Geochemistry for the pliocene carbonaceous rocks from southeastern denizli: Provenance signature and tectonic setting

Abstract

Carbonaceous rocks (bituminous shale, coal, clayey coal, coaly claystone etc.) is an aggregate of heterogeneous materials composed of organic and inorganic substances. The study area is located on the northern boundary of the Çameli-Acıpayam basin (in Southwestern Turkey), filled by thick Neogene sediments comprising local coal/carbonaceous rocks. This study presents geochemical properties of carbonaceous rocks collected from the Yeşilyuva town. In this concept, their major and trace element distribution and mineralogical compositions, trace element multi-element patterns were examined to characterize paleo-environment conditions and provenance properties. The total organic carbon (TOC, wt%) content of the Yeşilyuva samples varies from 8.8 wt.% to 43.8 wt.%, pointing excellent source rock. Quartz, clay+mica minerals (mostly illite and lesser amount of smectite, chlorite and kaolinite), feldspar, opaque minerals (pyrite and ilmenite) have been determined as mineral matters in XRD analysis. In NASC normalized diagram, there are clear enrichments in Na, Mg, Al, P, K, Ca, Ti, Mn, Fe, Ni and Y elements, whereas depletions in Rb, Sr, Zr, Ba and La elements. The elemental patterns of samples exhibit clear depletions in Sr, Rb, Ba, Pb, Zr, Sc, Hf, Th, U, Cu and Zn elements, while enrichment in Co, Ni, Cr, and Nd elements in PAAS normalized diagram. Although carbonaceous rocks are close to NASC and PAAS values, there are lesser or/negligible amount of depletions in LREE ((La/Sm)NASC=0.48-1.27; ((La/Sm)PAAS=0.39-1.03), HREE ((Sm/Lu)NASC=0.51-1.30; ((Sm/Lu)PAAS=0.46-1.18). Furthermore, all samples have slightly positive Eu anomalies ((Eu/Eu*)NASC=0.61-0.91; (Eu/Eu*)PAAS=0.88-1.38), reflecting alteration of plagioclase in the source rocks. Certain trace element ratios such as Cr/V (3.27-21.49), Y/Ni (0.001-0.0.014), La/Sc (0.17-2.15), Th/Sc (0.08-0.42), Th/Co (0.005-0.037), Th/Cr (0.001-0.004), and Eu/Eu* (0.17-0.29) indicate mafic-ultramafic source, derived from oceanic crust. The carbonaceous rocks have low ICV (3.3-5.4), K2O/Al2O3 (0.034-0.089) and K/Cs (68.41-1660.32) values, low-to-moderate CIA and PIA (24.61-71.49; 23.37-72.75, respectively) values, suggest relatively moderate weathering of the source rock. The SiO2/Al2O3-K2O/Na2O, La-Th-Sc, Th-Sc-Zr/10, K2O-Rb, Th/Sc-Zr/Sc and 15*Al2O3-Zr-300*TiO2 diagrams suggest deposition in active continental margin setting, under humid climatic conditions. Furthermore, all data imply poor sorting and rapid deposition of the sediments without important recycling processes. © SGEM2019.