(Table 3) Foraminiferal 87Sr/86Sr ratios and ages of ODP Hole 162-986D sediments

Site 986 was drilled to 965 meters below seafloor (mbsf) on the western Svalbard margin to record the onset of glaciations and to date and document the glacial evolution in the Svalbard-Barents Sea region during the Pliocene-Pleistocene. In this paper, results of sedimentological analyses are discussed in light of seismic stratigraphy and new age determinations. The latter were difficult to obtain in the glacial deposits, and datums are sparse. Through combined paleomagnetic data, biostratigraphy, and Sr isotopes, however, an overall chronology for the main evolutionary steps is suggested. The cored sequence at Site 986 is younger than 2.6 Ma, and the lower 60 m of the section contains no evidence of a major glacial influence. An initial glaciation is interpreted to have occurred at ~2.3 Ma, resulting in increased sand deposition from debris flows at Site 986 and forming a prominent seismic reflector, R7. However, glaciers probably did not reach the shelf break until ~1.6-1.7 Ma (Reflector R6), after which the depositional environment was dominated by diamictic debris flows. A gradual change in source area from the Barents Sea to Svalbard is recorded primarily by changes in carbonate and smectite content, ~355 mbsf (Reflector R5), at an interpolated age of 1.4-1.5 Ma. During the last ~1 m.y., Site 986 has undergone more distal deposition as the main depocenters have shifted laterally. This has resulted in less frequent debris flows and more turbidites and hemipelagic deposits, with a slight fining upward of the cored sediments.

研究人员在斯瓦尔巴西部陆缘布设986站位，钻探至海底以下965米（meters below seafloor, mbsf），以记录斯瓦尔巴-巴伦支海地区上新世-更新世冰期作用的起始时间，并确定该区域冰川演化历程并留存相关记录。本文结合地震地层学（seismic stratigraphy）分析结果与新的年代测定数据，对该站位的沉积学分析结果展开讨论。由于冰川沉积中难以获取可靠年代数据，地层基准点较为稀少，研究团队通过整合古地磁数据、生物地层学（biostratigraphy）资料与锶同位素（Sr isotopes）数据，初步构建了该区域主要演化阶段的年代序列。986站位的取心序列形成于2.6 Ma以来，其下部60米地层未发现显著冰川作用影响的证据。研究认为，区域初始冰期发生于约2.3 Ma，此次冰期导致986站位碎屑流（debris flows）沉积的砂质组分占比提升，并形成了标志性地震反射界面（seismic reflector）R7。不过直至约1.6-1.7 Ma（地震反射界面R6），冰川才抵达陆坡折带；此后沉积环境以混杂碎屑流（diamictic debris flows）沉积为主。约355 mbsf处（对应推算年龄1.4-1.5 Ma），碳酸盐与蒙脱石含量的变化记录了物源区从巴伦支海向斯瓦尔巴的逐步转变。近1 Ma以来，随着主要沉积中心（depocenters）发生侧向迁移，986站位的沉积环境逐渐向远端过渡，这一变化使得碎屑流沉积频率降低，浊积岩（turbidites）与半远洋沉积（hemipelagic deposits）占比提升，取心序列整体呈现轻微的向上变细（fining upward）特征。