Astronomically forcing salinity variations in a marginal-marine environment, Bohai Bay Basin, NE China

Wei，Wei1,2; Kemp，David B.1; Lu，Yongchao3; Wang，Zhixiang1; Ma，Yiquan4; Liu，Huiming5; Zhang，Shoupeng5; Zhang，Jingyu6; Teng，Xiaohua7; Robbins，Leslie J.8; Konhauser，Kurt2

2024-10-05

10.1016/j.chemgeo.2024.122300

Chemical Geology   影响因子和分区

0009-2541

Exploring the interdependence between watermass conditions and climate change in marginal marine regions is essential for gaining insights into contemporary environmental challenges arising from global warming. Salinity, a key parameter of watermass conditions in coastal areas, plays a crucial role in influencing nutrient availability, stratification, and the spatial-temporal distribution of redox conditions. Here, we focus on the cyclostratigraphic analysis of gamma-ray (GR) data obtained from Eocene strata in the Luo-69 drillcore from the Bohai Bay Basin (NE China). This analysis establishes a high-resolution astronomical time scale (ATS) for the lower third member of the Shahejie Formation (Es3l), spanning 39.04 Ma to 41.46 million years ago (Ma). Various proxies for watermass conditions, such as salinity, sedimentary structures, mineral content, total organic carbon (TOC), organic carbon isotopes and nitrogen isotopes (δC and δN), exhibit a strong correlation with 405-kyr long orbital eccentricity climate forcing. Notably, spectral analysis of salinity data (represented by the Sr/Ba proxy) reveals a clear astronomical control, with 405-kyr eccentricity cycles that align closely with variations in the GR data. Peaks in paleosalinity, as indicated by Sr/Ba (as well as B/Ga and S/TOC), correspond with maxima in 405-kyr long orbital eccentricity cycles in the GR data. As such, we infer that astronomical forcing regulated long-term changes in watermass conditions, likely through mediation of the East Asia monsoon system. Specifically, during eccentricity maxima, the basin would have experienced a warm and humid climate with pronounced seasonality and a robust summer monsoon. During such periods, increased continental runoff would lead to a rise in lake-levels, facilitating better connections with the ocean, and hence increased salinity. By contrast, during eccentricity minima, cooler and more arid conditions with weaker seasonality would result in lower lake levels which together with a global eustatic lowstand would result in as weakened connection with the open ocean restricting the ingress of seawater into the basin lowering salinity. Our dataset spans the Middle Eocene Climatic Optimum (MECO, ∼40.60–40.10 Ma), identified by elevated GR values and a conspicuous negative excursion in oxygen isotopes. This interval is characterized by a significant decline in salinity, likely attributed to enhanced freshwater runoff driven by an extremely warm and humid climate. The paleosalinity fluctuation recorded by the proxies B/Ga, Sr/Ba, and S/TOC in Bohai Bay Basin demonstrate the sensitivity of marginal-marine environment to subtle changes in climate driven by astronomical forcing. Our results provide new insights into how elemental salinity proxies can be utilized in paleoenvironmental reconstruction studies.

Cyclostratigraphy Middle Eocene Paleosalinity proxy Shahejie Formation

SCI ; EI

英语

通讯

GEOSCIENCES

2-s2.0-85200141348

Scopus

1.State Key Laboratory of Biogeology and Environmental Geology,School of Earth Sciences,China University of Geosciences-Wuhan,Wuhan,430074,China
2.Department of Earth and Atmospheric Sciences,University of Alberta,Edmonton,T6G 2E3,Canada
3.Faculty of Earth Resources,China University of Geosciences (Wuhan),Wuhan,430074,China
4.School of Earth Sciences,Chengdu University of Technology,Chengdu,610059,China
5.Geoscience Research Institute,SINOPEC Shengli Oilfield Company,Shandong,257000,China
6.Centre for Marine Magnetism (CM),Department of Ocean Science and Engineering,Southern University of Science and Technology,Shenzhen,China
7.Department of Tourism,Resources and Environment,Zaozhuang University,Zaozhuang,277160,China
8.Department of Earth Sciences,University of Regina,Regina,S4S 0A2,Canada

Wei，Wei,Kemp，David B.,Lu，Yongchao,et al. Astronomically forcing salinity variations in a marginal-marine environment, Bohai Bay Basin, NE China[J]. Chemical Geology,2024,665.

Wei，Wei.,Kemp，David B..,Lu，Yongchao.,Wang，Zhixiang.,Ma，Yiquan.,...&Konhauser，Kurt.(2024).Astronomically forcing salinity variations in a marginal-marine environment, Bohai Bay Basin, NE China.Chemical Geology,665.

Wei，Wei,et al."Astronomically forcing salinity variations in a marginal-marine environment, Bohai Bay Basin, NE China".Chemical Geology 665(2024).