Abstract Sediment is delivered by the rivers of SE Asia to the South China Sea where it provides an archive of continental environmental conditions since the Eocene. Interpreting this archive is complicated because sediment may be derived from a number of unique sources and the rivers themselves have experienced headwater capture that also affects their composition. A number of methods exist to constrain provenance, but not all work well in this area. Anthropogenic impacts, most notably agriculture, mean that the modern rivers contain more weathered materials than they did up until about 3000 years ago. The rivers have also changed their bulk chemistry and clay mineralogy in response to climate change, so that these proxies, as well as Sr isotopes, are generally unreliable provenance indicators. Nd isotopes resolve influx from Luzon, but many other sources in SE Asia have similar values and clear resolution of end members can be difficult. Instead, thermochronology methods are best suited, especially apatite fission track, which shows more diversity in the sources than either U–Pb zircon or Ar/Ar muscovite dating. Nonetheless, even fission track is best used as part of a multiproxy approach if a robust quantitative budget is desired.

Abstract Geochemical data from South China Sea sedimentary rocks show the effects of both source composition and depositional environments. This enables us to link tectonic trends with erosion in the Pearl River region since c. 32 Ma. In particular, a shift in the geochemistry appears to signal a response to a well-recorded regional tectonic event at c. 23–25 Ma, probably corresponding to a jump in the seafloor spreading axis from the west to the SW within the South China Sea. This may correlate with the uplift of the West Yunnan Plateau and possibly also the eastern Tibetan Plateau. Clay mineralogy, sand–mud ratio, and major and rare earth element concentrations, also varied in response to the environment in the drainage areas of the palaeo-Pearl River. By comparing data from the modern sources and the sedimentary record from the northern South China Sea, especially the erosion–transportation–deposition patterns, three groups of index minerals (Ati, GZi, ZTR), as well as rare earth elements can be recognized. These are used to characterize the Pearl River from the east to the west, representing three different parent rock sources. The evolution of the palaeo-Pearl River can be tracked by variations of heavy minerals and key elements that are indicative of provenance.

Abstract Reconstructing variations in the intensity of chemical weathering in river basins is crucial if we are to understand how climate change impacts environment and whether there are feedbacks between climate and weathering processes. Quantifying chemical weathering is, however, a complicated process, involving a number of competing proxies. We compare weathering records from the Pearl River delta of southern China and Ocean Drilling Program (ODP) Sites 1144 and 1146 on the northeastern slope of the South China Sea in order to test which proxies are the most widely applicable and robust. Comparison with speleothem rainfall records indicates that K/Al tracks precipitation variations most closely and out-performs the widely used Chemical Index of Alteration (CIA). Correlation of K/Al and kaolinite/illite indicates that this clay ratio is also an effective proxy of weathering intensity across all sites and timescales. Kaolinite/smectite, and to a lesser extent smectite/(illite+chlorite), are also indicative of weathering intensity, but show more scatter between sites that may be linked to provenance effects. Mg/Al is relatively immune to grain-size effects, but does not correlate well with other proxies. K/Rb is a reasonably reliable indicator of chemical weathering intensity and may be more sensitive than CIA or K/Al to weathering changes over short timescales and when weathering is not too intense. 87 Sr/ 86 Sr can be useful but can be influenced by both grain size and provenance effects. In general marine archives of fluvial sediment may record variations in weathering linked to climate, but these are increasingly signals of reworking going further offshore.

Abstract Geochemical investigations of sediments from core GC22 from the Tonkin Gulf, South China Sea, have been carried out in order to reconstruct the palaeoenvironmental evolution of the area during the Holocene. Vertical variations in Al/Ti, K/Al and Mg/Al clearly indicate the degree of chemical weathering in the source area. Zr/Ti and SiO 2 /Al 2 O 3 recorded the history of current velocity changes, and La/Co v. La/Sc, combined with distribution patterns of rare earth elements, suggested that Hainan Island was the main source of the sediments during the Holocene. Based on the results of the analysis, the evolution of palaeoenvironments in the Tonkin Gulf can be divided into four stages: (1) 10.12–6.46 ka BP, the regional climate got warmer, and the sea level of the gulf rose rapidly, which is indicated by rapid declines in Sr/Ba and CaO. (2) 6.46–4.3 ka BP, the gulf had a stable depositional environment, and the local climate became cold and dry. (3) 4.3–3.55 ka BP, the currents and sedimenary provenance in the gulf were significantly influenced by the opening of the Qiongzhou Strait. (4) 3.55 ka BP–present, the regional sea level remained roughly stable.

Abstract This study documents the Southern Beibu Gulf Mud Depocentre (SBGMD) for the first time using high-resolution sub-bottom seismic reflection profiles. The SBGMD is located near the southern mouth of the Beibu Gulf in water depths of 50–80 m, and covers an area of more than 11 000 km 2 . The acoustic architecture of the SBGMD is characterized by a homogenous seismic unit surrounded by an erosive area where gullies and sand/mud waves occur. The SBGMD unconformably overlies a parallel-bedded seismic unit. Based on 14 C-dating, together with acoustic, lithological and geochemical analysis of gravity core SO31, which was sampled within the high-sedimentation-rate area of the SBGMD, the post-glacial sedimentary history may be summarized as follows: (1) from 12.8 to 11.6 cal ka BP, the SBGMD was deposited in a low-energy, brackish/freshwater and intensely terrestrial-influenced environment; (2) from 11.6 to 8.4 cal ka BP, the SBGMD underwent marine transgression; and (3) from 8.4 cal ka BP to present, a continuous shallow-marine environment has prevailed. Comparing the age and depth of the SBGMD base with the established sea-level curve, lacustrine sedimentation is predicted to have occurred in the SBGMD area before 12.8 cal ka BP.

Abstract In order to investigate the relationship between sea-level changes during the Last Glacial Cycle (LGC) and seismic stratigraphic sequences on the NW continental shelf of the South China Sea, a sparker single-channel high-resolution seismic profiling was correlated with a sediment core taken offshore western Hainan Island. Interpretation of the seismic stratigraphy in relation to local and global sea-level changes could be refined. According to the age model, developed from AMS (accelerator mass spectrometry)- 14 C and OSL (optically stimulated luminescence) dates, and δ 18 O (oxygen isotope) stratigraphy, the 88.3 m sediment core reflects environmental change since 110 ka. Correlation with a sediment core in the adjacent basin based on stable oxygen isotope records allows a zonation of the top 15 m of the sediment core and the identification of marine isotope stages (MIS) 1–5e. Seven seismic reflectors interpreted as unconformities were identified. These erosional surfaces have been dated by interpolation using an age–depth model compared to global eustatic curves. The results indicate that seven sea-level cycles can be distinguished in the study area during the LGC, and these are correlated with regional and global sea-level change models. Further research confirms that seismic stratigraphy in the NW South China Sea can be intimately related to LGC sea-level changes associated with regional surface uplift and sediment supply.

Abstract This paper examines the Late Quaternary evolutionary history of the northern coast of the South China Sea by reviewing geological evidence from this coast. Results show that: (1) a lithostratigraphy with two marine sequences is observed in the deltaic basins of the Song Hong, Pearl and Han rivers, and these basins are all bounded by active faults; (2) whilst the upper marine sequence belongs to the present interglacial or the past 10.5 ka, the lower or older marine sequence was most likely deposited during the high sea level of the last interglacial period, c. 126–120 ka; (3) the burial depth of the older marine sequence is recorded at −15 m below modern sea level or deeper, implying localized subsidence of varying rates between these deltaic basins because the height of sea level during the last interglacial was close to that of the present; (4) this tectonic process is probably associated with the continuous long-term subsidence of the northern South China Sea continental shelf within the tectonic framework of southward continental extension of the Eurasian Plate during the Cenozoic; (5) fault activity has enhanced the localized subsidence of these deltaic basins, which led to marine inundation during interglacial high sea levels.

Abstract The East China Sea (ECS) is a typical marginal sea located between the Eurasian continent and west Pacific Ocean. In this study, we review state-of-the-art research progress on the possible sinks of the Changjiang-derived sediments in the ECS during the late Quaternary. The major sinks of these sediments in the ECS are on the outer shelf and the Okinawa Trough during the last glacial maximum corresponding to a lowstand of sea level. During the deglacial marine transgression, the gently dipping shelf was rapidly inundated and strong tides prevented fine sediment from deposition on the open shelf, resulting in the development of a unique tidal sand ridge system. With sea level reaching the present situation and the modern marine environment being completed in the early Holocene, the Changjiang sediments mostly accumulated in the river’s estuary to build a large delta, with only a fraction reaching the inner shelf and coastal embayments. The late-Quaternary changes in monsoon-climate-induced river flux, sea level and oceanic circulation primarily controlled the source-to-sink transport of the Changjiang sediments in the ECS, and further determined the stratigraphic framework and sedimentary facies on the shelf.

Abstract Contour-parallel sediment dispersal from the Yangtze Estuary into the East China Sea develops a large-scale mud belt on the inner shelf. The sediment dynamics of long-distance dispersal is, however, still an open question. This was investigated by field observations in the 2013 wet season. To clarify the physics of the large-scale mud belt, we examined: (a) shelf circulation currents and their interaction with the Yangtze River; (b) small-/meso-scale processes including bottom boundary-layer flows, stratification and mixing, upwelling, and fronts; and (c) river-borne sediment gravity and contour currents. Field observations demonstrated that estuarine turbidity maxima can trap benthic concentrated suspensions in the near-bed layer and move these downslope of the subaqueous delta, forming sediment gravity currents supported by tidal currents. Compared with near-bed sediment transports, the buoyant coastal current cannot be a controlling factor in the mud belt formation. A constant along-shelf flux of near-bed sediment transport is responsible for the long-distance dispersal of the large-scale mud belt on the East China Sea inner shelf. The upwelling events provide more turbulent energy to sediment suspension under unstably stratified boundary flow. Our recognition of a contour-parallel ‘sediment channel’ has deep implications for understanding this inner-shelf mud belt and ancient mud deposits.

Abstract The Pearl River is the largest river in southern China; it has eight outlets flowing into the South China Sea, four of which (Humen, Jiaomen, Hongqili and Hengmen) empty via Lingdingyang Bay. Tides, discharge strength and the presence of islands control sediments within these four outlets. Sediments are deposited, and form three shoals and two channels. The shoreline and its seabed topography have changed dramatically with increasing human impact. In order to understand the geomorphological evolution of Lingdingyang Bay and its hydrodynamics, we integrated data obtained from two marine environment investigations conducted by the Guangzhou Marine Geological Survey (GMGS) in 2003 and in 2012, together with remote sensing multi-temporal images and historical materials, and analysed them using a geographical information system (GIS). The results obtained show that the outlets are becoming narrower; the surface water area of Lingdingyang Bay is diminishing. Meanwhile, the sediment flux is reducing and becoming finer grained because the currents are being blocked by shoals and islands. Some parts of the bay are becoming deeper (27–37 m in the Chuanbi Channel). Correspondingly, the hydrodynamics in the bay are becoming weaker and sediments easier to deposit. Water exchange between the inner and outer sea is decreasing under the influence of unrestricted anthropogenic activities. Lingdingyang Bay should be managed and protected continuously based on a scientific framework: otherwise, it will become narrower and, perhaps, even evolving eventually into a river, which may result in serious futures disasters through flooding and tides.

Abstract Characterization of the evolution of delta lobes has theoretical significance for the formation of entire deltas. The Diaokou lobe of the Yellow River delta provides a typical example. The Yellow River transported a great deal of sediment to the Diaokou area during the period of 1964–76 after the river changed its course to the Diaokou River and formed a new delta lobe – the Diaokou lobe. The Diaokou lobe reflects the evolution of the modern Yellow River delta and contains a record that represents the complete modern Yellow River delta depositional system. Using grain-size characteristics, magnetism, and the accelerator mass spectrometry (AMS) 14 C dating of cores ZK10-3 and ZK30 in the northern part of the Diaokou lobe, combined with collected data from cores ZK227, ZK1 and ZK228, which are located further south on the Diaokou lobe, we analysed the Holocene and recent stratigraphy of the Diaokou lobe area and its evolution. The Holocene stratigraphy of the Diaokou lobe and the nearby area contains upwards-succession, shallow-marine, river and lake, salt-marsh, and delta facies. This area received deltaic deposits beginning in 1855 and experienced prodelta, delta-front (lateral) and delta-plain deposition. When the Diaokou lobe began to form, this area experienced four stages of deposition after 1964: (1) dispersed-flow deposition; (2) single-channel deposition; (3) diversion deposition; and (4) abandonment and erosion. Compared with the evolution of a lobe of the Mississippi delta, the Yellow River delta contains thick, laterally extensive deposits as a result of the higher sediment load.

Abstract A benthic foraminiferal proxy record of 290 kyr, acquired from Core SH7B in the northern continental slope of the South China Sea, was studied to identify the bottom-water environment changes since marine isotope stage (MIS) 8. The changes, including oxygenation and types of organic matter flux to the seafloor, reflect the palaeoproductivity fluctuations linked to monsoon variability. Four assemblages, characterizing different palaeoenvironmental changes, have been recognized by factor and cluster analysis with 32 foraminiferal species in 93 samples (>150 µm size fraction). Assemblage Pyrgo spp.– Hoeglundina elegans mainly dominates during interglacial periods of MIS 7, MIS 5 and MIS 3, suggesting well-oxygenated bottom environments with low sea surface productivity linked to a weak East Asian Winter Monsoon (EAWM). Assemblage Uvigerina spp.– Globocassidulina subglobulosa is composed of a constantly high percentage of shallow infaunal species, occurring in intervals of MIS 4, MIS 5, MIS 7 and MIS 8, which indicates that an enhanced EAWM led to a low seasonality of palaeoproductivity, a constant high flux of fresh and labile marine-derived organic particles to the seafloor and a low oxygen bottom environment. Assemblage Melonis barleeanus – Clavulina spp. is characterized by species that depend on seasonal supplies of more altered refractory organic matter and is mainly distributed in interglacial periods (late MIS 5, MIS 3 and MIS 1), suggesting a high seasonality of palaeoproductivity associated with a seasonal intensification of the EAWM. With low benthic foraminiferal diversity and abundance, assemblage Globobulimina affinis – Chilostomella mediterranensis was identified during the intermediate MIS 8 and early MIS 2. Both substantial input of terrigenous nutrients from an increased river run-off and an increased primary productivity correlated with an enhanced EAWM have led to abundant nutrient supplies and severe bottom-water oxygen depletion. As suggested by the composition of benthic foraminiferal in Core SH7B, changes in bottom-water environments of the northern South China Sea over the last 290 kyr were driven by the fluctuating palaeoproductivity linked to the high variability of the EAWM.

Abstract Paralia sulcata (Ehr.) Cleve, a common diatom microfossil species in shelf and adjacent deep-sea sediments, is becoming potentially useful in palaeoenvironmental reconstructions due to its coarsely silicified exoskeleton being well preserved in sediments. This paper presents the distributions of P. sulcata in sediment cores from the SE Asian marginal seas taken from formerly published and original materials. Paralia sulcata achieved variable abundance in the glacial–interglacial sediment analysed, showing spatial changes in the core profiles of the South China Sea, with lower abundances during the last glacial stage and higher values in the post-glacial. Conversely, in the East China Sea, it attains lower abundances during the Holocene, while higher ones in last glacial stage. Over a short timescale, variations in the abundance of this species responded quickly to the climatic and oceanographic fluctuations. We illustrate a ‘seesaw’ effect that its high abundances revealed in the East China Sea at 15–11 cal ka BP, whereas this occurred during period 11–8 cal ka BP in the South China Sea. The rapid increase in abundance of this species in the South China Sea is interpreted as an indication of a plausible link with the opening of the Taiwan Strait and the general coastal water circulation pattern during deglaciation.

Abstract The region consisting of the Bohai, Yellow and East China seas represents a typical wide continental shelf environment with abundant terrestrial sediment supply. Here, a variety of sedimentary systems have been formed during the Holocene period. These systems have unique characteristics in terms of spatial distribution, material composition, deposition rate, and the timing and duration for their formation, which are related to active sediment-transport processes induced by tides and waves, shelf circulations, and sediment gravity flows. The sedimentary records contained within the deposits have a high temporal resolution, but each with a limited temporal coverage. However, if these records are connected, then they may form a complete archive for environmental change studies. In the field of process–product relationship studies, the mid-Holocene coastal deposits on the Jiangsu coast, the early–middle Holocene sequences of the Hangzhou Bay, the Holocene mud deposits off the Zhejiang–Fujian coasts and the other mud areas over the region are of importance. These systems may be understood by identifying the material supply (from both seabed reworking during the sea-level rise events and river discharges), transport-accumulation processes, the formation of sediment sequences and the future evolution of the sediment systems, for which numerical modelling becomes increasingly important.

Abstract The rivers of East Asia are some of the largest and most important to human society and the global economy. They drain a variety of terrains from the Tibetan plateau, the hill country of southern China and the steep mountains of Taiwan. The sediment they carry potentially records the long-term evolution of continental environments within the marine stratigraphic record. Sediments reaching the ocean have to traverse the wide continental shelves where they may be reworked and transported by longshore currents, typhoon storm waves, as well as large ocean currents such as the Kuroshio. Deciphering any marine record requires us to understand the dynamics of sediment transport on the continental shelves, and this region acts as a global type example of such processes. Studies in this volume span a wide range of subdisciplines in the marine sciences and provide new insights into how sediment is distributed offshore after leaving the river mouths.