Benthic foraminifera, preserved in the Late Cretaceous organic carbon-rich sediments of Gamba, southern Tibet, provide high-resolution proxies for sea-level changes and dissolved oxygen fluctuations of southeastern Te...Benthic foraminifera, preserved in the Late Cretaceous organic carbon-rich sediments of Gamba, southern Tibet, provide high-resolution proxies for sea-level changes and dissolved oxygen fluctuations of southeastern Tethys. The fossils were statistically analyzed and divided into three faunas of ＂Cenomanian fauna＂, ＂Turonian fauna＂, and ＂Coniacian fauna＂. A middle neritic-upper bathal environment （50-250m） was estimated considering the ratios of planktonic and epifaunal benthic foraminifera （P/（P＋E））, the morphological analysis according to the studies of recent foraminifera and the abundant distributions of depth-related species such as Alabamina creta, Laevidentalina sp., Praebulimina spp., Pleurostomella cf. naranjoensis, Pyrulina sp., Quinqueloculina spp., Haplophragmoides spp., etc. The result shows an almost parallel trend with the global transgressive and regressive cycles, but the former fluctuates more frequently at upper Cenomanian, which probably indicates tectonic instability of the continental margin. According to the benthic foraminiferal richness （BFN）, Shannon-Weiner diversity （H（s））, as well as benthic foraminiferal oxygen index （BFOI）, five periods of oxygen depleted conditions （dysoxic-anoxic） have been recognized. They correspond to the OAE2, the lower Turonian, the upper Turonian, the Turonian- Caniacian boundary event and the probably OAE3. In addition, the oxygen fluctuations in Gamba might be controlled directly by sea-level changes, while the paleoproductivity and oxygen conditions interacted with each other under oxygen deficiency environments.展开更多
The Pulang （普朗） porphyry copper deposit, located in the southern segment of the Yidun-Zhongdian （义敦-中甸） island arc ore-forming belt of the Tethys-Himalaya ore-forming domain, is a recently discovered large c...The Pulang （普朗） porphyry copper deposit, located in the southern segment of the Yidun-Zhongdian （义敦-中甸） island arc ore-forming belt of the Tethys-Himalaya ore-forming domain, is a recently discovered large copper deposit. Compared with the composition of granodiorite in China, the porphyry rocks in this area are enriched in W, Mo, Cu, Au, As, Sb, F, V, and Na2O （K1≥1.2）. Compared with the composition of fresh porphyry rocks in this district, the mineralized rocks are enriched in Cu, Au, Ag, Mo, Pb, Zn, W, As, Sb, and K2O （K2≥1.2）. Some elements show clear anomalies, such as Zn, Ag, Cu, Au, W, and Mo, and can be regarded as pathfinders for prospecting new ore bodies in depth. It has been inferred from factor analysis that the Pulang porphyry copper deposit may have undergone the multiple stages of alteration and mineralization： （a） Cu-Au mineralization; （b） W-Mo mineralization; and （c） silicification and potassic metasomatism in the whole ore-forming process. A detailed zonation sequence of indicator elements is obtained using the variability index of indicator elements as follows： Zn→Ag→Cu→Au→W→Mo. According to this zonation, an index such as （Ag＊Zn）D/（Mo×W）D can be constructed and regarded as a significant criterion for predicting the Cu potential at a particular depth.展开更多
基金financially supported by the project of National key basic research and development of China("973" project) "Late Mesozoic Greenhouse Climatic-environmental evolution of East Tethys (No.2012CB822000-G)"
文摘Benthic foraminifera, preserved in the Late Cretaceous organic carbon-rich sediments of Gamba, southern Tibet, provide high-resolution proxies for sea-level changes and dissolved oxygen fluctuations of southeastern Tethys. The fossils were statistically analyzed and divided into three faunas of ＂Cenomanian fauna＂, ＂Turonian fauna＂, and ＂Coniacian fauna＂. A middle neritic-upper bathal environment （50-250m） was estimated considering the ratios of planktonic and epifaunal benthic foraminifera （P/（P＋E））, the morphological analysis according to the studies of recent foraminifera and the abundant distributions of depth-related species such as Alabamina creta, Laevidentalina sp., Praebulimina spp., Pleurostomella cf. naranjoensis, Pyrulina sp., Quinqueloculina spp., Haplophragmoides spp., etc. The result shows an almost parallel trend with the global transgressive and regressive cycles, but the former fluctuates more frequently at upper Cenomanian, which probably indicates tectonic instability of the continental margin. According to the benthic foraminiferal richness （BFN）, Shannon-Weiner diversity （H（s））, as well as benthic foraminiferal oxygen index （BFOI）, five periods of oxygen depleted conditions （dysoxic-anoxic） have been recognized. They correspond to the OAE2, the lower Turonian, the upper Turonian, the Turonian- Caniacian boundary event and the probably OAE3. In addition, the oxygen fluctuations in Gamba might be controlled directly by sea-level changes, while the paleoproductivity and oxygen conditions interacted with each other under oxygen deficiency environments.
基金supported by the National High Technology Research and Development Program of China (No 2006AA06Z113)the National Natural Science Foundation of China (No. 40772197)
文摘The Pulang （普朗） porphyry copper deposit, located in the southern segment of the Yidun-Zhongdian （义敦-中甸） island arc ore-forming belt of the Tethys-Himalaya ore-forming domain, is a recently discovered large copper deposit. Compared with the composition of granodiorite in China, the porphyry rocks in this area are enriched in W, Mo, Cu, Au, As, Sb, F, V, and Na2O （K1≥1.2）. Compared with the composition of fresh porphyry rocks in this district, the mineralized rocks are enriched in Cu, Au, Ag, Mo, Pb, Zn, W, As, Sb, and K2O （K2≥1.2）. Some elements show clear anomalies, such as Zn, Ag, Cu, Au, W, and Mo, and can be regarded as pathfinders for prospecting new ore bodies in depth. It has been inferred from factor analysis that the Pulang porphyry copper deposit may have undergone the multiple stages of alteration and mineralization： （a） Cu-Au mineralization; （b） W-Mo mineralization; and （c） silicification and potassic metasomatism in the whole ore-forming process. A detailed zonation sequence of indicator elements is obtained using the variability index of indicator elements as follows： Zn→Ag→Cu→Au→W→Mo. According to this zonation, an index such as （Ag＊Zn）D/（Mo×W）D can be constructed and regarded as a significant criterion for predicting the Cu potential at a particular depth.
