Eocene to Miocene sediment provenance features and evolution history of the western slope area in the Xihu Sag of the East China Sea Shelf Basin

Abstract

Rift basins are commonly characterised by multiple sediment sources (e.g. transverse and longitudinal) that change over time during different rifting evolution stages. Therefore, tracing sediment provenance to decipher the sedimentary source-to-sink analyses processes in rift basins is important to predict sandy reservoirs. The Xihu Sag in the East China Sea Shelf Basin, particularly its western slope, features large-scale sand bodies of unclear origin. We used petrography, heavy minerals and geochemistry to study sediment provenance in the Eocene Baoshi to Miocene Longjing formations. Our work suggests there are three distinct areas (namely zones A, B and C) affected by different source areas. Zone A, influenced by the Hupijiao uplift, primarily contains metamorphic rock minerals; Zone B, affected by the Haijiao and Hupijiao uplifts, contains igneous and metamorphic rock minerals; and Zone C, dominated by the Haijiao uplift, features igneous with some metamorphic sources, which increase over time, indicating stronger sediment input from the northern Hupijiao uplift. Rare earth element analysis suggests a continental margin and island arc setting, primarily with intermediate–acid felsic rock sources. However, a Eu negative anomaly in Eocene upper Pinghu Formation to the Miocene Longjing Formation indicates some basic source contributions, possibly from a volcanic belt east of the South Yellow Sea. This intermediate–basic volcanic rock belt is located to the northwest of the Hupijiao uplift and may provide clasts for zones A and B through axial channels. These findings indicate that varied sediment sources in the different zones and basin evolution stages with a growing extra-basinal contribution from the Eocene to Miocene, which align with the tectonic shift from the rifting to post-rift period, are essential for understanding the sedimentary filling in this area.

KEY POINTS

1. Three distinct regions are identified, each influenced by different source areas.

2. Rare earth elements indicate that the tectonic setting of the source terranes was active continental margin and continental island arc.

3. From Eocene to Miocene, there was a growing influence of distal source areas entering the basin through the axial fluvial channels.

4. Sediment provenance changes respond to the basin-scale tectonic evolution.

Keywords:

• Xihu Sag
• provenance
• heavy
• minerals
• rare earth elements
• petrographic features
• principal-component analysis

Acknowledgements

We would like to thank CNOOC Shanghai Branch for access to the samples and data as well as permission to publish. We want to thank the editor and reviewers for their insightful suggestions, which greatly enhance the quality of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors. The authors confirm that the data supporting the findings of this study are available within the article.

Data accessibility statement

The authors confirm that the data supporting the findings of this study are available within the article.

Additional information

Funding

This work is supported by China National Natural Science Foundation of China (No. 41902108).