Decoupled δ^(13)Ccarb and δ^(13)Corg records at Triassic–Jurassic boundary interval in eastern Tethys: Environmental implications for spatially different global response

摘要

Althoughδ^(13)C data(eitherδ^(13)Ccarb orδ^(13)Corg)ofmany Triassic–Jurassic(T-J)sections have been acquired,pairedδ^(13)Ccarb andδ^(13)Corg from continuous T-J carbonate sections,especially in eastern Tethys,have been scarcely reported.This study presents paired and decoupledδ^(13)Ccarb andδ^(13)Corg data from a continuous T-J carbonate section in Wadi Naqab.The T-J Wadi Naqab carbonate section,located in United Arab Emirates,Middle East,represents tropical and shallow marine sedimentation in eastern Tethys.At the T-J boundary interval,an initial carbon isotope excursion(CIE)is observed with different magnitude of isotope excursion and timing inδ^(13)Ccarb andδ^(13)Corg,while subsequently a positive CIE is only distinct inδ^(13)Ccarb.Based on petrological,carbon isotope,Rock-Eval and elemental analyses,theδ^(13)Ccarb is thought to record marine inorganic carbon,and theδ^(13)Corg to record terrigenous organic carbon.Therefore,the pairedδ^(13)Ccarb andδ^(13)Corg herein potentially document simultaneous changes in T-J atmospheric and marine settings of eastern Tethys.Their decoupled behavior may likely be caused by different changes or evolution of carbon pool between marine and atmospheric settings.The initial CIE present in bothδ^(13)Ccarb andδ^(13)Corg may indicate influence of isotopically light carbon release related to CAMP activity in both atmospheric and marine settings.The following positive CIE only inδ^(13)Ccarb suggests relatively steady carbon isotope composition in atmosphere,but enhanced burial of isotopically light carbon in marine settings.Furthermore,the T-J carbonates in the studied section were possibly deposited in normal and oxic shallow marine conditions.Global correlation based on the Wadi Naqab section and other T-J sections suggests spatially different T-J environmental parameters:in eastern Tethys and western Panthalassa,oxic condition,lacking organic-rich sediment,weaker ocean acidification and less influence of isotopically light carbon are more prevalent;in western Tethys and eastern Panthalassa,oxygen-depleted condition,black shales,stronger acidification and heavier influence of isotopically light carbon are more prevalent.These differences may be related to spatial distance from the CAMP or to different paleogeography.