Upper Precambrian through Lower Cambrian of Cape Breton Island: faunas, paleoenvironments, and stratigraphic revision

Abstract

Latest Precambrian through Early Cambrian tectonic history and stratigraphy are comparable in southeastern Cape Breton Island and the western Placentia–Bonavista axis, southeastern Newfoundland. The lithostratigraphic nomenclature of southeastern Newfoundland is used for this interval in Cape Breton Island. Upper Precambrian volcanic rocks of the Forchu Group (=“Giant Lake Complex,’ designation abandoned) are unconformably overlain by uppermost Precambrian through lowest Cambrian strata termed the “Morrison River Formation’ (designation abandoned). This depositional sequence consists of three formations: 1) red beds through tidalites of the Rencontre Formation (to 279+ m; =“Kelvin Lake Formation,’ designation abandoned); 2) prodeltaic clastics of the Chapel Island Formation (to 260 m); and 3) macrotidal quartzites of the Random Formation (to 71 + m). Post-Random block faulting and 300 m of local erosion took place prior to onlap of the “MacCodrum Formation’ (abandoned). Siliciclastic mudstones of the lower “MacCodrum’ are re-assigned to the middle Lower Cambrian Bonavista Group. Sub-trilobitic faunas from the Bonavista Group include“Ladatheca’ cylindricafrom the West Centre Cove Formation(?) and higher diversity faunas (23 species) in theCamenella balticaZone of the Cuslett and Fosters Point Formations. Trilobite-bearing, upper Lower Cambrian (Branchian Series) strata (Brigus Formation, =upper “MacCodrum’ and overlying “Canoe Brook’ Formations) unconformably overlie the Placentian Series in Cape Breton Island, southeastern Newfoundland, Shropshire, and, probably, eastern Massachusetts. Correlations based on small shelly fossils indicate an earlier appearance of trilobites in Avalon than on the South China Platform. Twenty-six species are illustrated.Halkieria fordin. sp., the conodont(?)“Rushtonites’ asiatican. sp., and the zhijinitid(?)Samsanoffoclavus matthewin. gen. and sp. are described.Ischyrinia? sp. may be the oldest ischyrinoid rostroconch.