Characteristics and Origin of Calcretes in a Subarctic Environment, Great Kobuk Sand Dunes, Northwestern Alaska, U.S.A.

Abstract

Carbonate cementation of dune sand forms under subarctic, almost semiarid conditions in an active dune field in the Kobuk Valley, northwestern Alaska. Calcretes are cemented by low-magnesium calcite derived from carbonate grains incorporated within the dune sands. Two types of calcrete can be distinguished. The first type, in which initial calcrete formation has been observed, lies a few decimeters below the surface in interdune areas. The second type comprises remnants of calcretes of early Holocene age, which occur extensively in various interdune areas and in a large deflation area and are presently being redistributed by frost action. These calcretes were buried by westerly migrating dunes and subsequently exhumed by deflation. Radiocarbon dates of the calcretes (approximately 10,000 yr BP) provide a minimum age for the dune formation. Stable-isotope analysis of the calcretes indicates precipitation of carbonate mainly due to a loss of CO₂ in the groundwater without significant evaporation, a process favored by cold climates.