The Xining and the Minhe Basins bordering on each other around Ledu innorthwestern China cover a wide area from the west of Lanzhou in Gansuprovince to the east of Xining in Qinghai province.In these inland basins,Mes...The Xining and the Minhe Basins bordering on each other around Ledu innorthwestern China cover a wide area from the west of Lanzhou in Gansuprovince to the east of Xining in Qinghai province.In these inland basins,Meso-Cenozoic terrestrial deposits about 6000-7000 meters in thicknessand rich in mineral resources,such as coal,oi1 as well as salts,had beenaccumunated,which yield abundant organic remains comprising microfossils,such as nonmarine ostracods,charophytes,spores and pollen and macrofos-si1s including bivalves.gastropods,esthierians,fishes,reptiles and plants.展开更多
Lanzhou-Minhe Basin is situated on the middle Qilian orogenic belt. Yanguoxia Formation contains abundance of maroon siltstones, mudstones and red sandstones of the lake facies. These sedimentary rocks recorded the pr...Lanzhou-Minhe Basin is situated on the middle Qilian orogenic belt. Yanguoxia Formation contains abundance of maroon siltstones, mudstones and red sandstones of the lake facies. These sedimentary rocks recorded the process of the tectonic uplift of Qilian Mountains during the Early Cretaceous. We discovered plentiful dinosaur footprints, worm burrows, bird footprints, worm tracks-trails, ripple marks and cross lamination in the Yanguoxia site. Integrated petrographic studies classified sandstones of Yanguoxia Formation as feldspathic litharenite. All plots in the QFL(Q or Qt, total quartz; F, feldspar; L, lithic grains) and Qm FLt(Qm, monocrystalline quartz; Lt, lithic grains plus polycrystalline quartz) diagrams fall in the recycled orogen provenance field and quartzose recycled field, respectively, implying the source occurred the tectonic activity. Furthermore, geochemical study indicates that the Yanguoxia standstone was formed in an unstable continental setting due to the northwards movement of Indian Plate triggered the collision between the Qilian fold belt and the Qinlingfold belt. These sediments were derived from a mixed source and then deposited in the Lanzhou-Minhe Basin. Most of the felsic components were derived from the granitoid rocks of the Qilian Mountains due to the rapid and intense uplift during the Early Cretaceous while the mafic components were contributed by the basic and ultrabasic rocks of the rapidly rising ophiolite in the Qilian Mountain area. Bivariant log-log plot of Qp/(F+L)(Qp, polycrystalline quartz) against Q/(F+L) shows that Yanguoxia Formation was deposited in the semihumid and semi-arid. Moreover, the pollen also exhibits that the environmental condition during the deposition of Yanguoxia Formation was warm and wet, which affirm such environment was benefit to dinosaur survival. Geochemical study also infers that the Yanguoxia Formation was deposited under the oxidizing condition in a shallow marine environment. The minerals identified from the X-ray diffraction(XRD) analysis of shale and siltstone samples are 4.74%-33.53% clays, 23.45%-41.70% carbonates and 33.99%-71.81% quartz, respectively, which infer that depositional conditions remained uniform during the formation of shales or siltstones of Yanguoxia Formation.展开更多
Fluvial sedimentation of alluvial facies prevailed during the Late Jurassic in the Minhe Basin. On the basis of the study of sedimentary facies of the Upper Jurassic series, this paper focuses on the river types using...Fluvial sedimentation of alluvial facies prevailed during the Late Jurassic in the Minhe Basin. On the basis of the study of sedimentary facies of the Upper Jurassic series, this paper focuses on the river types using the \!Architecture Element" analysis method proposed by Miall, and calculated all the quantitative parameters to reflect the characteristics of the stream channel geometry and hydrodynamic conditions of paleo\|rivers with the equations of Ethrideg, Schumm et al. Finally, we discussed the characteristics of environmental evolution of paleo\|rivers on the quantitative basis. Our conclusion indicates that the evolution of paleo\|rivers during the Late Jurassic, from early to late, shows such a tendency as alluvial fan river→braid river→alluvial fan river→mid\|sinuosity river→high\| sinuosity river.展开更多
文摘The Xining and the Minhe Basins bordering on each other around Ledu innorthwestern China cover a wide area from the west of Lanzhou in Gansuprovince to the east of Xining in Qinghai province.In these inland basins,Meso-Cenozoic terrestrial deposits about 6000-7000 meters in thicknessand rich in mineral resources,such as coal,oi1 as well as salts,had beenaccumunated,which yield abundant organic remains comprising microfossils,such as nonmarine ostracods,charophytes,spores and pollen and macrofos-si1s including bivalves.gastropods,esthierians,fishes,reptiles and plants.
基金Funds for the Central Universities(Grant No.862457)the Natural Science Foundation of China(Grant No.41571177)Gansu Youth Science and Technology Fund(1506RJYA094)
文摘Lanzhou-Minhe Basin is situated on the middle Qilian orogenic belt. Yanguoxia Formation contains abundance of maroon siltstones, mudstones and red sandstones of the lake facies. These sedimentary rocks recorded the process of the tectonic uplift of Qilian Mountains during the Early Cretaceous. We discovered plentiful dinosaur footprints, worm burrows, bird footprints, worm tracks-trails, ripple marks and cross lamination in the Yanguoxia site. Integrated petrographic studies classified sandstones of Yanguoxia Formation as feldspathic litharenite. All plots in the QFL(Q or Qt, total quartz; F, feldspar; L, lithic grains) and Qm FLt(Qm, monocrystalline quartz; Lt, lithic grains plus polycrystalline quartz) diagrams fall in the recycled orogen provenance field and quartzose recycled field, respectively, implying the source occurred the tectonic activity. Furthermore, geochemical study indicates that the Yanguoxia standstone was formed in an unstable continental setting due to the northwards movement of Indian Plate triggered the collision between the Qilian fold belt and the Qinlingfold belt. These sediments were derived from a mixed source and then deposited in the Lanzhou-Minhe Basin. Most of the felsic components were derived from the granitoid rocks of the Qilian Mountains due to the rapid and intense uplift during the Early Cretaceous while the mafic components were contributed by the basic and ultrabasic rocks of the rapidly rising ophiolite in the Qilian Mountain area. Bivariant log-log plot of Qp/(F+L)(Qp, polycrystalline quartz) against Q/(F+L) shows that Yanguoxia Formation was deposited in the semihumid and semi-arid. Moreover, the pollen also exhibits that the environmental condition during the deposition of Yanguoxia Formation was warm and wet, which affirm such environment was benefit to dinosaur survival. Geochemical study also infers that the Yanguoxia Formation was deposited under the oxidizing condition in a shallow marine environment. The minerals identified from the X-ray diffraction(XRD) analysis of shale and siltstone samples are 4.74%-33.53% clays, 23.45%-41.70% carbonates and 33.99%-71.81% quartz, respectively, which infer that depositional conditions remained uniform during the formation of shales or siltstones of Yanguoxia Formation.
文摘Fluvial sedimentation of alluvial facies prevailed during the Late Jurassic in the Minhe Basin. On the basis of the study of sedimentary facies of the Upper Jurassic series, this paper focuses on the river types using the \!Architecture Element" analysis method proposed by Miall, and calculated all the quantitative parameters to reflect the characteristics of the stream channel geometry and hydrodynamic conditions of paleo\|rivers with the equations of Ethrideg, Schumm et al. Finally, we discussed the characteristics of environmental evolution of paleo\|rivers on the quantitative basis. Our conclusion indicates that the evolution of paleo\|rivers during the Late Jurassic, from early to late, shows such a tendency as alluvial fan river→braid river→alluvial fan river→mid\|sinuosity river→high\| sinuosity river.
