Influences of fluvial and aeolian processes on palaeosols formation in Privlaka, Croatia

Abstract

The study was carried out on the pedo-sedimentary complex in Croatia's coastal region to describe the palaeosols' pedological, micromorphological and mineralogical properties and compare them with the recent soils. The field investigations comprised the definition, description and sampling horizons of an 8 m thick sequence of glacio-fluvial deposits, palaeosols and recent soils. Besides the field description and analyses of physico-chemical soil properties, the mineralogical composition was determined by XRD and soil thin sections were studied with a polarising microscope. The palaeosols are predominantly reddish in colour and have a considerable amount of carbonate concretions and rhizoconcretions, whereas the recent soils are brownish and without secondary carbonates. Large cracks filled with sandier material at the bottom of the sequence. The palaeosols are characterised by a higher percentage of sand particles and a lower percentage of silt particles than the recent soil. The recent soil has higher pH values and SOC contents, and lower CaCO₃ contents than the palaeosols. The mineralogical composition of the palaeosols and the recent soil consists of quartz and calcite with feldspars (K-feldspar and plagioclase), goethite and clay minerals (kaolinite and mica). They differ in the presence of chlorite, which was recorded only in the recent soil, while Ti- and Mn-oxides, and Ch-hydroxides were only found in the palaeosols. The micromorphology does not show any glacial nor periglacial features, but a reddish recarbonated groundmass in the palaeosols and signs of clay illuviation inside some of the coarse fragments (quarztites), indicating that they are formed by pedosediments of terra rossa from the Dinaric Alps. The results show that the original decarbonated and rubefacted material was subjected to recarbonation by mixing with underlying limestones and by younger carbonated materials deposited on top, probably under arid conditions generating deep fissures. These processes agree with the formation of terra rossa under a warm and humid climate in which stable minerals (kaolinite, Fe- and Mn- oxides and hydroxides) predominate in the sediments under oxidating conditions. In contrast to the palaeosols, the recent soil has a mineral composition that is more typical of a climate with cold, dry winters and warm, humid summers.