Abstract

In addition to minor postglacial weathering effects, a complex history of three distinct weathering events has been identified within the granitoids of the South Mountain Batholith of southwestern Nova Scotia. Weathering prior to deposition of Carboniferous strata produced a well-developed saprolite, an in situ weathering profile. Feldspars and micas are altered to clay minerals, and only weak preservation of granitic texture is evident. Subsequent burial and relithification have masked the original weathering mineralogy in this horizon. Beneath Triassic clastic sedimentary rocks is a thick horizon (30 m) of weathered granitoid. This argillaceous saprolite with relict biotite exhibits an intensifying-upward weathering zonation typical of weathered horizons, with increased proportions of clay minerals at the upper levels. A younger arenaceous saprolite of pre-Pleistocene age can be found beneath glacial till at a number of locations throughout the batholith. These paleoweathered horizons attest to relatively warmer climates at several times in the geologic past. Their patterns of preservation imply some were much thicker and more widely distributed before partial erosion. The eroded materials may have formed the sediment for quartz sand in the Carboniferous sequence, clay and silica sand deposits of Cretaceous age, and a sandy till of Pleistocene age. The remnants preserved in situ today serve as significant conduits for water, and the geochemistry, mineralogy, and textures of these weathered profiles may enhance mobility and migration of U and Rn. These weathered horizons are mechanically weak, and the possibility of their presence should be considered when selecting construction and waste-disposal sites.

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