PALEOSOLS IN PLIOCENE TO PLEISTOCENE SEQUENCES OF PREGLACIAL AND GLACIAL SEDIMENTS, TINTINA TRENCH, YUKON TERRITORY, CANADA

Paleosols in long sequences of Pliocene and Pleistocene preglacial and glacial sediments were studied at two sites, East Fifteen Mile River (EFR) and Rock Creek (RC), in the Tintina Trench near Dawson, Yukon Territory. Four buried paleosols at EFR display morphological features of modern Luvisols and Gleysols (Canadian System of Soil Classification), approximately equivalent to Alfisols and Aquic suborders (U.S. Soil Taxonomy). Features suggestive of pedogenesis in the EFR paleosols include accumulation of illuvial clay as conspicuous cutans, and coarse Fe-rich mottles. Crystalline Fe-oxide concentrations range from 1.5 to 2.5% in most horizons, except in the oldest paleosol, formed in preglacial sands, where values exceed 3.0%. Amorphous extractable Al concentrations are usually below 0.1%. At RC, two buried soils display weak structural development suggestive of clay illuviation, with levels of extractable Fe and Al similar to those at EFR. Clay mineral suites in the buried paleosols are dominated by varying proportions of smectite, mica, and kaolinite of probable detrital origin. The surface soil at RC has morphological, mineralogical, and chemical properties equivalent to the Wounded Moose soil found on early Pleistocene outwash deposits elsewhere in the Klondike region. These paleosols appear to consist of B horizons displaying relatively weak gradients in morphological and chemical differentiation with depth. Features suggestive of cryoturbation and periglacial processes appear absent in the buried paleosols at both sites. Paleoenvironmental interpretation is complicated by uncertainty over the degree of truncation of these soil profiles, the possibility of post-burial alteration, and the unknown duration of pedogenesis prior to burial.