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[Display omitted] • Investigation on Mesozoic plutons and metaclastic rocks from the northern SCS basement. • An Andean-type magmatic arc stretched from Hainan through northern SCS, to Taiwan and beyond. • The continuous 190–90 Ma arc was replaced by the Western Pacific plate margin soon after 90 Ma. Integrated analyses of in situ zircon U-Pb ages and geochemistry were conducted on both granitic and metasedimentary borehole samples from immediately below the Cenozoic sedimentary cover of the northern South China Sea basin. Our work suggests that basement rocks of the South China Sea basin are not Proterozoic or Paleozoic rocks, as previously speculated based on gravity-magnetic inversion work. The analyzed metavolcaniclastic and metasedimentary rocks were likely deposited at or soon after ca. 145 Ma but prior to ca. 85 Ma. A nearby source in coastal South China is proposed based on the generally immature nature of the metasedimentary rocks and the lack of detritus from older basement rocks farther inland. The vast majority of the metavolcaniclastic samples have sparse ca. 250–190 Ma (particularly 200–190 Ma) zircons. This magmatic quiescence is consistent with the existence of a coastal magmatic gap to the east of Hainan Island during this time, previously interpreted as reflecting a period of flat-slab subduction. Metaclastic samples mostly exhibit a dominant ca. 180–120 Ma zircon population, indicating extensive magmatism along the coastal areas. This finding, together with previously reported ca. 190–180 Ma I-type coastal granites and our newly dated ca. 115–98 Ma volcanic and granitic rocks under the western part of the South China Sea basin can best be interpreted by the former presence of an Andean-type continental arc during the Middle Jurassic – Early Cretaceous. Magmatism along this arc ceased soon after 90 Ma or before ca. 85 Ma, with its last pulse represented by a small group of ca. 100–85 Ma granitic intrusions in the eastern part of the northern South China Sea basin. The arc appears to have jumped toward the Western Pacific Ocean at or soon after 90 Ma, starting the development of the Western Pacific-type plate margin. [ABSTRACT FROM AUTHOR]

We systematically expound the processes of Cenozoic sedimentary evolution in the South China Sea (SCS) regions by synthesizing relevant previous research and our own long‐term sedimentological work. The process of changes in Cenozoic sedimentary environments and palaeogeography can be divided into three stages corresponding to the tectonic evolution of the SCS. Stage I, the formation and development of the Proto‐South China Sea (Proto‐SCS) from the Late Mesozoic to Early Cenozoic; the SCS was a vast erosion zone, and terrestrial lacustrine deposits were only distributed sporadically. Stage II, the subduction of the Proto‐SCS and the opening of the SCS since the Late Eocene. The northern basins of the SCS gradually changed from terrestrial to marine environments. Southern basins were affected by the disappearance of the Proto‐SCS in the early stage. The distribution of marine environments shrank in the Late Eocene–Early Oligocene, but as the SCS expanded, these marine environments gradually recovered. Stage III, the stagnation and atrophy of SCS expansion from the Late Miocene to the present. The sedimentary environment of the SCS is basically stable in this stage. The most prominent feature of sedimentary evolution is the development and destruction of carbonate platforms. [ABSTRACT FROM AUTHOR]

Rocks in extensional settings are generally sensitive to destruction and erosion, resulting in poor preservation potential and accumulation of their eroded components. The South China margin was dominated by a prolonged extensional setting from Late Mesozoic to Early Cenozoic, and this geological history is exactly archived in sediments within and surrounding the present South China Sea. However, the sedimentary evolution of the region, especially prior to the continental breakup and oceanic spreading, remains an issue of uncertainty and controversy, mostly due to limited borehole penetration and poor seismic reflection data for deeply buried sequences, as well as the lack of reliable regional stratigraphic framework. Here, we illustrate the Cretaceous–Palaeogene sedimentary evolution of the South China Sea region by synthesizing relevant data from previous literature and our own observations and displaying the evolution of lithofacies in sequential palinspastic reconstructions. The preferred palaeogeographic scenarios incorporate the latest interpretations of the conjugate relationship between continental margins as well as the birth and demise of the hypothetical Proto‐South China Sea. The patterns of lithofacies and depositional environments at regional scales, along with available provenance data, clearly reveal sedimentary responses to the significant Mesozoic–Cenozoic transition of plate geodynamics and magmatism along the Asian margin and provide implications for the potential mechanism of Cenozoic extension represented by distinct yet continuous processes of continental rifting and oceanic spreading. [ABSTRACT FROM AUTHOR]

Radiometric dates of key rock units indicate that a remnant Late Mesozoic ocean of the Huatung Basin is still preserved today east of the South China Sea (SCS). We integrate regional geology with a Cretaceous oceanic basement in the vicinity of the Huatung Basin to reconstruct the Huatung Plate east of the Eurasian continent. Results of geophysical investigations, four expeditions of deep-sea drilling and a renaissance of regional geology allow us to propose a hypothesis that the mechanism responsible for the SCS opening was raised from strike-slip fault on the east. The hypothesis suggests that the SCS opening could highly relate to the strike-slip faults inherited from Late Mesozoic structures onshore–offshore the SE Cathaysia Block to develop rhombic-shaped extensional basins en echelon on the thinned Eurasian continental crust in the Early Cenozoic. It was followed by sinistral strike-slip movements along the boundary between the Eurasian Plate and the Huatung Plate driven by oblique subduction of the Huatung Plate to the northwest coupled with slab-pull force by southward subduction of the Proto-SCS to open up the triangle-shaped oceanic East Sub-basin in the Early Oligocene (33/34 Ma). The spreading ridge then propagated southwestward in the step-over segment between the Zhongnan-Lile and the Red River strike-slip fault systems to open the triangle-shaped oceanic Southwest Sub-basin by 23 Ma. The plate boundary fault was subsequently converted into the Manila Trench when the Eocene Sierra Madre arc of the Huatung Plate had moved from the south to its present latitude by the Middle Miocene. [ABSTRACT FROM AUTHOR]

Geochemical and detrital zircon U-Pb dating data for drilled sediments from the Baiyun deepwater area of the northern South China Sea demonstrate a change of sedimentary sources from the Oligocene to the Miocene. Zircon ages of the pre-rift Eocene sequences are dominated by Yanshanian ages with various peak values (110-115 Ma for U1435 and L21; 150 Ma for H1), indicating local sediment supply from the pre-existing Mesozoic magmatic belt. For the Oligocene sediments in the northern part of the basin, the rare earth elements show different distribution characteristics, indicating sediment supply from the paleo-Zhujiang River (Pearl River), as also confirmed by the multimodal zircon age spectra of the Lower Oligocene strata in Well X28. By contrast, a positive Eu anomaly characterizes sediments from the western and southern parts of the basin, indicating potential provenances from intermediate to basic volcanic rock materials. The Baiyun Movement at the end of the Oligocene contributed to a large-scale subsidence in the deepwater area and also a northward retreat of continental shelf break, leading to deepening depositional environment in the basin. As a result, all the detrital zircon ages of the Upper Oligocene strata from Wells X28, L13, and L21 share a similar distribution, implying the possible control of a common source like the Zhujiang River. During the Miocene, whereas sediments in the northern area were mainly sourced from the Zhujiang River Delta, and those in the southern deepwater area continued to be affected by basic volcanic activities, the Dongsha Uplift could have contributed as the main source to the eastern area. [ABSTRACT FROM AUTHOR]

The pre-Oligocene sediment succession including shipboard lithological Units II (77.65–275.54 mbsf) and III (275.54–300 mbsf) from International Ocean Discovery Program (IODP) Hole U1435A in the northern South China Sea is characterized by greenish to dark gray sandstone and siltstone of coastal marine facies with age previously undetermined due to a lack of age-diagnostic fossils. Detrital zircon U Pb ages (9 samples) and thin sections (76 samples) from these two units, together with geochemical elements (197 samples) from Units I to III were analyzed to distinguish provenance, tectonic setting, and depositional age and environment. Petrographic study reveals that most samples are fine sandstones, mainly composed of subangular quartz (70–80%) and alkaline feldspar (10–15%; mostly K-feldspar), indicating a near proximal provenance. Discrimination diagrams, element ratios and chondrite-normalized rare earth element patterns suggest a relatively stable source of felsic rocks. Detrital zircon U Pb dating results reveal a dominance of Mesozoic ages with a pronounced Early Cretaceous peak at ~ 110 Ma. Fourteen zircon grains from 7 samples yield much younger ages between ~ 65 and 38 Ma, indicating middle to late Eocene deposition, broadly corresponding to the lacustrine-shallow neritic Enping-Wenchang Formations of the Pearl River Mouth Basin. Comparison among various elemental proxies from the Eocene sediments in Hole U1435A and in offshore industrial wells confirms a continental island arc setting in the Cretaceous when the zircons were produced. In the middle and late Eocene, these Cretaceous igneous rocks were likely the source of the sediment deposited in a coastal marine environment. The relatively minor variations in elemental distribution and the concentration of Paleogene zircons (~ 50–38 Ma) further imply a consistent supply of weathered material from this magmatic landmass during an active rifting period before the opening of the South China Sea. [ABSTRACT FROM AUTHOR]

A compilation of available marine deposition data from offshore S-SE China reveals evidence of rifting and breakup of the South China Sea (SCS) during the Paleogene. Marine deposition started earlier in the Paleocene in the East China Sea (ECS)-Taiwan region before expanding southwestward into the SCS region in the middle Eocene. Our data indicate the existence of an elongated Paleogene China Sea in these areas stretching along the northeasterly structural belts, probably as part of the marginal western paleo-Pacific. The southwestward shift of marine influence in the middle Eocene was responding to a period of intensive rifting and subsidence in the SCS region, while the sea in the ECS-Taiwan region started to shrink and shoal after the late Eocene, likely associated with local breakup and initial spreading in the Taiwan-Taixinan Basin area. The accumulation of hemipelagic sediments at ODP 1148 and IODP U1435 from near the continent-ocean boundary and at many other shelf-slope sites was in response to a large-scale breakup 34 to 33 Ma ago, subsequently leading to the birth of the SCS in the Oligocene. [ABSTRACT FROM AUTHOR]

The variations of lithostratigraphy, foraminifera, geochemical elements, and organic biomarkers in well XK1 from the Xisha (Paracel) Islands reveal the history of carbonate platform development since the early Miocene in the South China Sea. Our results indicate that reef growth was more active in the middle Miocene than in any earlier periods, decreased in the late Miocene, revitalized in the Pliocene, and active again in the Pleistocene interglacial periods. Unlike those limestone-rich intervals, the late Miocene succession in well XK1 is characterized by dolomitized limestones with a low deposition rate (30–60 m/Ma post-compaction). These late Miocene rocks also contain relative high MgO (~ 20%), more ∑ REE, abundant algae and some small sized foraminifera, but rare larger benthic foraminifera, very low land-sourced brGDGTs (0–0.5 ng/20 g), low BIT index (0.1–0.5), and low TEX86-derived sea temperature (~ 20–25 °C), indicating limited active reef growth in relative cooler mesophotic environments at > 30 m water depths. Similar dolomitized limestones of late Miocene age also occur in other carbonate platform areas including the Nansha (Spratly) Islands in the southern South China Sea. Together, these South China Sea records provide regional evidence of a recession in global carbonate platform development starting from the late Miocene. While carbonate platform reduction in other regions may have been triggered by global cooling and changing oceanic chemistry, accelerated basin subsidence coupled with monsoon cooling are considered as the main factors causing the reef decline in the late Miocene South China Sea. [ABSTRACT FROM AUTHOR]

The deep-water area of the Pearl River Mouth Basin in the South China Sea has received much scientific attention since the Ocean Drilling Program (ODP) Leg 184 in 1999 due to its potential economic prospects and distinct tectono-sedimentary evolutionary processes. In this study, we present the composition of major and trace elements from two newly sampled deep-water boreholes (BY6 and LW3) in the Baiyun Sag of the southern Pearl River Mouth Basin. The geochemical evolution in the Oligocene–Middle Miocene, as well as potential controlling factors, are investigated based on a comparative study with previous data from ODP site 1148 and borehole PY33. The Chemical Index of Alteration (CIA) and A–CN–K plot reveal that the observed weathering trends are not compatible for the four discussed boreholes. Sedimentary sorting is primarily observed in borehole PY33, where data trend away from the A apex to the feldspar join in the A–CN–K plot and show a spread of Al 2 O 3 /SiO 2 and Nb/Zr ratios. Compared to chemical weathering and hydrodynamic sorting, provenance has a greater impact on sediment composition of the deep-water area. From the north, the Pearl River was the primary sediment supply. However, a positive Eu anomaly and the provenance discrimination diagrams (i.e., La/Th versus Th/Yb and Zr/Co versus Th/Co) reveal the mafic nature of borehole BY6 sediments in the Zhuhai–Lower Zhujiang (32.0–18.5 Ma) and Upper Hanjiang (13.8–10.5 Ma) formations. These compositions are unusual and differ from the well-defined felsic sources in the majority of the Baiyun Sag; these discrepancies are likely related to multistage magmatism. The sediments at site 1148 are characterized by slightly enriched heavy rare earth elements and relatively high Zr/Co ratios, which could possibly be caused by zircon enrichment from local sources. [ABSTRACT FROM AUTHOR]

Abstract: We have analyzed core MD01-2392, ∼360km east of the Mekong River mouth in the South China Sea (SCS). Over the past 500ka, planktonic foraminiferal oxygen-isotopic values are consistently lighter than northern SCS and open-ocean records by up to 0.5‰, indicating the influence of run-off from the Mekong River during both glacial and interglacial periods. Carbonate content is higher during interglacials; sedimentation rates were higher during glacials. Increased sedimentation rates since 30ka imply increased run-off during the last glacial maximum and Holocene Period. Contrary to general experience, in which it is classed as a warm species for temperature estimates, the thermocline-dwelling species Pulleniatina obliquiloculata increased its numbers during glacial periods. This implies an estuarine circulation and even brackish-water caps during glacial periods, reinforcing the sense of strong run-off. In an overall decline of warm water, the thermocline shoaled stepwise, with rapid rises across the glacial terminations. We infer that the southern SCS was opened to an influx of Indian Ocean waters through southern passages at those times of rising sea levels. [Copyright &y& Elsevier]

• Detrital zircon U-Pb ages and seismic profiles were systematically used to investigate Paleogene source-to-sink pathways of the northern South China Sea. • Early Cenozoic longitudinal Kontum-Ying-Qiong River was identified in the deep-water basin of the northern South China Sea. • The Pearl River evolved to influence Zhu-II Depression as a transverse dispersal since Oligocene. • Sediment dispersal of the northern South China Sea was featured by the interplay between transverse and longitudinal transport. The northern South China Sea (SCS) experienced a significant transition from a lacustrine to marine environment in the Paleogene, and its deep-water basin of Zhu-II Depression is in particular extensively studied due to its richness in oil and gas resources. However, limited number of boreholes in the deep-water area has long constrained a better understanding on the provenance of the Paleogene strata and the associated sediment transport processes. In this study, detrital zircon U-Pb ages and three-dimensional (3D) seismic-reflection data were systematically employed to investigate the "source-to-sink" pathways and interplay of longitudinal and transverse sediment dispersal. Our results indicate that the Zhu-II Depression sediments of the northern SCS were predominantly derived from the surrounding nearby paleo-uplifts in the early and middle Eocene. A significant provenance shift took place in the late Eocene, when the local paleo-uplift source was replaced by a distant source from the western SCS. Sediments were transported from west to east by the "Kontum-Ying-Qiong River" as a longitudinal dispersal. In the Oligocene, the "Kontum-Ying-Qiong River" delivered large amounts of sediments from Central Vietnam to the eastern part of the northern SCS. Meanwhile, the Pearl River gradually evolved through regional tectonic processes and influenced the deep-water area of Zhu-II Depression as a transverse dispersal. Sediments from both "Kontum-Ying-Qiong" and Pearl Rivers converged and deposited as deep-water deltas in the Zhu-II Depression. This dual provenance system in the northern SCS deep-water area was featured by the interplay between longitudinal and transverse sediment dispersal. It was largely controlled by the tectonic-palaeogeographic pattern inherited from the Mesozoic arc system. [ABSTRACT FROM AUTHOR]

Secular variations in geochemistry and Nd isotopic data have been documented in sediment samples at ODP Site 1148 in the South China Sea. Major and trace elements show significant changes at ca. 29.5 Ma and 26–23 Ma, whereas ∊Nd values show a single change at ca. 26–23 Ma. Increases in Al/Ti, Al/K, Rb/Sr, and La/Lu ratios and a decrease in the Th/La ratio of the sediments beginning at 29.5 Ma are consistent with more intense chemical weathering in the source region. The abrupt change in Nd isotopes and geochemistry at ca. 26–23 Ma coincides with a major discontinuity in the sedimentology and physical properties of the sediments, implying a drastic change in sedimentary provenance and environment at the drill site. Comparison of the Nd isotopes of sediments from major rivers flowing into the South China Sea suggests that pre-27 Ma sediments were dominantly derived from a southwestern provenance (Indochina–Sunda Shelf and possibly northwestern Borneo), whereas post-23 Ma sediments were derived from a northern provenance (South China). This change in provenance from southwest to north was largely caused by ridge jumping during seafloor spreading of the South China Sea, associated with a southwestward expansion of the ocean basin crust and a global rise in sea level. Thus, the geochemical and Nd isotopic changes in the sediments at ODP Site 1148 are interpreted as a response to a major plate reorganization in SE Asia at ca. 25 Ma. [Copyright &y& Elsevier]

Pleistocene aeolianites on Shidao, Xisha Islands are one of the rare aeolianite successions found in Asia. There, the aeolianites, which unconformably overlie Pleistocene coral reefs (Marine Isotope Stage 5e), are 21.8 m thick and formed largely of grains derived from heterozoan organisms, including foraminifera (predominantly Amphistegina ), geniculate red algae, echinoderms, and molluscs. The aeolian sands were probably derived from a subtropical shallow subtidal environment. The variation in the distribution of metastable aragonite and high-Mg calcite (HMC) divides the aeolianite succession in core XK#1 into three intervals, which are unit 1 (11.5–21.8 m), unit 2 (3–11.5 m), and unit 3 (upper 3 m of core). The entire aeolianite succession underwent diagenetic alterations in relatively closed diagenetic environments with low water/rock ratios. Compared to the aeolianites in units 1 and 3, however, the aeolianites in unit 2 display lower amount of HMC, lower Sr and Mg concentrations, and more negative δ 18 O values of bulk samples. This evidence demonstrates that unit 2 underwent more extensive diagenetic alteration, probably due to the invasion of larger volumes of meteoric water. Correlation of the aeolianites in XK#1 to the aeolianites in surface exposures and subsurface core indicates that most Shidao aeolianites were deposited in MIS 3. The dry-cold climate combined with strong onshore winds blew the exposed marine sediments onshore where they formed the aeolian dunes. The palaeosols present in the Shidao aeolianite succession indicate multiple episodes of subaerial exposure with relatively more humid climate. Collectively, the results imply that aeolianites in ancient rock record can be used to examine the variations in palaeoceanography and the palaeoclimate. [ABSTRACT FROM AUTHOR]

Abstract: The 853 m thick sediment sequence recovered at ODP Site 1148 provides an unprecedented record of tectonic and paleoceanographic evolution in the South China Sea over the past 33 Ma. Litho-, bio-, and chemo-stratigraphic studies helped identify six periods of changes marking the major steps of the South China Sea geohistory. Rapid deposition with sedimentation rates of 60 m/Ma or more characterized the early Oligocene rifting. Several unconformities from the slumped unit between 457 and 495 mcd together erased about 3 Ma late Oligocene record, providing solid evidence of tectonic transition from rifting/slow spreading to rapid spreading in the South China Sea. Slow sedimentation of ∼20–30 m/Ma signifies stable seafloor spreading in the early Miocene. Dissolution may have affected the completeness of Miocene–Pleistocene succession with short-term hiatuses beyond current biostratigraphical resolution. Five major dissolution events, D-1 to D-5, characterize the stepwise development of deep water masses in close association to post-Oligocene South China Sea basin transformation. The concurrence of local and global dissolution events in the Miocene and Pliocene suggests climatic forcing as the main mechanism causing deep water circulation changes concomitantly in world oceans and in marginal seas. A return of high sedimentation rate of 60 m/Ma to the late Pliocene and Pleistocene South China Sea was caused by intensified down-slope transport due to frequent sea level fluctuations and exposure of a large shelf area during sea level low-stands. The six paleoceanographic stages, respectively corresponding to rifting (∼33–28.5 Ma), changing spreading southward (28.5–23 Ma), stable spreading to end of spreading (23–15 Ma), post-spreading balance (15–9 Ma), further modification and monsoon influence (9–5 Ma), and glacial prevalence (5–0 Ma), had transformed the South China Sea from a series of deep grabens to a rapidly expanding open gulf and finally to a semi-enclosed marginal sea in the past 33 Ma. [Copyright &y& Elsevier]

We present here the major and trace element data of the sediments at ODP Site 1144 of the last 230 ka with time resolution about 1.5 kyr to investigate their relations to the climate changes. Estimated from TiO2 and CaO contents, over 70% in weight of the sediments are terrestrial materials, and CaCO3 abundance ranges between 7% and 19%. The variation patterns of some of the major elements, such as Al, Fe, K, Mg and Mn, and some of the trace elements, such as the alkali elements (such as Rb and Cs), the alkali earth elements (such as Ba) and most transition metals (such as Sc, V, Co, Cr, Zn), well match that of the oxygen isotopes of the planktonic foraminifer, after normalized with Ti, with higher values during interglacial periods and lower values during glacial periods. Whilst the Na abundance exhibits inverse variation patterns with lower values during interglacial periods and higher values during glacial periods. However, most refractory elements, such as Y, Zr, Nb, Hf, Ta, REEs, Th and U, do not show such patterns. These agree well with the behaviors of these elements during chemical weathering. Therefore, the changes of chemical weathering intensity in South China, the source area of these sediments may account for such variation patterns. During interglacials, wet and warm climate might occur at South China, which resulted in stronger chemical weathering, and dry climate might occur during glacials, which resulted in weaker chemical weathering. Such paleoclimate interpretation agrees with those from other paleoclimate proxies, such as pollen records, indicating that change of the East Asian monsoon, especially change of the winter monsoon is the key for such paleoclimate variation patterns. [Copyright &y& Elsevier]