Recent fieldwork has extended the distribution of the Daohugou Bed deposits from the Daohugou Village to its several neighboring areas. The fossil-bearing Daohugou deposits uncomformably overlie complex bedrocks, and ...Recent fieldwork has extended the distribution of the Daohugou Bed deposits from the Daohugou Village to its several neighboring areas. The fossil-bearing Daohugou deposits uncomformably overlie complex bedrocks, and com- prise three major parts. The red shales in the lower part were misidentified as belonging to the Tuchengzi Formation. Field excavation has indicated that the shales of upper part of the bed are the major fossil-bearing horizon. Due to strong tectonic activities, sediments were often folded with the se- quences inverted in the region. Some newly recognized con- tacts between the Daohugou Bed and the volcanic rocks showed that the ignimbrite of the Tiaojishan Formation (159―164 Ma) underlies the Daohugou deposits, rather than overlying the latter as previously proposed. Thus, the age of the Daohugou deposits should be younger than the age of the ignimbrite, and thus it was incorrect to correlate the Dao- hugou Bed with the Middle Jurassic Jiulongshan Formation. Although biostratigraphic studies based on conchostracans and insects support a Middle Jurassic-early Late Jurassic age for the Daohugou deposits, vertebrate fossils such as Liaoxitriton, Jeholopterus and feathered maniraptorans show much resemblance to those of the Yixian Formation. In other words, despite the absence of Lycoptera, a typical fish of the Jehol Biota, the Daohugou vertebrate assemblage is closer to that of the Early Cretaceous Jehol Biota than to any other biota. We propose that the Daohugou fossil assemblage probably represents the earliest evolutionary stage of the Jehol Biota based on both vertebrate biostratigraphy and the sedimentological and volcanic features which suggest the Daohugou deposit belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group.展开更多
The Tianchi volcano in the Changbai Mountains is located on the boundary between China and North Korea.There are many times of eruptions of the Tianchi volcano during the Holocene.One of its large eruptions occurred a...The Tianchi volcano in the Changbai Mountains is located on the boundary between China and North Korea.There are many times of eruptions of the Tianchi volcano during the Holocene.One of its large eruptions occurred around 1000 years ago dated by ^(14)C method and historical records.Composition of products of the largest Tianchi volcanic eruption studied is characterized by comendi-tic Plinian fallout and unwelded ignimbrite,which are mainly distributed in China and North Korea.Caldera is about 4.4 km long and 3.4 km wide,which had filled with water(e.g.Tianchi Lake).The Tianchi volcanic cone is about 2700 m high above sea level.The Tianchi Lake is located on the summit of the volcanic cone,that is also highest peak of the Changbai Mountains in northeastern China.This study analyzed Cl,F,S and H_(2)O concentrations of melt inclusions in the phenocryst min-erals(anorthoclase and quartz)and co-existing matrix glasses using the electron microprobe and estimated environmental effect of Tianchi volcanic gases.The authors proposed a new method to evaluate future eruption of active volcano and estimate potential volcanic hazards based on contents of volatile emissions.Using this method,we made a perspective of future volcanic hazard in this region.展开更多
Four international standards,Ga1550,MMhb-1,Lp-6,Bern 4M,and one domesticstandard BT-1 have been intercalibrated.The repeated measurements on MMhb-1 with different massdemonstrate that MMhb-1 is inhomogeneous in age an...Four international standards,Ga1550,MMhb-1,Lp-6,Bern 4M,and one domesticstandard BT-1 have been intercalibrated.The repeated measurements on MMhb-1 with different massdemonstrate that MMhb-1 is inhomogeneous in age and its average age is 519.8 Ma.The results of Bern4M and Lp-6 reflect that they have an invariable value of^(40)Ar*/^(39)Ar_(k)(F)and the ages weobtained are consensus with their K-Ar age:Lp-6=127.7Ma;Bern 4M=18.2 Ma.Analyses of BT-1 agespectra,Ca/K and Cl/K spectra as well as inverse isochrons indicate that the sample is homogeneousand invariable and keeps close chemically,with its trapped argon isotope composition close to theatmosphere.The dating results show that age values are reproducible and steady,total fusion age,step-heating age,plateau age and isochron age are in accord with each other within the error range(2σ).Therefore,we recommend 28.7 Ma as the calibrated age of BT-1.We also discuss the variationin neutron flux gradients of Beijing 49-2 reactor.It was found that the neutron flux gradientvaries considerably,and more monitors(standard samples)are needed to fix the trend of variation.The coefficient of the 49-2 reactor that transfers the ratio of production rate of^(37)Ar_(Ca)/^(39)Ar_(K) into Ca/K ratio is 1.78.This is different from that reported earlier,2.0,which may be caused by the reconstruction of the reactor.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.40121202)the National 973 Project(Grant No.TG20000077706)the Chinese Academy of Sciences(Grant No.KZCX3-SW-142).
文摘Recent fieldwork has extended the distribution of the Daohugou Bed deposits from the Daohugou Village to its several neighboring areas. The fossil-bearing Daohugou deposits uncomformably overlie complex bedrocks, and com- prise three major parts. The red shales in the lower part were misidentified as belonging to the Tuchengzi Formation. Field excavation has indicated that the shales of upper part of the bed are the major fossil-bearing horizon. Due to strong tectonic activities, sediments were often folded with the se- quences inverted in the region. Some newly recognized con- tacts between the Daohugou Bed and the volcanic rocks showed that the ignimbrite of the Tiaojishan Formation (159―164 Ma) underlies the Daohugou deposits, rather than overlying the latter as previously proposed. Thus, the age of the Daohugou deposits should be younger than the age of the ignimbrite, and thus it was incorrect to correlate the Dao- hugou Bed with the Middle Jurassic Jiulongshan Formation. Although biostratigraphic studies based on conchostracans and insects support a Middle Jurassic-early Late Jurassic age for the Daohugou deposits, vertebrate fossils such as Liaoxitriton, Jeholopterus and feathered maniraptorans show much resemblance to those of the Yixian Formation. In other words, despite the absence of Lycoptera, a typical fish of the Jehol Biota, the Daohugou vertebrate assemblage is closer to that of the Early Cretaceous Jehol Biota than to any other biota. We propose that the Daohugou fossil assemblage probably represents the earliest evolutionary stage of the Jehol Biota based on both vertebrate biostratigraphy and the sedimentological and volcanic features which suggest the Daohugou deposit belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group.
基金supported by the National Natural Science Foundation of China(Grant No.40372045)the Chinese Academy of Sciences(Grant No.KZCX3-SW-145)the Chinese Academy of Sciences(Grant No.KZCX3-SW-145).
文摘The Tianchi volcano in the Changbai Mountains is located on the boundary between China and North Korea.There are many times of eruptions of the Tianchi volcano during the Holocene.One of its large eruptions occurred around 1000 years ago dated by ^(14)C method and historical records.Composition of products of the largest Tianchi volcanic eruption studied is characterized by comendi-tic Plinian fallout and unwelded ignimbrite,which are mainly distributed in China and North Korea.Caldera is about 4.4 km long and 3.4 km wide,which had filled with water(e.g.Tianchi Lake).The Tianchi volcanic cone is about 2700 m high above sea level.The Tianchi Lake is located on the summit of the volcanic cone,that is also highest peak of the Changbai Mountains in northeastern China.This study analyzed Cl,F,S and H_(2)O concentrations of melt inclusions in the phenocryst min-erals(anorthoclase and quartz)and co-existing matrix glasses using the electron microprobe and estimated environmental effect of Tianchi volcanic gases.The authors proposed a new method to evaluate future eruption of active volcano and estimate potential volcanic hazards based on contents of volatile emissions.Using this method,we made a perspective of future volcanic hazard in this region.
基金supported by the National Natural Science Foundation of China(Grant No.40473031).
文摘Four international standards,Ga1550,MMhb-1,Lp-6,Bern 4M,and one domesticstandard BT-1 have been intercalibrated.The repeated measurements on MMhb-1 with different massdemonstrate that MMhb-1 is inhomogeneous in age and its average age is 519.8 Ma.The results of Bern4M and Lp-6 reflect that they have an invariable value of^(40)Ar*/^(39)Ar_(k)(F)and the ages weobtained are consensus with their K-Ar age:Lp-6=127.7Ma;Bern 4M=18.2 Ma.Analyses of BT-1 agespectra,Ca/K and Cl/K spectra as well as inverse isochrons indicate that the sample is homogeneousand invariable and keeps close chemically,with its trapped argon isotope composition close to theatmosphere.The dating results show that age values are reproducible and steady,total fusion age,step-heating age,plateau age and isochron age are in accord with each other within the error range(2σ).Therefore,we recommend 28.7 Ma as the calibrated age of BT-1.We also discuss the variationin neutron flux gradients of Beijing 49-2 reactor.It was found that the neutron flux gradientvaries considerably,and more monitors(standard samples)are needed to fix the trend of variation.The coefficient of the 49-2 reactor that transfers the ratio of production rate of^(37)Ar_(Ca)/^(39)Ar_(K) into Ca/K ratio is 1.78.This is different from that reported earlier,2.0,which may be caused by the reconstruction of the reactor.
