Introduction

Large oil and gas reservoirs have been discovered in the Yinggehai and Qiongdongnan basins recently1,2,3,4,5,6. The Yinggehai and Qiongdongnan basins are located in northwestern part of the South China Sea (SCS), which received a large amount of sediments from the Red River to the northwest, the Hainan Island to the east and north, and Central Vietnam to the west during the Cenozoic7,8,9,10. Many records of the tectonic evolution, denudation characteristics, and climate change of the surrounding potential source areas have been achieved from Cenozoic sediments11,12,13,14.

Provenance analysis plays a critical role in determining source areas, sediment transport route, and basin evolution3,12,14,15. During weathering, transportation, sedimentation, diagenesis, and low-grade metamorphism, the chemical properties of rare earth elements (REE) are rarely changed, and are truly immobile, with low solubilities and high stabilities16,17,18. Stable REE are usually used as important tracers when studying sedimentary source evolution. The most fundamental reason for this is that REE exhibit a very strong inheritance from their parent rocks19,20. Previous provenance studies in the Yinggehai and Qiongdongnan basins were mainly based on heavy mineral, seismic, and mineralogical methods5,7,15, and both elemental geochemistry and detrital zircon ages have been adopted for provenance studies in the Yinggehai and Qiongdongnan basins during recent years9,13,21,22. Elemental geochemistry and detrital zircon ages from the Yinggehai Basin have indicated a continuous record of sedimentary provenance from the Red River since the Oligocene12,21,22,23,24. Furthermore, rivers originating from Hainan Island provided a lot of sediments in the Qiongdongnan Basin, and sediments provided by the Red River entered the Qiongdongnan Basin as early as the late Oligocene2,14.

Previous studies of the Yinggehai and Qiongdongnan basins have focused on individual tectonic settings and stratigraphic units, however systematic studies of the sedimentary provenance in the junction area of two basins have been ignored. Hainan Island Source (HIS), Red River Source (RRS), and Central Vietnam Source (CVS) are three potential sources of detrital sediment for the Yinggehai and Qiongdongnan basins during the Cenozoic, and our study area is located at the junction of the two basins (Fig. 1). However, the study area is the only passageway for the RRS to enter the Qiongdongnan Basin, and it is an ideal area to detect whether the detrital sediments from the RRS have been transported through the junction of the two basins. In this study, sandstone core samples were collected from five wells in different formations of Oligocene to Pliocene age for geochemical analysis. The aims of this paper are to explore the tectonic implications, analyse the parent rock characteristics and accurately trace the source of detrital sediments in this area. We combine these new data with results of previous studies to further explore the provenance evolution of the Yinggehai and Qiongdongnan basins during the Cenozoic.

Figure 1
figure 1

Map of tectonics and geology of Southeast Asia (modified from7) show the location of Yinggehai and Qiongdongnan basins (a). Tectonic zones of the Yinggehai and Qiongdongnan basins (modified from14) and the simplified geological map (modified from8) of the potential source areas showing the lithological distribution along river cources (b). Major fault zones and major drainage system modified from22. YGHB-Yinggehai Basin, QDNB-Qiongdongnan Basin, ND. R.-Nandu River, CH. R.-Chuanghua River, NY. R.-Ningyuan River, LS. R.-Lingshui River, WQ. R.-Wanquan River.

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Geological setting

Geological background of Yinggehai and Qiongdongnan basins

The NNW-SSE trending Yinggehai Basin, which is located on the continental shelf of SCS, is surrounded by the Red River and the Beibuwan Basin to the north, Hainan Island to the east, and bordered on the west by Central Vietnam and southeast by Qiongdongnan Basin, respectively (Fig. 1). The Yingxi Slope, Yingdong Slope, and Lingao Low-uplift are the western, eastern, and northern parts of the basin, respectively, and the main deposited area of Yinggehai Basin is the Central Depression (Fig. 1). A large amount of Cenozoic sediment was deposited in the Yinggehai Basin, and strata thickness in the center of the basin is up to 17 km7,25,26.

The Qiongdongnan Basin is a Cenozoic gas-bearing marine basin, and its long axis trends from southwest to northeast. It is bounded by Hainan Island in the north, Pearl River Mouth Basin in the west, and SCS in the south2,7,8 (Fig. 1). The Qiongdongnan Basin can be divided into three tectonic zones: the Northern and Central Depressions are close to Hainan Island and distributed in a NE-SW direction. The Southern Uplift is high in the middle and low in the northeast and southwest3,14,22,27 (Fig. 1).

Most previous studies suggest that the basins have experienced an early syn-rifting stage and later post-rifting stage (Fig. 2)7,25,28. During the syn-rifting stage, lacustrine, fluvial, and alluvial deposits were formed in the Eocene, while the later Oligocene strata are characterized by coastal and shallow marine sediments13,25,29,30. The post-rifting stage has been divided into steady thermal subsidence and rapid subsidence sub-stages by the abrupt change of the basins’ subsidence rates in the late Miocene, which correspond to the Miocene and Pliocene to Quaternary, respectively (Fig. 2)7,26,30,31. During the steady thermal subsidence sub-stage, the basins underwent thermal subsidence, characterized by attenuated fault activity. Moreover, tectonic inversion widely occurred in the northern part of the Yinggehai Basin due to the regional stress pattern switching from transtensional to transpressional7,26,32. Sea level fluctuated greatly during Miocene, and sedimentation was characterized by littoral and deltaic facies to neritic facies7,8,30. During the rapid subsidence sub-stage, the two basins experienced the similar subsidence rates, and the sedimentation was characterized by neritic-bathyal facies8,29,33,34.

Figure 2
figure 2

Cenozoic stratigraphic table of the Yinggehai and Qiongdongnan basins with lithostratigraphy, relative sea level curve, sedimentation rate, and regional tectonic events8,14,26.

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Provenance hypotheses

Previous studies have suggested three dominant source areas, including RRS, HIS, and CVS (Fig. 1). The sediment mainly originated from the mafic–ultramafic gneiss, schists, ophiolites, intermediate-mafic volcanic rocks, and sedimentary rocks in RRS8,11,24,35, and the Red River system delivered a large volume of sediment to the Yinggehai or Qiongdongnan basins. However, the Cenozoic capture of the upstream Red River has been debated for years36,37,38,39,40. Hainan Island is high in the central mountains and low in the peripheral plains, and many rivers originate from the center of Hainan Island and flow into the surrounding basins. The Nandu River flows into the Beibuwan Basin, the Chuanghua River and Ningyuan River flow into the Yingdong Slope in the Yinggehai Basin, and the Lingshui River and Wanquan River flow into the Northern Depression in the Qiongdongnan Basin (Fig. 1), resulting in a spokewise provenance system (HIS). Except for the limited modern basalts in the northern area, almost all parent rocks from the HIS are intermediate-felsic intrusions8,12 (Fig. 1). Hainan Island underwent a rapid cooling phase from late Eocene to Oligocene23. From north to south, several rivers (e.g., the Ma, Lam, Song Gianh, Song Thach Han, and Thubon rivers) originate from Central Vietnam and flow into the Yingxi Slope of Yinggehai Basin. The parent rocks in the CVS are Paleozoic–Mesozoic sedimentary rocks and a limited amount of rhyolite and mafic rocks8,21 (Fig. 1). However, it is suggested that the Central Vietnam source supplied only 17–21% of the total sediments now preserved in the Yinggehai Basin based on apatite fission track data and 10Be data41.

Samples and methods

Samples

A total of 39 samples were collected from five wells to analyze the geochemical characteristics of Oligocene to Pliocene sediments in the study area. The detailed information on the samples is listed in Table 1. All the samples are sandstone from the drill cores.

Table 1 Stratigraphic positions of the samples analyzed in this study.
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Methods

Before major element geochemical analysis, we mixed 0.6 g of each sample with flux at a ratio of 1:10, using a flux was of Li2B4O7, LiBO2, and LiF in a ratio of 9:2:1. NH4NO3 was used as an oxidant to fully melt the sample during digestion. This mixture was heated into a glass bead, and X-ray fluorescence spectroscopy (ZSX Primus II, RIGAKU, Japan) was conducted on the fused glass beads to determine the major elemental concentrations. The melting temperature and time were 1050 °C and 15 min, respectively. The concentrations of the major elements in the whole-rock samples were determined at a voltage of 50 kV and a current of 60 mA. The theoretical α coefficient method was used to correct the data, and the relative standard deviation of the corrected data is less than 2%. This analysis was carried out at the Wuhan Sample Solution Analytical Technology Co., Ltd., Wuhan, China.

An Agilent 7700e inductively coupled plasma mass spectrometer (ICP-MS) was used to analyze the trace element and REE concentrations of the whole-rock samples at the Wuhan Sample Solution Analytical Technology Co., Ltd., Wuhan, China. We used a mixture of HNO3 and HF for pressurized acid digestion of the samples. The minimum detection limit of the equipment is < 1 ppb, and the errors of the trace element and REE data obtained are within ± 6%. The trace element and REE analysis was conducted according to the detailed treatment process and analytical procedures described by reference42.

Results

Supplementary Table 1 presents the geochemical data obtained in this study, including major elemental data for 16 samples, trace elemental data for 39 samples, and REE data for 39 samples.

Major elements

The variation in the major elemental concentrations of samples is illustrated by the plot normalized to the Upper Continental Crust (UCC) (Fig. 3), and there are different distribution patterns among different formations. Compared to the Sanya and Huangliu formations (Fig. 3d and b), the UCC-normalized elemental distributions of the Yacheng, Lingshui, Meishan, and Yinggehai formations exhibit noticeable Ca and Na depletions (Fig. 3f,e,c, and a, respectively). Compared with the other formations, the UCC-normalized elemental distribution of the Huangliu formation exhibits obvious Ca enrichment (Fig. 3b). The Yinggehai formation exhibits significant Ca, K, and Na depletion and significant Fe, Mg, and Ti enrichment (Fig. 3a). The UCC-normalized major elemental distribution of the Sanya formation exhibits Ca and Si enrichment and Na and Ti depletion (Fig. 3d). Except for the Huangliu formation, most of the data for the Cenozoic samples are plotted in or close to the Si apex, suggesting that the clastic silicates are the major component of the Cenozoic sediments from the study area (Fig. 4).

Figure 3
figure 3

Normalized major elements of the upper continental crust43 of Cenozoic sediment samples obtained from five wells in the junction area of Yinggehai and Qiongdongnan basins.

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Figure 4
figure 4

Ca–Si–Al ternary diagram of Cenozoic sediment samples obtained from five wells in the junction area of Yinggehai and Qiongdongnan basins.

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Trace elements

The trace elements of Th, Zr, and Hf are relatively stable and exhibit a very strong inheritance from their parent rocks, so they are often used for identifying tectonic environments44,45. In general, Sc content and Sc/Cr, Ti/Zr, and Ba/Rb ratio increase, and Rb and Th content and Th/Sc and Rb/Sr ratio decrease systematically from the passive marginal environment to the active continental marginal environment, then to continental island arc environment, and then to continental island arc environment46,47. Five trace elemental ratios (Rb/Sr, Zr/Th, Sc/Cr, Zr/Hf and Th/Sc) of Cenozoic samples show overall stability, with slight local changes from the Oligocene to Pliocene (Fig. 5). The Rb/Sr, Sc/Cr, and Zr/Hf ratios exhibit less variation, while the Zr/Th and Th/Sc ratios fluctuate with a high frequency in the Sanya and Huangliu formations. Furthermore, the average Rb/Sr ratio of the Yacheng formation is 4.39, which is much higher than those of the upper formations (Fig. 5). In the Huangliu formation, the Zr/Th ratio ranges from 10.12 to 60.12, with an average of 28.02, higher than those of the other formations. The Th/Sc ratio of samples varies from 1.03 to 4.73, which is similar to sandstones whose parent rocks are felsic rocks.

Figure 5
figure 5

Comparative variations in the trace elemental ratios from Wells in the junction area of Yinggehai and Qiongdongnan basins, F.M.-Formation.

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Rare earth elements

Table 2 shows the statistical results of the REE contents of the Cenozoic sediments from the five wells in the study area. The average REE concentrations in all samples are higher than those of Post-Archean Australian shale (PAAS) (184.77 × 10−6), but the average REE concentrations of samples in the Sanya formation from well YC-3 and the Huangliu formation from wells LD-2 and YC-1 are significantly lower than those of UCC (146.37 × 10–6). The samples from the five wells are significantly enriched in light REE (LREE) relative to heavy REE (HREE), which is illustrated by the LREE/HREE ratios of 7.95–9.44. Furthermore, the obvious fractionation between the LREE and HREE can also be seen from the average (La/Yb)N ratios, ranging from 8.34 to 11.28. However, the average (La/Sm)N values range from 3.8 to 4.02, indicating marked fractionation of the LREE (Table 2). The chondrite-normalized REE distribution patterns of the samples are nearly parallel, with negative Eu anomalies similar to UCC and PAAS (Fig. 6). Based on the average δEu values from 0.53 to 0.76, the Cenozoic sediments in the study area were significantly influenced by intermediate-felsic volcanic sources (Table 2). Generally, the δCe value of sedimentary rocks, which parent rocks derived from terrigenous non-carbonate sediments, ranges from 0.8 to 1.2048. The average δCe values of the Cenozoic sediments in the study area range from 0.96 to 1.05, with no significant Ce anomalies, suggesting that these sediments have average δCe values similar to those of sediments deposited in a continental environment (from 0.8 to 1.20) during the Cenozoic48. In addition to distribution patterns similar to UCC and PAAS, the Cenozoic sediment samples also have large negative Eu anomalies and no significant Ce anomalies.

Table 2 Major rare earth elements (REE) characteristics of the Cenozoic sediments from the junction area of Yinggehai and Qiongdongnan basins.
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Figure 6
figure 6

Chondrite50 normalized REE concentrations in Cenozoic sediments from the junction area of Yinggehai and Qiongdongnan basins. Grey area indicates sediments likely from Hainan Island source51.

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Discussion

Tectonic implications

Tectonically, the Yinggehai and Qiongdongnan basins are located at the intersection of the Indochina Block, the Pacific Plate, and the southern margin of the South China Block31,35,52. Considerable information about the regional history has likely been recorded in the Cenozoic sediments from the Yinggehai and Qiongdongnan basins. Geochemical data could better interpret the regional tectonic background45,53. The samples of Cenozoic sediments from the study area are significantly enriched in LREE (Table 2) and show large negative Eu anomalies (Fig. 6), which have similar REE enrichment and distributed characteristics to andesite developed in continental island arc and passive continental margin environment49. According to the plot of SiO2 versus K2O/Na2O, except for the Huangliu formation samples, all the samples plot in the passive continental margin field (Fig. 7a). Furthermore, most Lingshui and Huangliu formation samples plot in the continental island arc field, while the Yacheng, Sanya, Meishan, and Yinggehai formations’ samples plot in the active and passive continental margin fields (Fig. 7b). The Cenozoic sediments in the study area were derived from the continental island arc and passive continental margin setting.

Figure 7
figure 7

(a) Plot of SiO2 vs K2O/Na2O and (b) ternary plot of Th-La-Sc to discriminate tectonic setting49,53.

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Parent rock characteristics

The distribution patterns of the major elemental chemistry of the samples in different formations are generally similar. The most obvious characteristic is that CaO and Na2O relative abundance decline significantly through time, while the Sanya and Huangliu formations are enriched in CaO relative to those from other formations (Fig. 3). The Ca and Na are degraded quickly during the process of weathering and transport on account of smectites, chlorites, and other clays which house Ca and Na are susceptible to weathering54,55, which may cause the relative abundance of CaO and Na2O decrease significantly. Due to the massive sea level fall during deposition of the Sanya and Huangliu formation, the calcium-rich minerals in the sediment source increased significantly30,56. As demonstrated in the previous studies, the REE of sediments from the HIS is characterized by enrichment of LREE and stable content of HREE with negative Eu anomalies51, while the sediments provided by the RRS exhibit positive Eu anomalies24, or unstable content of HREE with negative Ce and Eu anomalies57. The chondrite-normalized REE distribution patterns from our study are more consistent with those from the HIS, which indicate that the sediments in the study area are originated from HIS (Fig. 6).

When analyzing the sources of sediments, it is more effective to use the ratios of immobile elements to mobile elements than single elemental concentrations due to the geochemical stability of high field strength elements during transport and deposition46,47,48. Moreover, sediments derived from mafic and felsic parent rocks have significantly different trace element and REE contents46,47. Therefore, the parent rock information of sedimentary rocks can be identified by the ratios of La/Sc, Co/Th, Cr/V, and Y/Ni. Based on the cross plot of Cr/V–Y/Ni (Fig. 8a) and Co/Th-La/Sc (Fig. 8b), most of the Cenozoic sediments from the study area are plotted in or close to the felsic volcanic and granite fields. To furtherly investigate the nature of the parent rocks, the samples were plotted in the La/Yb-∑REE diagram (Fig. 9). It is shown that most of the samples are plotted at the intersection of the basalt, granite, and sedimentary rock fields, but samples of Sanya and Huangliu formations are plotted closer to the sedimentary rock field. Overall, the parent rocks of Cenozoic sandstone from the study area seem to be unique, indicating that these sediments are derived from Hainan Island, which contains igneous and ancient sedimentary rocks.

Figure 8
figure 8

(a) Plot of Cr/V vs Y/Ni and (b) plot of Co/Th vs La/Sc.

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Figure 9
figure 9

Parent rock discrimination from La/Yb vs ∑REE for Cenozoic sediments from the junction area of Yinggehai and Qiongdongnan basins58. 1: oceanic tholeiitic basalt, 2: continental tholeiitic basalt, 3: alkali basalt, 4: granite, 5: kimberlite, 6: carbonate rocks, and 7: sedimentary rock and calcareous mudstone.

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Provenance evolution

Based on seismic profiles and petrographic data of sandstones, previous studies have shown that the RRS, HIS, and CVS provided large amounts of sediment to the Yinggehai Basin7,25,32,59. Moreover, recently published detrital zircon U–Pb dating provenance studies have revealed that HIS was likely the major source of sediments in the Yingdong slope, but the Central Depression of Yinggehai Basin received a large amount of terrigenous sediment from both RRS and HIS during the Cenozoic8,9,12. Progradational clinoforms were identified on seismic profiles along the margin of Hainan Island in previous studies, suggesting that Hainan Island also provided sediments to the Qiongdongnan Basin25,28,29. Furthermore, the age distribution of Lingshui Formation detrital zircons in the Qiongdongnan Basin shows two major peaks at ca. 247 Ma and 441 Ma, and accompanied by nine subordinate age peaks from 35 to 1905 Ma (consistent with the zircon age distribution of RRS), which indicates that sediments from RRS were deposited in the western part of Qiongdongnan Basin as early as late Oligocene2,14. Most of the sediments from Central Vietnam were supplied to the Mekong River Basin, and the amount of sediment delivered to the Yinggehai Basin was limited11,57. Jonell et al. (2017) suggested that Central Vietnam had a slow regional bedrock exhumation rate throughout the Cenozoic based on detrital apatite fission track and 10Be data in the modern sediments, and 17–21% of the total sediments now preserved in the Yinggehai Basin may have been provided by CVS41. Therefore, Central Vietnam was a minor source of the sediments in the Yinggehai Basin, and it had little influence on the characteristics of the sediments in the Qiongdongnan Basin2,14,23,41. Different sources with positive or negative Eu anomaly characteristics can be identified by REE analysis. Furthermore, the sediments carried by the Red River exhibit positive Eu anomalies, while those derived from granitic and sedimentary parent rocks on Hainan Island exhibit negative Eu anomalies24. The provenance evolution from the Oligocene to the Pliocene can be explored based on the our geochemical data and REE data from other studies in the Yinggehai and Qiongdongnan basins.

Based on the REE patterns of the potential sources and the sediments deposited during the Oligocene (33.9 ~ 23.0 Ma; Fig. 10), the samples from wells N4 in the Central Depression of Yinggehai Basin and YC13 and YC19 in the junction area of the two basins exhibit positive Eu anomalies, and are similar to the RRS, which indicates that sediments deposited in the Central Depression of the Yinggehai Basin and the junction area of the two basins may have the contribution from the RRS. While the other samples from wells N3, YCH8-2–1, YCH21-1–3, YC-3, LS-A, LS33, Y19, and QE have negative Eu anomalies and are similar to the HIS. It is suggested that the sediments deposited in the Yingdong Slope of the Yinggehai Basin and the Qiongdongnan Basin during the Oligocene were mainly delivered from the HIS (Fig. 10). Overall, the RRS provided a great of the sediments for the Central Depression of Yinggehai Basin and the western part of Qiongdongnan Basin, while the sediments from the HIS were mainly deposited on the Yingdong Slope of Yinggehai Basin and the Qiongdongnan Basin, and the junction area of the two basins had a mixed sediments source consisting of the RRS and the HIS.

Figure 10
figure 10

Schematic source-to-sink evolution model and chondrite50 normalized REE patterns of Oligocene samples from the Yinggehai and Qiongdongnan basins. Eu-anomaly values are highlighted on each plot with gray (negative) or orange (positive) shades. The square part of the Yinggehai and Qiongdongnan basins in the upper map to display the provenance distribution. Intervals in each REE pattern plot indicate the Formation analyzed. PAAS—Post-Archean Australian shale.

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During the Miocene (23.0 ~ 5.7 Ma; Fig. 11), the sediments from wells N4, N5 and N6 exhibit positive Eu anomalies, while those from wells DF13 and LD-2 exhibit negative Eu anomalies in the Central Depression of Yinggehai Basin, which indicates that both the RRS and HIS provided sediments to the Central Depression of Yinggehai Basin (Fig. 11). Except for well N3, the Miocene sediments from other wells in the Yingdong Slope exhibit negative Eu anomalies, suggesting that the sediments in this area are not solely derived from the HIS, and another possible source is the RRS (Fig. 11). The sediments from wells QW and YC-35 exhibit positive Eu anomalies, similar to the positive Eu anomalies of RRS, while the sediments from the other wells in Qiongdongnan Basin with negative Eu anomalies, and are similar to the HIS (Fig. 11). The RRS only provided sediments for the western part of Qiongdongnan Basin. Consequently, the RRS and HIS may have had a combined effect on the composition of sediments in the Central Depression and Yingdong Slope of the Yinggehai Basin and the junction area of the two basins.

Figure 11
figure 11

Schematic source-to-sink evolution model and chondrite50 normalized REEpatterns of Miocene samples from the Yinggehai and Qiongdongnan basins.

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During the Pliocene (5.7 ~ 1.8 Ma; Fig. 12), except for samples from well LD-1, all samples (wells N5, DF1-1–5, DF29-1–2, and N6) in the Central Depression of the Yinggehai Basin exhibit positive Eu anomalies. From north to south in the Yingdong Slope, the sediments from wells N1, N2, and N3 all exhibit negative Eu anomalies, suggesting that the sediments deposited on the Yingdong Slope during the Pliocene were derived from the HIS (Fig. 12). In the western sags in the Qiongdongnan Basin, the sediments from wells QW and LS-A exhibit positive Eu anomalies. However, well QE was characterized by negative Eu anomalies, which indicates a different source for the sediments in the eastern and western parts of Qiongdongnan Basin. Most of the sediments deposited in the eastern part of Qiongdongnan Basin during Pliocene were derived from the HIS (Fig. 12). In general, the sediments deposited in the Central Depression of Yinggehai Basin and the western part of Qiongdongnan Basin were derived from the RRS, while the sediments deposited on the Yingdong Slope of Yinggehai Basin, northern and eastern parts of Qiongdongnan Basin during Pliocene were primarily derived from the HIS.

Figure 12
figure 12

Schematic source-to-sink evolution model and chondrite50 normalized REEpatterns of Pliocene samples from the Yinggehai and Qiongdongnan basins.

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From the Oligocene to the Pliocene (33.9 ~ 1.8 Ma), the RRS provided sediments to the Central Depression of the Yinggehai Basin and western part of the Qiongdongnan Basin. Meanwhile, most of the sediments preserved in the Yingdong Slope of the Yinggehai Basin and the Qiongdongnan Basin were derived from the HIS. During the Miocene (23.0 ~ 5.7 Ma), the RRS and HIS were also one of the sedimentary sources of the Yingdong Slope and Central Depression of the Yinggehai Basin, respectively. Last but not the least, the junction area of the two basins had a mixed source consisting of the RRS and HIS during the Cenozoic (33.9 ~ 1.8 Ma).

Conclusions

The major and trace elemental characteristics of Cenozoic sediment samples from the junction area of the two basins reveal that they were derived from continental island arc to passive continental margin settings.

The REE distribution patterns of sediments from the junction area of the two basins are nearly parallel and with large negative Eu anomalies, indicating they are derived from Hainan Island with exposed igneous and ancient sedimentary rocks.

During the late Cenozoic (33.9 ~ 1.8 Ma), the RRS provided sediments to the Central Depression of the Yinggehai Basin and the western part of Qiongdongnan Basin, the HIS provided sediments to the Yingdong Slope of the Yinggehai Basin and Qiongdongnan Basin; However, the RRS and HIS were also one of the sediment sources of the Yingdong Slope and Central Depression of the Yinggehai Basin during the Miocene (23.0 ~ 5.7 Ma), respectively; Furthermore, the junction area of the two basins had a mixed source consisting of the RRS and HIS during the Cenozoic.