The tectonics and depositional history of the Ordovician and Silurian rocks of Notre Dame Bay, Newfoundland: Discussion
Scarcity of fossils has been one of the major problems in unravelling the complex geologic history of Newfoundland. The new fossil findings reported by Amott et al. are thus very important. The authors combine these new data with the known fossil evidence from literature to make time-stratigraphic correlations across the Notre Dame Bay area. Then they use the paleontological and stratigraphic data "together with an appreciation of the influence of contemporary faulting on the sedimentation" (p. 607) to reconstruct the depositional and tectonic history of the area. However, the report suffers from repetition of some old ideas, which may no longer be acceptable in the light of available new evidence. The main theme of the Amott et al. review is the stratigraphic unity of the Notre Dame Bay area. A number of workers (see Dean (1978) and references therein) have contemplated this idea previously; however, most geologists were discouraged by the distinctiveness of the terranes to the north and south of the Lukes Arm fault zone (Home and Helwig 1969). Poor fossil control and a lack of understanding of the region's structural complexities have inhibited these investigations even further. In fact, the nature and timing of movements on major faults in the Notre Dame Bay area are still unresolved (e.g., Dean and Strong 1977; Karlstrom et al. 1982, 1983; P. F. Williams, personal communication, 1985). One must also bear in mind the disturbing possibility that some of these faults were reactivated in post-Ordovician or Silurian times, and, therefore, the restoration of the last recorded movement may not always recreate the original arrangement of presently fault-bounded sequences (Kay 1967). This complicates interpretation of time-stratigraphic correlations, as the fossil-based time equivalence of two rock sequences does not necessarily prove their geologic or geographic unity. Amot et al. attempt to overcome this dilemma by calling on a variety of sedimentological and geochemical evidence to support their idea of stratigraphic unity for the entire Notre Dame Bay region. However, we disagree with several of their conclusions and also wish to point out some flaws in their arguments. Our first series of comments concerns Amott et al.'s interpretations of the geochemical data on the Notre Dame Bay volcanic rocks. Throughout the report they use the term "Notre Dame Bay arc." This idea, although long held (e.g., Strong 1977; Dean 1978; Kean et al. 1981), is not firmly substantiated on geochemical grounds. It should be stressed