中国震旦纪至二叠纪古气候

恢复古气候应考虑到极地游移和大陆漂移,因为气候指示物必须与古纬度对比符合。通过古今纬度对比,可清楚地了解到极地游移,再通过不同大陆的古纬度对比,便可了解大陆漂移。这是一个确定大规模板块运动的方法^[4]。

ON THE PALAEOCLIMATES FROM SINIAN TO PERMIAN IN CHINA

To reconstruct the palaeoclimate,the polar wandering and continental drift should be considered,because the palaeoclimate indicators must be coincident with the palaeolatitudes.Through the comparison between the present and past latitudes of different continents,the polar wandering and continental drift are easily understood.This is a method of determining a plate movement in a large scale.The palaeoclimate indicators generally include the tillites,red beds,evaporites,phosphorites,bauxites,hematites,coals,thick carbonates,and the reef-building organisms.Til-lite is an indicator of a frigid climate.Continental glaciers usually occur within 40°of the poles,but mountain glaciers may take place on high mountains at middle or even low latitudes under the control of the landforms.Red beds,bauxites and hematites,all related to the lateritization,are indicators of tropical and subtropical climates,but the forming of red beds demand a warm or hot,arid or semiarid climate.Evaporites have always been deposited in a hot-dry climate and mainly confined between latitudes of 10°-40°.The reef-building organisms,composed of corals,sponges,bryozoans,stromatoporoids,foraminifera,Rudistes and certain algae all lived in the warm water of tropic and subtropic seas,within about 30° of the equator.Modern reef-corals do not live in seawater with an average temperature less than 20℃ and with a depth deeper than 40-60 meters.The algae which are symbiotic with the reef-corals,owing to the photosynthesis,are usually flourished in the shallow sea water of 10-15 m in depth,though they may live in a deeper water about 100 m in depth.The sedimentation of carbonates on a large scale,requirs temperature at least 24℃ and thus,thick beds of limestone may be considered as an indicator of warm tropical or subtropical climate.The formation of coal from plants is a diagenetic process,and the peat is the product of the first stage.Modern peat is generated in high latitudes as well as in temperate and tropical climates.Coal is an excellent indicator for humid climates but is insufficient to be an indicator of temperature,unless it is considered together with the fossil plants from which they were formed and other associated indicators.Based on these plalaeoclimate indicators,we learned that from Sinian to Permian,the territory of China was situated in the area from temperate to tropical climate.This coincides roughly with the palaeolatitude (about 10°-60°N),which is obtained from the data of palaeomagnetism^[2] (Fig.1-2).The glaciers spread in China during the Sinian time,might be the mountain glaciers rather than continental ice sheets.As shown on the above figurs,the palaeomagnetic North pole was located near Irian Island,Indonesia,during the Cambrian time and shifted northward to the Bering Sea,east of Kamchatka Pen.,during the Permian time.If judging from the present orientation,the palaeolatitudes were trending across the Chinese territory from NE to SW during the Early Palaeozoic and shifted gradually to about N-S direction during the Late Palaeozoic Era,approximately parallel to the present longitudes.On the whole,the palaeolatitudes in Chinese territory did not vary significantly during the Palaeozoic Era,so the variation of palaeoclimate zones at that time was indistinct.