Anatomy of the tidal scour system at Minas Passage, Bay of Fundy, Canada John Shaw a, ⁎, Brian J. Todd a , Michael Z. Li a , Yongsheng Wu b a Geological Survey of Canada (Atlantic), Natural Resources Canada, Bedford Institute of Oceanography, Dartmouth, NS, Canada B2Y 4A2 b Coastal Ocean Science Section, Ocean Science Division, Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada, Canada B2Y 4A2 abstract article info Article history: Received 20 February 2012 Received in revised form 17 July 2012 Accepted 18 July 2012 Available online xxxx Communicated by J.T. Wells Keywords: scour trough banner bank Bay of Fundy tides Strong currents have eroded thick Quaternary sediments to create a scour trough at Minas Passage, in the Bay of Fundy, Canada, site of Earth's largest tides. We describe this trough in the context of a larger system that comprises a range of elements, viz: 1) Scour troughs extending 170 m below mean sea level are incised into thick glaciomarine sediments and have exhumed bedrock over wide areas. The flanking uneroded ter- rain has low relief and a winnowed surface. 2) Sets of sand banner banks off Cape D'Or and Cape Chignecto. 3) The atypical set of banner banks at Cape Split, consisting of the Scots Bay dune field and its counterpart, a large gravel bank trapped in the Minas Passage scour trough. 4) Low-relief banks with sand ribbons and bar- chan dunes alongside some banner banks, and termed ‘shadow banks’. 5) A large (0.8 km 3 ) sediment drift at the entrance to Minas Channel (without large bedforms). The location of troughs and banks can be correlated with tidal-current patterns: trenches are located in regions of very strong bi-directional currents; banner banks near headland-sited tidal gyres; shadow banks in areas of maximum mean bottom stress asymmetry; and the sediment drift at the entrance to Minas Channel in an area of weak bottom stress at all stages of the tides. Previous work has argued that the scour system formed after 3400 14 C yrs BP (radiocarbon years before present) following collapse of a barrier system across Minas Passage. We speculate that formation of the scour trough system may have released vast quantities of sediment that have not been accounted for in pre- vious sediment budgets, and that much of this released sediment has been sequestered in the late-Holocene salt marshes at the head of the Bay of Fundy. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. 1. Introduction Minas Passage is a narrow channel connecting Minas Basin with the rest of the Bay of Fundy (Fig. 1). It was surveyed in the 1960s as part of studies in support of a proposal to build a barrage across the channel and generate electricity using tidal power. Results of detailed surveys published by Huntec Ltd. (1966) show the distribution of bedrock and the overlying Quaternary sediments. The report authors christened the deep trough in the passage as the ‘Minas Passage Scour Trench’. Eventually interest in the project waned, particularly since tidal modeling suggested that construction of the barrage could alter tidal regimes as far away as New England (Greenberg, 1975). Today Minas Passage is of interest once again, although rather than constructing a barrage the idea is to develop fields of in-stream tur- bines placed on the sea floor. In 2009 the Fundy Ocean Research Centre for Energy (FORCE) established a test site for in-stream tidal energy technology in Minas Passage, and began evaluating the first of several devices there. In advance of the selection of a site for pilot deployments, the area was surveyed with multibeam sonar systems, part of a systemat- ic survey of the entire Bay of Fundy that resulted in the publication of seventeen Geological Survey of Canada (GSC) 1:50,000 scale A-series maps in 2011. Sheet 16 covers most of the study area (Todd et al., 2011a) and sheet 15 the remainder (Todd et al., 2011b). These GSC surveys were followed by intensive surveys of the selected site, located at a depth of 45 m on a bedrock sea floor (Fig. 2). The surveys revealed for the first time the true com- plexity of Minas Passage and adjacent areas, revealing not only the scour trough but ancillary scour troughs and systems of bedforms of varying types. A range of studies has been conducted recently in order to model and ascertain flow conditions and determine the probability that the deployment of tidal devices might alter environmental conditions such as tidal range and sedimentation (e.g., Karsten et al., 2008). However, these efforts have proceeded without a thorough evalua- tion of the nature of the seafloor, and have in some instances relied on sparse sediment sample data (e.g., Wu et al., 2011). Because the available multibeam sonar data have been subject to groundtruthing during cruises in 2009 (Todd et al., 2010a) and 2011 (Todd et al., 2012), the time is now favourable for an evaluation of the morphology, surficial geology and short‐ and long‐term processes of this area. Accordingly it is the purpose of this paper to: • Describe the structure and morphology of the system of tidally- generated landforms at Minas Passage. Marine Geology xxx (2012) xxx–xxx ⁎ Corresponding author. E-mail address: johnshaw@nrcan.gc.ca (J. Shaw). MARGO-04802; No of Pages 12 0025-3227/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.margeo.2012.07.007 Contents lists available at SciVerse ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo Please cite this article as: Shaw, J., et al., Anatomy of the tidal scour system at Minas Passage, Bay of Fundy, Canada, Marine Geology (2012), http://dx.doi.org/10.1016/j.margeo.2012.07.007