Sedimentary architecture of the Holocene mud deposit off the southern Shandong Peninsula in the Yellow Sea

Newly acquired high-resolution seismic profiles reveal a nearshore and an of fshore mud depocenter of f the southern Shandong Peninsula in the Yellow Sea.The nearshore depocenter is distributed in bands along the south coast of Shandong Peninsula.The of fshore depocenter is part of the distal subaqueous deltaic lobe,which deposited around the southeastern tip of the Shandong Peninsula.Between the two depocenters is a linear depression.The mud deposits directly overlie the postglacial transgressive surface and can be divided into lower and upper units by the Holocene maximum flooding surface.The nearshore and off shore units display different seismic structures.The lower unit of the nearshore deposit exhibits basal onlap,whereas the upper unit is characterized by progradation.The lower and upper units of the off shore deposit display distinct acoustic features.The lower unit has low-angle aggradation with internal reflectors generally dipping seaward and truncated by the Holocene maximum flooding surface,whereas the upper unit is characterized by aggradation and progradation landward rather than seaward.Results of geochemistry analysis of QDZ03 sediments and mineral analysis of WHZK01 sediments suggest that the nearshore deposit and the lower unit of the of fshore deposit are derived from the proximal coastal sediments of the Shandong Peninsula and the Huanghe(Yellow) River sediments.The upper unit of the of fshore deposit is mainly Huanghe River-derived.The lower unit of the mud deposit represents a post-glacial transgressive system tract according to dates of core QDZ03,and the upper unit represents a highstand system tract from middle Holocene to the present.These results will be of great significance to further understanding of the transportation of the Huanghe River sediments into the Yellow Sea and the spatial distribution of the subaqueous delta.     

Sedimentary evolution since the late Last Deglaciation in the western North Yellow Sea

To decipher the sedimentary evolution and environmental changes since the late Last Deglaciation, two gravity cores were analyzed from the western North Yellow Sea (NYS). The two cores (B-L44 and B-U35) were sampled for grain size, clay minerals, detrital minerals, and 14C dating. They are comparable in lithofaies, and the observed succession was divided into four depositional units based on lithology and mineral assemblages, which recorded the postglacial transgression. Depositional unit 4 (DU 4) (before 11.5 ka) was characterized with enrichment in sand, and was interpreted as nearshore deposits in shallow water during the Younger Dryas Event. DU 3 (11.5-9.6 ka) displayed a fining-upward succession composed of sediments from local rivers, such as the Huanghe (Yellow) River, and from coastal erosion, which clearly were related to the Early Holocene transgression. Stable muddy deposition (DU 2) in NYS began to form at about 9.6 ka, which received direct supply of fine materials from the Shandong subaqueous clinoform. It is believed that the Yellow Sea circulation system played a major role in controlling the formation of fine sediment deposition in DU 1 (after 6.4 ka) after the sea level maximum.     

Characteristics of Heavy Minerals and Quantitative Provenance Identification of Sediments from the Muddy Area Outside the Oujiang Estuary Since 5.8 kyr

The heavy mineral compositions of the sediments in core D04 with a length of 20.2 m from the muddy area outside the Oujiang Estuary along the coast of Zhejiang-Fujian Provinces have been analyzed. Core D04 can be divided into three units: DU1(0–7.4 m), DU2(7.4–11.4 m) and DU3(11.4–20.2 m). The results showed that the heavy minerals are authigenic pyrite(65.6%)– hornblende(16.0%) – epidote(4.6%) assemblages. The core sediments are mainly composed of clayey silt, which belongs to the clinoform deposit formed since 5.8 kyr, indicating a weak hydrodynamic environment. The deposition rates changed in the trend of high-low-high upward. Quantitative analysis shows that the core sediments were mainly from the suspended sediments of the Changjiang(Yangtze) River, accounting for 79.2%, with only 10.0% from Oujiang, and 10.8% from other provenance. The Oujiang-derived sediments were gradually increased from the bottom unit DU3(3.1%) to the top unit DU1(17.8%), but the Changjiang-derived sediments were gradually decreased. The source changes are closely related to the development of Yangtze River Delta and Wenzhou Bay, climate changes and human activities. During the period of 2.1–3.7 kyr, the sediment supply was greatly reduced due to the poor reclamation capacity of the river basins, resulting in a low deposition rate. Since 2 kyr, the enhancement of human activities in the Yangtze River Basin and the Oujiang River Basin led to more soils to be eroded and transported to the study area. Due to the short distance of the site of core D04 from the Oujiang River mouth, the study area received more Oujiang-derived sediments when upper unit(DU1) deposited than the lower units(DU2 and DU3).     

A Holocene Yalu River-derived fine-grained deposit in the southeast coastal area of the Liaodong Peninsula

High-resolution seismic profiles and surface samples were studied in detail in order to determine the structures, provenance, and dynamic mechanisms of a fine-grained deposit in the southeast coastal area of the Liaodong Peninsula, China. Results indicate that there is a prominent fine-grained deposit distributed alongshore up to 14 m thick, which thins out to less than 2 m in both seaward and landward directions, forming an Ω-shaped pattern of cross-section. The deposit is 180–300 km away from the Yalu River mouth and extends along the southeast coast of the Liaodong Peninsula between the northeast of Dalian Bay and southwest of the Changshan Islands, in water depths of 20–40 m. The deposit, which is mainly derived from the Yalu River, represents a Holocene Highstand System Tract sequence formed since the highest sea level around 7.0 ka. The Yalu River-derived sediments were redeposited in the area off the southeast coast of the Liaodong Peninsula after resuspension and transportation by the Liaonan Coastal Current.     

Change in Sediment Provenance Near the Current Estuary of Yellow River Since the Holocene Transgression

Sedimentary sequence and sediment provenance are important factors when it comes to the studies on marine sedimentation. This paper studies grain size distribution, lithological characteristics, major and rare earth elemental compositions, micropaleontological features and ~(14)C ages in order to examine sedimentary sequence and sediment provenance of the core BH6 drilled at the mouth of the Yellow River in Bohai Sea. According to the grain size and the micropaleontological compositions, 4 sedimentary units have been identified. Unit 1(0–8.08 mbsf) is of the delta sedimentary facies, Unit 2(8.08–12.08 mbsf) is of the neritic shelf facies, Unit 3(12.08–23.85 mbsf) is of near-estuary beach-tidal facies, and Unit 4(23.85 mbsf–) is of the continental lake facies. The deposits from Unit 1 to Unit 3 have been found to be marine strata formed after the Holocene transgression at about 10 ka BP, while Unit 4 is continental lacustrine deposit formed before 10 ka BP. The provenances of core BH6 sediments show properties of the continental crust and vary in different sedimentary periods. For Unit 4 sediments, the source regions are dispersed while the main provenance is not clear, although the parent rock characteristics of a few samples are similar to the Luanhe River sediments. For Unit 3, sediments at 21.1–23.85 mbsf have been mainly transported from the Liaohe River, while sediments above 21.1 mbsf are mainly from the Yellow River and partially from the Liaohe River. For Unit 2, the sediments have been mainly transported from the Yellow River, with a small amount from other rivers. For Unit 1, the provenance is mainly the Yellow River catchment. These results help in better understanding the evolution of the Yellow River Delta.     

Phase evolution of Holocene paleoenvironmental changes in the southern Yellow Sea: Benthic foraminiferal evidence from core C02

Assemblages of benthic foraminifera in a sediment core (C02) near the western margin of the southern Yellow Sea Mud were studied to decipher the phase evolution of Holocene paleoenvironmental changes associated with the Holocene marine transgression. It appears that during the early Holocene (11.2–10.1 kyr BP), the faunal was dominated by low salinity and shallow water species Cribrononion subincertum, Buccella frigida and Ammonia beccarii, reflecting a near coast depositional environment. A rapid increase of the relative abundance of Ammonia compressiuscula between 10.1–9.3 kyr BP indicates that the sea level rose rapidly during that time period. From 9.3–7.7 kyr BP, the benthic foraminiferal assemblage was dominated by high percentage of A. compressiscula, suggesting that the sea level was relatively stable. An obvious transition of benthic foraminifera, from the A. compressiuscula-dominated assemblage to an Ammonia ketienziensis-dominated assemblage, occurred between 7.7–6.2 kyr BP, possibly corresponding to a second sea level rapid rise period in the Yellow Sea during the Holocene. This transition may correspond to the gradually strengthened Yellow Sea warm current (YSWC) and finally is established the modern-type circulation in the Yellow Sea. It may also mark the formation of the Yellow Sea cold bottom water (YSCBW) during that period. Since then, the benthic foraminiferal assemblage based on core C02 was dominated by typical YSCBW species, A. ketienziensis, Astrononion italicum and Hanzawaia nipponica, at 6.2–4 kyr BP. A non-deposition period occurred since ～4 kyr BP, which possibly related to the hydrology changes caused by the East Asia monsoon. The two obvious benthic foraminiferal transitions recorded in core C02 during the early and middle Holocene provide evidence that the Yellow Sea has undergone a two-phase rapid sea level rise during the Holocene marine transgression.     

Formation and evolution of the modem warm current system in the East China Sea and the Yellow Sea since the last deglaciation

To reconstruct the formation and evolution process of the warm current system within the East China Sea (ECS) and the Yellow Sea (YS) since the last deglaciation, the paleoceangraphic records in core DGKS9603, core CSH1 and core YSDPI02, which were retrieved from the mainstream of the Kuroshio Current (KC), the edge of the modem Tsushima Warm Current (TWC) and muddy region under cold waters accreted with the Yellow Sea Warm Current (YSWC) respectively, were synthetically analyzed. The results indicate that the formation and evolution of the modem warm current system in the ECS and the YS has been accompanied by the development of the KC and impulse rising of the sea level since the last deglaciation. The influence of the KC on the Okinawa Trough had enhanced since 16 cal kyr BE and synchronously the modem TWC began to develop with the rising of sea level and finally formed at about 8.5 cal kyr BP. The KC had experienced two weakening process during the Heinrich event 1 and the Younger Drays event from 16 to 8.5 cal kyr BP. The period of 7-6 cal kyr BP was the strongest stage of the KC and the TWC since the last deglaciation. The YSWC has appeared at about 6.4 cal kyr BP. Thus,the warm current system of the ECS and the YS has ultimately formed. The weakness of the KC,indicated by the occurrence of Pulleniatina minimum event (PME) during the period from 5.3 to 2.8 cal kyr BE caused the main stream of the TWC to shift eastward to the Pacific Ocean around about 3 cal kyr BP. The process resulted in the intruding of continent shelf cold water mass with rich nutrients. Synchronously, the strength of the YSWC was relatively weak and the related cold water body was active at the early-mid stage of its appearance against the PME background, which resulted in the quick formation of muddy deposit system in the southeastern YS. The strength of the warm current system in the ECS and the YS has enhanced evidently, and approached to the modern condition gradually since 3 cal kyr BP.     

Formation and evolution of the modern warm current system in the East China Sea and the Yellow Sea since the last deglaciation

To reconstruct the formation and evolution process of the warm current system within the East China Sea (ECS) and the Yellow Sea (YS) since the last deglaciation, the paleoceangraphic records in core DGKS9603, core CSH1 and core YSDP102, which were retrieved from the mainstream of the Kuroshio Current (KC), the edge of the modern Tsushima Warm Current (TWC) and muddy region under cold waters accreted with the Yellow Sea Warm Current (YSWC) respectively, were synthetically analyzed. The results indicate that the formation and evolution of the modern warm current system in the ECS and the YS has been accompanied by the development of the KC and impulse rising of the sea level since the last deglaciation. The influence of the KC on the Okinawa Trough had enhanced since 16 cal kyr BP, and synchronously the modern TWC began to develop with the rising of sea level and finally formed at about 8.5 cal kyr BP. The KC had experienced two weakening process during the Heinrich event 1 and the Younger Drays event from 16 to 8.5 cal kyr BP. The period of 7–6 cal kyr BP was the strongest stage of the KC and the TWC since the last deglaciation. The YSWC has appeared at about 6.4 cal kyr BP. Thus, the warm current system of the ECS and the YS has ultimately formed. The weakness of the KC, indicated by the occurrence of Pulleniatina minimum event (PME) during the period from 5.3 to 2.8 cal kyr BP, caused the main stream of the TWC to shift eastward to the Pacific Ocean around about 3 cal kyr BP. The process resulted in the intruding of continent shelf cold water mass with rich nutrients. Synchronously, the strength of the YSWC was relatively weak and the related cold water body was active at the early-mid stage of its appearance against the PME background, which resulted in the quick formation of muddy deposit system in the southeastern YS. The strength of the warm current system in the ECS and the YS has enhanced evidently, and approached to the modern condition gradually since 3 cal kyr BP. Supported by the National Natural Science Foundation of China (Nos. 90411014 and 40506015), the National major Fundamental Research and Development Project (No. 2007CB815903) and the CAS Pilot Project of the National Knowledge Innovation Program (No. KZCFX3-SW-233)     

Sediment flux and source in northern Yellow Sea by^210 Pb technique

1 INTRODUCTION The Yellow Sea is a shallow epicontinental sea surrounded by Chinese mainland and Korean Peninsula. It is connected with the East China Sea to the south, and with the Bohai Sea to the north- west. Water depth is generally less than 80 m with average of 44 m (Qin et al., 1989). The major sediment sources are the Huanghe and Changjiang (Yangtze) Rivers, providing annual sediment load of about 1.1×109 and 4.9×108 tons, respectively. A maximum of 1.6×108 tons of sedime…     

The Holocene Environmental Evolution of the Inner Hangzhou Bay and Its Significance

The Holocene environmental evolution in coastal area, including deltas and estuaries, is vital to the Neolithic colonization in the eastern China. A 29-m long sediment core XL was obtained from the region between the Taihu Lake and Qiantang Estuary, and multiple analyses on the core sediments have been done to investigate the evolution history of the inner coastal zone of Hangzhou Bay during the Holocene. Six sedimentary facies are identified since the late Pleistocene, including the paleosol at the bottom, overlain by tidal-flat-channel complex(TFC), tidal-distributary-channel(TDC), inner estuarine basin(IEB), subtidal-to-intertidal-flat, and fluvial-plain facies. The TFC and TDC facies are dated to be formed before 8500 cal yr BP, featured by relatively coarse sediments, high magnetic properties and less abundant foraminifera, denoting the tide-influenced setting with large terrestrial inputs. The IEB facies characterized by the most abundant foraminifera fossils and the lowest sediment magnetic properties, is inferred to be deposited during the maximum flooding period between 8500 and 7900 cal yr BP. The branch estuary was then infilled by local sediments with a shallowing-upward subtidal-to-intertidal sequence during 7900–4300 cal yr BP. At last the fluvial plain system developed since no later than 4300 cal yr BP, favouring the rapid development of Neolithic cultures in the region.     

Features of clay minerals in the YSDP102 core on the continental shelf of the southeast Yellow Sea

Ninety-eight clay mineral samples from the YSDP102 core were analyzed by x-ray diffractometer to study the four clay minerals: illite, chlorite, kaolinite and smectite. Twenty-eight samples had been analyzed on the laser particle-siz eanalyzer to reveal the particle features of the sediments. Distribution of the clay minerals and the particle characteristics in the YSDP102 core show that the core experienced three different depositional periods and formed three different sedimentary intervals due to different sediment sources and different depositional environments. Features of the clay minerals and the heavy minerals in the YSDP102 core indicate that coarse-grained sediments and fine-grained sediments result from different sources. The Yellow Sea Warm Current has greatly influenced the sedimentary framework of this region since the current‘s formation.     

利用黄河泥沙围出“渤海湖”的初步设想

本文是一个关于将渤海变成淡水湖的水利工程的构想。让黄河的大量泥沙通过人工导流的方式沿莱州湾南岸与渤海海峡沉积延伸,产生的陆地将渤海封闭并逐渐形成淡水湖。这一工程将陆地连接山东半岛与辽东半岛,并为华北提供巨大淡水库,具有显著的经济、生态效益。具体实施上,可通过两道渔网式围栏促使黄河泥沙定点沉积并阻挡浪潮侵蚀,通过加强汛期水量增加黄河口泥沙。     

Biomarker records of phytoplankton productivity and community structure changes in the Central Yellow Sea mud area during the Mid-late Holocene

The Yellow Sea (YS) environmental and ecological changes during the Holocene are driven by the interactions between the Yellow Sea Warm Current (YSWC), the East Asian Winter Monsoon (EAWM) and the Kuroshio Current (KC). We report marine biomarker records of brassicasterol, dinosterol and C37 alkenones in core ZY1 and core ZY2 from the South Yellow Sea (SYS) to reconstruct the spatial/temporal variations and possible mechanisms of phytoplankton primary productivity and community structure changes during the Mid-late Holocene. The contents of the corresponding biomarkers in the two cores are similar, and they also reveal broadly similar temporal trends. From 6 kyr to 3 kyr, the biomarker contents in the two cores were relatively low with small oscillations, followed by a distinct increase at about 3 kyr indicating productivity increases caused by a stronger EAWM. The alkenone/brassicasterol ratio (A/B) is used as a community structure proxy, which also showed higher values in both cores since 3 kyr, indicating increased haptophyte contribution to total productivity. It is proposed that the YS community structure has been mainly influenced by the YSWC, with stronger YSWC influences causing an increase in haptophyte contribution since 3 kyr. Some differences of the biomarker records between ZY2 and ZY1 suggest spatial variations in response to YSWC and KC forcing. When the KC was intensified during the periods of 6–4.2 kyr and 1.7–0 kyr, the YSWC extended eastward, exerting more influence on core ZY1. On the other hand, when the KC weakened during 4.2–1.7 kyr, the YSWC extended westward, exerting more influence on the ZY2.     

A new high-resolution Late Glacial-Holocene climatic record from eastern Nanling Mountains in South China

A 350-cm-long sediment core sequence from Dahu Swamp situated in the eastern Nanling Mountains was selected for high-resolution paleoclimatic reconstruction since the Late Glacial period. The multi-proxy records of this paper reveal several evidently dry and cold events that may coincide with the Oldest Dryas, the Older Dryas, the Younger Dryas in the late deglacial period. Two relatively wetter and warmer phases occurred in ca. 15,000–14,400 cal yr B.P. and 13,500–12,800 cal yr B.P. respectively may correspond to the Bølling and Allerød warming events. The Younger Dryas event (ca. 12,800–11,500 cal yr B.P.) revealed by multi-proxies was characterized by relatively colder and drier climate. A warmer and wetter climate, occurred in ca. 10,000–6000 cal yr B.P., was consistent with the Holocene Optimum, which coincided with the maximum Northern Hemisphere insolation. The “8.2kyr cool event” and even the “8.8kyr cool event” were indicated as well from our sediment core. A dry mid-Holocene period (ca. 6000–3000 cal yr B.P.) indicated by multi-proxies does not follow the traditional concept of the wet mid-Holocene conditions observed in other regions in China.     

Heavy mineral stratigraphy of sediments from the southern outer shelf of the East China Sea since the last glaciation using fuzzy C-means cluster method

Correspondence analysis and fuzzy C-means cluster methods were used to divide the stratigraphy of heavy mineral assemblages, and the sediment sources and depositional dynamics of the environment reconstructed. The assemblages were taken from marine sediments from the late Pleistocene to the Holocene in Core Q43 situated on the outer shelf of the East China Sea. Based on the variable boundaries of the mineral assemblage at 63 and 228 cmbsf (cm below sea floor), the core might have previously been divided into three sediment strata marked with units I, II and III, which would be consistent with the divided sediment stratum of the core using minor element geochemistry. The downcore distribution of heavy minerals divided the sedimentary sequence into three major units, which were further subdivided into four subunits. The interval between 0 and 63 cmbsf of the core (unit I), which spans the Holocene and the uppermost late Pleistocene, is characterized by a hornblende-epidote-pyroxene assemblage, and contains relatively a smaller amount of schistic mineral and authigenic pyrite. In comparison, the interval between 63 and 228 cmbsf (unit II), is representative of the Last Glacial Maximum (LGM), and features a hornblende-epidote-magnetite-ilmenite assemblage containing the highest concentrations of heavy minerals and opaque minerals. However, the interval between 228 and 309 cmbsf (unit III), which spans the subinterglacial period, is characterized by a hornblende-authigenic-pyrite-mica assemblage. Relative ratios of some heavy minerals can be used as tracers of clastic sediment sources. The lower part of the sediment core shows the highest magnetite/ilmenite ratio and relatively high hornblende/augite and hornblende/epidote ratios. The middle core shows the highest hornblende/augite and hornblende/epidote ratios, and the lowest magnetite/ilmenite ratio. The upper part exhibits a slightly higher magnetite/ilmenite ratio, and also the lowest hornblende/augite and hornblende/epidote ratios. The distribution of the mineral ratio is consistent with stratigraphic division in heavy mineral data using correspondence analysis and fuzzy C-means clustering. Variations in heavy mineral association and mineral ratio in core Q43 revealed changes in provenance and depositional environment of the southern outer shelf of the East China Sea since the late Pleistocene, well corresponding to interglacial and glacial cycles.     

SEDIMENT DISCHARGE OF THE HUANGHE RIVER AND ITS EFFECT ON SEDIMENTATION OF THE BOHAI SEA AND THE YELLOW SEA

The Huanghe (Yellow) River, with annual sediment discharge about 11 ×108tons, contributes about 17% of the fluvial sediment discharge of world's 21 major rivers to the ocean because its middle reaches flow across the great Loess Plateau of China. Sediment discharge of the Huanghe River has a widespread and profound effect on sedimentation of the sea. The remarkable shift of its outlet in 1128-1855 A.D. to the South Yellow Sea formed a large subaqueous delta and provided the substrate for an extensive submarine ridge field.The shift of its outlet in the modern delta every 10 years is the main reason why with an extremely heavy sediment input and a micro- tidal environment, the Huanghe River has not succeeded in building a birdfoot delta like the Mississippi. The Huanghe River has consistently brought heavy sediment input to sea at least since 0.7 myr.B.P. Paleochannels, paleosols, cheniers and fossils on the sea bottom indicate that the Yellow Sea was exposed during the late Quaternary glacial low-sea l     

Sedimentary Characteristics of the Second Marine Layer During the Late Marine Isotope Stage 3 in Southern Yellow Sea and Their Response to the East Asian Monsoon

We use the particle size of sediments in core YS01 A to study the sedimentary environment of the mud deposit in the central South Yellow Sea of China during late Marine Isotope Stages 3(MIS3;40.5 kyr–31.3 kyr).In addition,the East Asian Monsoon and its relationship with the North Atlantic Ocean climate change are discussed based on the sensitive grain-size calculation and the spectrum analysis.The results show that during late MIS3,the muddy area in the central South Yellow Sea experienced the evolution of coastal facies,shallow marine facies,coastal facies,and continental facies,with weak hydrodynamic conditions.Compared with other climate indicators,we found that there were many century to millennium-scale climate signals documented in the muddy area sediments in the central South Yellow Sea.According to our particle size results,three strong winter monsoon events occurred at 37.6 kyr,35.6 kyr and 32.2 kyr.The East Asian Winter Monsoon records in core YS01 A are consistent with the Greenland ice core and the Hulu cave stalagmite δ~(18)O.The millennial and centennial scale cycles,which are 55 yr,72 yr,115 yr,262 yr respectively,correspond to solar activity cycles,while the 1049 yr and 2941 yr cycles correspond to the Dansgaard-Oeschger cycles.These cycles indicate that the paleoclimate evolution of the area was controlled by the solar activities,with the high-latitude driving thermohaline circulation as the main energy conveyor belt,followed by the sea-air-land amplification of the winter monsoon variation in the central Yellow Sea in the late MIS3.     

Distribution and origin of sediments on the northern Sunda Shelf, South China Sea

ＩＮＴＲＯＤＵＣＴＩＯＮＯｎｅｏｆｔｈｅｍｏｓｔｅｘｔｅｎｓｉｖｅｓｈｅｌｖｅｓｏｆｔｈｅｗｏｒｌｄｌｙｉｎｇｗｉｔｈｉｎｔｈｅｓｏｕｔｈｅｒｎｐａｒｔｏｆｔｈｅＳｏｕｔｈＣｈｉｎａＳｅａｉｓｔｈｅ1850000ｋｍ2ＳｕｎｄａＳｈｅｌｆｌｏｃａｔｅｄｂｅｔｗｅｅｎｔｈｅｔｈｒｅｅｌａｒｇｅｉｓｌａｎｄｓｏｆＳｕｍａｔｒａ,Ｂｏｒｎｅｏ,ＪａｖａａｎｄｍａｉｎｌａｎｄＡｓｉａ(ＬａＦｏｎｄ,1966).ＴｈｅｎｏｒｔｈｅｒｎｐａｒｔｏｆｔｈｅＳｕｎｄａＳｈｅｌｆｉｓｓｅｐａｒａｔｅｄｆｒｏｍｔｈｅＪａｖａＳｅａｓ…     

Source Evolution and Its Relationship to Climate Change Since the Middle–Late Pleistocene in Laizhou Bay,China

Through the geochemical analysis of two hundred-meters cores KD4 and ZK3 from Laizhou Bay,in this study,we determined the distribution law and controlling factors of the geochemical elements.We analyzed 24 elements with respect to their R factors and major principal components,which were combined with the source discrimination functions DFCr/Th and DFCa/Al to obtain the sediment source index and its variation with depth for this area.A comparison of the changes in climate indicators suggests a clear correlation between the source and climate changes.The results show that the Yellow River and surrounding short-term rivers are the main sediment sources in this area.The PC3 of the KD4 core and PC2 of the ZK3 core(e.g.,CaO,MnO,SiO2)exhibit significant variations and reflect the relative contributions of Yellow River sources.The deposition process can be divided into six stages:in Phase I(MIS 5c–MIS 5a),the Yellow River formed,and the composition of the Yellow River had a greater influence on the sedimentary composition of the study area.In Phase II(MIS 5a–MIS 3),the sediment sources of the Yellow River and the short-term streams in this area were wavering,with the sediments derived from short-term rivers playing a more important role.In Phase III(MIS 3),with a sharp drop in temperature,the study area was in the process of retreat,and the sediment source changed from the Yellow River to short-term rivers,after which the Yellow River source material remained the main sediment source for the region.A similar process occurred three more times in Phase IV(MIS 3–MIS 2),Phase V(MIS 2–MIS 1),and Phase VI(MIS 1).With changes in climate,especially during alternating sea-land phases,the sediment source varied in marine-terrestrial-marine phases,and the changes are observed as Yellow River source-surrounding provenance-Yellow River source.However,this process of change is not synchronized with the sea-land strata alternation.     

Inversion and Prediction of Consolidation Settlement Characteristics of the Fluvial Sediments Based on Void Ratio Variation in the Northern Modern Yellow River Subaqueous Delta,China

The modern Yellow River delta is formed near the estuary of the Yellow River with the characteristics of short formation time, efficient sedimentation rate and loose structure which make sediments prone to be compacted and consolidate under the geostatic stress and overburden stress. It is one of the key areas with land subsidence disasters in China, bringing a series of safety hazards to production and living. Based on the data of massive surface cores and ten drill holes ranging from 12 to 40 m obtained from the northern modern Yellow River subaqueous delta, the inversion method suitable for the calculation of consolidation settlement characteristics of the modern Yellow River subaqueous delta is discussed, and the consolidation settlement characteristics of the delta sediments are inversed and predicted in this paper. The actual void ratio of the delta sediments at the depth from 3 to 15 m shows a significant power function relationship with the depth, while the void ratio of the sediments below 15 m changes little with depth. The pre-consolidation settlement(from deposition to sampling) of the delta sediments is between 0.91 and 1.96 m, while the consolidation settlement of unit depth is between 9.6 and 14.0 cm m~(-1). The post-consolidation settlement(from sampling to stable) of the subaqueous delta sediments is between 0.65 and 1.56 m in the later stage, and the consolidation settlement of unit depth is between 7.6 and 13.1 cm m~(-1) under the overburden stress. The delta sediments with a buried depth of 3 to 7 m contribute the most to the possible consolidation settlement in the later stage.