This paper studies the Late Cretaceous dinosaur eggshell fossils from the Xixia Basin, Henan Province, by microscopy and carbon isotope method. Careful observation under microscope revealed that all dinosaur eggshell ...This paper studies the Late Cretaceous dinosaur eggshell fossils from the Xixia Basin, Henan Province, by microscopy and carbon isotope method. Careful observation under microscope revealed that all dinosaur eggshell fossils consist of primary calcite and secondary calcite. The content of the former is about 60.5% and the latter 39.5% according to image analysis. The δ\{\}\+\{13\}C values of secondary carbonate mineral filling within the dinosaur eggs in the strata range from -5.63‰ to -5.68‰, with an average value of -5.65‰. The δ\{\}\+\{13\}C values of sixteen dinosaur eggshell fossils are in the range from -5.88‰ to -7.79‰. Then we calculated the δ\{\}\+\{13\}C values of primary carbonate minerals, ranging from -6.03‰ to -9.19‰. Based on the δ\{\}\+\{13\}C values of the primary carbonate, the ancient food type and food proportion of dinosaurs were deduced. The dinosaur’s food proportions of C\-3 plant and C\-4 plant are 61% and 39%, respectively. Finally, it is inferred that the palaeoclimate in the Xixia Basin should be a warm—sub\|humid—sub\|arid climate in the subtropical zone of the Xixia Basin.展开更多
Glauconite is widely distributed in space and time.In China glauconite-bearing strata are extensive occurrence ranging from Late Cretaceous to Middle Proterozoic in age.X-ray powder analysis,X-ray diffracition analysi...Glauconite is widely distributed in space and time.In China glauconite-bearing strata are extensive occurrence ranging from Late Cretaceous to Middle Proterozoic in age.X-ray powder analysis,X-ray diffracition analysis and differential thermal analysis revealed that glauconite has a mica-type structure between dioctahedron and trioctahedron.Its chemical composition is:Al2O310.6%,SiO249.23%,MgO3.24%,Fe2O317.40%,FeO1.8%,and K2O7.92%,Its crystal form and thermal properties are very similar to those of mica-like clay minerls.According to isotopic age determinations of glauconite in modern oceans (including the East China Sea,the South China Sea and the Yellow Sea),we consider that in the extreme case glauconite is an authigenic mineral.It is generally formed in sedimentary rocks.Is has further proved that glauconite can be used to determine the ages of sedimentary rocks.展开更多
It has been suggested that eclogites in the Dabie orogenic be lt are exhumation products, which had subducted into the deep-seated mantle and undergone ultra-high pressure metamorphism during the Triassic. But no dire...It has been suggested that eclogites in the Dabie orogenic be lt are exhumation products, which had subducted into the deep-seated mantle and undergone ultra-high pressure metamorphism during the Triassic. But no direct evidence supports this process except the calculated p-T conditions from mineral thermobarometers. The Late Cretaceous basalts studied in the prese nt paper, however, have provided some geochemical evidence for crust-mantle int eraction in the area. These basalts are distributed in Mesozoic faulted basins i n central and southern Dabie orogenic belt. Since little obvious contamination f rom continental crust and differentiation-crystallization were observed, it is suggested, based on a study of trace elements, that the basalts are alkaline and resultant from batch partial melting of the regional mantle rocks, and share th e same or similar geochemical features with respect to their magma source. In th e spider diagram normalized by the primitive mantle, trace element geochemistry data show that their mantle sources are enriched in certain elements concentrate d in the continental crust, such as Pb, K, Rb and Ba, and slightly depleted in s ome HFSE such as Hf, P and Nb. Pb-Sr-Nd isotopic compositions further suggest the mantle is the mixture of depleted mantle and enriched one . T his interaction can explain the trace element characteristics of basaltic magmas , i.e., the enrichment of Pb and the depletion of Hf, P and Nb in basalts can be interpreted by the blending of the eclogites in DOB (enriched in Pb and deplete d in Hf, P and Nd) with the East China depleted mantle (As compared to the primi tive mantle, it is neither enriched in Pb nor depleted in Hf, P and Nb). It is a lso indicated that the eclogites in the Dabie orogenic belt were surely derived from the exhumation materials, which had delaminated into the deep-seated mantl e. Moreover, the process subsequently resulted in compositional variation of the mantle (especially in trace elements and isotopes), as revealed by the late man tle-derived basalts in the Dabie orogenic belt.展开更多
文摘This paper studies the Late Cretaceous dinosaur eggshell fossils from the Xixia Basin, Henan Province, by microscopy and carbon isotope method. Careful observation under microscope revealed that all dinosaur eggshell fossils consist of primary calcite and secondary calcite. The content of the former is about 60.5% and the latter 39.5% according to image analysis. The δ\{\}\+\{13\}C values of secondary carbonate mineral filling within the dinosaur eggs in the strata range from -5.63‰ to -5.68‰, with an average value of -5.65‰. The δ\{\}\+\{13\}C values of sixteen dinosaur eggshell fossils are in the range from -5.88‰ to -7.79‰. Then we calculated the δ\{\}\+\{13\}C values of primary carbonate minerals, ranging from -6.03‰ to -9.19‰. Based on the δ\{\}\+\{13\}C values of the primary carbonate, the ancient food type and food proportion of dinosaurs were deduced. The dinosaur’s food proportions of C\-3 plant and C\-4 plant are 61% and 39%, respectively. Finally, it is inferred that the palaeoclimate in the Xixia Basin should be a warm—sub\|humid—sub\|arid climate in the subtropical zone of the Xixia Basin.
文摘Glauconite is widely distributed in space and time.In China glauconite-bearing strata are extensive occurrence ranging from Late Cretaceous to Middle Proterozoic in age.X-ray powder analysis,X-ray diffracition analysis and differential thermal analysis revealed that glauconite has a mica-type structure between dioctahedron and trioctahedron.Its chemical composition is:Al2O310.6%,SiO249.23%,MgO3.24%,Fe2O317.40%,FeO1.8%,and K2O7.92%,Its crystal form and thermal properties are very similar to those of mica-like clay minerls.According to isotopic age determinations of glauconite in modern oceans (including the East China Sea,the South China Sea and the Yellow Sea),we consider that in the extreme case glauconite is an authigenic mineral.It is generally formed in sedimentary rocks.Is has further proved that glauconite can be used to determine the ages of sedimentary rocks.
文摘It has been suggested that eclogites in the Dabie orogenic be lt are exhumation products, which had subducted into the deep-seated mantle and undergone ultra-high pressure metamorphism during the Triassic. But no direct evidence supports this process except the calculated p-T conditions from mineral thermobarometers. The Late Cretaceous basalts studied in the prese nt paper, however, have provided some geochemical evidence for crust-mantle int eraction in the area. These basalts are distributed in Mesozoic faulted basins i n central and southern Dabie orogenic belt. Since little obvious contamination f rom continental crust and differentiation-crystallization were observed, it is suggested, based on a study of trace elements, that the basalts are alkaline and resultant from batch partial melting of the regional mantle rocks, and share th e same or similar geochemical features with respect to their magma source. In th e spider diagram normalized by the primitive mantle, trace element geochemistry data show that their mantle sources are enriched in certain elements concentrate d in the continental crust, such as Pb, K, Rb and Ba, and slightly depleted in s ome HFSE such as Hf, P and Nb. Pb-Sr-Nd isotopic compositions further suggest the mantle is the mixture of depleted mantle and enriched one . T his interaction can explain the trace element characteristics of basaltic magmas , i.e., the enrichment of Pb and the depletion of Hf, P and Nb in basalts can be interpreted by the blending of the eclogites in DOB (enriched in Pb and deplete d in Hf, P and Nd) with the East China depleted mantle (As compared to the primi tive mantle, it is neither enriched in Pb nor depleted in Hf, P and Nb). It is a lso indicated that the eclogites in the Dabie orogenic belt were surely derived from the exhumation materials, which had delaminated into the deep-seated mantl e. Moreover, the process subsequently resulted in compositional variation of the mantle (especially in trace elements and isotopes), as revealed by the late man tle-derived basalts in the Dabie orogenic belt.
