The Toarcian Oceanic Anoxic Event(T-OAE,∼183 Ma)is marked in the sedimentary record by a sharp negative carbon isotope excursion,thought to be causally linked to the emplacement of the Karoo-Ferrar Large Igneous Prov...The Toarcian Oceanic Anoxic Event(T-OAE,∼183 Ma)is marked in the sedimentary record by a sharp negative carbon isotope excursion,thought to be causally linked to the emplacement of the Karoo-Ferrar Large Igneous Province and the associated release of^(12)C-enriched carbon.The T-OAE coincided with global climate and environmental changes,as well as biotic events,indicating substantial modifications in ecosystems.Recent studies have focused on the evidence of geological responses to the T-OAE in Early Jurassic terrestrial basins in China,particularly the Sichuan Basin.Nevertheless,debate remains over the identification of this event,owing to inadequate age-constraints of many sections,and a lack of robust correlations of the carbon isotope records.Moreover,the long-term evolution of the terrestrial carbon isotope record through the Early Jurassic,and its correlation to marine records,is still not firmly established.In this paper,we present new carbon isotope analyses of carbonate(δ^(13)C_(carb))from lacustrine carbonates and terrestrial organic matter(δ^(13)C_(org))from bulk rocks within the Ma’anshan and Da’anzhai members of the Ziliujing Formation from the Dacao‘D’(DCD)section in the eastern Sichuan Basin.Palynological-palynofacies analysis reveals a predominance of Classopollis pollen together with marker taxa such as Ischyosporites variegatus,Contignisporites problematicus,in the palynological assemblage,indicating a Pliensbachian–Toarcian age.A negative carbon isotope excursion(NCIE)is recorded in the organic carbon isotope data at the topmost part of the Pliensbachian Ma’anshan Member,which can be correlated to the Pliensbachian–Toarcian Boundary Event.This is followed,in the Toarcian Da’anzhai Member,by a major NCIE recorded in both organic matter and carbonate carbon isotope data which can be correlated to the T-OAE NCIE.A long-term carbon isotope record spanning the Sinemurian to Toarcian in Sichuan terrestrial sediments is also been reconstructed and its correlation with coeval marine records is proposed.A broader review of δ^(13)C data from Chinese terrestrial basins spanning the Pliensbachian–Toarcian highlights a distinct^(13)C-depleted signature in the Sichuan Basin compared to basins at higher latitudes.Changes in latitudinal gradients and organic matters in the lake sediments were likely important factors influencing the amplitudes of the T-OAE NCIE and the carbon isotope values in terrestrial sedimentary records.展开更多
Characterization of transport pathways and depositional changes in Mercury(Hg)and their connection to climatic and environmental changes on various time scales are crucial for better understanding the anthropogenic im...Characterization of transport pathways and depositional changes in Mercury(Hg)and their connection to climatic and environmental changes on various time scales are crucial for better understanding the anthropogenic impacts on the global Hg cycle in the Anthropocene epoch.In this study,we examined Hg variations recorded in a stalagmite from central China,covering the period from 25.5 to 10.9 thousand years ago.Our data show a marked increase in Hg concentrations during the late Last Glacial Maximum,which coincided with the period of highest dust deposition on the Chinese Loess Plateau.Hg concentrations were lower during Heinrich events 1 and 2 and the Younger Dryas but higher during the BùllingAllerùd and the early Holocene.We suggest that regional dust load,which enhances atmospheric dry deposition of Hg,is the primary factor influencing Hg deposition in central China on glacialinterglacial timescales.On millennial-to-centennial timescales,climate also plays a significant role.Warmer and wetter conditions increase vegetation,litterfall,and soil/rock weathering,which in turn boost mineral dissolution and soil erosion in the vadose zone.These processes collectively result in higher Hg concentrations in the stalagmite.展开更多
Nearly 90% of the Ediacaran Period(635–541 Ma) of the Neoproterozoic is represented by the Doushantuo Formation(DST Fm) in South China.Its lowest Member I is a 3.7 m-thick cap carbonate deposited at the termination o...Nearly 90% of the Ediacaran Period(635–541 Ma) of the Neoproterozoic is represented by the Doushantuo Formation(DST Fm) in South China.Its lowest Member I is a 3.7 m-thick cap carbonate deposited at the termination of the Cryogenian Marinoan glaciation.The DST Fm consists of alternating organic-rich black shale and thinly bedded dolostone, and it contains some of the oldest records of multicellular life and three pronounced negative carbon isotope excursions.The Jiulongwan(JLW) section is a well-studied reference section for these Ediacaran events.Spectral analysis of geochemical data through the lower DST Fm(22.3 m) shows 27 predominant ～90 cm sedimentary cycles that correspond to 405-ka long eccentricity cycles.The power spectra of the 405-ka tuned Ca and Fe/Ti series show significant peaks at ～1.2-Ma, 405-ka, 133-ka, 128-ka, 100-ka, 82-ka, ～31-ka and 29-ka periods, respectively.A 11.16 Malong astronomical time scale has been constructed for the lower DST Fm and provide a duration of 1.6 Ma for the cap carbonate(Member Ⅰ) based on the 405-ka long eccentricity cycle tuning.Using the U-Pb age of 635.2 ± 0.6 Ma for the volcanic ash bed at the Member Ⅰ/Ⅱboundary, we proposed a 636.8 Ma age for the base of the DST Fm.These ages and astronomical timescale provide important new constraints on the subdivision of Ediacaran strata, and have implications for understanding the character of the first negative δ^(13)C excursion(EN1).Orbital forcing may have been played an important role for the climate changes and the evolution of Ediacaran multi-cellular life and the carbon cycle variations.展开更多
基金The research of VB is conducted in the scope of the internal research project“WEGETA”at the Croatian Geological Survey,funded by the National Recovery and Resilience Plan 2021-2026 of the European Union-NextGenerationEU,and monitored by the Ministry of Science,Education and Youth of the Republic of Croatia.
文摘The Toarcian Oceanic Anoxic Event(T-OAE,∼183 Ma)is marked in the sedimentary record by a sharp negative carbon isotope excursion,thought to be causally linked to the emplacement of the Karoo-Ferrar Large Igneous Province and the associated release of^(12)C-enriched carbon.The T-OAE coincided with global climate and environmental changes,as well as biotic events,indicating substantial modifications in ecosystems.Recent studies have focused on the evidence of geological responses to the T-OAE in Early Jurassic terrestrial basins in China,particularly the Sichuan Basin.Nevertheless,debate remains over the identification of this event,owing to inadequate age-constraints of many sections,and a lack of robust correlations of the carbon isotope records.Moreover,the long-term evolution of the terrestrial carbon isotope record through the Early Jurassic,and its correlation to marine records,is still not firmly established.In this paper,we present new carbon isotope analyses of carbonate(δ^(13)C_(carb))from lacustrine carbonates and terrestrial organic matter(δ^(13)C_(org))from bulk rocks within the Ma’anshan and Da’anzhai members of the Ziliujing Formation from the Dacao‘D’(DCD)section in the eastern Sichuan Basin.Palynological-palynofacies analysis reveals a predominance of Classopollis pollen together with marker taxa such as Ischyosporites variegatus,Contignisporites problematicus,in the palynological assemblage,indicating a Pliensbachian–Toarcian age.A negative carbon isotope excursion(NCIE)is recorded in the organic carbon isotope data at the topmost part of the Pliensbachian Ma’anshan Member,which can be correlated to the Pliensbachian–Toarcian Boundary Event.This is followed,in the Toarcian Da’anzhai Member,by a major NCIE recorded in both organic matter and carbonate carbon isotope data which can be correlated to the T-OAE NCIE.A long-term carbon isotope record spanning the Sinemurian to Toarcian in Sichuan terrestrial sediments is also been reconstructed and its correlation with coeval marine records is proposed.A broader review of δ^(13)C data from Chinese terrestrial basins spanning the Pliensbachian–Toarcian highlights a distinct^(13)C-depleted signature in the Sichuan Basin compared to basins at higher latitudes.Changes in latitudinal gradients and organic matters in the lake sediments were likely important factors influencing the amplitudes of the T-OAE NCIE and the carbon isotope values in terrestrial sedimentary records.
基金supported by the National Natural Science Foundation of China(42325705 and 42230208)the Chinese Academy of Sciences(xbzg-zdsys-202217)。
文摘Characterization of transport pathways and depositional changes in Mercury(Hg)and their connection to climatic and environmental changes on various time scales are crucial for better understanding the anthropogenic impacts on the global Hg cycle in the Anthropocene epoch.In this study,we examined Hg variations recorded in a stalagmite from central China,covering the period from 25.5 to 10.9 thousand years ago.Our data show a marked increase in Hg concentrations during the late Last Glacial Maximum,which coincided with the period of highest dust deposition on the Chinese Loess Plateau.Hg concentrations were lower during Heinrich events 1 and 2 and the Younger Dryas but higher during the BùllingAllerùd and the early Holocene.We suggest that regional dust load,which enhances atmospheric dry deposition of Hg,is the primary factor influencing Hg deposition in central China on glacialinterglacial timescales.On millennial-to-centennial timescales,climate also plays a significant role.Warmer and wetter conditions increase vegetation,litterfall,and soil/rock weathering,which in turn boost mineral dissolution and soil erosion in the vadose zone.These processes collectively result in higher Hg concentrations in the stalagmite.
基金supported by the Natural Science Foundation for Distinguished Young Scholars of Hubei Province of China (2016CFA051)the National Natural Science Foundation of China (41772029, 41322013)+2 种基金Overseas Expertise Introduction Project for Discipline Innovation (B08030)the National Basic Research Program of China (2014CB239101)the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (CUGCJ1703, CUGQYZX1705)
文摘Nearly 90% of the Ediacaran Period(635–541 Ma) of the Neoproterozoic is represented by the Doushantuo Formation(DST Fm) in South China.Its lowest Member I is a 3.7 m-thick cap carbonate deposited at the termination of the Cryogenian Marinoan glaciation.The DST Fm consists of alternating organic-rich black shale and thinly bedded dolostone, and it contains some of the oldest records of multicellular life and three pronounced negative carbon isotope excursions.The Jiulongwan(JLW) section is a well-studied reference section for these Ediacaran events.Spectral analysis of geochemical data through the lower DST Fm(22.3 m) shows 27 predominant ～90 cm sedimentary cycles that correspond to 405-ka long eccentricity cycles.The power spectra of the 405-ka tuned Ca and Fe/Ti series show significant peaks at ～1.2-Ma, 405-ka, 133-ka, 128-ka, 100-ka, 82-ka, ～31-ka and 29-ka periods, respectively.A 11.16 Malong astronomical time scale has been constructed for the lower DST Fm and provide a duration of 1.6 Ma for the cap carbonate(Member Ⅰ) based on the 405-ka long eccentricity cycle tuning.Using the U-Pb age of 635.2 ± 0.6 Ma for the volcanic ash bed at the Member Ⅰ/Ⅱboundary, we proposed a 636.8 Ma age for the base of the DST Fm.These ages and astronomical timescale provide important new constraints on the subdivision of Ediacaran strata, and have implications for understanding the character of the first negative δ^(13)C excursion(EN1).Orbital forcing may have been played an important role for the climate changes and the evolution of Ediacaran multi-cellular life and the carbon cycle variations.
