A Possible Time Span for the Late Precambrian of the Avalon Peninsula, Southeastern Newfoundland in the Light of Worldwide Correlation of Fossils, Tillites, and Rock Units within the Succession

Abstract

Since too few absolute age determinations have been carried out on late Precambrian rocks of the Avalon Peninsula, southeastern Newfoundland, a stratigraphic approach has been adopted to obtain the necessary dates on which to base a possible time-span for the whole succession. The correlatable 'features' of the Avalon Peninsula late Precambrian—fossils, tillites, and volcanic episodes, have been correlated with similar 'features' in late Precambrian sequences in other parts of the world where these 'features' have been dated isotopically. Some of the correlations are probable, others only possible as long-distance correlation involves an element of speculation.Conception Group sedimentation may have lasted from 710 m.y. ago, the possible age of the 'basal' conglomerate, to ca 600 m.y. ago, and possible ages for the Conception Group tillites and fossils (Mistaken Point fauna) are 670–715 m.y. and 610 to 630 m.y. respectively. Harbour Main volcanism began some 795 m.y. ago and continued until about 715 m.y. before present. These ages indicate a possible age-range for the late Precambrian of the Avalon Peninsula from ca 800 m.y. to 570 m.y. (age of base of Cambrian accepted here), a time span of ca 230 m.y. that is equivalent to the greater part of the Proterozoic Hadrynian Era.The soft-bodied metazoan fossils of the Conception Group Mistaken Point fauna are comparable to those of the Australian Ediacara fauna and related forms in other parts of the world. Conception Group tillites are correlated with glaciogenic deposits of the uppermost Precambrian ice age in central Australia, the Rybachiy Peninsula, U.S.S.R., and Scotland (Dalradian tillites). Harbour Main Group volcanics are correlated with part of the Coldbrook Group volcanic sequence, southern New Brunswick; the Fourchu Group and Morrison River Formation of southeast Cape Breton Island are believed younger, and possibly, the time equivalent of the upper part of the Musgravetown Group together with the Random Formation, western Avalon, although the possibility of the Morrison River Formation being Cambrian cannot be excluded. Correlation of Harbour Main volcanics with volcanics of late Precambrian age in the British Midlands is considered a possibility but remains conjectural.A single intrusive event is favored for emplacement of the Holyrood granite 607 ± 11 m.y. ago. This necessitates there having been older granite in the area to provide a source for the granite clasts in the Conception Group conglomerates and tillites. A second, less likely, alternative is that the Holyrood granite was emplaced over a substantial period by successive pulses of magma; the 607 m.y. age is then that of the last intrusion of magma.