Sea-level and climate signatures recorded in orbitally-forced continental margin deposits over the last 1 Myr: New perspectives from the Bohai Sea

• Published in: Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 2020-07, Vol.550, p.109736, Article 109736
• Main Authors: Yao, Zhengquan, Shi, Xuefa, Liu, Yanguang, Kandasamy, Selvaraj, Qiao, Shuqing, Li, Xiaoyan, Bai, Yazhi, Zhu, Aimei
• Format: Article
• Language: English
• Subjects: Monsoon; Orbital forcing; Principal components analysis; Sedimentary facies; Transgression
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2020.109736

Sediment accumulation in continental margins during the Quaternary Period was substantially influenced by both sea-level fluctuations and climate changes. However, the response of sediment accumulation to these changes on an orbital timescale, remains poorly understood, for two main reasons: the scarcity of sedimentary records with a high-resolution chronology, and the difficulty in distinguishing the role of sea-level from regional climate signals. Here we present the results of sediment color reflectance (c*), grain size and total organic carbon (TOC) content of core BH08 (212.4 m in length, spanning the last ~1 Myr) recovered from the Bohai Sea, China. The chronology of core BH08 on the orbital timescale is constrained by both magnetostratigraphy and astronomical tuning. Sedimentary facies analysis suggests that the sedimentary sequence is dominated by the alternation of a deltaic system and floodplain deposition. Principal components analysis of the grain-size data reveals two principal components (PCs), including PC1, reflecting the 31–500 μm fraction, and PC2, reflecting the 18–66 μm fraction. Comparison of sample scores on PC1, PC2 and c* with the alternation of sedimentary environments reveals that PC1 and c* reflect cycles of deltaic and floodplain deposition at ~100-kyr and ~40-kyr periodicities, while PC2 exhibits a ~20-kyr periodicity, in addition to the ~100-kyr and ~40-kyr cycles. We infer that PC1 and c* are mainly sea-level dependent, whereas PC2 is controlled by the combination of changes in monsoon climate and sea level. We suggest that Milankovitch-scale monsoon climate fluctuations controlled the sediments supply to the Bohai Sea during the last ~1 Myr, while the redistribution of sediments by marine processes (e.g., tidal currents) has partially obscured the monsoonal signal in the grain-size proxy (e.g., PC1) which instead is sensitive to sea-level change. Our results provide an example of the influence of climate and sea-level on sediment accumulation in a shallow continental margin setting influenced by monsoonal climate in an icehouse world. •A 1-Myr record of orbitally-forced continental margin deposits is presented.•Principal components analysis of grain size reveals sea-level and climate signals.•Sedimentation in the Bohai Sea is influenced by sea level and monsoonal climate.•Monsoon signal could be obscured by marine process (e.g., tidal currents).