Based on the systematic study of two fossil skeleton specimens collected from the top of the third member of the marine Lower Triassic Jialingjiang Formation of Yuanan, Hubei Province, South China, a new Early Triassi...Based on the systematic study of two fossil skeleton specimens collected from the top of the third member of the marine Lower Triassic Jialingjiang Formation of Yuanan, Hubei Province, South China, a new Early Triassic primitive ichthyosaur Chaohusaurus zhang]iawanensis sp. nov. is reported and described. The beds yielding the type material are correlated with the Neospathodus homeri-N, triangularis Conodont zone. The new taxon is most similar to Chaohusaurus geishanensis Young and Dong, 1972 in the shape and configuration of the scapula, forefin, pelvic girdle and hindfin, presacral vertebral count and well-developed caudal peak, but distinguished from the latter by its larger size, the position of the pineal foramen in the centre of the parietal, the occurrence of a larger calcaneum in hindfin and the first sacral rib with distal expansion. The new species exhibits common features of primitive ichthyosaurs such as： （1） the prefrontal has an antero-dorsal shelf projecting towards the orbit; （2） the upper temporal fenestra is small; （3） the postorbital and the squamosal meet laterally to the upper temporal fenestra; and （4） cylindrical centra. However, more derived ichthyosaur characters are seen with the frontal separated from the orbital dorsal margin by the contact of the prefrontal and postfrontal, which offer new clues to the early radiation of ichthyosaurs.展开更多
Conodonts,as a biotic group,next to ammonoids,pollen and spores,crustaceans and vertebrates,provide proxy clues for environment and age assessments of the rocks in which they occur.Conodonts are widely used for Triass...Conodonts,as a biotic group,next to ammonoids,pollen and spores,crustaceans and vertebrates,provide proxy clues for environment and age assessments of the rocks in which they occur.Conodonts are widely used for Triassic marine biostratigraphy.However,there are various discussions about their multielement taxonomy and evolutionary lineages(e.g.,generation,speciation).Although first studies reported that most Triassic conodont species were unimembrate,studies carried out in the following years maintained that all Triassic conodonts were multimembrate.Although statistical reconstructions of a number of Triassic apparatuses were attempted,the discovery of fused clusters and natural assemblages has subsequently demonstrated that Triassic conodonts are indeed multimembrate,and all of the elements exist together in the same apparatus.The present paper aims to clarify the evolutionary relationship and array of some Lower Triassic conodonts.Columbitella dagisi n.sp.is described.展开更多
Since the West Pingdingshan Section in Chaohu was proposed as the candidate of the Global Stratotype Section and Point of the Induan-Olenekian boundary in 2003, the Lower Triassic of Chaohu has been extensively studie...Since the West Pingdingshan Section in Chaohu was proposed as the candidate of the Global Stratotype Section and Point of the Induan-Olenekian boundary in 2003, the Lower Triassic of Chaohu has been extensively studied. Based on the studies on the Lower Triassic of Chaohu, （1） a continuous conodont zonation is established, which has become an important reference for Lower Triassic stratigraphic correlation over the world; （2） the First Appearance Datum of conodont Neospathodus waageni was suggested and has been basically accepted as the primary marker to define the InduanOienekian boundary; （3） a characteristic Lower Triassic excursion of carbon isotopes was brought to light and has been proven to be not only an excellent index for the stratigraphic correlation but also a unique indication for the perturbation of ecological environments in the aftermath of the end-Permian mass extinction; （4） a magnetostratigraphic sequence is constituted with a certain biostratigraphic control in the low-latitude region and it presents an important correlation to the Boreal sequence; （5） a cyclostratigraphic study provides an alternative method to constrain the age of the chronostratigraphic units; and （6） a scheme of the Olenekian subdivision is recently suggested to define the boundary between the Smithian and Spathian Substages. In addition, Chaohu is also the type locality of the Chaohuan Stage, the upper stage of the Lower Triassic in the China Chronostratigraphic System.Thus, the Lower Triassic of Chaohu is not only a classic sequence in South China, but also a key reference sequence to the investigation of the corresponding stratigraphy and geological events over the world. The recent achievements are viewed here for an overall understanding of the sequence. Then the current situation of the Induan-Olenekian and Smithian-Spathian boundaries is discussed to provide a reference for later works.展开更多
The West Pingdingshan Section in Chaohu, Anhui Province, has been extensively studied in recent years and become one of the classic Lower Triassic sequences well-clarified in multiple stratigraphies. Also it is an imp...The West Pingdingshan Section in Chaohu, Anhui Province, has been extensively studied in recent years and become one of the classic Lower Triassic sequences well-clarified in multiple stratigraphies. Also it is an important section that defines the Smithian-Spathian (S-S) boundary within the Olenekian Stage. The S-S boundary strata at the section are restudied in high-resolution conodont biostratigraphy and carbon isotopes. The refined S-S boundary defined by the FAD of conodont Neospathodus pingdingshanensis is at 30 cm above the base of Bed 52, corresponding to a rapid diversification of conodonts. A sharp positive shift of δ13Ccarb curve co-occurs at the S-S boundary and it can be used as a key reference to define the boundary. The defined S-S boundary position and carbon isotopes curve can be well correlated globally.展开更多
The Early Triassic was a period of ecological restoration for the earth＇s system after the end-Permian mass extinction. Geochemical records linked to the variations in marine ecosystems during this period have attrac...The Early Triassic was a period of ecological restoration for the earth＇s system after the end-Permian mass extinction. Geochemical records linked to the variations in marine ecosystems during this period have attracted the interest of geologists for many years. Based on petrographic analysis of samples and evaluations of their reliability as proxies for original seawater, this study investigated the carbon and oxygen isotopic compositions of 350 carbonate rock samples from the Lower Triassic （and adjacent strata） in the southern Longmenxia section of Guang＇an, eastern Sichuan Basin. The results indicate that the Triassic carbonate rocks from the southern Longmenxia section favorably preserved the original seawater＇s δ13C signal. Furthermore, carbon and oxygen isotopic compositions are found to be poorly correlated, with a determination coefficient as low as 0.0205 and only 44 rock samples show results of Mn/Sr〉2 and/or 6180〈-6.5%0. The complete carbon isotopic curve for the Lower Triassic is established using the data from the remaining 306 samples with MrdSr〈2 and/or 6180〉-6.5%o. This curve presents favorable comparability on a global scale, specifically in the δ13C minima near the Permian-Triassic boundary, at the top of the Jial and within the the Jia3, as well as in the δ13C maxima at the tops of the Yel and Ye4, at the base of the Jia2 and at the top of the Ye3. The peaks and troughs corresponding to these maxima and minima all reflect global signals. By comparing these results to previous research on coeval carbon isotopic curves established within the chronostratigraphic framework, the ages of these critical evolution points are determined. The results show that the Yel roughly corresponds to the Griesbachian substage; the Ye2 through Ye4 correspond to the Dienerian substage; Jial corresponds to the Smithian substage; from the Jia2 to the lower part of the Jia4 correspond to the Spathian substage; and the middle and upper parts of the Jia4 belongs to the Aegean Substage of the Middle 展开更多
基金supported by the China Geological Survey (Grant No. 1212010611603 and 1212011120148)
文摘Based on the systematic study of two fossil skeleton specimens collected from the top of the third member of the marine Lower Triassic Jialingjiang Formation of Yuanan, Hubei Province, South China, a new Early Triassic primitive ichthyosaur Chaohusaurus zhang]iawanensis sp. nov. is reported and described. The beds yielding the type material are correlated with the Neospathodus homeri-N, triangularis Conodont zone. The new taxon is most similar to Chaohusaurus geishanensis Young and Dong, 1972 in the shape and configuration of the scapula, forefin, pelvic girdle and hindfin, presacral vertebral count and well-developed caudal peak, but distinguished from the latter by its larger size, the position of the pineal foramen in the centre of the parietal, the occurrence of a larger calcaneum in hindfin and the first sacral rib with distal expansion. The new species exhibits common features of primitive ichthyosaurs such as： （1） the prefrontal has an antero-dorsal shelf projecting towards the orbit; （2） the upper temporal fenestra is small; （3） the postorbital and the squamosal meet laterally to the upper temporal fenestra; and （4） cylindrical centra. However, more derived ichthyosaur characters are seen with the frontal separated from the orbital dorsal margin by the contact of the prefrontal and postfrontal, which offer new clues to the early radiation of ichthyosaurs.
文摘Conodonts,as a biotic group,next to ammonoids,pollen and spores,crustaceans and vertebrates,provide proxy clues for environment and age assessments of the rocks in which they occur.Conodonts are widely used for Triassic marine biostratigraphy.However,there are various discussions about their multielement taxonomy and evolutionary lineages(e.g.,generation,speciation).Although first studies reported that most Triassic conodont species were unimembrate,studies carried out in the following years maintained that all Triassic conodonts were multimembrate.Although statistical reconstructions of a number of Triassic apparatuses were attempted,the discovery of fused clusters and natural assemblages has subsequently demonstrated that Triassic conodonts are indeed multimembrate,and all of the elements exist together in the same apparatus.The present paper aims to clarify the evolutionary relationship and array of some Lower Triassic conodonts.Columbitella dagisi n.sp.is described.
基金supported by the Ministry of Science and Technology project (no. 2006FY120300-11)Ministry of Education project (no. 200804910503)National Natural Science Foundation of China (nos. 40830212, 40921062, 40972003)
文摘Since the West Pingdingshan Section in Chaohu was proposed as the candidate of the Global Stratotype Section and Point of the Induan-Olenekian boundary in 2003, the Lower Triassic of Chaohu has been extensively studied. Based on the studies on the Lower Triassic of Chaohu, （1） a continuous conodont zonation is established, which has become an important reference for Lower Triassic stratigraphic correlation over the world; （2） the First Appearance Datum of conodont Neospathodus waageni was suggested and has been basically accepted as the primary marker to define the InduanOienekian boundary; （3） a characteristic Lower Triassic excursion of carbon isotopes was brought to light and has been proven to be not only an excellent index for the stratigraphic correlation but also a unique indication for the perturbation of ecological environments in the aftermath of the end-Permian mass extinction; （4） a magnetostratigraphic sequence is constituted with a certain biostratigraphic control in the low-latitude region and it presents an important correlation to the Boreal sequence; （5） a cyclostratigraphic study provides an alternative method to constrain the age of the chronostratigraphic units; and （6） a scheme of the Olenekian subdivision is recently suggested to define the boundary between the Smithian and Spathian Substages. In addition, Chaohu is also the type locality of the Chaohuan Stage, the upper stage of the Lower Triassic in the China Chronostratigraphic System.Thus, the Lower Triassic of Chaohu is not only a classic sequence in South China, but also a key reference sequence to the investigation of the corresponding stratigraphy and geological events over the world. The recent achievements are viewed here for an overall understanding of the sequence. Then the current situation of the Induan-Olenekian and Smithian-Spathian boundaries is discussed to provide a reference for later works.
基金supported by Ministry of Science and Technology (Grant No. 2006FY120300-11)National Natural Science Foundation of China (Grant Nos. 40830212, 40921062, 40972003)
文摘The West Pingdingshan Section in Chaohu, Anhui Province, has been extensively studied in recent years and become one of the classic Lower Triassic sequences well-clarified in multiple stratigraphies. Also it is an important section that defines the Smithian-Spathian (S-S) boundary within the Olenekian Stage. The S-S boundary strata at the section are restudied in high-resolution conodont biostratigraphy and carbon isotopes. The refined S-S boundary defined by the FAD of conodont Neospathodus pingdingshanensis is at 30 cm above the base of Bed 52, corresponding to a rapid diversification of conodonts. A sharp positive shift of δ13Ccarb curve co-occurs at the S-S boundary and it can be used as a key reference to define the boundary. The defined S-S boundary position and carbon isotopes curve can be well correlated globally.
基金supported by the National Natural Science Foundation of China(Grant No.41272130)
文摘The Early Triassic was a period of ecological restoration for the earth＇s system after the end-Permian mass extinction. Geochemical records linked to the variations in marine ecosystems during this period have attracted the interest of geologists for many years. Based on petrographic analysis of samples and evaluations of their reliability as proxies for original seawater, this study investigated the carbon and oxygen isotopic compositions of 350 carbonate rock samples from the Lower Triassic （and adjacent strata） in the southern Longmenxia section of Guang＇an, eastern Sichuan Basin. The results indicate that the Triassic carbonate rocks from the southern Longmenxia section favorably preserved the original seawater＇s δ13C signal. Furthermore, carbon and oxygen isotopic compositions are found to be poorly correlated, with a determination coefficient as low as 0.0205 and only 44 rock samples show results of Mn/Sr〉2 and/or 6180〈-6.5%0. The complete carbon isotopic curve for the Lower Triassic is established using the data from the remaining 306 samples with MrdSr〈2 and/or 6180〉-6.5%o. This curve presents favorable comparability on a global scale, specifically in the δ13C minima near the Permian-Triassic boundary, at the top of the Jial and within the the Jia3, as well as in the δ13C maxima at the tops of the Yel and Ye4, at the base of the Jia2 and at the top of the Ye3. The peaks and troughs corresponding to these maxima and minima all reflect global signals. By comparing these results to previous research on coeval carbon isotopic curves established within the chronostratigraphic framework, the ages of these critical evolution points are determined. The results show that the Yel roughly corresponds to the Griesbachian substage; the Ye2 through Ye4 correspond to the Dienerian substage; Jial corresponds to the Smithian substage; from the Jia2 to the lower part of the Jia4 correspond to the Spathian substage; and the middle and upper parts of the Jia4 belongs to the Aegean Substage of the Middle
