桂林水南洞洞穴沉积物的古地磁记录及其古环境意义

通过对桂林水南洞2.5m厚的洞穴沉积物剖面的古地磁初步研究,其结果及地质证据表明该沉积剖面形成期可能与贾拉米洛正向期对应。根据磁化率、磁性矿物的特征和沉积学特征,对该地区这一地质时期的古环境变化提出以下认识:1.第三暖湿期,以钙华沉积为特征;2.第二干冷期,以含有少量钙质的黄褐色粘土为特征,并以含有高矫顽磁性矿物和低磁化率为特征;3.第二暖湿期,以互层的红褐色粘土、含高含量钙质的粘土或钙华为特征,并以含有低矫顽磁性矿物和高磁化率为特征;4.第一干冷期,以褐灰色粘土为特征,并以含有高矫顽磁性矿物和低磁化率为特征;5.第一暖湿期,以地下河沉积相(砂卵石为主)为特征。 

PALAEOMAGNETIC RECORDS FROM SHUINAN CAVE SEDIMENTS, GUILIN AND ITS BEARING ON PALAEOCLIMATIC CHANGES

A detailed palaeomagnetic study of a 2.5m thick section of cave sediment has been made in order to retrieve a record of palaeoenvironmental change in Guilin area. The palaeomagnetic results and geological evidence show that the sediments might have been deposited during the Jaramillo Polarity subchron, i.e. from 0.97 Ma to 0.90 Ma. Based on the susceptibility, the magnetic minerals(S ratios, SIRM etcs.), and sediments characteristics), and a correlation with the loess records in north China, a conceptual model of the palaeoclimatic changes in Guilin area in proposed as follows:1. a warm and wet period (since 0.90 Ma) characterised by travertine deposit; 2. a dry and cold period(0.92 to 0.90 Ma) characterised by yellowish-brown clay with less calcareous content, high coercivity minerals and low susceptibility; 3. a warm and period (0.94 to 0.92Ma) characterised by the interbedded redish-brown clay, calcareous material and travertine, low coercivity minerals and high susceptibility; 4. a dry and cold period (0.96 to 0.94Ma) characterised by greyish-brown clay with less calcareous material, high coercivity minerals and low susceptibility; and 5. a warm and wet period(>0.96 Ma) characterised by the sandy gravel (underground river facies).