Geological Mapping at Parrsboro (Cape Sharp to McKay Head), Nova Scotia

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1 Report of Activities Geological Mapping at Parrsboro (Cape Sharp to McKay Head), Nova Scotia J. H. Calder, R. D. Naylor, J. W. F. Waldron 1, K. Adams 2, T. Fedak 2, E. George 3, P. S. Giles 4 and R. Stevens 5 History of Project In , a team of geologists led by R. D. Naylor and comprising J. H. Calder, P. S. Giles, R. Stevens and J. W. F. Waldron, and assisted by C. Kennedy, T. Costain and J. Hunter, undertook mapping of the Parrsboro coastal geology to provide the Fundy Geological Museum (FGM) with an up-to-date, detailed resource to assist in their interpretive programing and paleontological curation. Paleontological investigation and discovery along the shore included the work of the Sternbergs at West Bay during the 1930s, Donald Baird at West Bay and Parrsboro Harbour in the 1950s and 1960s, and the lifelong work of Eldon George from 1950 to the present. The field seasons saw completion of mapping from Cape Sharp in the west to Greenhill, east of McLaughlin Bluff. In 2012, at the urging of then Director of the FGM, Ken Adams, mapping was extended eastward to include geologically complex Clarke Head. Subsequently in 2013, Wasson Bluff was included due to its paleontological significance and focus for the FGM. Mapping was pushed still farther to the east during 2014 to include The Brothers (offshore islands) in order to help constrain revisions to the geology in the cove of Swan Creek and to provide geological continuity with outcrop of North Mountain Basalt eastward to Five Islands. This also allowed inclusion of the type section of the McCoy Brook Formation. Inland exposures of predominantly Carboniferous strata have been mapped north to the Cobequid Fault, effectively the southern limit of mapping currently in progress by Trevor MacHattie and Chris White (this volume). Map Units Map units span the early Carboniferous (Mississippian) to Early Jurassic, comprising the Windsor, Mabou, Cumberland and Fundy groups. Many of the map units are assigned informal status in the Lexicon of Canadian Stratigraphy (Williams et al., 1985), including the West Bay, Parrsboro, and Scots Bay formations. The West Bay and Parrsboro formations, along with the McLaughlin Bluff conglomerate, will be formally proposed and type sections identified in an accompanying paper. Formal and informal formations represented in the map area are summarized in Table 1. Revisions to Existing Map Interpretations Clarke Head During the 2014 field season, the Clarke Head megabreccia (Fig. 1) was mapped in detail (1: 5000 scale) by John Waldron and the first author, assisted by Jeff Minichello. This represents the most detailed mapping yet undertaken of this enigmatic section. Although discrete stratal blocks in the order of 100 metres can be assigned with confidence to the Windsor and Mabou groups (Bromley, 1987), these units occur within the larger fault zone as broken formations. Within this broad fault zone, a more intensely deformed zone occurs wherein rounded, mylonitic, allochtonous megaclasts, and mafic and less commonly felsic igneous elements that are variously metamorphosed (some forming sea stacks), occur in a pulverized matrix of sedimentary affinity (Fig. 2). These exotic 1 Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3 2 Fundy Geological Museum, 6 Two Island Rd., Parrsboro, NS B0M 1S Whitehall Rd., Parrsboro, NS B0M 1S0 4 Geological Survey of Canada Atlantic, P.O. Box 1006, Dartmouth, NS B2Y 4A2 5 Deceased Calder, J. H., Naylor, R. D., Waldron, J. W. F., Adams, K., Fedak, T., George, E., Giles, P. S. and Stevens, R. 2015: in Geoscience and Mines Branch, Report of Activities 2014; Nova Scotia Department of Natural Resources, Report ME , p. 1-5.

2 2 Geoscience and Mines Branch Table 1. Map units of the Parrsboro map sheet. McCoy Brook Formation (Fundy Group) North Mountain Formation (Fundy Group) Blomidon Formation (Fundy Group) ---- unconformity ---- Parrsboro formation (Cumberland Group) McLaughlin Bluff conglomerate (Cumberland Group) ---- unconformity ---- West Bay formation (Mabou Group) Windsor limestone (unassigned Windsor Group) elements were sampled for petrographic, whole-rock, and potentially geochronological analyses. The complex history of the Clarke Head section spans initiation of ductile shearing in the late Devonian (369 Ma based on U-Pb from granulite-grade mylonite; Gibbons et al., 1996) to the megabrecciation event. Our mapping indicates that the megabrecciation event is constrained to post-mabou Group deposition and pre-cumberland Group deposition, presumably at the Mississippian- Pennsylvanian boundary. The Mississippian- Pennsylvanian unconformity ca. 300 Ma represents a regional tectonic event coinciding with the late stages of the Alleghenian orogeny (Gibbons et al., 1996; Calder, 1998). Swan Creek The relationship of North Mountain basaltic flows and underlying Mesozoic sedimentary strata north of Clarke Head and south of Swan Creek has been reinterpreted as a conformable contact (Figs. 3, 4). Earlier interpretations (Donohoe and Wallace, 1982; Withjack et al., 1995; Olsen et al., 2005; Waldron et al., 2005) have depicted a reverse fault displacing North Mountain basalt over younger Jurassic strata of the McCoy Brook Formation. Sedimentary strata east of Swan Creek incorporate basaltic boulders of the North Mountain Formation and therefore post-date the North Mountain Formation (Olsen et al., 2005), and their assignment to the McCoy Brook Formation (Donohoe and Wallace, 1982) is supported by our mapping. West of Swan Creek, however, the sedimentary strata conformably underlie the North Mountain Formation and are assignable to the Late Figure 1. The Clarke Head megabreccia.

3 Report of Activities Figure 2. Gabbroic clast within mylonitized gypsum, from within the Clarke Head megabreccia. Triassic Blomidon Formation. These two map relations can only be accommodated by a normal fault in the vicinity of Swan Creek, which is supported by the pronounced topographic signature of Greenhill. The presence of the inferred Swan Creek fault had a role in the decision to extend the map eastward to address the position of the basaltic islands of The Brothers. Figure 3. Basalt flow conformably overlying sedimentary strata reassigned to the Blomidon Formation.

4 4 Geoscience and Mines Branch Figure 4. Close-up of the chilled contact of North Mountain Formation basalt overlying Blomidon Formation sedimentary strata. A New Template for a Geological Map The map units represented in the map area record the assembly of Pangea during the Carboniferous and the initiation of its breakup in the Late Triassic- Early Jurassic. The history of life bears witness to early tetrapod evolution and the rise of dinosaurs. Both are exceptional opportunities for geological education and research, and the map is being designed with this in mind in collaboration with Tim Fedak, Director of the Fundy Geological Museum. References Bromley, M. H. 1987: Geology of the mélange at Clarke Head, Cumberland County, Nova Scotia; BSc. thesis, Acadia University, Wolfville, N.S., 114 p. Calder, J. H. 1998: The Carboniferous evolution of Nova Scotia; in Lyell: the Past is the Key to the Present, eds. D. J. Blundell and A. C. Scott; Geological Society of London, Special Publication 143, p Donohoe, H. V. Jr. and Wallace, P. I. 1982: Geological Map of the Cobequid Highlands, Cumberland Colchester and Pictou Counties, Nova Scotia; Nova Scotia Department of Mines and Energy, Map 82-7, Sheet 2, scale 1: Gibbons, W., Doig, R., Gordon, T., Murphy, B., Reynolds, P. and White, J. C. 1996: Mylonite to megabreccia: tracking fault events within a transcurrent terrane boundary in Nova Scotia, Canada; Geology, v. 24, p Olsen, P., Whiteside, J. and Fedak, T. 2005: The Triassic-Jurassic faunal and floral transition in the Fundy Basin, Nova Scotia; Geological Association

5 Report of Activities of Canada Annual Meeting Field trip A7; Atlantic Geoscience Society, Special Publication no. 26, 53 p. Waldron, J. W. F., White, J. C., MacInnes, E. and Roselli, C. G. 2005: Transtension and transpression along a continental transform fault: Minas Fault Zone, Nova Scotia; Geological Association of Canada Annual Meeting Field trip B7; Atlantic Geoscience Society, Special Publication no. 33, 65 p. Lexicon of Canadian Stratigraphy, Volume VI, Atlantic Region; Canadian Society of Petroleum Geologists, Calgary, 572 p. Withjack, M. O., Olsen, P. E. and Schlische, R. W. 1995: Tectonic evolution of the Fundy basin, Canada: evidence of extension and shortening during passive-margin development; Tectonics, v. 14, p Williams, G. L, Fyffe, L. R., Wardle, R. J., Colman-Sadd, S. P. and Boehner, R. C. 1985: