Geochemical records in subaerial exposure environments in Croatia using discriminant function analysis of bauxite data

Abstract

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.

Posušje bauxites in Bosnia and Herzegovina: A source of critical raw materials and a paleoclimatic marker

“…The Jajce and Posušje bauxite deposits in Bosnia and Herzegovina are formed on the Adriatic-Dinaric carbonate platform. Eight bauxite-bearing horizons have been previously identified (Sakač, Šinkovec, 1991) and subsequently confirmed in the adjacent Croatian territory (Ilijanić et al, 2023). These horizons cover a time period from the Triassic (BX1) to the Miocene (BX8).…”

“…The well-preserved zircons in the Posušje bauxites, largely transported as volcanic ash, are in favor of the new concept for isovolumetric interaction between the carbonate bedrock and airborne material as proposed by Merino and Banerjee (2008). The model combining the terra rossa as the proto-bauxitic material with processes of karst weathering is accepted by Ilijanić et al (2023) for the Croatian bauxite deposits of the ADCP. Under this paradigm, the parent material of the Posušje bauxites can be regarded as a paleosol derived from the interaction between the carbonate rock and airborne siliciclastic material, whether eolian, volcanic, or even terrestrial in nature.…”

A time-space window between Eocene karst bauxite genesis and the first molasse deposition in the Dinaric Foreland Basin in the North Dalmatia, Croatia

“…The trace element composition (Maksimović, 1968;Maksimović,1976;Maksimović and Pantó, 1978;Deady et al, 2016;Radusinović and Papadopoulos, 2021;Tomašić et al, 2021) and content of Zr, Ga, and Cr (Özlü, 1983;Ilijanić et al, 2023) of the Frontiers in Earth Science frontiersin.org 16 bauxites in the Mediterranean belt show no genetic relationship with the calcareous basement. REEs become concentrated in bauxite deposits either by adsorption on the surface of clay-size constituents (Estrade et al, 2019) or by authigenic REE-bearing minerals crystallised during bauxitisation (Deady et al, 2014).…”