Carbon Isotope Compositions In Mesoproterozoic Samples From North China Platform And Paleo-environmental Changes

More than 600 Mesoproterozoic samples were collected from three drill-cores,JQ1,JQ2 and JQ3 in the northern Hebei Depression of North China Platform.Geochemical analyses including carbon-isotope,oxygen-isotope and TOC were carried out about those samples.According to carbon isotopic data,high-resolution Mesoproterozoic carbon isotope curves were constructed,and Mesoproterozoic atmospheric CO₂concentrations were calculated.This study may provide new insight into carbon cycle and environmental evolution in the Mesoproterozoic.?¹³C values of carbonates vary at the range of-3.1⁺2.8‰in the Mesoproterozoic.In general,those Mesoproterozoic samples show relative stable?¹³C values,most of those vary at the range of 0±1‰.The carbon isotopic records from North China Platform can be correlated with those in the world.Carbon isotopic records indicate that the perturbations of carbon cycle remain in a small range,and a stable environment developed in the Mesoproterozoic.The Mesoproterozoic atmospheric CO₂ concentrations estimated from carbon isotope data show higher levels than modern atmosphere's level.If the surface seawater temperature was 25?in the Mesoproterozoic,atmospheric CO₂concentrations changed at the range from 548 ppm to 4099 ppm with an average of 2150 ppm in the Gaoyuzhuangian,atmospheric CO₂ concentrations varied at the range from 341-2489ppm with an average of 1072 ppm in the Wumishanian,atmospheric CO₂ concentrations varied at the range from 492-1313 ppm with an average of 878 ppm in the Hongshuizhuangian,and the CO₂ concentrations were at the range from 476 ppm to3895ppm with an average of 1117 ppm in the Tielingian.If the Mesoproterozoic solar luminosity is close to that on morden Earth,high atmospheric pCO₂ levels suggest a greenhouse environment could exist in the Mesoproterozoic.If the solar luminosity on the early Earth was lower,high atmospheric pCO₂ levels could play an important role in compensating for lower solar luminosity and maintaining the normal temperature on the Mesoproterozoic Earth's surface.