Coupled Variation of C and Mg Isotopes in the Middle to Late Cambrian Carbonate Ramp Deposits of the Machari Formation in the Yeongweol Area, Korea

Abstract:

Stable carbon and magnesium isotopes in carbonates can be a useful proxy for reconstructing the plaeo-oceanic condition because C isotope tends to reflect anoxic or oxidation state of ocean while Mg isotope does weathering regime. Carbonates from the Machari Formation in the Yeongweol Area, South Korea, deposited in the middle to outer carbonate ramp of the Middle to Late Cambrian in age, were investigated to find any correlation between two geochemical proxies. The stratigraphic interval displaying the Steptoean positive carbon isotope excursion (SPICE) corresponds to the interval of negative excursion of δ²⁶Mg values. The SPICE interval shows δ¹³C values ranging from +0.6 to +4.4‰, and δ²⁶Mg values from −3.0 to −1.0‰. The correspondence of the SPICE with the interval of negative δ²⁶Mg excursion could be caused by the lowering of sea level which increased the rate of input of terrigenous sediments. In short, high rate of influx of terrigenous sediments might have enhanced the rate of burial of organic matter which in turn resulted in the increase of δ¹³C values of ocean and carbonates, while low δ²⁶Mg values might have been caused by regressive sea level which resulted in the enhanced chemical weathering