ASTROCHRONOLOGICAL COMPARATIVE STUDY OF THE EARLY JURASSIC TOARCIAN OCEANIC ANOXIC EVENT
The Early Toarcian Oceanic Anoxic Event(T-OAE)during the Early Jurassic Period is marked by a major negative carbon isotope excursion(nCIE),mass extinction,marine transgression,and global warming.This significant shift in the Early Toarcian paleoclimate system is directly linked to the global carbon cycle.The nCIE associated with the T-OAE displays similar carbon isotope excursion characteristics across many locations,and there is evidence that marine carbon isotope variations recorded astronomical forcing signals.However,due to the uncertainties in the chronological constraints of the T-OAE across various global sections,understanding the causal mechanisms of this global event remains limited.To address these issues,this study selected twelve profiles,including the Peniche profile in Portugal(39° N,9°E),the Mochras core in Wales(54°N,4°E),the Yorkshire profile in England(51°N,6°E),the Denkingen core in Germany(48°N,8°E),the Zazriva profile in Slovakia(49°N,19°E),the Sancerre core in France(47°N,2°E),the East Tributary profile in Canada(51°N,115°W),the Sakuraguchi-dani profile in Japan(35° N,131°E),the Arroyo Lapa North(35°S,69° W)and the Arroyo Lapa South(39°S,70° W)profiles in Argentina,and the Asientos profile(27°S,69° W)and the El Peñon profile(28° S,69°W)in Chile.Cyclostratigraphic analysis methods were used to reanalyze the carbon isotope sequences from these twelve T-OAE sections across different regions worldwide.The results indicate that the onset times of the sections studied fluctuate between 182.50 Ma and 183.05 Ma,with six significant carbon isotope cycles recorded in the nCIE of each section.The duration of the Toarcian in the Western Tethys Ocean is estimated to be between 600 ka and 670 ka.In the northeastern and central Panthalassa Ocean,the duration is between 610 ka and 620 ka,and in the southern Panthalassa Ocean,it is between 610 ka and 640 ka.By comparing the Toarcian sections from the Western Tethys Ocean,northeastern and central Panthalassa Ocean,and southeastern Panthalassa Ocean,the study reveals different responses of the global carbon cycle during the T-OAE period.Volcanic activity provided nutrients to the marine environment,carbon cycle perturbations accelerated the hydrological cycle,and the intensity and direction of monsoons affected local biogeochemical cycles and primary productivity.Therefore,during the T-OAE,the geographic location and sedimentary environment of the profiles,the activity of the Karoo-Ferrar volcanism,carbon cycle perturbations,and monsoon activity all influenced the response time and duration of the T-OAE event to varying degrees.This caused heterogeneity in the start and end times and duration of the T-OAE across different profiles.The intense phase of the carbon isotope negative excursion during the T-OAE roughly corresponds to the maximum periods of short eccentricity modulation cycles or the transition period from larger to maximum eccentricity.During periods of maximum eccentricity,climate variations are pronounced,often indicative of strong monsoonal climates.Enhanced monsoon activity typically implies a significant increase in rainfall,leading to increased surface runoff.This runoff washes more terrestrial sediments and nutrients into rivers and eventually into the oceans,enhancing primary productivity and promoting vigorous biological growth.This process consumes large amounts of dissolved oxygen,triggering anoxic events and causing mass extinctions.This indicates the coupling relationship between cycles in geological records and astronomical signals,revealing the high sensitivity of Earth's climate,volcanic activity,and monsoon systems to changes in Earth's orbital cycles.This study deepens the understanding of the triggering mechanisms of the Toarcian Oceanic Anoxic Event(T-OAE)and provides new insights into the integrated use of stratigraphic data and astronomical models to explore paleoclimate changes.
Toarcian Oceanic Anoxic Event(T-OAE)Earth orbital periodastronomical tuningMilankovitch cycles
万方数据
维普
