The Magnetic Properties of Lake Sediments from Dongying Depression and Their Relation to the Change of Environment

Shu Xiaoxin; Liu Zhiwei; Wang Huizhong; Liu Chuanlian; Chen Dongjing; HOng Taiyuan

There are lot of Tertiary lake sediments along the east part of China. Many of them are composed of muds and shales and have high oil-bearing potentialities. To understand the genesis of those sediments, a new magnetic method drawn from environmental magnetism has been introduced. Also, feasibility in applying it to research Tertiary lake sediments has been evaluated. We chose the Niu 38 core composed of red and grey muds and black shales from dingying Depression as research material. Susceptibility (Sus.) of those rocks has been measured. Heavy mineral analysis and total iron, reactive iron and total sulfur analyses of the controlling samples have been done to explain the causes of the Sus. properties in those sediments.From the profile of Sus., we can get three interesting facts: the first is that sediments with different colors, shes have their own special Sus. ; the second is that the change rythem of the Sus. is very clear and it can be divided into three main cycles from the bottom to the top; the third is that the Sus. profile is more sensible to the change of muds and shales than resistivity logs.Heavy mineral analysis shows that red muds with high Sus. are composed chiefly of haematites; grey muds with low Sus. contains less haematites and a bit of pyrites ; black shale with low Sus. mainly pyrites.DOP index suggests that the red muds formed under oxygen water and black shell in euxinic environment.Maeanwhile the grey muds form in a condition of high rate of sedimentation. So we can conclude that the shift of reactive iron to pyrites in the sediments under different redox conditions is the main controlling factor of change of Sus. Then the link between the change of Sus. in Tertiary sediments and their environmental significance can be set up. It is possible for us to predict sedimentary conditions through analyses of Sus. logs.

1 Marine Geology Department, Tongji University, Shanghai 200092;

2 Drilling Company of Shengli Oilfield,Dongying 257000

Publish Date: 1995-12-10

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Abstract: There are lot of Tertiary lake sediments along the east part of China. Many of them are composed of muds and shales and have high oil-bearing potentialities. To understand the genesis of those sediments, a new magnetic method drawn from environmental magnetism has been introduced. Also, feasibility in applying it to research Tertiary lake sediments has been evaluated. We chose the Niu 38 core composed of red and grey muds and black shales from dingying Depression as research material. Susceptibility (Sus.) of those rocks has been measured. Heavy mineral analysis and total iron, reactive iron and total sulfur analyses of the controlling samples have been done to explain the causes of the Sus. properties in those sediments.From the profile of Sus., we can get three interesting facts: the first is that sediments with different colors, shes have their own special Sus. ; the second is that the change rythem of the Sus. is very clear and it can be divided into three main cycles from the bottom to the top; the third is that the Sus. profile is more sensible to the change of muds and shales than resistivity logs.Heavy mineral analysis shows that red muds with high Sus. are composed chiefly of haematites; grey muds with low Sus. contains less haematites and a bit of pyrites ; black shale with low Sus. mainly pyrites.DOP index suggests that the red muds formed under oxygen water and black shell in euxinic environment.Maeanwhile the grey muds form in a condition of high rate of sedimentation. So we can conclude that the shift of reactive iron to pyrites in the sediments under different redox conditions is the main controlling factor of change of Sus. Then the link between the change of Sus. in Tertiary sediments and their environmental significance can be set up. It is possible for us to predict sedimentary conditions through analyses of Sus. logs.

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The Magnetic Properties of Lake Sediments from Dongying Depression and Their Relation to the Change of Environment

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