Carbon isotope composition and its implications of Lower Cretaceous Aptian-Albian shallow water carbonates in the Cuoqin Basin, North Tibet

摘要

The δ~(13)C values of Lower Cretaceous Aptian-Albian platform-type carbonates in the Cuoqin Basin, North Tibet vary between 2.48 per thousand and 5.46 per thousand. The mean value is 3.93 per thousand. The values are not only provided with positive excursion, but also 1.17 per thousand higher than those of contemporaneous pelagic carbonates which possess pretty high δ~(13)C values. The origin is approached. During the oceanic anoxic events, a great number of organisms were rapidly buried, causing the increase of the δ~(13)C value of oceanic total dissolved carbon (TDC) and generally promoting the values of marine carbonates. After that, owing to the organisms undergoing different isotopic fractionation in the paleo-ocean with stratified structure, δ~(13)C values of shallow sea carbonate were obviously higher than those of pelagic carbonates.