NWT RESEARCH DATABASE

Tags: physical sciences, geology, sedimentology, fossils, stratigraphy, coastline, paleogeology, deposition

Objective(s): To re-log the stratigraphic units that comprise the length of Duck Hawk Bluffs; to apply new techniques pertaining to the geochronology, paleoecology and glacial sedimentology of these deposits; and to synthesize the new observations and determine how this geological record correlates with other Quaternary events in the surrounding region (Beaufort Sea and Arctic Ocean).

Project Description: The research team proposes to revisit Duck Hawk Bluffs (DHB), southwest Banks Island, the “type section” for the formerly reported subsurface record. DHB offers an exceptional exposure along the north shore of Thesiger Bay, measuring 8 km long and up to 60 m high. Previous work assumed that the bluffs were composed of an undeformed “layer-cake” stratigraphy recording discrete depositional events up to 5-6 million years old. The objectives of this research project are: 1) to re-log the stratigraphic units that comprise the length of DHB; 2) to apply new techniques pertaining to the geochronology, paleoecology and glacial sedimentology of these deposits; and 3) to synthesize the new observations and determine how this geological record correlates with other Quaternary events in the surrounding region (Beaufort Sea and Arctic Ocean). Revisiting DHB is essential based on past observations at nearby Worth Point where previously unreported and pervasive deformation (glaciotectonism) dismisses its purported layer-cake stratigraphy and proposed geological history (Vincent 1983). The research team will map and describe the stratigraphy of individual units along the bluffs. Each unit will be further described based on its sedimentology (texture, structure, sorting and fossil content) in order to determine its depositional environment (marine, fluvial, glacial etc.). Particular attention will be placed on determining the style and magnitude of folding and faulting by former ice sheets. Fossil material will be collected and identified where present and used to characterize the paleo-ecology. These include both terrestrial organics (vascular and non-vascular plants, Matthews et al. 1986) and marine molluscs that have been reported. This mapping can be directly compared to the completed survey of the 6 km long section at Worth Point (2010), 30 km to the northwest. Chronological investigations will include multiple techniques that span a range of time scales appropriate to the proposed age of the sediments comprising DHB. These include: a) Radiocarbon dating by Accelerator Mass Spectrometry (14C AMS) of deposits younger than 50,000 yrs BP (<50 ka yr BP). During our reconnaissance of DHB, numerous fine-grained marine sediments, as well as glacial deposits, were noted to be fossiliferous (shell-bearing). Surprisingly, none of these shells have been previously radiocarbon dated (Vincent 1983; Matthews et al. 1986). Collections, from similar deposits at other sites around Banks Island have yielded finite 14C dates ranging from 10 to 50 ka BP, identifying a widespread late Wisconsian ice advance previously discounted by earlier reconstructions (Vincent 1982). b) Optically Stimulated Luminescence (OSL). During the 2010 field season samples of marine sand were collected from raised beaches and glaciotectonized coastal sections that yield robust ages spanning 90 to >400 ka BP. These results demonstrate the utility of OSL dating of sediments beyond the range of 14C AMS that may comprise the upper parts of DHB. Dating 2-3 samples per unit is anticipated in order to test their concordance and make correlations as robust as possible along the 8 km of coastal exposure. Dating 5-10 units is anticipated in the upper part of the bluffs where previous research indicates ages younger than 780 ka BP (based on paleomagnetism), potentially within the range of OSL dating (<400 ka BP). c) Terrestrial Cosmogenic Nuclide (TCN) Dating. Earth and Atmospheric Sciences, University of Alberta, has a Cosmogenic Preparation Lab that will be used for both surface and subsurface samples. Surface samples will include erratics transported by the LIS and will be dated by TCN exposure dating (10Be, 26Al, 36Cl) that has a range of ca. 1 million years (1 Ma). The objective with this methodology is to test the current model indicating the passage of Late Wisconsinan Laurentide ice across this landscape. Samples will be collected from subsurface units to determine TCN burial ages (time since deposition) that has a useful range of up to 5 Ma. This methodology is particularly valuable for its ability to distinguish between preglacial fluvial gravel (Beaufort Fm.) and younger glaciofluvial outwash that may share the same stratigraphic position due to glaciotectonism. d) Paleomagnetism. Previous studies have characterized the magnetostratigraphy of DHB, reporting both glaciations and interglaciations that purportedly predate the Brunhes-Matuyama boundary (>780 ka, Barendregt et al. 1998). This model will be tested using all of the methodologies listed above, including additional paleomagnetic analyses on key stratigraphic units. Methodologies limited to samples <780 ka BP are required at DHB because the previous reconnaissance demonstrates glaciotectonic displacement that potentially invalidates previous paleomagnetic measurements. The prospect of glaciotectonism - apparently unaccounted for during the original paleomgnetic survey - necessitates a fundamental reassessment. The research team will visit Sachs Harbour to hold public discussions at the community centre and in the school. These talks will include an overview of the current research as well as our previous field work spanning most of Banks Island, including Aulavik National Park. In particular, the research team will discuss current rates of coastal erosion, which is impacting many communities in the western Canadian Arctic. This work was done between 2005 and 2010 under J. England's NSERC Northern Research Chair Program. The research on Banks Island is also shared with students in ENRTP at Aurora College, Inuvik, allowing them to see local examples of environmental topics covered in their curriculum. The fieldwork for this study will be conducted from June 20, 2012 to July 30, 2012.