The Cenozoic Yanyuan basin is located in the huge Longmenshan—Jinpingshan nappetectonic belt along the eastern margin of the Qinghai—Tibet plateau. The basin is the largest and the best\|preserved intraorogenic basi...The Cenozoic Yanyuan basin is located in the huge Longmenshan—Jinpingshan nappetectonic belt along the eastern margin of the Qinghai—Tibet plateau. The basin is the largest and the best\|preserved intraorogenic basin above 2300m ASL.The basin has deposited different kinds of sediments with 1600m in depth. The early Tertiary strata were first named as Lijiang formation in 1961, and later named as Hongyanzi formation. The later Tertiary strata, the lignite\|bearing strata, were once named as Xigeda formation. Li Yougheng(1978) found some mammal fossils in the strata, so they named it Yanyuan formation. The Hongyanzi Formation which thickness is 1022m can be divided into five members according to the lithologic characters. The first one is mainly made of purplish\|red coarse conglomerates. The composition of gravel mainly consists of limestone and purplish\|red sandstone and marl. The second one consists of sandstone interbedded with conglomerate. The member has three cyclic sequences from conglomerate to sandstone. The composition of gravel of this member is mainly limestone. From bottom to top the degree of sorting and roundness tends to be well. In sandstones or sand lenticules the oblique bedding and trough cross\|bedding can be seen. The third one is the member of sandstone and mudstone. The sandstone is light purple while the mudstone is purplish red. Ripple marks can be seen in the sandstone. The forth one consists of conglomerate interbedded with mudstone, The conglomerate and the sandstone assume three cyclic sequences. The composition of the gravel is chiefly limestone. The fifth one is a member of light purple massive conglomerate. The composition of the gravel is limestone. The imbricate structure can be seen in the conglomerate. The strata belong to later Eocene epoch in accordance with the fossils of mammals, plants and ostracoda in it.展开更多
The southeastern edge of the Tibetan plateau is marked by several thrust sheets trending roughly in E\|W direction. The Yanyuan thrust sheet is bounded by three arcuate thrust belts, marked by high mountain ranges wit...The southeastern edge of the Tibetan plateau is marked by several thrust sheets trending roughly in E\|W direction. The Yanyuan thrust sheet is bounded by three arcuate thrust belts, marked by high mountain ranges with the Jinhe belt on the north, the Qianhe belt on the south and the Ninglang belt on the west. Within the Yanyuan thrust belt are sedimentary cover rocks of the Yangtze platform, with ages ranging from Sinian to Triassic. In the north, the thrust sheet is overlain by the Muli thrust sheet along the Jinhe belt, while in the south, it is underlain by the Kangdian paleoland along the Qianhe belt. The youngest rocks on the foot wall are late Eocene to Oligocene in age, indicating that the thrusting occurred in the late Tertiary. The top of the Yanyuan thrust belt is truncated by a flat erosion surface similar to that on the plateau to the north. Along a north\|dipping normal fault bordering the Yanyuan basin on the south, the erosion surface is tilted to the south against Triassic rocks. The basin is filled with coal\|bearing clastic sediments of Pliocene and early Pleistocene age, which gives the timing of the normal faulting. Based on the faulting pattern, we propose that the southeastern edge of the Tibetan plateau underwent a large amount of N\|S shortening and uplift along the Yanyuan thrust sheet in the late Tertiary, while the subsequent normal faulting that had occurred along the Yanyuan basin during the Pliocene and Pliocene can be interpreted to have accommodated gravitational collapse of the crust.展开更多
文摘The Cenozoic Yanyuan basin is located in the huge Longmenshan—Jinpingshan nappetectonic belt along the eastern margin of the Qinghai—Tibet plateau. The basin is the largest and the best\|preserved intraorogenic basin above 2300m ASL.The basin has deposited different kinds of sediments with 1600m in depth. The early Tertiary strata were first named as Lijiang formation in 1961, and later named as Hongyanzi formation. The later Tertiary strata, the lignite\|bearing strata, were once named as Xigeda formation. Li Yougheng(1978) found some mammal fossils in the strata, so they named it Yanyuan formation. The Hongyanzi Formation which thickness is 1022m can be divided into five members according to the lithologic characters. The first one is mainly made of purplish\|red coarse conglomerates. The composition of gravel mainly consists of limestone and purplish\|red sandstone and marl. The second one consists of sandstone interbedded with conglomerate. The member has three cyclic sequences from conglomerate to sandstone. The composition of gravel of this member is mainly limestone. From bottom to top the degree of sorting and roundness tends to be well. In sandstones or sand lenticules the oblique bedding and trough cross\|bedding can be seen. The third one is the member of sandstone and mudstone. The sandstone is light purple while the mudstone is purplish red. Ripple marks can be seen in the sandstone. The forth one consists of conglomerate interbedded with mudstone, The conglomerate and the sandstone assume three cyclic sequences. The composition of the gravel is chiefly limestone. The fifth one is a member of light purple massive conglomerate. The composition of the gravel is limestone. The imbricate structure can be seen in the conglomerate. The strata belong to later Eocene epoch in accordance with the fossils of mammals, plants and ostracoda in it.
文摘The southeastern edge of the Tibetan plateau is marked by several thrust sheets trending roughly in E\|W direction. The Yanyuan thrust sheet is bounded by three arcuate thrust belts, marked by high mountain ranges with the Jinhe belt on the north, the Qianhe belt on the south and the Ninglang belt on the west. Within the Yanyuan thrust belt are sedimentary cover rocks of the Yangtze platform, with ages ranging from Sinian to Triassic. In the north, the thrust sheet is overlain by the Muli thrust sheet along the Jinhe belt, while in the south, it is underlain by the Kangdian paleoland along the Qianhe belt. The youngest rocks on the foot wall are late Eocene to Oligocene in age, indicating that the thrusting occurred in the late Tertiary. The top of the Yanyuan thrust belt is truncated by a flat erosion surface similar to that on the plateau to the north. Along a north\|dipping normal fault bordering the Yanyuan basin on the south, the erosion surface is tilted to the south against Triassic rocks. The basin is filled with coal\|bearing clastic sediments of Pliocene and early Pleistocene age, which gives the timing of the normal faulting. Based on the faulting pattern, we propose that the southeastern edge of the Tibetan plateau underwent a large amount of N\|S shortening and uplift along the Yanyuan thrust sheet in the late Tertiary, while the subsequent normal faulting that had occurred along the Yanyuan basin during the Pliocene and Pliocene can be interpreted to have accommodated gravitational collapse of the crust.
