Clay-mineral distribution in recent deep-sea sediments around Taiwan: Implications for sediment dispersal processes
Introduction
The provenance study of detrital sediments in the ocean is essential for a better comprehension of environment and climate interactions that occurred in nearby land source areas. Climatic variability and tectonics were regarded to be the primary controlling variables for erosion on different geological timescales, though their comparative roles are still heavily debated (Burbank et al., 2003; Clift et al., 2006; Dadson et al., 2003; Liu et al., 2007b; Molnar, 2004; Peizhen et al., 2001; Reiners et al., 2003). High sediment discharge and tectonic elevation in tropical southeast Asia make river basins important areas for studying variables that regulate weathering (Dadson et al., 2003; Huang et al., 2016; Milliman et al., 1999; Milliman and Syvitski, 1992). Such discussion further strengthened the need for a better comprehension of the variables controlling weathering and erosion in mountain ranges and the largest river basins in the world (Canfield, 1997; Gaillardet et al., 1999; Kandasamy and Chen, 2006; Liu et al., 2007b; McLennan, 1993; Milliman and Syvitski, 1992; Singh et al., 2005; Summerfield and Hulton, 1994).
Taiwan is known to be an area with one of the world's highest sediment yields (Dadson et al., 2003; Li et al., 2011). The variability and intensity of the processes controlling sediment transport around Taiwan, which include frequent typhoons, heavy rainfall, strong tectonic activity, and intense oceanic circulation, make it an ideal area to study the effect of these processes on sediment transfer to the deep-sea. This paper, therefore, seeks to understand how different variables play a role in the distribution of detrital fine-grained sediments around Taiwan. The offshore areas around Taiwan receive detrital sediments from various sources including the Taiwan Island, rivers in southeast China (e.g., the Jiulong River and Pearl River, specifically supplying sediments to offshore southwest Taiwan), the Luzon Islands, and the Ryukyu Islands through various sedimentary processes (Fig. 1). Deep-water sediments around offshore Taiwan are dominated by hemipelagites and gravity-flow deposits. This may lead to different clay mineral distributions in offshore Taiwan, where it encompasses various types of tectonic settings and basins.
There have been a few studies using clay mineralogy to unravel the sediment source-to-sink for the seafloor sediments in the Northeast South China Sea (NE SCS) e.g., (Liu et al., 2010b; Liu et al., 2008b; Wan et al., 2007). However, no study has been done using clay minerals as tracers to study sediment source-to-sink in offshore eastern Taiwan, in the upper-slope of the Manila accretionary wedge, and the Luzon forearc basin. We study clay mineralogy to unravel the source-to-sink movement of recent deep-sea sediments around Taiwan, including the Ryukyu subduction zone, Huatung Basin in the Philippine Sea Plate, the Manila subduction zone, and the rifted continental margin of the NE South China Sea near Taiwan (Figs. 1b, 2). We focused on determining the changes in clay mineral distributions in different sedimentary facies (hemipelagites and turbidites, in particular) in the top 50 cm of seafloor sediments around Taiwan to understand the sediment dispersal processes. River-mouth samples from 31 Taiwanese rivers and a few grabbed surface sediment samples from southern Taiwan Strait (Tainan Shelf) were collected and analyzed for a better understanding of the sediment sources.
The objectives of this research are:
- 1)
To explore the sedimentary processes responsible for various deep-sea sediment facies around Taiwan.
- 2)
To unravel the distribution patterns of clay minerals in different sedimentary facies of deep-sea surface sediments.
- 3)
To decipher how sediments are dispersed through river-fed turbidity currents, hypopycnal plumes, and oceanic currents, more specifically the Kuroshio Current, around Taiwan.
Section snippets
Geological setting and environmental background
Taiwan is situated at the tectonic collision boundary between the Philippine Sea Plate and the Eurasian Plate, leading to a rapid uplift rate of 5–7 mm/a in the Taiwan orogen (Dadson et al., 2003; Li et al., 2011). The Taiwan orogen connects two opposite dipping subduction systems: the Manila subduction zone to the south where the South China Sea lithosphere is being subducted eastwards beneath the Philippine Sea Plate, building an accretionary wedge; and the Ryukyu subduction zone to the
Sample collection
A set of 36 deep-sea sediment cores from eastern, southern, and southwestern offshore parts of Taiwan, together with 31 river-mouth sediment samples from major Taiwanese rivers and 5 grabbed surface sediment samples from southern Taiwan Strait (near the shelf edge called Tainan Shelf) were collected for this study (Fig. 2). The gravity (G), piston (P), calypso-piston (C), and box (BC) cores were collected onboard R/V Ocean Researcher I during OR1–891, OR1–1013, OR1–1048, OR1–1138, OR5–0032
Sediment facies for seafloor sediments
Based on both sedimentological data and grain-size data, we distinguished two end-member sediment facies (turbidite and hemipelagite facies) for the studied cores from different provinces around Taiwan (Fig. 3, Figs. S1-S13). Most of the studied cores are characterized by both facies. For example, the core MD18–3527-BC, located in the East Nanao Basin, consisting of both hemipelagites and turbidite (Fig. 3). Nearly 1/4 of the studied cores are composed mainly of homogeneous silty-clay,
Clay minerals at sediment sources
The main terrestrial sediment sources for the deep-sea areas around Taiwan are the Taiwan Island, the Luzon volcanic arc, Ryukyu Islands, and SE China. Prior studies pointed out that smectite is the characteristic clay mineral from Luzon Island and kaolinite is an index mineral from SE China, in particular from the Pearl River (Liu et al., 2007b; Liu et al., 2009; Liu et al., 2016b). As for the Ryukyu Islands, there is no literature reporting the characteristic clay minerals in river sediments.
Conclusions
For the first time, we studied the clay mineralogy of recent deep-sea sediments around Taiwan in hemipelagites and turbidites within the top 50 cm of the sediment cores to determine the source and transport of detrital fine-grained sediments. River-mouth sediments around Taiwan were also studied for clay mineralogy to constrain the source characteristics of the Taiwanese rivers. Our results show that the clay mineral assemblages in both hemipelagites and turbidites of different provinces
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
This research was funded by the Ministry of Science and Technology, Taiwan, through grant MOST108-2116-M-008-002 and MOST109-2611-M-008-001. We thank Dr. Li Lo of National Taiwan University, Taiwan for providing core material from OR1-GI2B-G. Constructive comments and detailed instructions from the guest editor, Frederic Mouthereau, and reviewers, Elda Miramontes and the other anonymous reviewer are highly appreciated.
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