Contributions to stratigraphy

The cratonic Boothia Uplift constitutes a major geological province in the Canadian Arctic. It is 800 km long and 150 km wide and extends from Boothia Peninsula on the continental mainland to about the geographic centre of the Canadian Arctic Archipelago. Rocks of Precambrian and Phanerozoic ages are included in the Uplift. The principal crustal movements by which the uplift achieved its present areal extent and many of its present structural characteristics occurred in Late Silurian and Early Devonian times. These movements exerted a profound influence on local sedimentation, effecting complex and diverse facies changes that have necessitated the establishment of different formational successions in rocks of Late Silurian to Early Devonian ages in most of the major islands and Boothia Peninsula that comprise the uplift. Uncertainty has surrounded the ages of several formations within this interval of time, and this has precluded a clear understanding of correlations, as well as the timing and areal extent of the crustal movements that produced the Boothia Uplift. The present study deals mainly with the lithe- and biostratigraphy of Upper Silurian to Lower Devonian rocks in the environs of the Boothia Uplift. It commences with the Upper Silurian Cape Storm Formation which was deposited shortly before the onset of crustal movements in the Boothia Uplift in Paleozoic time and ends with the Lower Devonian Disappointment Bay Formation that lies with angular unconformity on the bevelled and truncated rocks of the uplift, and thus provides a firm upper age limit to principal crustal movements that produced the uplift. Much new information is provided on the ages of the various Upper Silurian to Lower Devonian formations in the environs of the uplift, and this is based largely on the study of conodonts (by T.T. Uyeno) and graptolites. The present study has also indicated a need for revisions to the formational nomenclature of rocks in the report area. The Cape Storm Formation is now recognized in the Cornwallis Island area where its basal part is made up of beds included previously in the Allen Bay Formation while its upper part includes beds assigned previously to the lower part of member A of the Read Bay Formation. The remainder of member A, as defined in Cornwallis Island, is herein assigned to the Douro Formation. Rocks referred to the Read Bay Formation in Somerset and Prince of Wales Islands and Boothia Peninsula, and those formerly included in the lower part of the Read Bay in Devon Island are assigned also to the Douro Formation. The rocks formerly considered as members B and C of the Read Bay Formation are included in a single formation for which the new name Barlow Inlet is proposed, whereas member D, which previously constituted the uppermost part of the Read Bay Formation is raised to the rank of formation and given the name Sophia Lake. The Read Bay Formation is raised to the status of group, and includes in order upward the Douro, Barlow Inlet and Sophia Lake Formations. As so defined, the Read Bay Group is distributed only in the Cornwallis Island area and adjacent parts of Devon Island. Southern and northern parts of the Boothia Uplift, which are separated by Barrow Strait, are characterized by different deformational histories within the Late Silurian to Early Devonian interval of time. Diastrophism commenced south of the strait (Somerset and Prince of Wales Islands, and Boothia Peninsula) in the late Ludlovian, whereas north of the strait (Cornwallis Island, northwestern Devon Island, and eastern Bathurst Island), it commenced in the early Lochkovian. From the early Lochkovian to the early Zlichovian, diastrophism appears to have proceeded simultaneously in both parts of the uplift.