Composite Fingerprints Of Detrital Minerals In The South Yellow Sea: Qualitative And Quantitative Provenance Tracing

The marginal sea is usually the gathering area of sediment transport of the river into the sea.It is a key scientific problem in the catchment-coast-shelf source-sink system to distinguish the fluvial sediment from the marginal sea sediment,quantitatively analyze the different sources,and deeply understand the diffusion range of each source.The core of solving these problems is to construct the characteristic fingerprints of the source-sink system,which should meet the requirements of being identifiable,quantifiable and traceable.The South Yellow Sea in the east of Asia is affected by the sediments from the Huanghe River and the Changjiang River,so it is of typical value for the identification and quantitative study of marginal marine provenance.In this study,50 surface samples(11 from the Changjiang River,9 from the Huanghe River,3 from the abandoned Huanghe River,and 27 from the South Yellow Sea)and one core(AHD4,304 cm in length)in the South Yellow Sea were used as research materials.A composite analysis method composed of multiple-grained heavy mineral analysis and single mineral geochemical element analysis was used to carry out the research.The multiple-grained heavy mineral analysis method extends the identification grain size of single mineral from within 3Φ-4Φ to multiple grain size(1Φ-6Φ,with an interval of 1Φ),and the types and content characteristics of heavy minerals in sediments are analyzed comprehensively.The geochemical elements of amphibolite and magnetite at the very fine sand and coarse silt grain sizes of each sample were tested.To select reliable heavy mineral assemblages and single mineral trace element tracer composite indicators for qualitative and quantitative analysis of the terrestrial origin of sediments at different grain levels in the South Yellow Sea.The main conclusions are as follows:The multiple-grained heavy mineral analysis method has rich mineral species and more grain size content,which can reflect the heavy mineral characteristics of fluvial detrital sediments more comprehensively.The heavy mineral assemblage in the Changjiang River is hornblende + epidote + limonite,the characteristic mineral is sphene.The heavy mineral assemblage is hornblende + limonite + epidote in the Huanghe River,while that of abandoned Huanghe River is hornblende amphibole +limonite + hydrobiotite,and the characteristic mineral both are garnet.Therefore,using the heavy minerals garnet(Grt)-sphene(Spn)-magnetite(Mgt)and amphibole(Amph)-epidotite(Ep)-limonite(Lm)to establish the endmember assemblages,the sediments from the Changjiang River and the Huanghe River could be qualitatively distinguished visually.Analysis of amphibole and magnetite population particles geochemical elements showed that,the content of Y,Sc,Cs and Tl in amphibole from the Huanghe River is high,while the amphibole in the Changjiang River is characterized by high content of Hf,Th,Rb and Li.The Huanghe River magnetite is characterized by high concentration of large ion lithophile elements such as Zr,Ba,Sr and Pb,while the Changjiang River magnetite is relatively rich in Nb,Sc,Ce and Ta.The mineral element content of the northern part of the South Yellow Sea and the off-shore area of the abandoned Huanghe River estuary is strongly influenced by the Huanghe River,and the southern part are similar to those of the Changjiang River.The principal component analysis(PCA)of amphibole trace elements and the ratios of trace elements,such as Zr/Sc-Y/Hf and Nb/Y-Sc/Hf,can also be used to qualitatively distinguish the detrital sediments from the Changjiang and Huanghe rivers.According to the K-S test,CV test and RD analysis,the classification fingerprints of sediment from the Changjiang River and the Huanghe River is Zr,Be,Ga,Ge,Nb,Cd and Hf elements of amphibole.The coarse slit can be distinguished by Ba,Zr,Li,Rb and Hf elements of amphibole.Six provenance identification fingerprints,Ba,Cu,Nb,Cs,Th and U,were selected for the coarse-silt grade magnetite.Combined with the qualitative fingerprint of characteristic mineral assemblage and the quantitative fingerprint of geochemical elements,the composite fingerprints of fluvial source sediment in the South Yellow Sea shelf area was constructed.Based on the Chemical Mass Balance model,the average contribution of the Huanghe River sediments to the very fine sand and coarse silt in the South Yellow Sea is 45% and 57.6%,respectively,while the average contribution of the Changjiang River sediments to the very fine sand and coarse silt in the study area is 54.8% and 42.4%,respectively.The boundary between the source of the Huanghe River and the Changjiang River is approximately(121°E,34°N)to(123°E,35°N).The coarse silt from the Huanghe River and the Changjiang River has a longer transport distance and a higher mixing degree than that from the very fine sand.The core(AHD4)is located in the adjacent sea area outside the estuary of the abandoned Huanghe River,and the sediments are mainly supplied by the source of the Huanghe River(the abandoned Huanghe River).In the very fine sand grade,the supply of the Huanghe River is between 70% and 98.9%,and in the coarse silt grade,the contribution content of the Changjiang River is between 76.7% and 97.9%.In the very fine sand grain size,the contribution of the Changjiang River sediment ranges from 1.1%to 30%,while in the coarse silt grade,the content varies from 2.1% to 23.3%.The contribution of the Huanghe River and the Changjiang River to the AHD4 core was influenced by the historical climate of the basin at the end of the Late Holocene,river diversion events and large-scale human activities.This study shows that heavy mineral end-member assemblages with the wide grain size and multiple-window mineral strategy,detrital amphibole and magnetite trace elements can form an effective composite identification fingerprint of fluvial sediment,which has a more comprehensive provenance indication significance and higher accuracy of provenance exclusivity.It provides a good example for qualitative and quantitative provenance research and analysis of terrigenous sediment mixed areas in marginal sea.