The Middle Jurassic is characterized by major plate tectonic changes,variable atmospheric CO2 concentrations(pCO2),and climate oscillations in both marine and terrestrial realms.However,the limited evidence from the terrestrial sedimentary records hampers a comprehensive understanding of global climate state in this period.Well-exposed strata of the Shaximiao Formation in the Sichuan Basin,Southwest China,preserve successions of paleosols that offer the possibility of evaluating the terrestrial paleoclimatic changes during the Middle Jurassic(Bajocian to Callovian).A total of 151 paleosol profiles belonging to four paleosol types(Entisol-like,Inceptisol-like,Aridisol-like and argillic Inceptisol-like paleosols)were identified and characterized.The quantitative paleoclimate reconstructions based on the bulk geochemistry of paleosol horizons and depths of carbonate nodules indicate a generally semiarid-subhumid climate alternating with arid-humid and cool/warm-temperate climates during this time interval.This dynamic climate terminated in a dry,subhumid,humid/perhumid and superhumid moisture regime characterized by steppe/wet or rain forest floral provinces.We suggest that these climatic fluctuations may have been related to global geodynamic(e.g.,the fragmentation of Pangea,"megamonsoonal"circulation,and bolide impacts)and regional tectonic uplift(e.g.,the uplift of the Longmenshan Mountains in the South China Block)during the Middle Jurassic.The pCO2 estimates suggest relatively low pCO2 levels within the range of～100 ppm-～890 ppm during the Bajocian to Callovian.Our results coincide with the threshold for the initiation of glaciation and may help to explain the occurrence of cool intervals in the generally warm Jurassic.These pCO2 fluctuations,which coincide with paleotemperature variations in the low paleolatitudes of the Northern Hemisphere,are possibly attributable to global geological events(e.g.,wildfire events,eustatic sea-level oscillations,and the transient develop-ment of glaciations)in the Middle Jurassic.

Jun Li;Cheng-Min Huang;Guo-Lin Yang;Yuan-Yuan Pan;Xing-Yue Wen

College of Urban Environment,Lanzhou City University,Lanzhou 730070,Gansu Province,China;Department of Environmental Science and Engineering,Sichuan University,Chengdu 610065,Sichuan Province,China;BaiLie School of Petroleum Engineering,Lanzhou City University,Lanzhou 730070,Gansu Province,China;School of Environmental Science and Engineering,China West Normal University,Nanchong 637002,Sichuan Province,China

古地理学报（英文版）

[1]Jun Li;Cheng-Min Huang;Guo-Lin Yang;Yuan-Yuan Pan;Xing-Yue Wen-.Middle Jurassic climate oscillations from paleosol records of the Sichuan Basin,SW China)[J].古地理学报（英文版）,2022(01):97-122

Shaximiao,Callovian,Inceptisol,Aridisol,subhumid,perhumid,superhumid,megamonsoonal,bolide,Longmenshan,paleolatitudes,eustatic

Middle,Jurassic,oscillations,from,records,Sichuan,Basin,SW,China,characterized,by,major,plate,tectonic,changes,variable,atmospheric,concentrations,pCO2,both,marine,terrestrial,realms,However,limited,evidence,sedimentary,hampers,comprehensive,understanding,global,state,this,period,Well,exposed,strata,Formation,Southwest,preserve,successions,paleosols,that,offer,possibility,evaluating,paleoclimatic,during,Bajocian,total,profiles,belonging,four,types,Entisol,like,argillic,were,identified,quantitative,paleoclimate,reconstructions,bulk,geochemistry,horizons,depths,carbonate,nodules,indicate,generally,semiarid,alternating,cool,warm,temperate,climates,This,terminated,dry,moisture,regime,steppe,wet,rain,forest,floral,provinces,suggest,these,fluctuations,may,have,been,related,geodynamic,fragmentation,Pangea,circulation,impacts,regional,uplift,Mountains,Block,estimates,relatively,low,levels,within,range,ppm,Our,results,coincide,threshold,initiation,help,explain,occurrence,intervals,These,which,paleotemperature,variations,Northern,Hemisphere,are,possibly,attributable,geological,events,wildfire,sea,transient,develop,glaciations

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