Paleomagnetic results of the Cretaceous marine sediments in Tongyouluke, southwest Tarim  

作　　者：SHEN Zhongyue1, CHEN Hanlin1, FANG Dajun1, DING Jinghai1, ZHANG Shiben2, HUANG Zhibin2 & LI Meng2 1. Department of Earth Sciences, Zhejiang University, Hangzhou 310027 China 2. Tarim Oil Field Company, PetroChina Company Limited, Korla 830011, China 

出　　处：《Science China Earth Sciences》2005年第3期406-416,共11页中国科学（地球科学英文版）

基　　金：supported in pat by the National Natural Science Foumdation of hina(Gramt Nos.40274014);Tarim Oil Field Company,PetroChina Compay Limited(Contract No.4130109 008).

摘　　要：Paleomagnetic and rock magnetic studies on samples of 18 sites from the Creta- ceous marine sedimentary rocks in the Tongyouluke section, Akto County, southwest Tarim, China show that the magnetic carriers of the Lower Cretaceous are dominated by hematite with some magnetite, while the magnetic carriers of the Upper Cretaceous are characterized by a combination of magnetite and titanomagnetite as well as hematite and goethite. Stepwise thermal demagnetization is performed and vector analysis is used to isolate magnetic components, which illustrates a single magnetic component or double magnetic components. The high temperature stable components are dual polarities and pass polarity test, reversal test and consistency test. The overall mean direction of the Lower Cretaceous is D = 27.0°, I = 42.0°, α95=6.5° with pole position at φ = 190.3°, λ=63.1°, dp=4.9°, dm=8.0°. The overall mean direction of the Upper Cretaceous is D = 29.1°, I = 39.4°, α95=11.2° with pole position at φ =190.9°, λ=60.3°, dp= 8.0°, dm=13.4°. Compared with the inclination of the Early Cretaceous from red beds of north Tarim, the contemporary inclination of southwest Tarim is 10.0°±7.8° sharper, but it is still 8.1° ±8.9°, shallower than that of Early Cretaceous basalts in southwest Tarim. Although these pa- leomagnetic data show slightly larger confidence limit, the paleolatitude of the marine Cretaceous tends to lie between that of terrestrial red beds and volcanic rocks.Paleomagnetic and rock magnetic studies on samples of 18 sites from the Creta- ceous marine sedimentary rocks in the Tongyouluke section, Akto County, southwest Tarim, China show that the magnetic carriers of the Lower Cretaceous are dominated by hematite with some magnetite, while the magnetic carriers of the Upper Cretaceous are characterized by a combination of magnetite and titanomagnetite as well as hematite and goethite. Stepwise thermal demagnetization is performed and vector analysis is used to isolate magnetic components, which illustrates a single magnetic component or double magnetic components. The high temperature stable components are dual polarities and pass polarity test, reversal test and consistency test. The overall mean direction of the Lower Cretaceous is D = 27.0°, I = 42.0°, α95=6.5° with pole position at φ = 190.3°, λ=63.1°, dp=4.9°, dm=8.0°. The overall mean direction of the Upper Cretaceous is D = 29.1°, I = 39.4°, α95=11.2° with pole position at φ =190.9°, λ=60.3°, dp= 8.0°, dm=13.4°. Compared with the inclination of the Early Cretaceous from red beds of north Tarim, the contemporary inclination of southwest Tarim is 10.0°±7.8° sharper, but it is still 8.1° ±8.9°, shallower than that of Early Cretaceous basalts in southwest Tarim. Although these pa- leomagnetic data show slightly larger confidence limit, the paleolatitude of the marine Cretaceous tends to lie between that of terrestrial red beds and volcanic rocks.

关 键 词：TARIM paleomagnetism  Cretaceous  magnetic inclination  red beds  marine sedimentary rock. 

分 类 号：P534.53[天文地球—古生物学与地层学]