摘要
Information from eleven profiles of eolian earthy red silty clay and loess of the middle of the Late Miocene to Holocene age have been studied and correlated. A complete summary profile with projected isotopic ages and fossil-bearing beds has been assembled. The profile is subdivided into 12 stratigraphic units proceeding from the lower (older) to the upper (younger) one. The character of mammalian assemblages contained in each unit was analyzed and the corresponding pa- leo-climatic environments were deduced. The environmental character of each period and the change from the middle of the Late Miocene at about 8.0 Ma B.P. up to the Holocene progressed from the hot semiarid and semi-moist, warmer-moist, warm-moister of the Late Miocene. To slightly less warm moist, cool-dry, slight-warmer-moister of the Pliocene; later the cool to cold dry periods alternated frequently with the mild semiarid and semi-moist periods of the Quaternary. Vegetation progressed from the grasslands with sparse woods, wooded shrub-grasslands and subtropical forest-grasslands of the Late Miocene age to sparse grasslands and dry grasslands of the Pliocene; and to sparse grasslands, dry grasslands and tundras of the Quaternary. The climate changes in the Neogene were of low-amplitute in a generally warm-humid background. Those of the Quaternary were of higher am- plitude with a longer phase. Cool or cold dry and slightly warm semiarid and semi-moist climates al- ternated on a generally cool-dry background. The tendency since the start of the Quaternary was the change to more northern and western shift in the Loess Plateau, with progressively cooler and dryer conditions. The dramatic uplift of the Qinghai-Xizang (Tibet) Plateau and the forming and expansion of the Arctic ice sheet might be the main reasons of the more pronounced changes in the Quaternary.
Information from eleven profiles of eolian earthy red silty clay and loess ofthe middle of the Late Miocene to Holocene age have been studied and correlated. A complete summaryprofile with projected isotopic ages and fossil-bearing beds has been assembled. The profile issubdivided into 12 stratigraphic units proceeding from the lower (older) to the upper (younger) one.The character of mammalian assemblages contained in each unit was analyzed and the correspondingpa-leo-climatic environments were deduced. The environmental character of each period and the changefrom the middle of the Late Miocene at about 8.0 Ma B.P. up to the Holocene progressed from the hotsemiarid and semi-moist, warmer-moist, warm-moister of the Late Miocene. To slightly less warmmoist, cool-dry, slight-warmer-moister of the Pliocene; later the cool to cold dry periodsalternated frequently with the mild semiarid and semi-moist periods of the Quaternary. Vegetationprogressed from the grasslands with sparse woods, wooded shrub-grasslands and subtropicalforest-grasslands of the Late Miocene age to sparse grasslands and dry grasslands of the Pliocene;and to sparse grasslands, dry grasslands and tundras of the Quaternary. The climate changes in theNeogene were of low-amplitute in a generally warm-humid background. Those of the Quaternary were ofhigher amplitude with a longer phase. Cool or cold dry and slightly warm semiarid and semi-moistclimates alternated on a generally cool-dry background. The tendency since the start of theQuaternary was the change to more northern and western shift in the Loess Plateau, withprogressively cooler and dryer conditions. The dramatic uplift of the Qinghai-Xizang (Tibet) Plateauand the forming and expansion of the Arctic ice sheet might be the main reasons of the morepronounced changes in the Quaternary.
作者
XUE Xiangxu1,2, ZHANG Yunxiang1,2 & YUE Leping1,2 1. State Key Laboratory of Continent Dynamics (Northwest University), Institute of Cenozoic Geology and Environment, De- partment of Geology, Northwest University, Xi’an 710069, China
2. Institute of Earth Environment, State Key Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences, Xi’an 710075, China
