New correlations of Hadrynian strata, south-central British Columbia

Abstract

The Hadrynian (Late Proterozoic) Kaza Group is 3800 m thick in the southern Cariboo Mountains of south-central British Columbia, and it consists of a lower division of pelite and psammite (700 m), a middle division of granule conglomerate with thick pelite intervals and some quartzite and carbonate (1400 m), and an upper division of granule conglomerate with little pelite (1700 m). Contacts with both the overlying Isaac Formation of the Cariboo Group and with underlying marble, semipelite, and amphibolite are gradational. The underlying strata can be traced southeastward into the middle marble and the semipelite–amphibolite division of the Hadrynian Horsethief Creek Group. The upper clastic division that caps the Horsethief Creek Group in the Selkirk Mountains is a southeastward-thinning equivalent of the Kaza Group.Two southeastward-tapering wedges of granule conglomerate, pelite, and carbonate constitute the bulk of the Hadrynian Windermere Supergroup of southern British Columbia. The lower wedge is represented by the Horsethief Creek Group, exclusive of its upper clastic division. The upper wedge is represented by the upper clastic division, the Kaza Group, the overlying Cariboo Group, and the middle and upper Miette Group. The two wedges indicate two pulses of crustal thinning and stretching during Hadrynian rifting of western North America.