Polygenetic soil formation on Late Glacial Loess on the Susak Island reflects paleo-environmental changes in the Northern Adriatic area

摘要

A polygenetic soil formed on Late Glacial Loess on the Island of Susak was investigated by means of high-resolution depth approach to give pedosedimentary and palaeoenvironmental reconstructions of the Late Glacial/Holocene pedosequence. The complete polygenetic profile (A-2C1-2C2-3Btb-4Ck), defined as Eutric Leptic Regosol (Geoabruptic, Siltic, Ruptic) over Argic horizon over loess deposit, is a result of the interaction of the sediments (loess) with environmental conditions from the Late Glacial throughout the Holocene. Both normal pedogenesis and erosion/sedimentation-driven pedogenesis influenced its development. Therefore, this profile bears valuable imprints of climate, vegetation, land surface, and land use changes in this part of the Adriatic area for the time period covering the past 16 ka. The 4Ck horizon is a remnant of an A-C soil profile, whose incipient formation corresponds to a steppe-like palaeo-vegetation and a semi-humid to semi-arid palaeo-climate. The 3Btb horizon has blocky structure; common clay coatings and infillings that are related to the walls of channel macrovoids; increased CIA, Al/Si and Ba/Sr ratios due to the increase of the Al and clay contents; highest Fet, Fed, Mnt and Mnd values due to abundant redox concentrations; and specific clay mineralogy. Since the obtained age of the loess deposit (4Ck horizon) underlying the 3Btb horizon is 16.1 +/- 1.3 ka (can be correlated to the Late Glacial Maximum, i.e., OIS-2), we find that the period of the Bolling-Allerod warming might have enabled the formation of the highly weathered 3Btb horizon within a Luvisol-like soil. After the period of surface stability, a period of forest decay and surface instability took place, resulting with the erosion of the Luvisol. The 3Btb horizon was then covered with a homogeneous loess material (whose deposition can presumably be related to the Younger Dryas period), inside of which the horizons 2C1 and 2C2 are recognized. Both these horizons are negligibly affected by pedogenesis and contain artefacts. The incipient soil formation in the upper part of the profile, along with the irregular lower boundary of the A horizon and the lithic discontinuity between the A horizon and the 2C1 horizon, points to the possibility of a very recent and minor aeolian deposition. However, one should not overlook the potential impacts of human activities and/or colluvial depositions on the properties of the A, 2C1, and 2C2 horizons. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.