Seasonal isotopic imprint in moonmilk from Caverne de l'Ours (Quebec, Canada): implications for climatic reconstruction

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Publication Date

12-1-2004

Publication Title

Canadian Journal of Earth Science

Volume Number

41

Issue Number

12

Abstract

Moonmilk, which is often seen coating walls in temperate caves, is a porous secondary calcite deposit composed of an aggregate of microcrystalline calcite and water. This study, based on moonmilk deposits found in Caverne de l'Ours, Ottawa Valley region, proposes a model for its formation based on the calcite and water isotope chemistry and evaluates its use as a climatic proxy. In Caverne de l'Ours, non-calcitic mineral inclusions protrude from the bedrock (Grenville marble) into the moonmilk, while others are entirely enclosed within the moonmilk. This observation suggests a mechanism of bedrock dissolution and reprecipitation for the formation of moonmilk, which is controlled by the changing seasonal climate in the cave. The δ 18 O of the moonmilk interstial water indicates that the condensation of water vapour occurs mostly in winter and spring. The condensation of water vapour on the surface of the walls allows for the dissolution of the Grenville marble and releases ions necessary for the precipitation of moonmilk. The δ 18 O and δ 13 C of calcite and δ 18 O of the moonmilk interstitial water indicate that precipitation of moonmilk occurs during summer and fall. During these seasons, the relative humidity in the cave decreases resulting in moonmilk growth through the slow evaporation of calcite-saturated water. A comparison of the δ 18 O record of moonmilk from caves in Gaspésie (Canada) and from Aven d'Orgnac (France) shows that this material retains temperature information valuable for paleoclimatic reconstructions.

Document Type

Article

Digital Object Identifier (DOI)

https://doi.org/10.1139/e04-080

Language

English

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