Sea-level changes and carbonate platform evolution of the Xisha Islands (South China Sea) since the Early Miocene

Biogenic reefs and carbonate platforms are valuable natural resources, playing an important role in modulating the global climate and in carbon cycles through biological processes. Biogenic reefs in the Xisha (Paracel) Islands began in the late Oligocene and covaried with the deep-sea basin of the South China Sea and with the aeolian deposit in the Chinese Loess Plateau. Core XK-1 was drilled into the Xisha Islands to their granitic base and well dated by magnetostratigraphy, offering an opportunity to reveal the details of how the Xisha reefs initiated. In this report, the lower section of the biogenic reefs (23.0–24.5 Ma) was sampled for studying magnetic properties. The main results are as follows: (1) magnetic minerals in the XK-1 biogenic reefs are dominated by low-coercivity and relatively coarse-grained magnetite; (2) the variabilities of magnetic parameters can be clustered into two sections around 23.6 Ma, and the differences between the two units are evident both in the amplitudes and the means; and (3) changes in the concentration-dependent magnetic parameters can be well correlated with the records of global deep-sea oxygen and carbon isotopes, and the sea level during the Oligo–Miocene boundary. Based on these results, a close link was inferred between biogenic reef evolution in the Xisha Islands and global climate change. This link likely highlights the covariation or the dominant role of the Asian monsoon in biogenic reefs and involves different responses to global temperature, CO2, and sea-level changes on various timescales. Therefore, we proposed that the origin of biogenic reefs in the Xisha Islands was likely paced by orbital obliquity from a long-term perspective.

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Spatially Modeling the Synergistic Impacts of Global Warming and Sea-Level Rise on Coral Reefs in the South China Sea

Remote Sensing ◽

10.3390/rs13132626 ◽

2021 ◽

Vol 13 (13) ◽

pp. 2626

Author(s):

Xiuling Zuo ◽

Fenzhen Su ◽

Kefu Yu ◽

Yinghui Wang ◽

Qi Wang ◽

...

Keyword(s):

Global Warming ◽

South China Sea ◽

Coral Reefs ◽

Sea Level Rise ◽

Sea Level ◽

South China ◽

The South China Sea ◽

Nansha Islands ◽

Xisha Islands ◽

China Sea

Global warming and sea-level rise (SLR) induced by rising atmospheric CO2 concentrations can cause coral bleaching, death, and submergence of the world’s coral reefs. Adopting the GIS and RS methods, we modeled how these two stressors combine to influence the future growth of the atolls and table reefs of three archipelagoes in the South China Sea (SCS), based on geomorphic and ecological zones. A large-scale survey of the coral communities in Xisha Islands in 2014, Dongsha Islands in 2014–2016 and Nansha Islands in 2007 provided zone-specific process datasets on the range of reef accretion rates. Sea surface temperature and extreme (minimum and maximum) SLR data above 1985–2005 levels by 2100 in the SCS were derived from the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) models forced with the Representative Concentration Pathways (RCPs). Our model projected that: (1) the Xisha Islands and Dongsha Islands may have a better growth status, because the reef flat biotic sparse zone may be recolonized with hard coral and become a biotic dense zone; (2) the southern Nansha Islands reefs have a risk of stopping growing due to their earlier annual bleaching years. The increasing of water depths of these reefs is stronger in the RCP with more emissions. Our approach offers insights into the best-case and worst-case impacts of two global environmental pressures on potential future reef growth under a changing climate.

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Seismic expressions of the Yongle Atoll and the Sansha Yongle Blue Hole in the Xisha Islands, Northwestern South China Sea

10.5194/egusphere-egu2020-7210 ◽

2020 ◽

Author(s):

Jinwei Gao ◽

Hanyu Zhang ◽

Shiguo Wu ◽

Benjun Ma ◽

Wanli Chen ◽

...

Keyword(s):

South China Sea ◽

South China ◽

Seismic Data ◽

Carbonate Platform ◽

Seismic Profiles ◽

Xisha Islands ◽

China Sea ◽

Blue Hole ◽

Intrusive Activity ◽

Seismic Reflections

<p>Sansha Yongle Blue Hole is an oceanic blue hole and is located at the northeastern edge of the Yongle Atoll, in the Xisha Islands of the northwestern South China Sea. The 301.19 m deep makes it to be the deepest known blue hole in the world. Despite the 3-D morphology, hydrochemical properties and chemocline of the blue hole have been comprehensive investigated, its karst formation process is still enigmatic. This study presented new acquired multi-channel seismic data across the Yongle Atoll and seismic data across the Sansha Yongle Blue Hole to describe the seismic reflection characteristics of the carbonate platform and the blue hole in extensive detail. Combined with the scientific wells drilled on the atoll, our results show that carbonate sequences including Lower Miocene, Middle Miocene, Upper Miocene, Pliocene and Quaternary developed on the platform. The magmatically intrusive activity and related magmatic hydrothermal fluid flows have been very active since 5.5 Ma around/on the Yongle Atoll, and may remain active on both slopes and the carbonate platform of the Yongle Atoll at present. Seismic profiles also show that the blue hole is characterized by chaotic seismic reflections which are easily distinguished from surrounding carbonate rocks with sub-parallel, continuous, low to medium amplitude, and low to medium seismic reflections. It seems that the depth of the blue hole is deeper than that measured according to the seismic images. The results of &#948;<sup>18</sup>O from scientific wells show that the phreatic extent in the Xisha Islands is from 14.75 &#8211; 38.89 m to 152.06 &#8211; 183.29 m. Therefore, different from other classic karstological blue holes formed by the phreatic dissolution processes, a hydrothermal &#8211; phreatic model with magmatic hydrothermal pipes and collapse of deep seated phreatic dissolution voids was proposed to describe the formation of the Sansha Yongle Blue Hole.</p>

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Radiocarbon Profiles of Rocky Islet, Xi-Sha Islands: Evidence of Recent Crustal Movements in the South China Sea

Radiocarbon ◽

10.1017/s0033822200005658 ◽

1983 ◽

Vol 25 (2) ◽

pp. 375-379 ◽

Cited By ~ 1

Author(s):

Chen Yee-Chein ◽

Jiao Wen-Qiang

Keyword(s):

South China Sea ◽

Coral Reefs ◽

Sea Level ◽

South China ◽

Granite Gneiss ◽

The South China Sea ◽

Sea Level Changes ◽

The South ◽

Crustal Movements ◽

China Sea

The Xi-Sha Islands comprise 35 coral reefs, cays, and islets lying to the northwest of the South China Sea. Since Miocene time, > 1200m of bioherms developed on slowly subsiding granite-gneiss bed rock. These sediments provide evidence for sea-level changes and crustal movements in the South China Sea.

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Effects of sea-level variation and sedimentary noise variation on the development of biogenic reefs since the Pliocene among the Xisha Islands, South China Sea

Geological Society of America Bulletin ◽

10.1130/b36138.1 ◽

2021 ◽

Author(s):

Ke Zhao ◽

Xuebin Du ◽

Jixin Jia ◽

Xinong Xie ◽

Fang Hao ◽

...

Keyword(s):

South China Sea ◽

Coral Reefs ◽

Sea Level ◽

South China ◽

Oil And Gas ◽

Level Variation ◽

Carbonate Platforms ◽

Xisha Islands ◽

China Sea ◽

Sea Level Variation

Carbonate strata are a vital and favorable reservoir for global oil and gas exploration, and carbonate sedimentary systems record ancient oceanic and paleoclimatic conditions, including paleoenvironmental variations throughout geologic periods. Carbonate platforms are widely distributed among the Xisha Islands in the South China Sea and contain large amounts of oil and gas resources. Biogenic reefs are the dominant parts of the carbonate platforms in the Xisha Islands; however, research on the factors that control and affect biogenic reef development is lacking. In this study, a core from well XK-1, which is located on Yongxing Island in the Xisha Islands, a sedimentary noise model, and time-series analyses were used to determine the effects of sea-level fluctuations from 5.3 Ma to present. The results show that coral reefs in the Xisha Islands are sensitive to eustatic fluctuations and that a decrease in sea level essentially corresponds to an increase in sedimentation rate. Indexes of the East Asian monsoon and other environmental indexes show that the Pleistocene and Holocene were suitable for coral growth; however, the trends shown by these indexes and the sea-level variation indicate that the future growth of coral reefs will be at a disadvantage. Research on the controlling factors of biogenic reefs is of significance for understanding reef growth, performing global reef comparisons, and encouraging the future protection of coral reefs.

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