt. Kindle Formation zircons are predominantly 1.8-1.9 Ga (78 grains), with a small population of 2.4 – 2.8 Ga (7 grains), smaller populations of 2.0 – 2.1 Ga, and 450 – 500 Ma (3 grains a piece) and single grains at 1.1 Ga and 3.4 Ga. In general this sample is similar to other Middle to Late Ordovician from along the western North America Cordillera and suggests this quartz arenite was derived from the Transcontinental Arch to the south, implying a north dipping depositional slope. However, the three 450 – 500 Ma grains are unique and may represent either: windblown ~ 455 to 470 Ma ash beds derived from the Taconic orogeny or Late Cambrian volcanism along the North American Cordillera.
Two samples from the Upper Ordovician Bad Cache Rapids Group, directly overlying Precambrian basement have a large population of 1.8-1.95 Ga zircon grains (39 grains), a moderate number of 2.5 – 2.75 Ga grains (20 grains), a small number (2-4 grains) of 2.0 – 2.1 Ga, 2.2 – 2.5 Ga, and 2.9 – 3.0 Ga grains, and a single 4.2 Ga grain. Most of these grains indicate local derivation during Late Ordovician flooding of Laurentia. The 4.1 Ga grain in this sample was derived from the Slave Craton to the west indicating it was either re-worked from older sediments during the transgression or possibly that the paleoslope had changed by the Richmondian. Evaluation of detrital zircon populations of Middle-Late Ordovician quartz arenites surrounding the Transcontinental Arch provide further insights into the coeval flooding of Laurentia.
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