Bulk mineralogy, elemental geochemistry, and magnetic properties of Holocene sediments in the Estuary and Gulf of St. Lawrence

Physical properties, grain size, bulk mineralogy, elemental geochemistry, and magnetic parameters of three sediment piston cores recovered in the Laurentian Channel from its head to its mouth were investigated to reconstruct changes in detrital sediment provenance and transport related to climate variability since the last deglaciation. The comparison of the detrital proxies indicates the succession of two sedimentary regimes in the Estuary and Gulf of St. Lawrence (EGSL) during the Holocene, which are associated with the melting history of the Laurentide Ice Sheet (LIS) and relative sea-level changes. During the early Holocene (10-8.5 ka cal BP), high sedimentation rates together with mineralogical, geochemical, and magnetic signatures indicate that sedimentation in the EGSL was mainly controlled by meltwater discharges from the local retreat of the southeastern margin of the LIS on the Canadian Shield. At this time, sediment-laden meltwater plumes caused the accumulation of fine-grained sediments in the ice-distal zones. Since the mid-Holocene, postglacial movements of the continental crust, related to the withdrawal of the LIS (~6 ka cal BP), have triggered significant variations in relative sea level (RSL) in the EGSL. The significant correlation between the RSL curves and the mineralogical, geochemical, magnetic, and grain-size data suggest that the RSL was the dominant force acting on the sedimentary dynamics of the EGSL during the mid-to-late Holocene. Beyond 6 ka cal BP, characteristic mineralogical, geochemical, magnetic signatures and diffuse spectral reflectance data suggest that the Canadian Maritime Provinces and western Newfoundland coast are the primary sources for detrital sediments in the Gulf of St. Lawrence, with the Canadian Shield acting as a secondary source. Conversely, in the lower St. Lawrence Estuary, detrital sediments are mainly supplied by the Canadian Shield province. Finally, our results suggest that the modern sedimentation regime in the EGSL was established during the mid-Holocene.

本研究对劳伦琴海峡（Laurentian Channel）自源头至河口的三处活塞沉积岩芯开展了物理性质、粒度、全岩矿物学、元素地球化学及磁学参数测试分析，以期重建末次冰消期以来与气候波动相关的陆源碎屑沉积物物源与搬运过程变化。通过碎屑代用指标对比分析，发现全新世圣劳伦斯河口湾及圣劳伦斯湾（Estuary and Gulf of St. Lawrence, 简称EGSL）存在两套沉积序列，其分别与劳伦冰盖（Laurentide Ice Sheet, 简称LIS）消融历史及相对海平面变化密切相关。全新世早期（10~8.5 ka cal BP），较高的沉积速率配合矿物学、地球化学及磁学特征指示，EGSL的沉积作用主要受控于加拿大地盾（Canadian Shield）上劳伦冰盖东南缘局地退缩产生的融水径流。此阶段，携带沉积物的融水羽状流会在冰缘区造成细粒沉积物的堆积。进入全新世中期以来，与劳伦冰盖消退（约6 ka cal BP）相关的冰后大陆地壳运动，引发了EGSL区域相对海平面（relative sea level, 简称RSL）的显著波动。相对海平面曲线与矿物学、地球化学、磁学及粒度数据间的显著相关性表明，全新世中晚期，相对海平面是调控EGSL沉积动力学过程的主导因素。在6 ka cal BP之后，特征矿物学、地球化学、磁学信号及漫反射光谱数据显示，圣劳伦斯湾的陆源碎屑沉积物主要来源于加拿大大西洋沿岸省份（Canadian Maritime Provinces）与纽芬兰岛西部海岸，加拿大地盾仅作为次要物源区。与之相反，圣劳伦斯河下游河口区的陆源碎屑沉积物主要由加拿大地盾供给。综上，本研究结果表明，EGSL现代沉积格局形成于全新世中期。