Paleosols in Devonian red-beds from northwest China and their paleoclimatic characteristics

Abstract

Paleosols have been discovered in the late Devonian (Famennian) Shaliushui Formation near Pingchuan City, Gansu province, China, and are recognized by evidence of root traces, soil horizons and soil structures. Root traces are remnants of substantial woody plants, reaching deeply within profiles as clayey infills and as drab-haloed root traces. Soil horizons include thick layers of large calcareous nodules (Bk horizon), and subsurface accumulations of clay (Bt horizon), and slickensided claystone (vertic Bw horizon). Soil structures include blocky peds and calcareous nodules. The nodules and drab-haloed root traces formed syndepostionally during the late Devonian, because they were also observed in clasts of paleosol and nodules in fluvial conglomerates interbedded with the paleosols. Analyses for Rb/Sr and Ba/Sr ratios and magnetic susceptibility measurements confirm that the more strongly developed paleosols with larger calcareous nodules and higher clay content are also more chemically differentiated and have higher magnetic susceptibility under semi-arid climates. This suite of paleosols is evidence of semi-arid to sub-humid, highly seasonal climate under dry woodlands and shrublands. Paleosols of the Shaliushui Formation are a potentially valuable archive of late Devonian palaeoclimates of northwest China.