Stable Isotope Preservation in Ancient Carbonate Rocks and Its Geological Applications

This paper discusses the preservation of stable isotopes from carbonate rocks based on stable isotope analysis at Permian-Triassic boundary sections in South China, and from the top and bottom of the‘mung bean rock’ units between the Lower and Middle Triassic. The results are examined in combination with the regional geological setting and stratigraphy, palaeontological features, and sedimentary facies and environments. Though initial isotope values from open marine, sabkha and salt lake deposits show some variation during early submarine diagenesis, epidiagenesis, neometamorphism and anadiagenesis, the original isotope signature generally remains clearly preserved. For example, δ¹³C values remain unaltered, δ¹⁸O values, however, show great changes. The unbalanced variations in δ¹⁸O values may be attributed to dedolomitisation and desulphatisation processes. It is important not to ignore this factor when applying stable isotope analysis methods in ancient carbonate rocks to stratigraphic devesion, and the reconstruction of sedimentary environments and sea-level fluctuations.