CGRG Bibliography of Canadian Geomorphology
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Author : Agosta, S.E.; Lauriol, B.; Lacelle, D.; Clark, I.D.; and Pozzi, J.P.
Date : 2009.
Title : Crystallographic, geochemical and geomagnetic paleointensity record of a Tertiary-Age speleothem, northern Yukon Territory, Canada.
Publication : CANQUACGRG Biennial Meeting. May 3-8, 2009. Simon Fraser University, Burnaby Campus, Burnaby, British Columbia.
Issue : Programme and Abstracts Volume.
Page(s) : 28.
Abstract
Bear Cave Mountain, located in the Yukon, contains some of the highest latitude speleothem deposits in the world. Located at the Arctic Circle, these deposits were shielded in the ice-free corridor of Beringia during the Quarternary glaciations. A flowstone was collected from Bear Cave in 1985; this flowstone has well defined crystal structures with distinct colour variations and contains at least four major depositional hiatuses, two magnetic inversions and an He age of 6Ma, which makes it an excellent specimen for crystallographic and geochemical analysis. The purpose of this study is two fold. The first is to present a record of speleothem growth in relation to paleoclimatic/paleoenvironmental/paleohydrological conditions in the unglaciated regions of Northwestern Canada. This will be accomplished by comparing variations in the crystallography (microfabric and greyscale values), paleomagnetism (magnetic intensity and moment), stable O-C isotopes and trace elements chemisry along the major growth axis of the flowstone to see if any relationship exists between the three components, and to try and obtain useful paleoclimatic signals. The second objective is to compare the results of each of these components at various resolutions (cm to ΅m). The mean d18O content of modern precipitation in the region is approximately -22, whereas the mean value observed in the flowstone from Bear Cave is -17, with extreme values around ¬19 and -15, which are consistant with other interglacial deposits in the Rocky Mountains of British Columbia and Alberta. This leads to the conclusion that deposition took place in climate conditions slightly warmer than today. d13C values range from -4 to -8. The 68 cm thick flowstone consists of two main types of crystal fabrics: a hard, dark-brown translucent fabric, and a softer, lightly-coloured opaque calcite. A total of eight distinctly different microfabrics were identified in the flowstone. Higher d18O values are generally associated with a columnar fabric with sparite and branching crystals in between the crystal boundaries. This represents the coldest environmental conditions of formation, but still occur over a relatively large range (-14.8 to ¬17.5). Warmer conditions of deposition are represented by a palisade calcite fabric, which are associated with lower d18O values (-16.6 to -18.4), which is also similar to a simple columnar fabric with euhedral crystal boundaries (-16.2 to -17.9). Dendritic fabrics were found to have formed under the narrowest of conditions with d18O values ranging from -16.4 to -17.3 and d13C values on the lower end ranging from -7.0 to -7.6. This likely represents warmer and dryer environmental conditons of formation in the region, consistent with decreased meteoric water and increased plant growth. In general, lighter/opaque/softer/microcrystalline calcite tends to be associated with more depleted d13C values, whereas darker/translucent/harder/columnar calcite is associated with less depleted d13C.
Bibliography of Canadian Geomorphology