Syntectonic Conglomerates in Southwestern Montana: Their Nature, Origin, and Tectonic Significance

Contributions to Late Cretaceous stratigraphy and paleontology, western Montana

“…), and resultant implications for the tectonic history of this part of the Cordillera are the subjects of our ongoing research. Preliminary results suggest that the character of the subBeaverhead unconformity changes laterally from the back Ryder and Scholten (1973) with interbedded quarzite-clast conglomerates and lithologies typical ofthe Aspen Formation.…”

“…They stated that their Aspen Formation is overlain with profound angular unconformity by the Beaverhead Formation in the Lima region (Scholten and others, 1955, p. 368). Ryder and Scholten (1973) discussed the basal Beaverhead contact in detail, but their basal Beaverhead is equivalent in part to rocks that we consider to be either Frontier Formation or the underlying Blackleaf Formation ( fig. 1 ).…”

“…Recent work has shown that Belt quartzite clasts also occur in conglomerates in the Blackleaf (Dyman and Nichols, 1988) and Frontier Formations (Dyman and others, 1989). Ryder and Scholten (1973) identified a minor(?) disconformity between their Aspen and Beaverhead Formations near Monida, where the Beaverhead lacks quartzite clast conglomerates.…”

“…On the west slope of Shine Hill ( fig. 2), Ryder and Scholten (1973) designated conglomerate beds that are conformable with underlying and overlying strata as basal Beaverhead (see appendix for additional comments regarding the Shine Hill beds). Where no unconformity was observed, they placed the Aspen-Beaverhead contact at the "first appearance of conglomerates with Middle Proterozoic Belt Series (now Supergroup) quartzite clasts."…”

“…2 Clover Creek sandstone unit of Perry and others (1989) is correlative with Monida sandstone unit of Ryder and Scholten (1973) and lower part of Monida Formation of Wilson (1970) and Monida Sandstone of Perry and others (1989).…”