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Principal Component Analysis around the Transitional and Sandy Dolomite boundary in the Velebit Mt. (Croatia)

The Principal component analysis (PCA) was used to identify patterns of positive and negative covariation for Transitional and Sandy Dolomite samples, such as those expected between Al and trace elements included in clay matrices, or relations between Mg and Ca and siliciclastic minerals. Al, Si, K and Ti in the TD and SD datasets show high scores on the first principal component, indicating strong positive covariation. Elements with high coefficient of determination (R2) that correlate to Al2O3 content are those which tend to stay bound with clays during weathering and erosion, and therefore can be related to the terrigenous source area. Ca, Mg, S and Sr are generally more closely related within the Transitional Dolomite and may be connected to relatively abundant fossil content in these deposits. Transitional Dolomite is characterized by the positive Ca–Mg correlation (R2 = 0.59) and low variability in Ca/Mg ratio (1.48-1.50), indicating consistency in carbonate stechiometry. Sandy Dolomite with more variable Ca/Mg ratio (1.39-1.52) and low negative Ca–Mg correlation (R2 = -0.25) indicate more diverse carbonate mineralization. The increase in Mg content and its variability in Sandy Dolomite can be explained by sediment dolomitization and diagenesis. Correlations between Ca and S content in both units are positive (R2 = 0.46 in TD and 0.30 in SD). Mg and S are uncorrelated in the TD (R2 = 0.01), but show negative correlation in the SD unit (R2 = -0.48), suggesting that Mg source is not related to organic matter. This is consistent with the lack of the Mg-calcite skeletal remains in the lowermost part of the SD unit.

Statistical correlation; Transitional Dolomite; Sandy Dolomite; Upper Permian; Velebit Mt.

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