| Summary: | The McAdams Lake Formation consists of a lower member composed of green-grey to black sandstone, silt-stone, shale, and minor conglomerate, and an upper member composed predominantly of grey conglomerate and sandstone, with minor black shale. A lens of red shale, siltstone, and sandstone with minor conglomerate is also present in the upper member. The total thickness of the formation is approximately 1 km. Fossil plant fragments and palynology indicate an age of latest Emsian to Early Eifelian (latest Early to Middle Devonian). The presence of a small, fine-grained quartz syenite intrusion probably led to the previously reported occurrence of volcanic rocks in the formation. Characteristics of the lower member suggest deposition in a shallow lacustrine shoreline setting with intermittent, rapid deposition of coarse sediments in a fan delta near a faulted margin. The upper member is interpreted to represent an increase in topographic relief and a progradation of the fan delta to fill the basin, with braided channels present near the fan delta toe. The presence of carbonaceaous shale in this member indicates intermittent swampy conditions or transgression of lacustrine conditions over the fan delta. The McAdams Lake Formation was deposited on the Mira terrene in a half-graben formed by extension along the boundary between die Mire and Bras d'Or terrenes, at the initial stage of development of the Sydney Basin. A hiatus of ca. 40 Ma occurred between deposition of the McAdams Lake Formation and the unconformably overlying Grantmire Formation. During this time the McAdams Lake Formation underwent a period of compressive deformation that resulted in northeast-trending minor folds on an antiformal structure. The McAdams Lake Formation and equivalent units in Atlantic Canada may represent an earlier Horton-like basin system with similar facies and economic possibilities that have been previously unexplored. RÉSUMÉ La Formation de McAdams Lake est constitute d'un membre inférieur formé ...
|
|---|