Petrography,geochemistry and provenance of the sediments of the Early Cretaceous Yanguoxia Formation,Lanzhou-Minhe Basin,Northwest China     

Ding-ding Du  Muhammad Saleem Mughal  Cheng-jun Zhang 《山地科学学报》2018,15(9):2068-2088

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 QmFLt (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 Qinling fold 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 semi-humid 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%-4l.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.  相似文献   

First Record of the Belemnite Genus Hibolithes from Late Jurassic–Early Cretaceous Turbidites from Malaysia     

Muhammad MURTAZA  Abdul Hadi Abd RAHMAN  Joerg MUTTERLOSE  Najiatun NAJLA  Mazshurraiezal Bin NASIR 《《地质学报》英文版》2021,95(2):333-341

Discovery of the remains of belemnites referred to the Hibolithes sp. from the Jurassic–Cretaceous Pedawan Formation in Sarawak, on the island of Borneo(Malaysia) comprises four fragments of belemnite rostra. The specimens are characterized by multiple fractures and vein filling. Two fragments measuring about 130 mm are relatively intact, with only part of the alveolar region missing; a third piece represents the middle part of a rostrum, and the fourth specimen is too fragmentary to be assigned to any specific part of the rostrum. Based on specimen characteristics, a Tithonian–Hauterivian age is plausible. The sedimentary succession that yielded the belemnite material comprises thick shale that reflects the Te division of Bouma sequence. The occurrence of a Hibolithes taxon in the uppermost Jurassic to lowermost Cretaceous Pedawan Formation sediments in Borneo reflects a near to global palaeobiogeographic distribution of this genus.  相似文献   

Correction to: A local scale flood vulnerability assessment in the flood‑prone area of Khyber Pakhtunkhwa,Pakistan     

Nazeer  Muhammad  Bork  Hans‑Rudolf 《Natural Hazards》2022,111(1):1103-1103

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影响三大洲的北非强沙尘暴动力机制WRF-chem模拟与分析北大核心          下载免费PDF全文

Altayeb Raga  王坚红  Abdoul Aziz Saidou Chaibou  Muhammad Arsha  Mohammed AbdAllah  Birhanu Asmerom Habtemicheal 《气象科学》2022,42(6):769-780

基于WRF-chem模式对北非2018年3月下旬的典型强沙尘暴过程进行模拟,分析了此次强沙尘发生季节、持续时间、局地特征以及传输路径的关键动力系统与动力机制。鉴于起沙是沙尘暴发生的关键点之一,并且起沙主要取决于风力和下垫面沙源性质,本文测试了三种起沙参数化方案的影响,并将模拟结果与卫星MODIS监测及其再分析资料MERRA-2进行了对比,又经系列统计方法检验。结果显示,宏观思路的起沙方案GOCART比AFWA和UoC两种起沙方案更适合此次大尺度强沙尘暴数值模拟(锋面跨度接近60个经度)。综合沙尘暴关键系统的动力机制分析和数值模拟结果显示,强沙尘暴关键系统为深厚的西风槽、沙尘冷锋锋面和锋后的地面高压反气旋。北非中部深厚的西风槽为后倾槽,该系统稳定,造成沙尘暴持续时间长。沙尘暴锋后反气旋中的下沉气流抑制了扬沙向高层扩散,造成低层能见度恶劣。沙尘锋区结合了动力、热动力以及湿热动力不稳定,因此锋区风力大,地面沙尘驱动力强。而西风槽和强大反气旋依托环流形势,提供了沙尘传输到三大洲的长途输送力。  相似文献