A tropical soil (Ferralsol) identified in the northernmost part of the Mediterranean (Istria, Croatia)

Terra rossa soils on the Istrian peninsula are generally considered polygenetic relict soils. They overlie and mark the youngest subaerial unconformity in the northwestern part of the Adriatic Carbonate Platform and are sus-ceptible to erosional and redepositional processes. Terra rossa soils represent a valuable archive of information that can be used to understand present and past soil formation processes in the context of climate variability and landscape dynamics, especially in low-lying parts of the karst landscape where thicker deposits are typically found. We studied a 3 m thick terra rossa profile in a karst depression on the northernmost part of the south-western Istrian planation surface and analysed the micromorphology, physical/chemical properties, geochem-istry, bulk and clay mineralogy, and composition of heavy and light mineral fractions. The profile shows several signs of colluviation and polygenesis with clay distribution along the profile, clearly indicating lithic disconti-nuities. Kaolinization, along with iron oxide formation, is the dominant process in the studied profile. Ferrali-tization and lessivage processes were diagnosed throughout the profile, with intense clay translocation occurring despite the extremely stable soil microaggregates. In accordance with the WRB system, the profile is classified as Lixic Rhodic Ferralsol (Clayic, Aric). This implies that some terra rossa soils, previously classified as e.g. Cam-bisols or Luvisols, might actually be Ferralsols or other tropical soils (e.g. Lixisols), in which relict properties are preserved in the present climate. The finding of a Ferralsol in the study area indicates the old age of the surface of the karst depression and provides the first data on the burial history of the southwestern Istrian planation sur-face. We suggest the older Quaternary interglacials, the mid-Piacenzian Warm Period (Pliocene) and the Miocene Climatic Optimum as favourable periods for the formation of the studied soil.