PROVENANCE OF LOWER CRETACEOUS DEPOSITS OF THE WEST ERN PART OF THE SILESIAN NAPPE IN POLAND (OUTER CARPATHIANS): EVIDENCE FROM GEOCHEMISTRY

The turbiditic to hemipelagic, fine-grained deposits of the Hradiste Formation(Hauterivian, 132 Ma) to the Lhoty Formation(Albian-Cenomanian, 99 Ma) in the west ern part of the Silesian Nappe (Polish Outer Carpathians) were studied mineralogically and geochemically to deter mine if the main factors con trol ling the chemistry of the sedimentary material can be attributed to provenance, or to post-depositional processes. A high degree of weathering of the source rocks is in dicated by the chemical index of alteration (CIA) that varies from 75.98 to 89.86, and Th/U ratios (similar to 4 with outliers at 1.85 and > 6). The co-occurrence of rounded and unabraded grains of zircon and rutile, the enrichment in Zr and Hf, as well as the high Zr/Sc ratios suggest that the Hradiste and Verovice Formations contain recycled material. Plots of La/Th versus Hf and Th against Sc show that samples occur in the field of felsic and mixed felsic/basic sources. On a ternary La-Th-Sc diagram, all of the sediments studied are re fer able to the continental is land-arc field. The European Plate, as an alimentary area, has a mosaic structure consisting of Cadomian and Variscan elements. The Proto-Silesian Ridge was detached from the continent, be cause of rifting. There fore, it could have cor responded to a continental is land arc. The concentrations of Fe and trace metals (e. g., Mo, Au, Cu) in the Verovice Formation and silica and potassium additions to the Verovice and Lhoty Formations, as well as the fractionation of REE, and Nb, Ta, Zr, Hf, and Y can be explained by the action of basinal brines. The fluids were of hydro thermal origin and/or were re leased, owing to the dewatering of clay minerals. Diagenetic processes could have exerted a greater influence on sedimentary rock chemistry than the provenance and sedimentary processes. A distinction be tween primary, terrigenous elements and those changed diagenetically is necessary for the reliable determination of provenance.