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Core M1‐A from Mljet Island, Croatia, was retrieved from a submerged sinkhole to investigate tephra and reconstruct past sea levels. Eleven tephra layers were found, out of which six are macroscopically visible, while five are cryptotephra. For two of the tephra layers, glass shard concentrations were below the critical amount necessary for reliable analysis, while two more originated from a stratigraphical interval likely disturbed by drilling operations. Major and trace element compositions of glass shards were determined by wavelength dispersive spectroscopy (WDS) using an electron microprobe analyser (EMPA) and by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS). The tephra discrimination relied on a novel approach based on a multivariate analysis of element selection and the use of log‐ratio scatterplots and common bivariate plots. The results enabled correlation of five tephra to known eruptions originating from Somma‐Vesuvius and Campi Flegrei. Specifically, we identified Avellino Pumice, Mercato, Agnano Monte Spina and Neapolitan Yellow Tuff, extending known distributions for Avellino and Agnano Monte Spina. Moreover, our findings possibly support an earlier proposition that Agnano Monte Spina tephra originated from two eruptions with a pause of a few decades in between. Based on the tephra correlations and radiocarbon dating, an age‐depth model was compiled that provided chronological constraints for the sea level during the formation of the lake (10.7 cal. ka BP, 49 m b.s.l.) and sea intrusion (2.3 cal. ka BP, 2.5 m b.s.l.).

Definition of geochemical background in exploration and environmental geochemistry has always been regarded as contingent upon scale and investigated locality but mostly under assumption that hosts of processes that produce the data more or less conform individually to Gaussian law of ''central tendencies''. Recently, understanding of pedogenesis as synergetic process being characterized by non-linear dynamics renders thermodynamic approach directly applicable in assessment of geochemical thresholds, with concepts of linearity and normality set alongside in solving the problems of soil geochemistry. Seen from this perspective the work is an attempt to relate conceptual fundamentals of non-linear dynamical theory to basic statistical methods in order to elucidate the nature and origins of element subpopulations hidden in the original geochemical data from the soils of Istrian Peninsula (western Croatia). To this purpose the two major groups of soils were selected for analysis depending on the type of bedrock as one of the main soil-forming factors. Geochemical data were subjected to the trimming procedure by which the outliers were removed from the total data collective and attributed to non-linear causes precluding simple cause-and-effect relationships as the sine qua non of Gaussian distribution. Geochemical background is then defined as the normal range of data of the remaining (trimmed) dataset indicating the ''thermodynamic branch'' of the specific soil processes as opposed to outliers being described as dissipative structures.