Paleoenvironmental Traces of Carbon and Oxygen Isotopes in Carbonate Rocks: An Example From Dengying Formation in Xichuan Area, Henan Province

The carbon and oxygen isotope composition of carbonate rocks is an important index for accurate analysis of the paleo-sea environment, which depends on Mn/Sr, δ 18 O > -10‰, correlativity of δ 13 C and δ 18 O and “age effect” of δ 18 O. This study reports carbon and oxygen isotope data of carbonate rocks from the Dengying Formation in the Xichuan area. δ 13 C values range -1.58‰ to 3.76‰, with an average value of 1.55‰, and δ 18 O values are -14.91‰ to -1.88‰, with an average value of -6.95‰. The δ 18 O values of three samples are less than -10‰, so they are excluded and taken to be correlative with the cracking of the Rodinia supercontinent during the Neoproterozoic. The paleotemperature range 7.40°C to 35.05°C, with an average value of 21.09°C. Paleo-salinity range 8.38‰ to 19.30‰, with an average value of 13.89‰. Z values range 127.80 to 135.03 and thus all exceeded 120, with an average value of 131.25. These calculations indicate that the Xichuan area had deposited marine carbonate rocks, with the hot and dry tropical monsoon climate, and a transgressive process overall during the Dengying age.