Evidence for an alternative concept of the Finow soil formation

Abstract

Paleosols can widely be used as chronometric markers, and the so-called Finow soil is reported to be a supraregional marker in the sandy deposits in northern central Europe and Siberia. The Finow soil is thought to be associated with pedogenesis between the Allerød and the Younger Dryas with subsequent fossilization by eolian activity. The formation of the 5- to 15-cm-thick brownish Finow soils is often explained by brunification and some minor illuviation of clay. Although the Finow soil has been described at several distant sites, the lack of an entire soil sequence consisting of a topsoil and a subsoil recently raised doubts about the formation of the Finow soil.We present a micromorphological approach together with grain size analysis from two sites in northeastern Germany (Glashütte and Jänschwalde in Brandenburg) and one site in Poland (Błędno) where purported Finow soils have been reported and were dated in earlier studies to investigate the processes that led to the formation of the Finow soil.Our findings show that the three studied Finow soils are characterized by clay migration, rather than brunification, and that the Finow soils are situated below well-drained sandy deposits at hydrological barriers. Whereas at Glashütte, the soil organic matter of an Usselo soil acts as a hydrological barrier, at Jänschwalde and Błędno, changes in the granulometry of the sandy deposits presumably act as a hydrological barrier. At Jänschwalde, the illuvial horizon is the least developed of the three sites and the eluvial horizon has a depth of only 40 cm, but at Glashütte, the Finow soil below the 330-cm-thick sandy deposit shows extensive features of clay illuviation. Hence, we propose that the thickness of the eluvial horizon strongly influences the degree of clay illuviation in the Finow soil. Further, we propose that due to the well-drained character of the sandy substrates, the formation of the Finow soil is limited to the supply of clay for the clay migration rather than being time limited. Therefore, the clay illuvial features of the Finow soil are indicative of neither the suggested pre-Holocene soil development nor of the lack of the eluvial and topsoil horizons of the supposedly truncated Finow soil due to late Quaternary soil erosion or landscape activity. Indeed, the clay illuviation that causes the formation of the Finow soil can visually accentuate sedimentological changes, but because the clay illuviation is a post-sedimentary process, the indicative potential of the Finow soil is site specific. Hence, we conclude that the use of the Finow soil as a supraregional chronometric or pedostratigraphic marker should be avoided.