GS-3 Far North Geomapping Initiative: palimpsest bedrock macroforms and other complex ice-fl ow indicators near Churchill, northern Manitoba (part of NTS 54L16) by M.S. Trommelen and M. Ross1 Trommelen, M.S. and Ross, M. 2011: Far North Geomapping Initiative: palimpsest bedrock macroforms and other complex ice-fl ow indicators near Churchill, northern Manitoba (part of NTS 54L16); in Report of Activities 2011, Manitoba Innovation, Energy and Mines, Manitoba Geological Survey, p. 29–35. Summary Introduction A 30 km stretch of well-exposed bedrock on the Bedrock outcrops accessible southwestern coast of Hudson Bay, near Churchill, from Churchill, Manitoba, were Manitoba, was thoroughly examined for erosional ice- visited during summer 2011 to look for bedrock-inscribed fl ow indicators. Low-lying Churchill quartzite outcrops ice-fl ow evidence. This project was initiated because inland and higher rocky bluffs near the shoreline preserve recent mapping in the nearby Great Island–Kellas Lake a complex palimpsest record of whaleback drumlins and area (Trommelen et al., 2010) has shown that the ice-fl ow roches moutonnées commonly grooved in numerous record was signifi cantly more complex than previously orientations. Crosscutting relationships and position on mapped. Questions arose regarding the behaviour of the bedrock outcrops suggest ice fl owed over time to the Laurentide Ice Sheet (LIS), especially in the Churchill area north-northwest to northwest→south→west→east-sout (Figure GS-3-1), where it has been suspected that paleoice heast→southeast→south→southwest→west-southwest fl owed from both the Keewatin Sector to the northwest with late deglacial fl ow between east and east-southeast and the Quebec-Labrador region to the east (Shilts, 1980; and west and northwest. These ice-fl ow indicators likely Boulton and Clark, 1990; Dredge and Nixon, 1992). The record more than just the late Wisconsinan glaciation and presence of complex ice-fl ow indicators at Churchill were were formed by a mix of Keewatin and Quebec-Labrador hinted at in Dredge (1992) but never mapped in detail ice sources. (Dredge and Nixon, 1981a, b). 94°15'W 94°W 0 2.5 5 Prince of Wales Fort kilometres Hudson Bay Bluff A Cape Bluff B Merry Bluff C Bluff D Bird Churchill Cove 58°45'N Churchill River Airport CChurchillhurchill NNorthernorthern SStudiestudies CCentreentre 58°45'N Bedrock 26 Glaciomarine Hudson Bay 28 29 25 27 19 22 30 16 15 20 23 31 14 17,18 1,2 32 Churchill 24 21 13 10 Bird 5 58°45'N 12 9 Cove 3 4 11 Churchill River 7 6 8 94°15'W 94°W Figure GS-3-1: Field area in northeastern Manitoba, with Spot 4 imagery as background in top map and simplifi ed surfi cial geology in bottom map (Dredge et al., 2007). Field sites are numbered. 1 Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. West, Waterloo, Ontario N2L 3G1 Report of Activities 2011 29 Churchill quartzite outcrops along the Hudson Bay outcrop were assumed to be youngest. Rare ice-fl ow coast in the Churchill area (Manitoba Department of indicators present on some part of the outcrop other than Energy and Mines, 1980). These outcrops form resistant the top were assumed to be old. Relative ages, and a ridges inland, and large rock bluffs along the shore summary of trends, was compiled for each site; based on (Bluffs A to D, Figure GS-3-1). Most outcrop surfaces are compiled ice-fl ow indicators from at least four outcrops at variably striking swales, plucked faces and stoss slopes, each site. After the fi eld season, compiled data from each which proved to be ideal for protection and preservation site was upscaled to devise a regional ice-fl ow history for of older ice-fl ow indicators. nine locations in the area. Ice-fl ow reconstructions in northern Manitoba suggest that the region was covered at least twice by ice from the Results Keewatin sector, and at least three times by ice from the Multifaceted, crossgrooved quartzite outcrops, similar Labradorean sector (Dredge et al., 1986; Dredge and to those described by Veillette and Roy (1995) in James Thorleifson, 1987; Boulton and Clark, 1990; Dredge et Bay, were found to be widespread in the Churchill area. al., 1990; Dredge and Nixon, 1992). Stratigraphic sections These palimpsest (characteristics predominately related in northeastern Manitoba broadly suggest the presence of to an earlier glacial movement in a different direction, a pre-Illinoian Harts/Sundance till (Keewatin) capped by and only partially modifi ed by glacial movement in a an interglacial paleosol, overlain by the Illinoian Amery younger new direction) features preserve a wide range till (Labradorean), overlain by interglacial Sangamonian of ice-fl ow indicators formed over time by different ice- Nelson River sediment, overlain by Wisconsinan Seal fl ow orientations. The fi eld data collected last summer till (Keewatin), and Long Spruce and Sky Pilot tills in the Churchill area can be found in Data Repository (Labradorean). For more details on stratigraphic work Item DRI20110012. Locations of 32 visited fi eld sites are in the fi eld area, the reader is referred to the following shown on Figure GS-3-1, where a total of 291 ice-fl ow papers: Klassen (1986), Nielson et al. (1986), Berger and indicator measurements were taken. Nielson (1990), Dredge et al. (1990), Dredge and Nixon (1992), Nielson (2001, 2002), Nielson and Fedikow (2002) and Kaszycki et al. (2008). Near the end of the late Palimpsest macroforms Wisconsinan deglaciation (between 8000 and 7700 C14 Upon close inspection of most bedrock outcrops, BP), the Churchill region was inundated by the Tyrrell Sea stoss/lee macroforms are present but the dominant (Dredge and Nixon, 1992). Beaches at 165 m elevation, orientation varies (Figure GS-3-2) from site to site and northwest of Churchill, record the maximum marine limit also at a single site (Figure GS-3-3a–d). Furthermore, for the area (Dredge, 1992). some macroforms are clearly palimpsest, whereby they have been moulded by ice in one direction, and then partially re-moulded by ice in a different direction. Methods Regionally, macroforms record ice-fl ow to the southwest (two phases), northwest, southeast, south-southeast One week was spent in the Churchill area, in the and south. The surfaces of roche moutonnées are often summer of 2011, to thoroughly map all fi eld-based ice- multifaceted. This can be seen in Figure GS-3-3d to g, fl ow indicators. Erosional ice-fl ow indicators documented where younger grooves and striae on macroform tops in the fi eld area include nondirectional indicators, such as truncate older ice-fl ow indicators on the protected sides/ striae and grooves, and directional indicators, such as rat faces of the macroform. These palimpsest landforms are tails, chattermarks, gouges, crescentic fractures and stoss- textbook examples of the ‘vanished protector’ (Veillette lee relationships. Macroform features encountered in the and Roy, 1995), whereby till cover likely prevented the study area include roches moutonnées and whalebacks destruction of a striated surface, while ice moulded the (rock drumlins). Visited outcrops were surveyed in detail outcrop in a different orientation. This protective till to record rare and protected ice-fl ow indicators and their was later removed (vanished) by wave-washing from position on bedrock outcrops, in addition to the dominant the Tyrell Sea (Dredge and Nixon, 1992), exposing the indicators. Whenever possible, rare and/or protected ice- multifaceted outcrops. fl ow indicators were confi rmed to be present on multiple outcrops at a site, before being documented. Striae clearly indicative of ice defl ection around bedrock outcrops were Complex crossgrooved record not collected. Where crosscutting patterns were found, the A summary of fi eld-based ice-fl ow indicators, relative ages of fl ows were determined where possible. for nine different areas, is depicted in Figure GS-3-4. Ice-fl ow indicators preserved on the top and side of an Regionally, ice-fl ow indicators trend to the southwest 2 MGS Data Repository Item DRI2011001, containing the data or other information sources used to compile this report, is available online to download free of charge at http://www2.gov.mb.ca/itm-cat/web/freedownloads.html, or on request from [email protected] or Mineral Resources Library, Manitoba Innovation, Energy and Mines, 360–1395 Ellice Avenue, Winnipeg, Manitoba R3G 3P2, Canada. 30 Manitoba Geological Survey 94°15'W 94°W Macroform orientation S 230–240 young S 0 2.5 5 S S Hudson Bay S S 180–190 S S S S kilometres S 160–170 S S S S S 140–150 S S S S S S 280–330 S S 230–240 old S S S S Churchill S S S S Bird 58°45'N S S Cove S Churchill S River S 58°45'N Figure GS-3-2: Macroform locations and orientation in the fi eld area, with the Shuttle Radar Topography Mission (SRTM) 90 m resolution hillshade (United States Geological Survey, 2004) as background. Most orientations can be found regionally, with the exception of the young 230–240°, which was only found at bluff A. (two phases), west, northwest (two phases), east-southeast probably during the pre-late Wisconsinan. North- (two phases) and southeast to south-southwest (two northwest- to northwest-trending (350–280°) ice-fl ow phases). Bedrock surfaces were moderately weathered, indicators represent the oldest preserved ice-fl ow phase and most ice-fl ow indicators mapped are grooves; in the Churchill region; likely formed by Labradorean- shallower fi ner striae were rarely seen. Likely owing to sourced ice. The fi rst set of southwest-trending (230– the vanished protector (Veillette and Roy, 1995), ice-fl ow 250°) and south-southeast- to south-southwest-trending indicators are present on all faces, including gentle stoss (140–190°) ice-fl ow indicators were likely formed tops and sides, steep lee slopes and steeper stoss slopes by Keewatin-sourced ice.