Three positive carbon isotope excursions are reported from Middle-Upper Ordovician in Tahe oil-gas field, northern Tarim Basin. Based on conodont biostratigraphy, the Middle Darriwilian Isotope Carbon Excursion(MDICE...Three positive carbon isotope excursions are reported from Middle-Upper Ordovician in Tahe oil-gas field, northern Tarim Basin. Based on conodont biostratigraphy, the Middle Darriwilian Isotope Carbon Excursion(MDICE) and the Guttenberg Carbon Isotope Excursion(GICE) are identified from Darriwilian to Early Katian by the aid of whole-rock carbon isotope data from two well cores. Positive excursion within conodont Pygodus anserinus zone is developed in Early Sandbian, and the fluctuation range is no less than MDICE. Because the range of this excursion in the generalized global carbon isotope curve is short, previous studies paid little attention to it, and named Early Sandbian Isotope Carbon Excursion(ESICE) in this paper. Furthermore, these positive excursions are not directly related to sea level fluctuations and the MDICE and GICE identified in northern Tarim can be globally correlated to that in southern China, North America, South America, and Europe. The Saergan Fm. source rocks of Middle-Upper Ordovician in Kalpin Dawangou outcrop are in accord with the geologic time of MDICE and ESICE, and GICE have strong ties to the source rock of Lianglitag Fm. in basin. Abundant organic carbon burial is an important factor in genesis of positive isotope carbon excursions. Positive oxygen isotope excursion, conodont fauna turnover, decreased conodont total diversity, and the change of sedimentary facies indicated that dramatic changes of paleoceanographic environment of Early-Middle Ordovician in Tarim Basin started from the end of Darriwillian, and an obvious icehouse climate of Late Ordovician occurred in ESICE.展开更多
Ecosystem health assessment is one of the most important issues in regional ecological quality and safety studies.It also has a great significance to ecological conservation and regional development.This study focused...Ecosystem health assessment is one of the most important issues in regional ecological quality and safety studies.It also has a great significance to ecological conservation and regional development.This study focused on assessing the health status of forest,agriculture and urban ecosystems in the southwestern Beijing,China,including the Fangshan and Fengtai Districts.Based on field surveys and data collection,an assessment index system containing the vigor,organization and resilience factors was developed to measure the ecosystem health.Each index was scored from 1 to 5,representing five levels that contribute to the whole ecosystem health.The analytic hierarchy process(AHP)method was used to measure the weights of each index and three factors,and thus an overall score for a certain ecosystem was calculated.The results show that the forest ecosystem in the Fangshan District had higher health value than the Fengtai District,while the urban ecosystem had a slightly lower value in the Fangshan District than the Fengtai District.Both districts show lower resilience values in forest and urban ecosystems.Maintaining the ecosystem health will definitely benefit the long-term development of two districts.This study suggested that an approach for assessing the regional ecosystem health could be further developed to address spatial and synergy relationships between ecosystems and the three health factors.展开更多
基金supported by the National Key Scientific Project of China (No. 2011ZX05005-0042016ZX05005-002)the National Basic Research Program of China (973 Program) (No. 2012CB214806)
文摘Three positive carbon isotope excursions are reported from Middle-Upper Ordovician in Tahe oil-gas field, northern Tarim Basin. Based on conodont biostratigraphy, the Middle Darriwilian Isotope Carbon Excursion(MDICE) and the Guttenberg Carbon Isotope Excursion(GICE) are identified from Darriwilian to Early Katian by the aid of whole-rock carbon isotope data from two well cores. Positive excursion within conodont Pygodus anserinus zone is developed in Early Sandbian, and the fluctuation range is no less than MDICE. Because the range of this excursion in the generalized global carbon isotope curve is short, previous studies paid little attention to it, and named Early Sandbian Isotope Carbon Excursion(ESICE) in this paper. Furthermore, these positive excursions are not directly related to sea level fluctuations and the MDICE and GICE identified in northern Tarim can be globally correlated to that in southern China, North America, South America, and Europe. The Saergan Fm. source rocks of Middle-Upper Ordovician in Kalpin Dawangou outcrop are in accord with the geologic time of MDICE and ESICE, and GICE have strong ties to the source rock of Lianglitag Fm. in basin. Abundant organic carbon burial is an important factor in genesis of positive isotope carbon excursions. Positive oxygen isotope excursion, conodont fauna turnover, decreased conodont total diversity, and the change of sedimentary facies indicated that dramatic changes of paleoceanographic environment of Early-Middle Ordovician in Tarim Basin started from the end of Darriwillian, and an obvious icehouse climate of Late Ordovician occurred in ESICE.
基金project of Environ-mental Impact Assessment of Regional Development in the Southwest Beijing,sponsored by Environmental Protection Bureau of BeijingTsinghua-Alcoa foundation project of The Sustainable Development in Rural Area of China.
文摘Ecosystem health assessment is one of the most important issues in regional ecological quality and safety studies.It also has a great significance to ecological conservation and regional development.This study focused on assessing the health status of forest,agriculture and urban ecosystems in the southwestern Beijing,China,including the Fangshan and Fengtai Districts.Based on field surveys and data collection,an assessment index system containing the vigor,organization and resilience factors was developed to measure the ecosystem health.Each index was scored from 1 to 5,representing five levels that contribute to the whole ecosystem health.The analytic hierarchy process(AHP)method was used to measure the weights of each index and three factors,and thus an overall score for a certain ecosystem was calculated.The results show that the forest ecosystem in the Fangshan District had higher health value than the Fengtai District,while the urban ecosystem had a slightly lower value in the Fangshan District than the Fengtai District.Both districts show lower resilience values in forest and urban ecosystems.Maintaining the ecosystem health will definitely benefit the long-term development of two districts.This study suggested that an approach for assessing the regional ecosystem health could be further developed to address spatial and synergy relationships between ecosystems and the three health factors.