苏北盆地兴化1#钻孔沉积物的岩石磁学特征

Rock magnetism characteristics of the deposits in Xinghua Core in the Northern Jiangsu Basin,China

对苏北盆地兴化1#钻孔岩心沉积物进行了质量磁化率、频率磁化率、变化曲线、等温剩磁和磁滞回线等参数的测试分析,结果表明,粘土质沉积物中的主要载磁矿物为磁铁矿和赤铁矿;砂质沉积物中的磁性矿物除了磁铁矿和赤铁矿外,还含有少量的磁赤铁矿和针铁矿.针铁矿普遍存在于钻孔下部的样品中.整个钻孔沉积物中的磁性矿物颗粒都是介于单畴和多畴之间的准单畴颗粒,但粘土质沉积物中的磁性矿物颗粒更趋近于单畴颗粒,而砂质沉积物中的磁性矿物颗粒更趋近于多畴.根据不同的磁性矿物组合特征,选择合理的温度和磁场强度区间对古地磁退磁结果进行分析,得到沉积物可靠的特征剩磁方向,为古地磁年代学提供依据.

Rock magnetism measurements were carried out on representative samples from a 350 m core obtained at Xinghua, Northern Jiangsu Basin. Combined mass susceptibility, frequency dependent susceptibility, temperature dependent susceptibility, isothermal remanent magnetization acquisition and hysteresis measurements found that magnetite and hematite are dominate magnetic minerals of the whole core, while maghematite and goethite present as well in sandstones but absent in mudstones. Goethite exists in the lower part of the core, and it leads to the decrease of the magnetic susceptibility. All the magnetic minerals are generally pseudo-single-domain in dimension, but that in mudstones are more close to single-domain and that within sandstones are more close to multi-domain. This recognition of various combinations of magnetic minerals will provide vital information to interpret demagnetization results during paleomagnetic stratigraphy chronology and to understand the environment magnetic proxies as well.