Late Paleozoic strike slip tectonics of the Northern Appalachians
Dwight Culver Bradley 1984
A dissertation submitted to the Faculty of the State University of New York at Albany in partial fulfillment of the requirements for the degree of Doctor of Philosophy
College of Science and Mathematics, Department of Geological Sciences
Advisors: J.F. Dewey and W.S.F. Kidd

During the interval between Devonian collision and Triassic rifting, the Northern Appalachians were the site of a wide, strike-slip plate boundary zone. Episodic motion on northeast- and east-trending faults resulted in the relative displacement of the Avalon and Meguma Terranes with respect to North America, and at the same time caused the subsidence and later deformation of about 25 more-or-less distinct sedimentary basins. The result is an exceedingly complex rock record characterized by along- and across-strike variations through regimes of pure strike slip, rapid and continuous basin subsidence, and local, compressional deformation.
A large body of geologic evidence (first synthesized by Webb, 1969) shows that during Carboniferous times, the sense of displacement was dextral, and its magnitude was in the range of a few hundred kilometers. On the other hand, recent paleomagnetic work (e.g. Kent and Opdyke, 1978) has suggested that about 2000 km of sinistral motion occurred in the Northern Appalachians during this interval. Accordingly, the first purpose of this study was to reexamine the geologic evidence bearing on the sense-of-motion question. Results of this analysis (Chapter 2) show (as Webb believed) that displacement (1) was dominantly dextral and (2) probably amounted to a few hundred kilometers. These dextral faults were moving precisely during that interval when the paleomagnetic evidence implies sinistral faulting. Furthermore, although Kent and Opdyke's interpretation of the paleomagnetic data absolutely requires the existence of a major left lateral fault, geologic links across all known faults in Newfoundland and New Brunswick show that none can have accomodated even a significant fraction of the required left-lateral motion. Another explanation of the paleomagnetic data must therefore be sought. One of the most striking features of this transform is the extent to which strike slip faulting was accompanied by basin subsidence. A survey of the 25 major sedimentary basins (Chapter 3 and Appendix 1) reveals a population of (1) pull-apart basins, including those that underwent late thermal subsidence (Magdalen), and those disrupted by later strike slip (Moncton); (2) basins bounded in part by thrust faults (Cumberland); (3) basins at strike slip fault intersections (Deer Lake); and (4) basins of unknown origin (Narragansett).
Field studies of two Carboniferous sedimentary basins in Cape Breton Island (Chapters 4 and 5) are consistent with regional evidence that basin subsidence was driven by dextral faulting. Mapping at 1:10,000 in the Big Pond Basin indicates that it is a dextral pull apart that formed during Visean times at a right step in the newly recognized Big Pond fault zone. Although the origin of the Bay St. Lawrence Basin is less obvious, 1:12,000 mapping along the eastern margin shows that subsidence in early and medial Carboniferous was associated with at least 3 km of dextral slip on the St. Lawrence fault.
The ultimate goal in a strike slip system such as this is the construction of a set of palinspastic, paleogeographic maps illustrating the evolving relationships between faulting and sedimentation (Chapter 6). While the displacement histories of most faults in the Canadian Appalachians are still inadequately understood, this goal will be within reach after a few well focussed field seasons.

Bradley, D.C., 1984. Late Paleozoic strike slip tectonics of the Northern Appalachians. Unpublished PhD dissertation, State University of New York at Albany. 286pp., +xiv; 3 folded plates (maps)
University at Albany Science Library call number:  SCIENCE MIC Film QE 40 Z899 1984 B72
Copies of this PhD dissertation can be ordered from Proquest UMI

        Front matter (title, table of contents, abstract, acknowledgements) - 0.4MB pdf file
        Photo pages in dissertation (greyscale photos with captions): - 7MB pdf file

        Plate 1 (1.1) - Geologic/tectonic map of the Upper Paleozoic of the Northern Appalachians
                    (uncoloured geological map, scale 1:1,000,000)
        Plate 2 (4.1) - Geologic map of the Big Pond Basin, Cape Breton Island
                    (uncoloured geological outcrop map and cross sections, scale 1:10,000)
        Plate 3 (5.1) - Geologic map of the Bay St. Lawrence Basin, Cape Breton Island, Nova Scotia
                    (uncoloured geological outcrop map and cross sections, scale 1:12,300)

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