GEOCHEMICAL CHARACTERISTICS OF MIDDLE CAMBRIAN-EARLY ORDOVICIAN LIMESTONE AND PALEO-OCEAN RECONSTRUCTION BASED ON δ¹⁸O_SMOW, ⁸⁷Sr/⁸⁶Sr AND RARE EARTH ELEMENTS, TARIM BASIN

In the middle Cambrian to lower Ordovician of Tarim Basin, occurs a little limestone, which is the studied object in this research, aimed at seawater geochemical reconstruction. Geochemical results showed that a linear correlation was demonstrated between the oxygen isotope values and the MgO% content, which indicates that dolomitization will lead to higher oxygen isotope values. The intercept of the line on the δ¹⁸O axis is -8.6‰, representing the oxygen isotope value of original limstones, and the oxygen isotope value of paleo-seawater can be calculated with value of -8.9‰. The average ⁸⁷Sr/⁸⁶Sr value is 0.708 918, which can be considered as the value of paleo-seawater. In the PAAS-normalized Rare Earth Elements diagram, LREE-enriched pattern can be seen in the studied limstones, which might represent the REE characteristics of paleo-seawater.