Preservation and diagenesis in ancient speleothems: evidence from Bear Cave, Yukon Territory

Abstract

Speleothems are rare in high-latitude and high-altitude caves, which is why Bear Cave in the north-western Yukon Territory is particularly unique, as it houses some of the oldest and highest latitude speleothem in the world. In this study, a detailed petrographic and geochemical study was conducted along the profile of a 68-cm long late-Miocene flowstone from Bear Cave (BC1) to reveal the processes that took place at the time of deposition, in addition to those that followed, in aims to determine its paleoclimatic suitability. These studies suggest that softer facies are generally representative of disequilibrium conditions, where in-filled textures provide evidence for diagenic phenomena; these processes ultimately obscure the original climate signal, compromising the integrity of the flowstone in terms of its paleoclimatic suitability. Conversely, harder facies are likely deposited in isotopic equilibrium and resistant to post-depositional diagenesis, and are therefore more reliable for detailed paleoclimatic analysis. The variability of the calcite sequences in the profile of BC1 imply that environmental conditions have been considerably variable of the course of deposition, reflecting alternating cool/dry (softer facies) and warm/wet (harder facies) climatic conditions. Results from radiogenic 4He-dating constrain the timeframe of deposition, with ages centering around 9.35 +/- 0.52 Ma, which are in line with regional geomorphic interpretations. This study emphasizes the importance of a complimentary petrographic study in speleothem geochemical studies used in paleoclimatic and paleoenvironmental research.