Abstract

A variety of calcrete paleosols were developed in northwestern Pangea during the Late Carboniferous. Exposed today on Ellesmere Island, the calcretes are found hosted by four different sedimentary facies: floodbasin sandstones, alluvial fan sandstones, alluvial fan conglomerates and shallow marine limestones.

Because of the strong influence of depositional environments on calcrete development a relatively distinct association of calcrete profiles, horizons and fabrics was formed within each sedimentary facies. Nodular/massive profiles, consisting ideally of a succession of cryptic, nodular, massive and laminar horizons are restricted to the floodbasin sandstone and alluvial fan sandstone facies. Plugged profiles, comprising ideally cryptic, plugged and laminar horizons occur essentially in the alluvial conglomerate facies. Massive/brecciated profiles, characterized by cryptic, massive/brecciated and laminar horizons were observed only in the shallow marine limestone facies. The different horizons contain a great many fabrics, including Microcodium, circum-granular cracking, in situ brecciation, dense micrite, root structures, alveolar textures, peloids/clotted micrite, laminated micrite, coated grains, ooids/pisoids, plant fragments, micro-deformation structures and calcrete dykes.

The widespread development of calcrete paleosols in the Upper Carboniferous of the Sverdrup Basin represents a useful climatic indicator for northwestern Pangea. While a favourable syn-rift paleogeography was unfolding the Sverdrup Basin was migrating northwards on Pangea and crossing a semi-arid climatic belt conducive to calcrete development. During the Permian the Sverdrup Basin entered a phase of passive regional subsidence and witnessed the establishment of a megamonsoon climate, during which the development of calcrete paleosols was reduced and eventually inhibited.