Provenance Identification Of Cumulic Red Earth In The Jinqu Basin

As a typical aeolian sediment of the Quaternary,the cumulic red earth in southern China records important information about the evolution of the Quaternary paleoenvironment,and the study of its provenance is of great significance for the comprehensive understanding of the climate change process and the evolution of the East Asian monsoon in southern China.In recent years,the provenance of aeolian cumulic red earth has made great progress.Some studies believe that the southern cumulic red earth belongs to the southward extension of northern loess in geographical space,while some studies support the bare leakage of the Yangtze River floodplain sediment during the glacial period as its potential source.some other research support that the provenance of the southern cumulic red earth is a mixture of distant aeolian sediments and near-source sediments.Some studies have further focused on provenance of cumulic red earth at different particle sizes and found that the sediments with fine-grained components（<20μm）contained northern loess signals,while provenance of coarse-grained components（>20μm）was the Yangtze River floodplain sediment,which had obvious particle size effects.Aeolian cumulic red earth in the Jinqu Basin of central Zhejiang is widely distributed,and whether there is a particle size effect for provenance of different grain sizes in the basin geomorphological background remains to be studied.Based on field investigation of aeolian cumulic red earth in the Jinqu Basin,this study focused on Tangxi（TX）and Pujiang Liangku（PJLK）profiles which contains vermicular red clay samples and typical red clay samples.Each sample were then separated into five subsamples based on its particle size,including bulk samples,<4μm,4～20μm,20～63μm,and 4～63μm.Elemental geochemical methods and detrital zircon U-Pb age spectroscopy methods were combined to analyze the provenance of cumulic red earth with different particle sizes（bulk,<4μm,4～20μm,20～63μm,and 4～63μm）.This study will provide data support for clarifying the potential sources of aeolian cumulic red earth in the Jinqu Basin of central Zhejiang,and at the same time,based on the comprehensive work of previous people,it will provide new evidence for whether there are regional differences in provenance of aeolian cumulic red earth in the Jinqu Basin of central Zhejiang,and the main conclusions obtained are as follows:（1）The particle size characteristics of cumulic red earth in different regions of southern China indicate that cumulic red earth is aeolian sedimentation.Specifically,the red earth in the Jinqu Basin,southern Anhui,northern Gan and Dongting Lake areas have silt（4～63μm）as the dominant particle level,with a content of53.67%～74.02%,and the content of 10～50μm basic aeolian particle level is30.88%～36.96%.However,there are differences in the distribution characteristics of major elements of cumulic red earth in the Jinqu Basin,southern Anhui,northern Jiangxi,and Dongting Lake areas.on the standardization of Upper Continental Crust（UCC）,the distribution pattern of major elements in different regions show different performance.The results indicate that there are regional differences in the source of cumulic red earth in southern China,and there may be differences in the material composition of different laterite profiles in the Jinqu Basin of central Zhejiang.（2）The concentrations of major elements in aeolian red earth in the Jinqu Basin are mainly Si O₂,Al₂O₃and Fe₂O₃,among which Si O₂content is the highest.The average content of Si O₂（58.38%）in TX samples is lower than PJLK samples（63.22%）,but the average contents of Al₂O₃and Fe₂O₃in TX samples that are easily enriched in clay minerals are higher than those in PJLK samples.The results of the correlation between Si O₂and other major elements in bulk samples of the two profiles show that although the samples of TX and PJLK show a negative correlation between Al₂O₃,K₂O,Fe₂O₃and Si O₂,there are significant differences in the relationship between the other major elements and Si O₂content.The UCC standardization results of different types of samples in the two profiles show that there are differences in the enrichment and loss of major elements in TX and PJLK profiles,but the enrichment loss of the vermicular red clay samples and typical red clay samples of the same profile tend to be consistent.The characteristics of the major elements,the correlation results between the other major elements and Si O₂and the loss of element enrichment indicate that there may be differences in the weathering degree and mineral composition of the TX and PJLK samples,but the material composition of the vermicular red clay samples and typical red clay samples within the same profile are similar.（3）The CIA of the red earth of different types in silt samples of the two profiles is smaller than that of the bulk samples.The ratio of Na₂O/Al₂O₃and K₂O/Al₂O₃in the bulk samples of the two profiles is lower than that of silt samples,which indicate that silty size samples can effectively weaken the weathering in the bulk samples of red earth.The immobile element ratio results of the two profiles showed that there are differences in the grain size of 4～63μm,4～20μm and 20～63μm,which may indicate that the material sources of cumulic red earth of different granular levels are different or the material contribution of the same source area to different granular red earth is different.（4）Most of the zircon in aeolian cumulic red earth samples and parent rock weathering samples are irregularly rounded,sub-angular and angular.This suggests that most of the particles probably come from a relatively close source zone.Most zircons have a distinct oscillatory magmatic zoning with a Th/U ratio of>0.4,indicating that they come from magmatic rocks.The U-Pb age spectrum characteristics of detrital zircon between aeolian red earth in the Jinqu Basin and its potential source areas explain that the source of aeolian red earth is affected by both parent rock weathering and Yangtze floodplain sediments.The Multidimensional Scaling analysis of the U-Pb age spectrum data of aeolian red earth in the Jinqu Basin and its potential provenance is consistent with the characteristics of the U-Pb age spectrum of detrital zircon.（5）The comparison of different particle fraction of cumulic red earth and potential source areas in the Jinqu Basin show that parent rock weathering near the profile and Yangtze floodplain sediment contribute to the sources of red earth in this area.The ratio of Ti O₂/Al₂O₃vs Si O₂/Al₂O₃show that bulk samples of cumulic red earth is like the sediments of Yangtze floodplain,but there is a significant difference with northern loess.The stable element ratio,such as Zr/Rb vs Zr/Nb,La/Nb vs Zr/Rb,reveal that the material sources of different particle fraction of red earth in the Jinqu Basin are closely related to the sediments of the Yangtze River floodplain.It is most prominent in 4～63μm and 4～20μm.The provenance function（PI,DF）is used to identify the links between different particle fraction of cumulic red earth and potential source area（parent rock weathering and Yangtze River floodplain sediments）in the Jinqu Basin.also confirm that the source of aeolian cumulic red earth in the Jinqu Basin is controlled by the sediments of the floodplain of the Yangtze River and the parent rock weathering in the region,and the results show that Yangtze floodplain sediment and parent rock weathering contributed to the source of every particle size in the two profiles,but the degree of influence on each particle size is different.