Review of Illuvial Bands Origin; What Might the Presence of Dark Brown Bands in Sandy Infillings of Archaeological Features or Cultural Layers Mean?

Abstract

The presence of lamellae (or bands) often promises an interesting sedimentary archive related to the occupation or abandonment history of a site. How exactly might such types of bands be interpreted, and how do their presence change the original primary features preserved within the archaeological structure? For this review, two archaeological sites are introduced, both distinct in many aspects, located in different climatic regions, but with the presence of bands preserved inside of the infill, as well as in the locality’s background. One site is related to the Magdalenian/Epigravettian occupation in south-western Poland, and the second related to the Neolithic occupation in central Bohemia. What connect these two localities are their permeable sandy background, presence of human occupation, and the development of the above-described textural features. Sedimentological observations supported by micromorphology and geochemistry, as well as by magnetic susceptibility, revealed that, in both localities, the presence of dark brown bands was the result of repeated illuviation due to a kind of podsolization process not necessarily related to human presence. The illuvial lamellae/bands at the Kly site probably originated during the Subboreal due to the increased humidity connected with the presence of the disturbed background of the infill in the ditch. The Sowin site displays, at the very least, two phases of origin. One of the phases is pre-dated by glacial conditions, and the second is of late glacial or Holocene origin. The origin of these features in both study sites is due to precipitated water and the movement of clay down the section, but under their different conditions. IANSA 2019 ● X/1 ● 19–28 Lenka Lisá, Aleš Bajer, Klement Rejšek, Valerie Vranová, Lenka Vejrostová, Andrzej Wisniewski, Petr Krištuf: Review of Illuvial Bands Origin; What Might the Presence of Dark Brown Bands in Sandy Infillings of Archaeological Features or Cultural Layers Mean? 20 but their appearance in other soils is not excluded. Several of the best-developed examples of soils with illuvial bands described in Holocene (as well as Pleistocene) soils are the humic podzols of the European Aeolian Sand Belt (Koster, 2009). Gerasimova and Khitrov (2012) classified similar soils located in glacifluvial sand in south western Poland. What is the process whereby the illuvial bands develop? What role does climate, natural processes, or human influence play in the origin of these features? The origin of illuvial bands is generally not well understood and it remains controversial. It seems that some “trigger” (increased precipitation – Pelle et al., 2013) activates the movement of clay, which then stops moving at a certain depth where there is some textural inhomogeneity (Bouabid et al., 1992). Another possibility is that the origin is triggered by the precipitation, but these bands start to form at the limit of the capillary water reach (Van Reeuwijk and de Villiers, 1985), or on a transition to a more calcareous zone, i.e. at a point of a distinct pH change (Schaetzl, 1992). Stefanovits (1971) suggested that illuvial bands are the result of unfavourable conditions triggered by climate. On the other hand, the same author, as well as Tsigirintsev (1968) and Ugla and Ugla (1979), propose that illuvial bands are the result of the impact of forest vegetation. Their assumption is that the clay movement is activated by a change of pH that has been triggered by the acid “waste” from conifer trees. In this scenario, active maintenance of the vegetation by humans may play a role in the origin or absence of these features. Another trigger, differing from those mentioned above, is the local hydrology (see review in Ibrahim, 2011). Here the underground water is transporting a quantity of some iron compound that may transform at one point in time (and place) and thus form the illuvial bands. The primary sedimentary accumulation of iron, and later pedological transformation of these accumulations, may also play a role in the development of these bands (Schaetzl, 2001). This paper aims to review the possible formation processes that lead to the origin of illuvial bands and, in addition, how micromorphology and geochemistry methodological tools may help with interpreting these formation processes. What might the main triggers be and what exactly might the presence of illuvial bands mean for interpretation of human presence and the environment of a site?