| As a typical period of global transition from greenhouse to ice chamber,paleoclimate research in Eocene plays an important role in the study of global change.The Yilan basin is a well-developed area of Cenozoic Eocene strata in northeast China.The Dalianhe Formation of Eocene is 768.45 m thick and has continuous deposition,which is a good carrier to analyze the paleoclimatic evolution process of Eocene.For high precision sampling,the profile of 640 samples were extracted plant silica body,on the basis of microscopic identification and analysis of characteristics of combination,using principal component analysis,clustering analysis,the ancient vegetation index,the index of wet and dry cold hot paleoclimate reconstruction during the period of ancient vegetation characteristics,further combining with the ignition loss reflect changes of organic matter and carbonate,Based on the analysis of paleoclimate evolution of dalianhe Formation in Yilan basin,the following conclusions are obtained:There are 18 phytatites in the sediments of dalianhe Formation in Yilan basin,including broadleaf,long saddle,short saddle,bell-shaped,fan,square,rectangular,coniferous,toothed,smooth rod,rough rod,pointed,needle,cap,wedge,elliptic,multilateral and ladder-type.The content of the long saddle type is relatively high in the sediments of 588.0?193.4 m.The short saddle type was 457.5?193.4 m.The sediment of fan type 241.5?216.6 m is relatively more;The square type and rectangular type have the highest content in 327.7?193.4 m,while the multilateral type has the highest content in 311.8?132.0 m.The high content of smooth rod and rough rod is 617.5?584.0 m in oil shale and 241.5?132.0 m in sand shale.The high content of spiky type and spiky type occurs in oil shale section 630.5?588.0 m and sand shale section 584.0?132.0 m.The cap type is 617.5?584.0 m in the oil shale and 216.6?193.4 m in the sand shale,the ellipse 899.2?704.2 m in the coal and oil shale conglomerate,and the wedge type is899.2?704.2 m in the coal and oil shale conglomerate and 704.2?m in the oil shale The number is 588.0m.Silicon body ancient vegetation index D/P(broad-leaved vegetation index),Pi/P(conifers vegetation index),T/P(woody vegetation index),according to the Yilan Basin Ypresian vegetation from the grasses vegetation to woody vegetation,middle broad-leaved forest coverage rate,coverage rate of conifers is smaller,the total woody coverage.In the Lutetian broad-leaved forest coverage decreased,coniferous vegetation coverage changed little,and total woody coverage decreased slightly.In the Bartonian,woody vegetation coverage showed strong instability,with obvious fluctuation of low-high-low-high-low.The phytolith paleoclimatic indices Iw(warm index)and Iph(drought index)show that the temperature changed from cold to hot and humidity increased in the Ypresian in Yilan basin.In the Lutetian,the temperature changed to warmer and the humidity was mainly humid.In the Bartonian,the temperature showed a decreasing trend,and experienced two small increases in temperature.The humidity was characterized by relatively humid,and experienced four periods of humidity decrease.The variation of organic matter and carbonate content revealed by the sediment burning loss shows that the early Yilan Area of the Dalianhe Formation was characterized by low productivity and cold and dry climate,while the productivity and temperature of the late Yilan Formation were significantly higher than that of the early Yilan Area.In the early stage of The Lutetian stage,the productivity of palaeo-vegetation was the highest,and the paleo-temperature decreased first and then increased.The productivity of Bartonian paleo-vegetation decreased,and the paleo-temperature also decreased and then increased.The Eocene paleoclimatic processes in this area can be divided into 22 secondary processes of 3 climatic stages,which are colder and drier-warmer and drier-warmer and wetter-warmer and wetter-hot and wet.Lutetian climate stage: warm and humid-warm and humid-warm and humid;And the Bartonian climate stage: warm and arid-warm and humid-warm and humid-warm and humid-warm and humid-warm and humid-cold and humid-cold and humid-warm and humid-warm and humid-warm and humid-warm and humid-warm and humid-cold and humid-cold and humid.The mid-and long-term change trend of temperature and humidity in The Eocene in Yilan area is firstly increasing and then gradually decreasing.Compared with the results from other regions,it is found that the mid-to-long-term temperature variation in the Yilan Area is consistent with that in northeast China,but lags behind the global deep-sea oxygen isotope temperature.The cold,warm,dry and wet evolution analysis of Eocene phytolite paleoclimate in Yilan region provides more detailed research data for the evolution of paleo-temperature and paleo-humidity,enrichis the basic information of Eocene paleoclimate research in northeast China,and provides effective evidence for the response of northeast China to global climate change. |
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