关于晚新生代准1.2Ma周期构造气候旋回

构造气候旋回的理论要点是构造作用驱动气候变化,因而不同于Milankovitch冰期气候旋回,但两者又都是受地球轨道要素控制的。本文主要根据青藏高原和黄土高原的晚新生代地质记录,以磁性地层为时间标尺,以黄道倾斜(ε)最大变幅位置为模式年龄,划分最近8Ma的准1.2Ma周期构造气候旋回的主旋回层,即MTC₇、MTC₆、MTC₅、MTC₄、MTC₃、MTC₂、MTC₁、MTC₀,它们的界线年龄分别为7.3、6.1、4.9、3.7、2.5、1.3和0.2MaBP。在此基础上,分析了青藏高原构造隆升和黄土高原风尘沉积各自显示的准1.2Ma周期的演变特征,表明它们之间具有构造驱动气候的因果关系。文中还探讨了最近7.3MaBP的古环境变迁,获得了有关晚新生代东亚季风形成演变和环境分异是在轨道气候旋回背景下受构造气候旋回控制的新认识。 

ON TECTONOCLIMATIC CYCLE OF QUASI PERIOD OF 1.2Ma IN LATE CENOZOIC

The tectonoclimatic cycle which states that the climate is determined by tectonic movement is different from Milankovich's glacioclimatic cycle.However,both of them are controlled by the Earth's orbit.On the basis of the late Cenozoic geological records in the Qinghai-Xizang (Tibet) Plateau and the Loess Plateau,with the magnetostratigraphy as timescale and the maximal amplitude position of ecliptic tilt (ε) as model age,the major cyclothems of tectonoclimatic cycle with a quasiperiod of 1.2Ma in the last 8Ma are divided as MTC₇、MTC₆、MTC₅、MTC₄、MTC₃、MTC₂、MTC₁、MTC₀,whose horizon lines in the red clay loess sequence and boundary ages in the ε curve are RCL₄/Br 7.3Ma,RCL₃/RCS₄ 6.1Ma,RCL₂/RCS₃ 4.9Ma,RCL₁/RCS₂ 3.7Ma,WL₃/RCS₁ 2.5Ma,L₁₅/WS₁ 1.3Ma and L₂/S₂ 0.2Ma B P,respectively.And an analysis of the evolution of the eolian deposits of Loess Plateau in periods of about 1.2Ma and the tectonic uplift of Qinghai-Xizang Plateau shows that there existsa causality between them that the climate depends on the uplifting.
The uplift model of the Qinghai-Xizang Plateau constructed by the related information indicates that it has undergone different tectonic stages.First,the pre plateau stage,in which no integrated Qinghai-Xizang block had been formed,existed before 7.3Ma B P in the late Miocene.Second,the stage of isostatic adjustment of the newly- formed inner plateau block ensued during a time from 7.3 to 2.5 Ma B P,in which the uplift of the West Kunlun Mts.has began since 3.7Ma B P.Third,the stage of forming plateau surface followed from 2.5 to 1.3Ma B P,in which the Qilian-Qaidam block coalseced with the major part of the plateau,to form an initial Qinghai-Xizang Plateau similar to its present cnfiguration,and the aggradational plateau surface reached a mean altitude of 2400m.An en bloc uplifting stage has commenced since 1.3Ma B P in which the plateau surface has uplifted from a mean altitude of ca.2400m,successively to ca.2900m(0.9Ma B P),ca.3600m(0.6Ma B P),ca.4200m(0.13Ma B P),ca.4560m(0.09 Ma B P) and today's mean altitude of ca.4800m.
It is evident that the differences of climatic and environmental effects on the eastern China monsoon area,including the Loess Plateau,have been produced around the time of formation and uplift of the Qinghai-Xizang Plateau,in which the change of seasonality resulting from the stage-strengthening winter monsoon is most important.At first the winter monsoon was not conspicuous for a time span of 7.3-3.7Ma B P and strengthened somewhat after 3.7Ma B P.Afterwards,the East Asian monsoon being typical of a much stronger winter monsoon than summer monsoon have been formed.Then,in the process of winter monsoon strengthening,it abruptly changed before 2.5Ma B P,transformed before 1.3Ma B P and altered progressively before 0.2Ma B P,in which the different features of strong-weak associations of the winter and summer monsoon have been shown in every variation,enhanced seasonality step by step and resulted in the differentiation of ecological environment between south ant north,east and west.