西太暖池区生物组分对海底表层沉积物物理力学性质的影响

西太平洋暖池区是指位于热带西太平洋及印度洋东部海表温度常年在28 ℃以上的海域,是全球海表温度最高的深海区,构造环境与沉积环境复杂,沉积物中的生物组分含量差异较大,生物组分会对深海沉积物物理力学性质产生显著影响,但目前对沉积物中生物组分含量和沉积物物理力学性质之间的相关性关系尚不明确。本文对西太平洋暖池区核心部位的表层沉积物样品进行现场物理力学性质测试和室内涂片鉴定,研究深海表层沉积物的物理力学性质与生物组分之间的关系。结果表明:研究区表层沉积物含水率范围为61.1%~435.1%,天然密度范围为1.04~1.76 g/cm³,贯入阻力范围为0~100 kPa,十字板剪切强度范围为0~8.6 kPa,整体具有高含水率、低密度、低强度等典型的深海沉积物物理力学性质特点。西加洛林海脊、海山等CCD以浅的区域为钙质生物组分>50%的钙质沉积区;西加洛林海槽西南部及其周边的深水沟槽地区一般为硅质生物组分>50%的硅质沉积;西加洛林海盆内部则主要为黏土沉积区。随钙质生物组分减少和硅质生物组分增多,表层沉积物类型分别为钙质沉积物、黏土沉积物和硅质沉积物,天然含水率变高,天然密度、贯入阻力和十字板剪切强度降低,表明深海表层沉积物的物理力学性质与生物组分含量密切相关:贯入阻力、十字板剪切强度、天然密度与钙质生物组分含量呈正相关,与硅质生物组分含量呈负相关;而天然含水率正好相反,与钙质生物组分含量呈负相关,与硅质生物组分含量呈正相关。本文建立了深海沉积物中生物组分与物理力学性质之间的相关关系,提出了沉积物生物组分含量与物理力学性质之间的拟合公式,可以为深海沉积物工程性质的评价提供参考。

Effects of biocomponent on the geotechnical properties of seafloor surface sediments in the Western Pacific Warm Pool

The Western Pacific Warm Pool (WPWP) is located in the tropical western Pacific and the eastern Indian Ocean with an average annual surface water temperature of over 28 ℃. Due to the varying depositional environments under different tectonic settings, the biocomponent contents in pelagic sediments of the WPWP differ greatly. Biocomponents have a significant impact on the geotechnical properties of deep-see sediments, however, the correlation between the two has not been studied previously. To fill this gap, we investigated the geotechnical properties of surface sediments in the core of the WPWP and identified the sediment components under microscope. As results show, the natural moisture content ranges from 61.1% to 435.1%, natural density from 1.04 to 1.76 g/cm³, penetration resistance from 0 to 100 kPa, and vane shear strength from 0 to 8.6 kPa. The high natural moisture content, low natural density, and low shear strength are consistent with the characteristics of typical geotechnical properties of deep-sea sediment. Calcareous sediments of the Western Carolingian ridge, seamounts and other areas with water depths less than the CCD (Carbonate Compensation Depth) generally contain more than 50% calcareous biocomponents, and the same proportion of siliceous biocomponents is likely found in siliceous sediments of the southwestern Western Carolingian trough and surrounding deep trench areas; whereas clay sediments mainly distribute in the Western Carolingian basin. With decreasing calcareous and increasing siliceous biocomponents, the surface sediment varies from calcareous to clay to siliceous and its natural moisture content increases while its natural density, penetration resistance and vane shear strength decrease. It suggests that the geotechnical properties of deep-sea surface sediment are correlated with the contents of biocomponents—specifically, its penetration resistance, vane shear strength and natural density are positively influenced by calcareous biocomponents and negatively influenced by siliceous biocomponents, while the opposite holds true for natural moisture content. This paper establishes the relationship between biocomponent and geotechnical properties of abyssal sediments, and proposes a fitting formula between the biocomponent content and geotechnical properties, which is useful for evaluating the geotechnical properties of deep-sea sediments.