中国中东部白垩纪沙漠的时空分布及其气候意义

SPATO-TEMPORAL DISTRIBUTION OF THE CRETACEOUS DESERTS IN CENTRAL AND EASTERN CHINA AND ITS CLIMATIC SIGNIFICANCE

关键词:  白垩纪  沙漠分布  气候带漂变

Key words:  Cretaceous  desert distribution  climatic zone drift

摘要:

本文介绍了中国中东部白垩纪沙漠沉积的时空分布,探讨了时空分布规律,认为:(1)中东部白垩纪沙漠分布严格受气候带控制,其实际分布限于北纬20—40°的干旱带(横跨当时的副热高压带),主要分布于鄂尔多斯盆地、四川盆地、江汉盆地和苏北盆地之中;(2)各盆地沙漠发生的时间不同,鄂尔多斯盆地为早自垩世,四川盆地为中白垩世晚期,江汉盆地为晚白垩世早期,苏北盆地为晚白垩世中期;(3)沙漠发生的穿时性反映了各盆地进入干旱带的顺序,由北到南,由西及东;(4)造成这种顺序的原因是由于亚洲在白垩纪时其总体为顺时针旋转,因而使西北部鄂尔多斯盆地率先进入干旱带,其次是西南部的四川盆地,然后是中部的江汉盆地。晚白垩世的降温事件迫使干旱带南移而使其滞后的最东部的苏北盆地进入干旱带,(5)中国白垩纪沙漠的存在说明处于"温室效应"的大气环流不仅不会"呆滞"而且还有所增强,季风的存在也说明当时的气候并不均一。本文提出了气候带漂变(climatic zone drift)的概念,认为气候变化的表现形式为气候带漂变。漂变既有长周期和短周期漂变之分,又有相对和绝对漂变之别。中国中东部白垩纪沙漠的时空变迁就是干旱气候带漂变的结果。

Abstract:

The spato-temporal distribution of the Cretaceous deserts in central and eastern China is described in this paper.The conclusions are summarized as follows.
1.The distribution of the Cretaceous deserts in central and eastern China is mainly controlled by climatic zones within the extent of the Cretaceous dry climatic zones crossing the subtropical high-pressure zone (palaeolatitudes of 20—40°N) mainly in the Ordos, Sichuan,Jianghan and Subei Basins.
2.The deserts in various basins occur in different times.For instance,the desert appeared in the Ordos Basin during the Early Cretaceous;in the Sichuan Basin during the late Middle Cretaceous;in the Jianghan Basin during the early Late Cretaceous,and in the Subei Basin during the middle and late Late Cretaceous.
3.The diachronism of the desert initiation has revealed that these basins once entered the dry climatic zones in the following order;from north to south and from west to east.
4.This order is attributed to the clockwise rotation of the Asian continent during the Cretaceous,which permit the above-mentioned basins to enter the dry climatic zones in the following order:the Ordos Basin,Sichuan Basin and Jianghan Basin.The southward drift of the dry climatic zones caused by the catathermal events in the middle and late Late cretaceous made the lagged Subei Basin in the easternmost enter the dry climatic zones as the last one.
5.The existence of the Cretaceous deserts in China indicates that the general atmospheric circulations in the "greenhouse" period would not be "sluggish" but strengthened. The existence of the monsoon system also indicates that the climates were not equable at that time.
The concept of climatic zone drift is proposed in this paper.It is believed that the climatic changes are manifested in the climatic zone drift.The drift can be long or short period drift and relative or absolute drift.The temporal and spatial changes of the Cretaceous deserts in central and eastern China might be caused by the dry climatic zone drift at that time.