Abstract
Abstract. Climatic oscillations have been developed through the (Early) Jurassic from marine sedimentary archives but remain unclear from terrestrial records. This work presents investigation of climate-sensitive sediments and carbon and oxygen isotope analyses of lacustrine and pedogenic carbonates for the Early Jurassic Ziliujing Formation taken from the Basin in southwestern China. Sedimentary and stable isotope proxies manifest that an overall secular (semi)arid climate dominated the Sichuan Basin during the Early Jurassic, except for the Hettangian. This climate pattern is similar to the arid climate in the Colorado Plateau region in western North America but is distinct from the relatively warm and humid climate in northern China and at high latitudes in the Southern Hemisphere. The estimated atmospheric CO2 concentration (pCO2) from carbon isotopes of pedogenic carbonates shows a range of 980–2610 ppmv (∼3.5–10 times the pre-industrial value) with a mean of 1660 ppmv. Three phases of pCO2 (the Sinemurian 1500–2000 ppmv, the Pliensbachian 1000–1500 ppmv, and the early Toarcian 1094–2610 ppmv) and two events of pCO2 rapidly falling by ∼1000–1300 ppmv are observed, illustrating the pCO2 perturbation in the Early Jurassic. The perturbation of pCO2 is compatible with seawater temperature and carbon cycle from the coeval marine sediments, suggesting a positive feedback of climate to pCO2 through the Early Jurassic.
Highlights
Global paleotemperatures were possibly 5–10 ◦C higher than present during the Jurassic period based on climate modeling results (e.g., Rees et al, 1999; Sellwood and Valdes, 2008)
The climate became dry through the Early Jurassic, manifesting as climatesensitive sediments and stable isotopes, there are two lithofacies packages reflecting two major lake stages in the grand Sichuan paleobasin (GSB)
The Early Jurassic pCO2 values show that a range between 980 and 2610 ppmv is ∼ 3.5–10 times the preindustrial value 275 ppmv and that the mean 1720 ppmv is ∼ 6 times the pre-industrial value
Summary
Global paleotemperatures were possibly 5–10 ◦C higher than present during the Jurassic period based on climate modeling results (e.g., Rees et al, 1999; Sellwood and Valdes, 2008). Data from the terrestrial realm provide important details of environmental and climatic change (e.g., Hesselbo et al, 2000; Suan et al, 2010; Jenkyns, 2010; Philippe et al, 2017), from which the oscillated climate could be observed and revealed as well.
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