Compound soil horizons with mixed calcic and argillic properties — examples from the northern Great Basin, USA

Palaeosols between deposits of the last two deep-lake cycles in the northern Great Basin have multiple carbonate-engulfed horizons, and compound calcic and argillic properties at depth. They are difficult to explain pedogenetically because they bifurcate in places, especially in basin centres where they are separated by sediments of a minor lake expansion of probable early Wisconsinan age. One sequence of processes can account for all phenomena: two cycles of colluviation and synchronous admixture of loess particles were each succeeded by the formation of an argillic over a calcic horizon. Carbonate enrichment resulting from the later period of soil formation affected the buried older soil. This led to welding of the two soils and the formation of a compound horizon carrying the argillic properties of the first and the calcic properties of the second pedogenic phase. Steady aeolian influx to the same soil surface, the commonly invoked mechanism, cannot explain the bifurcated palaeosols and is not needed to explain the welded ones.