Authigenic Iron Sulfides Indicate Sea‐Level Change on the Continental Shelf: An Illustration From the East China Sea

Abstract

Driven by glacio-eustatic processes, the Earth has experienced a phase of large-amplitude sea-level change as intensive as any during its history since the Quaternary (Rohling et al., 2014), which has branded profound imprints in marine sediments. For example, with regard to deep-sea sediments, a remarkable feature is the variations in the oxygen isotope records of benthic foraminifera (BF), such as the well-known "LR04 stack" (Lisiecki & Raymo, 2005). Likewise, for sedimentary records on continental shelves, which serve as a link between the land and the deep ocean, sea-level fluctuations over glacial-interglacial timescales (e.g., the cycles in the Earth's orbital eccentricity of ∼100-kyr) are generally expressed as transgression-regression cycles (Shi et al., 2016). Due to their wide and gentle landforms, as well as relatively shallow water depths, continental shelves are much more sensitive to sea-level changes than abyssal regions; even trifling fluctuations in sea-level can give rise to considerable shoreline migration (Yao et al., 2020). Nevertheless, besides the easily identified transgression-regression cycles, it is difficult to trace changes in sea-level over much shorter timescales, which, however, is of great significance to human activities in coastal areas (Yang et al., 2015). This problem is more prominent in relation to sedimentary units with homogenous lithologies, especially for fine-grained sediments which are relatively poor in BF due to high sedimentation rates and

Exploring Spatiotemporal Paleoenvironmental and Paleoceanographic Changes on the Continental Shelf Using Authigenic Greigite: A Case Study From the East China Sea

“…(2007), and calibrated by using the Calib 8.20 program with an updated calibration curve, the Marine20 (Heaton et al., 2020). The AMS 14 C ages from DU1–DU3 (i.e., 0–19.7 m) show obvious reversals (Figure 2a and Table 1), implying low reliability, which is similar to cores DG11 (Figure 1b; Berné et al., 2002) and DH03 (Figure 1b; J. X. Liu et al., 2021) and was suggested to be caused by the strong influence of modern tidal dynamics and/or mixing and re‐accumulation of multiperiod sediments (Z. X. Liu & Xia, 2004). In contrast, the ages of DU4 show a downward increase (Figure 2a and Table 1), indicating high fidelity, which undoubtedly assigns this unit to the MIS 3 deposits.…”

“…Moreover, although Unit 3 is magnetically dominated by greigite in both cores, its B c values in core DH03 are evidently higher than those in core DH02, with averages of ∼47 mT (J. X. Liu et al, 2021) and ∼35 mT, respectively (Figure 10a). The possible direct cause is the higher proportion of SD greigite (with high coercivity) relative to coarse-grained (titano-)magnetite (with low coercivity) in core DH03 than in core DH02.…”

“…Similar to core DH03 (J. X. Liu et al, 2021), based on above-mentioned variations in rock magnetic parameters, the interval of interest from core DH02 could also be split into four subintervals, namely Unit 1 (∼35.3-39.3 m), Unit 2 (∼24.9-35.3 m), Unit 3 (∼19.7-24.9 m), and Unit 4 (∼8.7-19.7 m), which roughly correspond to the early, middle, late MIS 3, and last deglacial deposits, respectively (Figure 3).…”

“…Considering that Unit 4 in both cores primarily comprises sandy sediments magnetically dominated by MD magnetite (Figures 3 and 4, Figure S1 in Supporting Information S1; J. X. Liu et al, 2021), the paleomagnetic data of only Units 1-3 were further analyzed in this study. A soft remanence component that constitutes a small portion of the NRM was ubiquitous in all the measured samples, and it could be easily removed by AF demagnetization to 5-15 mT (Figure 6, Figures S2a, S2b, S3a, and S3b in Supporting Information S1).…”

“…However, it is challenging to reconstruct paleoenvironmental and paleoceanographic evolution based on homogeneously lithologic segments that were deposited within much shorter periods such as a single marine isotope stage (MIS), or even suborbital timescales (J. X. Liu et al, 2021). However, such reconstructions are much more vital for projections of future environmental changes and hence human development in coastal areas (Z. Q.…”