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The origin and emplacement of Lower Paleogene Bauxites discussed here relies on recent perceptions concerning the development of the collision-induced diachronous discontinuity surfaces in certain parts of the Adriatic-Dinaric Carbonate Platform (ADCP), and in the Istrian Peninsula in particular. This process, related to forebulge uplift during the initial stages of the orogeny, is amply recorded in the geochemical signature of related Istrian Lower Paleogene bauxites (ILPB) as was shown in previous investigations. As their self-evident extension, due attention is paid here to the effects of a flexural bulge in another part of the platform with its own suite of Lower Paleogene bauxite deposits (LPB), notably in its Dinaridic unit. Explication of the typical patterns of bauxite formation is grounded in the development of discriminant function models based on the Compositional Data (CoDa) analysis of geochemical data. This method provides the solid ground for separation of the various a priori defined bauxite groups deposited in the different subaerially exposed platform palaeoenvironments. In the final analysis, the discriminant model characteristic for the westernmost compartment of the Adriatic SW Unit (Istrian Karst) is cross-compared with the analogous model of the entire ADCP taken from earlier investigation but reconsidered within the CoDa framework. It is done with the purpose of assessing the geochemical correspondence between the two event-markers (ILPB and LPB) and clarifying the nature of the pertinent tectonostratigraphic constraints. The computer models show that the forebulge unconformity is not a widespread phenomenon, being distinctly recognized only in the Istrian part of the ADCP.

Croatian bauxites are long known for their chemical and physical diversity arisen from their characteristic origin and emplacement within the area of the Adriatic–Dinaric carbonate platform (ADCP). They include eight horizons spanning the period between the Upper Triassic (Carnian) and the Miocene, formed on subaerially exposed platform paleoenvironments. The bauxite genesis is recorded in the bauxite geochemical composition as a unique signature of tectonostratigraphic evolution of the different parts of the Croatian Karst, including, for example, the forebulge unconformity typical for the Istrian area. In this work, an explanation of the typical patterns of bauxite formation is based on the construction of a discriminant function model (DFM) resulting from the compositional data (CoDa) analysis of bauxite geochemical data (major and trace elements). The model shows that the greatest part of the variation contained in the analyzed bauxite data (the first discriminant function, DF1) is associated with systematic alteration of geochemical composition in time, emphasizing characteristic decrease in clay component and gradual enrichment in heavy metals from oldest (Upper Triassic) to the youngest (Miocene) bauxites. In the general scheme, particular bauxite horizons represent standalone groups (Upper Triassic) while others form clusters showing increase and/or decrease of a particular set of elements signaling the changes in environmental conditions during the considered geological history of ADCP. Other discriminant functions (DF2 and DF3) also contribute to the all-inclusive distinction between the eight a priori defined bauxite groups discriminated by the characteristic set of geochemical variables where DF2 typically refers to the process of desilication, while DF3 to that of deferralitization.