Depositional control on the sulfur content and isotope of sedimentary pyrite from the southeast coast of China since MIS5

Abstract

The content and isotopic composition of pyrite sulfur are significantly affected by local depositional conditions and are sensitive to environmental evolution. Here, we use core QK11, collected from Xiapu Bay, southeast coast of China, to reveal how local depositional conditions constrained pyrite formation and sulfur isotopic composition since MIS5. Our results show that the content of pyrite sulfur is mainly controlled by the TOC content during interglacial intervals and is limited by the supplement of sulfate in glacial intervals. Therefore, the C/S ratios can effectively identify three transgressions since MIS5. The sulfur isotopic composition of pyrite ranges from -36.7 to 18.4‰ in the whole core. The occurrence of isotopically “heavy” pyrite is observed at the depth of 2.2~9.2, 27.2~33.8, and 43.5~62.5 mbsf, which is attributed to the influence of sulfate reservoir effect, depositional event, unsteady diagenetic environment, and other factors, highlighting the influence of local depositional and diagenetic processes on the isotopic composition of pyrite sulfur. Pyrite sulfur in other layers is generally depleted in 34S, as low as -36.7‰, indicating that the early-stage organiclastic sulfate reduction (OSR) plays an important role in sulfur isotopic fractionation. The results also suggest that organic carbon indicators (TOC/TN ratio and δ13C) combined with the C/S ratio can effectively distinguish between freshwater and marine environments, which is of great significance to reveal depositional evolution in deep time.

Authigenic pyrite and gypsum minerals in offshore Zhoushan sediments: morphology, formation, and environmental implications

“…In Zone 3, the lithological characteristics consist of massive mud sediments with a few sand clumps and horizontal bedding, which indicate tidal facies. Previous research showed that the study area receives significant terrestrial inputs from rivers such as the Yangtze and Qiangtang rivers, with an ample supply of reactive iron (Sun et al, 2020;Zhao et al, 2021;Chang et al, 2022). The presence of abundant iron oxides did not restrict the formation of sedimentary pyrite (Figure 9).…”

Holocene millennial-scale variability of coastal environments on the southern coast of Korea and its controlling factors

“…Recently, several studies have tested the applicability of C/S ratios by measuring the ratios from present river and innercontinental sediments (e.g., Liu et al, 2021Liu et al, , 2022Chang et al, 2022). For example, Liu et al (2021) established a new C/S ratio data set from surface sediments of five rivers (Aojiang, Feiyunjiang, Jiaojiang, Oujiang, and Qiantangjiang Rivers), as well as core sediments offshore the Oujiang Estuary.…”

“…To examine whether these fluctuations occurred locally or regionally, we compared the time series of C/S ratios in this study with those from Goheung Bay on the southern coast of Korea (Lim et al, 2019) and from the previously seawater-filled Daesan Basin (paleo-Daesan Bay) located in the middle reach of the present Nakdong River, Korea (Lim et al, 2022). Based on the relationship between salinity and C/S ratio (Berner, 1984;Berner and Raiswell, 1984;Woolfe et al, 1995 and references therein) and differences from present river and innercontinental sediments (e.g., Liu et al, 2021Liu et al, , 2022Chang et al, 2022), the C/S ratios at the three sites (cores STP16-20 [Lim et al, 2019], STP17-14 [this study], and STP18-06 [Lim et al, 2022]) revealed frequent coastal environmental changes in terms of anoxic conditions (Fig. 7).…”

“…Based on the C/S ratios from the various environmental conditions, they suggested that a C/S ratio of 2.8 can effectively separate freshwater environments (river sediments) from marine environments (Liu et al, 2021). But these studies suggested that C/S ratios should be interpreted with other geochemical indicators, because sedimentation processes, including influence of sea-level change, can modulate the diagenetic path in the marine sediments (Chang et al, 2022; Liu et al, 2022). Thus, the combined information of C/S ratios, the δ 34 S values, and δ 13 C values in coastal sediments can be used to diagnose past anoxia and test possible controlling factors.…”