PRINCIPAL COMPONENTS ANALYSIS OF GEOCHEMICAL DATA AND IMPLICATIONS FOR THE PROVENANCE OF CLAY DEPOSITS FROM THE SILE REGION, NORTHWEST TURKEY

Principal components analysis (PCA) was used to assess variance a geochemical dataset from a range of rock types in the Sile Region. Cretaceous andesites and flysch deposits and Paleozoic shale were gathered from near the clay deposits as potential parent rocks. These kaolinite rich, lens-shaped, and coal-bearing clay deposits occur in Neogene lacustrine basins. Considered in this study is the modification of signatures due to ciritcal zone processes at different periods of geologic time, including modern changes. Data were log transformed and processed in R to fulfill multivariate normality and applied to major oxides and rare earth elements (REE). PCA of major oxides (PCA1) demonstrates that 82% of the variation was determined by the first three principal components (PC1, PC2,PC3). High loadings for PC1 are Si, Ca, Al, Ti, and LOI, reflect weathering processes and formation of kaolinite rich clays. High loadings for PC2 are Mn, Fe, Na, Si and Ti imply redox and hydrolysis weathering reactions operate under different Eh-pH conditions. PC3 has strong loadings for Mn, Mg, K, and Ca, which is related to the presence of illite and smectite type clays. Ti serves as a conservative tracer, suggesting that with increasing weathering volcanic and shale rocks are becoming more similar to the clay deposits. REE assemblage PCA (PCA2) shows that 94% of the variation was explained by the first two principal components (PC1 and PC2). The high loading element group for the PC1 is Tb, Dy, Ho, Er, Tm, Yb and Lu have a strong negative correlation with the PC1 as well. PC2 has high loadings for Ce, Pr, Nd, Sm, Eu. Ce has strong positive correlataiın with the PC2 while others are negatively correlated. This also implies different Eh- pH conditions experinced during progressive cycles of critical zone weathering to concentrate REE into the clays. Shale samples correlate well with most of the clays deposits. Highly weathered volcanic rocks have a strong correlation too. There is less correlation between REE signals in the flysch deposits, but they still may contribute to clay formation. PCA reveals that genesis of the clay deposits might be related to multiple source rocks, transported from within the vicinity. Further investigations by more sampling and examining mineralogy by X-ray diffraction and optical microscopy would lead to better interpretations.