engleski

The Pakoštane loess plateau revisited; dating, sedimentological, mineralogical and geochemical characterization

Loess and loess-like deposits represent valuable material of past climate change in areas where long-term terrestrial records are scarce, such as Dinaric karst on the Eastern Adriatic coast. Quaternary sediments of the so-called Pakoštane Loess Plateau (Marković-Marjanović, 1975) are exposed on the steep vertical profiles on the coast and extend 1 km in length east from the town Pakoštane in central Dalmatia, Croatia. Previously, it was described based on the lithological composition as the sediment of eolian origin (Marković-Marjanović, 1975). Here, we present the time frame and the environmental significance of variations in the magnetic susceptibility (χ), frequency-dependent magnetic susceptibility (χfd), rock-magnetic data, the grain size, clay and heavy mineral and geochemical composition of the sediment profile. The sediment succession developed on limestone bedrock consists of red paleosol, brown paleosol, sand, conglomerate, loess and topsoil. It has been dated by the optically stimulated luminescence (OSL) method to the marine isotope stages MIS 4, 71.2 ± 5.9 ky BP (base of the loess). Brown paleosol and sandy deposits below conglomerate indicate ages between 122.5 ± 9.3 and 203 ± 18 ky BP. Our results indicate that the paleosol and loess deposits consist of both detrital dust and material produced during pedogenesis. An integrated analysis of records of magnetic susceptibility and remanence data (χ, χfd, ARM, SIRM) indicates the magnetic enhancement in red and brown paleosol compared to the rest of the profile, as well as higher clay content. The proportion of the clay fraction decreases upwards, suggesting a relatively drier and colder climate. Bulk grain sizes are compared to the non-carbonate fraction, which showed that upper parts of the loess profile belong to fine-sand fraction, while lower loess to the coarse-grained silt fraction. Clay and heavy minerals reveal the similar composition of paleosol and loess deposits and similarity to the loess deposits on the Island of Susak. The presence of calcite suggests reduced weathering. The REE distribution patterns of the loess and paleosol samples are remarkably similar in shape, with enriched LREE and fairly flat HREE profiles and clear negative Eu anomaly. These chemical characteristics provide further evidence for eolian sedimentation of the loess deposits. Determination of Pakoštane loess plateau as eolian material from the river Po, as the well-known loess on the Island of Susak (northern Adriatic Sea), would make it an important site as the southernmost loess in Croatia.

loess, Adriatic Sea, Pakoštane platou, geochemistry, magnetic minerals

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