渤海BH08孔磁学参数变化机制与环境指示

边缘海-陆架区是研究海陆交互作用的理想区域,该区沉积物记录了海平面、气候与构造变化的重要信息.渤海作为我国的内海,前人对该区虽然进行了环境磁学方面的研究,但是受复杂的沉积环境影响,渤海沉积物的磁性变化机制十分复杂,因而需要对该区沉积物磁学性质及变化机制进行深入研究.针对这一问题,本文详细研究了渤海BH08孔岩芯沉积物的磁学性质,结果表明:①沉积物中主要载磁矿物是磁铁矿,部分层位含有高矫顽力的矿物;②岩芯整体磁学性质变化复杂,各项磁学参数变化剧烈,其总体波动与S/Cl值、沉积物红度a*和深海底栖有孔虫δ18O相关性较好;③在主要的海陆交替边界层位发现胶黄铁矿,表明是富硫的弱还原环境,而快速变化的沉积环境和较高的沉积速率是胶黄铁矿得以保存的重要因素,因而胶黄铁矿可作为沉积环境发生转变的一种特征矿物.这些新认识为深入开展渤海地区,乃至陆架-边缘海区古环境研究提供了新的思路和方法.

Marginal sea is an ideal area for studying the interaction of ocean and continent, and its sediment has recorded valuable information of climate and tectonic change. As an important part of Chinese marginal sea, previous researchers have systematically conducted magnetic and paleoclimatic studies on sediments of the Bohai Sea. However, due to complex environmental influences, the magnetic variation mechanism of the Bohai sediments is complicated. In this paper, we study magnetic properties of BH08 core sediments from the Bohai Sea. The core BH08 was drilled to a depth of 212. 4 m in the central Bohai Sea with water depth of similar to 25 m. Magnetic measurements were carried out on selected samples, mainly including the magnetic susceptibility (chi, mass specific), hysteresis loop, acquisition curve of isothermal remanent magnetization (IRM), the first-order reversal curve (FORC) diagram, temperature dependent curves of magnetic susceptibility (chi-T curve) and low-temperature remanent magnetization curves. Results indicate: 1) the main magnetic minerals in sediments are magnetite and greigite, along with some high coercivity minerals such as hematite; 2) magnetic variations are complicated, and are controlled mainly by the fluctuation of sea level according to the correlation between magnetic parameters and S/Cl value, redness (a*) and delta O-18; 3) greigite has been spotted in some layers, which indicates rapid changes in the depositional environment. Based on the high resolution chronology from Yao et al. (2014), we discussed the variation mechanism for magnetic proxies and its environmental implications, which are significant for the following environmental studies in the area.