A Pliensbachian submarine slope and conglomeratic gully-fill succession: Richthofen to conglomerate formation transition (Laberge Group), Brute Mountain, Yukon

The diachronous Richthofen-Conglomerate Formation transition separates lithostratigraphic subunits of the Jurassic Laberge Group, Whitehorse Trough. The contact is superbly exposed on the west flank of Brute Mountain, south-central Yukon. This succession of Pliensbachian marine shales, sandstones and conglomerates records submarine gully and slope apron progradation. Distal prodelta shales and sandstones, conglomeratic chute-gully fill sequences, slope shales and slope conglomerates were deposited from the Middle Pliensbachian to the Early Toarcian. Submarine chutes fed coarse clastic detritus past the shelf-break and across the slope. Ponding of coarse-grained mass flows built an onlap wedge against the slope, followed by deposition of mud turbidites and pelagic sediments. A rise in relative sea level continued during the deposition of the entire succession, suggesting the intercalated sequence formed as a result of variations in the rate of clastic input. The Brute Mountain succession is entirely of deep marine origin, typical of Laberge Group exposures elsewhere in the Whitehorse Trough. Collision between the allochthonous Lewes River Arc and the cratonic margin of North…

Publisher

Government of Yukon

Resources

3

Catalogue metadata updated

2026-08-26