Carbon, oxygen and strontium isotope geochemistry of the late Neoproterozoic carbonate platform deposit Hyangsanni Dolomite of the Okcheon metamorphic belt, Korea

The age-unknown Hyangsanni Dolomite is distributed in the northeastern part of the Okcheon metamorphic belt in central South Korea. It has been claimed as Early to Middle Cambrian because of the misidentified Archaeocyatha fossil in the past, but the time of sedimentation has not yet been confirmed. We performed ele-mental and isotopic analyses for the Hyangsanni Dolomite. The REE + Y patterns of the samples of the Hyangsanni Dolomite are generally flat and Ce negative anomaly is generally negligible to the extent that it ap-pears only weakly in some samples. Y/Ho values are in the range of 29-43, which is fairly lower than typical Y/Ho ratio of seawater, indicating the influence of terrigenous materials. REE and trace element geochemical discrim-ination diagrams indicate that the Hyangsanni Dolomite was deposited in a continental margin environment rather than an open ocean. We suggest that the Hyangsanni Dolomite was deposited in a rift basin connected to the ocean rather than in the passive continental margin, considering occurrence of magmatism related to con-tinental rifting within the Okcheon metamorphic belt. Carbon and oxygen isotope analysis was performed on do-lomite powders scraped off from polished surfaces unstained with Alizarin-Red-S in order to avoid the recrystallized calcite. The Hyangsanni Dolomite has delta C-13(V-PDB) values between +2.9 parts per thousand and + 6.2 parts per thousand, and delta O-18(V-SMOW) values between +11.3 parts per thousand and + 24.5 parts per thousand. These 513C values are markedly higher than the Cambro-Ordovician values, and are consistent with the Neoproterozoic values. The minimum value of Sr-87/Sr-86 ratio obtained from the Hyangsanni Dolomite also refers to Neoproterozoic, not Phanerozoic. We suggest that the Hyangsanni Dolomite belongs to the sedimentary sequence of the Neoproterozoic, along with other sedi-ments of the northeastern Okcheon metamorphic belt. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The age-unknown Hyangsanni Dolomite in the Okcheon metamorphic belt in central South Korea is thought to belong to the sedimentary sequence of the Neoproterozoic, deposited in a continental margin environment. Elemental and isotopic analyses suggest the influence of terrigenous materials and the presence of magmatism related to continental rifting in the deposition environment. The flat REE + Y patterns and Ce negative anomaly of the samples indicate a rift basin connected to the ocean.