AVALON—NON-GONDWANAN MICROCONTINENT BY THE LATE PRECAMBRIAN: NEW EVIDENCE FROM THE PROTEROZOIC–CAMBRIAN BOUNDARY INTERVAL

Avalon is distinguished as a terrane in the Caledonian–Acadian orogen by thick, Late Proterozoic volcanics and siliciclastics; later Proterozoic orogeny; and a siliciclastic-dominated Cambrian–Silurian cover sequence with provincially distinct faunas. New evidence strengthens interpretations that: 1) Avalon was a high-latitude continent unrelated to tropical Gondwana-Cadomia in the earliest Cambrian and 2) “west” and “east” Avalon were confluent and did not successively rift away from Gondwana in the Cambrian and Ordovician. New work shows that depositional sequence (“d.s.,” below) 1 and 2 and a unified lithostratigraphy based on formations first defined in the Burin Peninsula, eastern Newfoundland, are recognizable on the Avalonian outer platform from New Brunswick to North Wales. This succession has terminal Precambrian rift–marginal marine facies (Rencontre Fm.), lowest Cambrian marine mud- and sandstones (Chapel Island Fm.) with the d.s. 1–2 boundary in its middle part and common volcanic ashes in its upper part, and an overlying quartz arenite (Random Fm.) in the Burin Peninsula. In southern New Brunswick, the Chapel Island Fm. (earlier “Ratcliffe Brook Fm.”) shows significant erosion at the d.s. 1–2 contact. Nodules from lowest d.s. 2 (Mystery Lake Mbr.) have upper Watsonella crosbyi Zone small shelly fossils (SSFs) that allow correlation into the lower Mystery Lake in the Burin Peninsula, eastern Newfoundland. In Cape Breton Island, limited “MacCodrum Fm.” outcrop long confused Proterozoic–Lower Cambrian correlations. Landing (1995, 1996) showed that individual “MacCodrum” outcrops are referable to the sub-trilobitic Bonavista Group or trilobite-bearing Brigus Formations. Re-investigation of the type “MacCodrum Fm.” and sparse SSF recovery now 1) allow its identification with the much older Chapel Island Formation and 2) permit recognition of the d.s. 1–2 boundary. D.s. 1–2 correlations between North Wales (“Basal Series;” Purple, red, and blue slates; and “Basal grit”) and the Burin are suggested (Rencontre, Chapel Island, Random, respectively), and may be bolstered by U-Pb zircon dates on Welsh ashes.