ABSTRACT

The Dogtooth High is interpreted as an area of erosion or non-deposition of the latest Proterozoic/Early Cambrian Hamill Group above a regionally recognized "sub-Cambrian" unconformity. It is located in the western Dogtooth Range of the northern Purcell Mountains and is of unknown areal extent. In the Dogtooth Range, the "sub-Cambrian" unconformity places the Lower Cambrian or uppermost Proterozoic Hamill Group on different stratigraphic units of the Late Proterozoic (Hadrynian) Horsethief Creek Group. This surface is interpreted to be associated with uplift and large scale tilting at the onset of the latest Proterozoic/Early Paleozoic rifting. A second unconformity, displaying locally angular stratal relationships, is observed within lower Cambrian strata of the western Dogtooth Range, at the boundary between the Hamill Group and the overlying Donald Formation. The Fish Lake volcanics directly overlie this unconformity. They are interpreted as evidence for tectonic activity after deposition of the Hamill Group. In the central Dogtooth Range, the Hamill Group is interpreted to thin southwestward between the two unconformities until it is absent in the Quartz Creek thrust sheet. This pinch-out may be the result of onlap to the southwest onto the Dogtooth High. Abrupt westward thickening of the Hamill Group to the west of the Dogtooth Range suggests the existence of a major northwest-striking syndepositional normal fault, located between strata that are now exposed in the Selkirk Mountains and the Dogtooth Range. The Dogtooth High is interpreted to be the western edge of a fault block which was rotated and partly uplifted during latest Proterozoic/Early Cambrian rifting. The Dogtooth High and the Windermere High in the central Purcell Mountains may have formed a series of fault blocks that were in part subaerially exposed during latest Proterozoic/Early Cambrian time.

RESUME

Le Dogtooth High est interprete comme etant une region d'erosion ou de non-deposition du groupe Hamill du Proterozoique superieur/Cambrien inferieur au-dessus d'une discordance regionale "sub-Cambrienne." Il est situe dans le Dogtooth Range occidental des Purcell Mountains du nord et est d'une etendue inconnue. Dans le Dogtooth Range, la discordance "sub-Cambrienne" place le groupe Hamill Cambrien inferieur ou Proterozoique superieur sur differentes unites stratigraphiques du groupe Horsethief Creek Proterozoique superieur (Hadrynien). Cette surface est interpretee comme etant associee a l'elevation et au basculement a grande echelle du commencement du dernier episode de formation de rift Proterozoique superieur/Paleozoique inferieur. Une seconde discordance, ayant localement des relations angulaires par rapport aux strates, est observee dans les couches du Cambrien inferieur dans le Dogtooth Range occidental, entre le groupe Hamill et la formation Donald sus-jacente. Les couches volcaniques de Fish Lake recouvrent directement cette discordance. Elles sont interpretees comme evidence de l'activite tectonique suivant le depot du groupe Hamill. Dans le Dogtooth Range central, le groupe Hamill est interprete comme s'amincissant vers le sud-ouest entre les deux discordances jusqu'a sa disparition dans la nappe de charriage Quartz Creek. Cet amincissement est peutetre le resultat d'un recouvrement vers le sud-ouest sur Dogtooth High. L'epaississement abrupt vers l'ouest du groupe Hamill a l'ouest de Dogtooth Range suggere l'existence d'une faille normale majeure syn-sedimentaire orientee vers le nord-ouest, situee entre les strates qui maintenant affleurent dans les Selkirk Mountains et dans le Dogtooth Range. Le Dogtooth High est interprete comme etant la limite occidentale d'un bloc de faille qui fut bascule et partiellement sureleve durant l'episode de formation de rift Proterozoique superieur/Cambrien inferieur. Le Dogtooth High et le Windermere High dans les Purcell Mountains centrales auraient pu former une serie de blocs failles qui furent en partie exposes de facon subaerienne durant le Proterozoique superieur/Cambrien inferieur.

Traduit par Patrice de Caritat

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