Abstract

The upper Jackson unit in the northern Bowser Basin includes marine strata of Late Jurassic (middle Oxfordian to Tithonian) age on the basis of the presence of Vaugonia doroschini (Eichwald), Buchia concentrica (Sowerby), Buchia mosquensis (Von Buch), Buchia piochii (Gabb), and Buchia fischeriana (d'Orbigny). Herzogina Chavan and plant macrofossils in the overlying Currier Formation indicate an Early Cretaceous age. Macrofloras of the overlying McEvoy and Devils Claw formations are most similar to Early Cretaceous, pre-Albian floras of the Western Interior Basin of North America.A model of continuous sedimentation from the Jurassic to Early Cretaceous time is proposed, with a progression from marine conditions of the Jackson unit to marginal marine conditions, with lower delta plant deposition in the Currier Formation, to nonmarine fluvial conditions, with upper delta plain deposition in the McEvoy Formation. This stratigraphic sequence culminated in alluvial deposits of the Devils Claw Formation.The present evidence indicates uninterrupted deposition from the Jackson unit to the Devils Claw Formation.

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