Research paper
Sill-related seafloor domes in the Zhongjiannan Basin, western South China Sea

https://doi.org/10.1016/j.marpetgeo.2020.104669Get rights and content

Highlights

  • First insight of sill-folds-dome structures in the western South China Sea.

  • Identification and characterization of forty-two domes in the northeastern Zhongjiannan Basin.

  • Correlation of seafloor domes with subsurface forced folds and igneous intrusions.

Abstract

Magmatism can exert significant impact on sedimentary basins such as the Zhongjiannan Basin (ZJNB), western South China Sea. We have evaluated multibeam bathymetric and multichannel seismic reflection data acquired by the Guangzhou Marine Geological Survey in recent years, in order to investigate the distribution, the characteristics and the subsurface structures related to seafloor domes found in the northeastern ZJNB. Our data revealed forty-two domes at water depths between 2312 m and 2870 m, which are clustered around volcanic mounds, large seamounts and along the edge of the central depression in the study area. These domes are generally circular to elongate or irregular in plan view with large basal areas, and they also have gentler flanks (dips of 1.46°–7.73°) with vertical reliefs ranging from tens to hundreds of meters. In seismic sections, majority of the domes are underlain by variably shaped and complex magmatic sills, which provide a cause-effect relationship between domes formation and igneous intrusions. These intrusions heat surrounding organic-rich sediments, release hydrocarbons, fluidize sediment pore waters and form gas-rich fluids, which fill in sediment and uplift overlying strata immediately above the sills to form forced folds, which are manifested as seafloor domes. These sill-folds-dome structures have important implications for understanding geomorphologic features caused by sills emplaced at depth.

Introduction

Analysis of seafloor geomorphologic features can provide a hint for understanding subsurface structures and processes developed in many sedimentary basins. This is the case of seafloor domes related to igneous sills emplaced at depth along magma-rich margins (Hansen and Cartwright, 2006; Sánchez-Guillamón et al., 2018a, 2018b). These magmatic intrusions have important implications for hydrocarbon exploration (Hansen et al., 2008; Holford et al., 2012), metal mineralization (Nelson, 2000), global climate change (Svensen et al., 2004), and basin-scale processes (Song et al., 2017). Examples of sill-dome structures have been well described in the southern Australian margin (Jackson et al., 2013), the Norwegian Sea (Planke et al., 2005; Omosanya et al., 2017), the eastern central Atlantic (Medialdea et al., 2017; Sánchez-Guillamón et al., 2018a, 2018b) and other worldwide magma-rich margins. Igneous intrusions are also widely distributed among the South China Sea (SCS) basins and continental slopes (Yan et al., 2006; Song et al., 2017; Wang et al., 2019). For instance, sill-fed volcanic mounds and hydrothermal vents have been observed in the Pearl River Mouth Basin (Sun et al., 2014; Zhao et al., 2014) and in the Qiongdongnan Basin (Wang et al., 2019) respectively.

Igneous intrusions may take various forms when emplaced in sedimentary layers (Lee et al., 2006), among which sills are the most common ones. Emplacement of igneous sills within sediments can result in the development of forced folds (Hansen and Cartwright, 2006; Jackson et al., 2013; Sun et al., 2014; Omosanya et al., 2017; Zhang et al., 2017) and/or formation of hydrothermal vent complexes (Jamtveit et al., 2004; Svensen et al., 2004; Planke et al., 2005; Hansen et al., 2008; Magee et al., 2015; Medialdea et al., 2017; Omosanya et al., 2018; Wang et al., 2019). These sill-related forced folds typically manifest as domes on the seafloor (Sánchez-Guillamón et al., 2018a, Sánchez-Guillamón et al., 2018b), and some may be overlain by younger strata, which will date the timing of intrusion event (Trude et al., 2003; Hansen and Cartwright, 2006; Jackson et al., 2013).

Compared to the extensive studies carried out on other geomorphologic features pockmarks, gullies and mud volcanoes in the adjacent northwestern Zhongjiannan Basin (ZJNB, Bai et al., 2014; Chen et al., 2015a, 2015b; Geng et al., 2017; Chen et al., 2018), forced folds or domes in the northeastern basin are barely understood. Domes, as well as volcanic mounds and seamounts, can delineate in detail subsurface magmatic activity, which will help to understand volcanism effects in the ZJNB. Here, we focus on the study of the distribution and morphology of these newly recognized domes and their relationship with massive igneous intrusions at different depths within the basin. With this aim, accurate renderings of these sill-folds-dome structures are provided in the ZJNB, western SCS.

Section snippets

Geological settings

The ZJNB is a Cenozoic sedimentary basin located in the western SCS continental margin. The NNE-strike ZJNB covers an area over 113,900 km2, at water depths ranging from 50 m to 3800 m (Fig. 1). As shown in Fig. 1b, the ZJNB is dominated by tensional normal faults, accompanying by secondary faults with similar strikes arranged in echelon fashion (Qiu et al., 2005). These faults control the development of the basin's uplift-depression frameworks and divide the ZJNB into six secondary structural

Data and methods

Several multichannel seismic reflection sections, together with multibeam bathymetric data acquired by the Guangzhou Marine Geological Survey are used to analyze the distributions, the characteristics and the subsurface structures of domes and igneous sills in the northeastern ZJNB. The multichannel seismic reflection data were acquired in 2001 using a 1587.5 m long streamer with 128 channels (group interval 12.5 m). The seismic source volume is 0.0492 m3 And the shot interval is 25 m. The main

Results

As shown in Fig. 2b, most of the study area lies in a depression with low slope gradients (average value of 0.26°) surrounded by different reliefs (seamounts, cones, mounds, ridges, etc). In the central depression, the second obvious features are the large seamounts and volcanic mounds in the western part of the study area. Forty-two seafloor domes with gentler slopes are found in the study area, which show subcircular, elongate or irregular in plan view (Fig. 2). These domes are distributed in

Domes, igneous sills and forced folds

In the study area, forty-two domes have been identified by the multibeam bathymetric and multichannel seismic reflection data (Fig. 1, Fig. 2). All the domes' formation and development in the study area are closely related to igneous intrusions in the deep strata. The seafloor domal structures correlate well with the underlying igneous intrusions (e.g. Jackson et al., 2013; Sun et al., 2014). As shown in Fig. 13, the igneous intrusions act as a major heat source in the sedimentary basin. Due to

Conclusions

  • (1)

    A total of forty-two domes and their related subsurface structures have been identified by the multibeam bathymetric and multichannel seismic reflection data in the northeastern ZJNB, western SCS. They mainly cluster in the edge of the central depression, around the volcanic mounds or large seamounts, at water depths between 2312 m and 2870 m. These domes generally show circular to elongate or irregular in plan view, with perimeters between 3 km and 26 km and vertical reliefs no larger than

CRediT authorship contribution statement

Minghui Geng: Conceptualization, Methodology, Writing - review & editing, Investigation. Haibin Song: Investigation, Writing - original draft. Yongxian Guan: Data curation, Visualization. Jiangxin Chen: Writing - review & editing. Ruwei Zhang: Software, Validation. Baojin Zhang: Investigation. Xudong Zhang: Investigation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank the Guangzhou Marine Geological Survey for the permission of releasing these data for scientific research. We are grateful to thank Dr. Omosanya, Dr. Schofield and another anonymous reviewer for their constructive comments. This work is supported by the National Key R&D Program of China [grant number 2018YFC0310000]; the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) [grant number GML2019ZD0207]; the National

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