Characteristics And Provenance Of The Heavy Minerals In Modern Sediments Of Liaohe Estuary

Detrital sediments record the provenance change,paleoclimate change,river channel migration and geomorphologic evolution in the coastal area.Investigating the heavy mineral combination and characteristics is of scientific significance for better understanding of the sedimentary transportation and history of the river channel migration,as well as for establishment of the source-to-sink system in the multi-river dominated coasts.The North Bohai Coast is dominated by multiple rivers.The Liaohe,Dalinghe,Daliaohe and Raoyang Rivers,as well as the other local rivers flow into Liaodong Bay.A large amount of terrigenous debris from Hebei,Inner Mongolia,Jilin and Liaoning Provinces are transported by the rivers and deposited in the North Bohai Coast.20 surface sediments were collected from the Middle and Lower Liaohe River and the Dalinghe River,for heavy mineral and zircon morphology analysis.Characteristics of the heavy minerals for the sediments from the main stream and the main tributaries of the Liaohe and the Dalinghe Rivers were determined.The provenance identification indexes of the Liaohe and the Dalinghe Rivers were yielded.30 samples collected from 3 cores in North Bohai Coast were used to investigate the evolution of provenance in the North Bohai Coast during the last 400 years on the basis of the lithological characteristics,heavy mineral analysis,210 Pb chronology and the heavy mineral index of the Liaohe and Dalinghe Rivers.Q-type cluster analysis was applied for vertical zoning.The main conclusions of heavy mineral investigations,the evolution of provenance of the sediments in the North Bohai Coast during the last 400 year,as well as the controlling factors are drawn as follows:(1)The content of the heavy minerals is less than 0.1% in Liaohe and Daliaohe Rivers,while it is more than 1% in Dalinghe River.The heavy mineral assemblages in the Lower Liaohe River are ilmenite-epidotite-magnetite-garnet,whilst those in the Middle Liaohe River are garnet-epidote-ilmenite-amphibore.The zircon grains are mostly transparent,pale pink,and well-rounded.In the Lower Dalinghe River,the heavy mineral assemblages are garnet-epidote-magnetite-ilmenite;while those are ilmenite-magnetite-garnet-limonite – ilmenite,and magnetite-garnet-limonite-ilmenite in the Middle and Upper Dalinghe River,respectively.The zircon grains are purplish red and light pink,with poorly-rounded and sorting.(2)Outcomes of provenance analysis of river surface samples show that the sediments in the Middle Liaohe River are mainly derive from the Upper Laoha River,while the sediments in the Lower Liaohe River are dominated by the Middle and Upper Liaohe River,the East Liaohe River and local areas.Sediment in the Middle Dalinghe River derive from the Mangniuhe river and the source rock of the upstream basin,while sediment in the Lower Dalinghe River is affected by Xihe rivers.(3)According to the vertical change of heavy mineral contents in cores LH24,LH40 and LH48 and the210 Pb chronology,the provenance of sediments in the North Bohai Coast changed in the last 400 years.Before 1896,when the Liaohe river channel migrated to the current position,the sediments mainly derived from the Dalinghe River,while the Liaohe River has influenced the sedimentary process in the North Bohai Coast with the increasing proportion of Liaohe material after 1896.It also indicates that the Dalinghe River channel has migrated for several times during the last 400 years.