Geochemistry and Pb Isotopic Proof for Sources of Heavy Metal(Loid)s in Late Cretaceous Sandstones From Eastern Pontides (NE Turkey)

Abstract

Upper Cretaceous sedimentary rocks are widely exposed around Trabzon, Giresun and Gümüşhane in the eastern Pontides. The sedimentary rocks are mainly composed of sandstones and marls, and the thicknesses of these rocks range from 170 m to 400 m. This paper focused on Late Cretaceous sandstones of Trabzon, Giresun and Gümüşhane regions to identify the concentrations, sources, deposition environment and conditions of certain heavy metal(loid)s (Zn, Pb, Cu, Ni, As, Co, Mo and V). Enrichment factor (EF), geo-accumulation index (Igeo), Pollution index (Pi), Pollution load index (Pln), Pb isotope and multivariate statistical analysis were performed to elucidate the pollution levels and sources. The mean concentrations of Zn, Pb, Cu, Ni, As, Co, Mo and V were 16.5, 10.8, 9.4, 13.2, 2.1, 4.4, 0.2 and 21 mg/kg, respectively in the Trabzon area, 35, 5.8,18.8, 102, 3.2, 18.6, 0.5 and 109 mg/kg, respectively in the Giresun area, and 36, 8.9, 14.7, 82, 3.9, 16.9, 0.3 and 106 mg/kg, respectively in the Gümüşhane area. In general, the evaluation indices exhibited that the sandstones were moderately polluted by As in the Trabzon area, and strongly polluted by Ni and As, moderately polluted by Co and V in the Giresun and Gümüşhane areas. The results of multivariate statistical analyses indicated that As and partly Pb might be originated from anthropogenic sources, whereas other metals were derived from geogenic origin. Lead isotopic analysis demonstrated two characterized signatures of the pollution sources in the sandstones, one related to geogenic origin and the other to coal, gasoline and pesticides. The sandstones were deposited in transition – marine environment under oxic – weak oxic conditions and paleoclimatic conditions ranged from arid to moist during Late Cretaceous period.