Abstract
In NW Iran, the bluish grey pencil shale intercalated with thin detritic limestone and siltstone was deposited on the grey limestone of Paleocene. Based on the X-ray diffraction results, the shale forming minerals are composed of calcite, quartz, feldspar, dolomite, muscovite, hematite and clay minerals including chlorite, illite, montmorionite, kaolinite and palygorskite. The comparison of major and trace element content of the shale with the typical samples indicates abundance in CaO, Sr, and Cs and scarcity in SiO2, Al2O3, and Ba. The values of weathering indices imply moderate weathering in the source area and deposition of sediments in an area with relatively high uplift. According to the major and trace elements ratios, provenance of the shale was probably felsic and/or intermediate igneous rock. The elemental ratios and geochemical parameters values such as Ti/Zr = 38, Th/Sc = 0.55, La/Sc = 1.9, La/Th = 3.4, ΣREE = 117.34, Eu/Eu* = 0.76, and (La/Yb)N = 8.3 suggest a immature continental arc setting for the studied shale. The inferred tectonic setting for the studied shale is in agreement with the tectonic evolutionary history of NW Iran during the Upper Cretaceous-Upper Paleocene. The detailed observation of facies distribution in the NW Iran during Cretaceous-Paleocene shows that the studied shale could be supplied from the volcanic-sedimentary succession of Upper-Cretaceous in a basin related to the Neo-Tethys II subduction.
Highlights
IntroductionThe study of mudrocks is important for understanding a large portion of the earth’s sedimentary rocks, because they are 65 percent of all sedimentary rocks [14]
The detailed observation of facies distribution in the NW Iran during Cretaceous-Paleocene shows that the studied shale could be supplied from the volcanic-sedimentary succession of Upper-Cretaceous in a basin related to the Neo-Tethys II subduction
The present paper describes the mineralogy and major and trace element geochemistry of Upper Paleocene pencil shales from Goouydaraq-Goouradaraq (GG), NW Iran and discusses inferred source rocks, paleoweathering pattern and paleotectonics
Summary
The study of mudrocks is important for understanding a large portion of the earth’s sedimentary rocks, because they are 65 percent of all sedimentary rocks [14]. Illite is the predominant component of marine shales more so than in nonmarine shales [15]. Due to the fine-grained nature and impermeability, mudrocks retain most of the mineral constituents of the source rocks [16]-[18]. Th/Sc ratio and Zr/Sc ratio increase going from mafic to felsic source areas, but passive margin muds show anomalous Zr related to recycling of older sediments [5]
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