| The Cretaceous period is a typical period of the greenhouse climate,during which not only the world's most devastating creatures have been recorded,but the paleoclimatic temperature is so high.Studies have shown that the surface water temperature in the equatorial region is about 8-10 ?;atmospheric C02 concentration is 2-4 times today,the sea level is about 50 m higher than today.At present,global warming has been widely concerned by modern society.Whether the future trend and trend of climate change are close to the Cretaceous-Paleogene climate model and the study of paleoclimatic records in the strata can help us profound understanding of the past Earth's climate and interpretation of the current state of climate warming.At present,there are few geological records in the Cretaceous-Paleogene,and the paleoclimate research can not be further studied.The NanXiong basin in Guangdong Province revealed a relatively complete Cretaceous red formation and continued until early Paleocene.Previous studies have found a large number of fossils,in addition to dinosaurs,dinosaur eggs,there are many turtles,fish,and numerous micro-fossils.It is currently the highest degree of Cretaceous stratigraphy research,the most complete Cretaceous profile.The Datang section of Nanxiong basin has a good late Cretaceous-early Paleocene terrakus reddish,continuous deposition and fossil enrichment,which is the ideal geological profile of Cretaceous-Paleogene boundary in China.However,it is a discussion of the problem to indicate the large pond section of the red stratigraphic record of the ancient climate evolution.Based on the detailed field investigation and systematic sampling of the Datang section,this study,through the system of rock magnetism measurement,combined with rare earth element testing,particle size measurement and carbonate content determination and other non-magnetic means.And the magnetization characteristics of the section are discussed,and the paleoclimatic information recorded by the sediments is explored from the magnetic point of view.(1)In the field observation,it is found that the classification of the rock structure is mainly composed of silty mudstone and argillaceous siltstone and the sandstone.The whole conglomerate shows the fine-coarse-fine pattern.The paleo-soil features and paleosol layers are developed in many strata,especially among red mudstones.Based on the previous research results,this paper argues that the large pond profile is a large set of red pale soil sequences that have not yet been fully understood.(2)Rare earth elements(REE)analysis showed that,although the different layers or age of the selected cross-section of the sample,its distribution pattern was highly similar such as the rare earth element content of each sample are very close to the slopes are negative,light rare earth elements Enrichment,Eu negative anomaly and so on.REE distribution pattern shows that the sediments of the strata in the Datang section have experienced the evolution of the paleoclimatic environment in different geological periods,but their source is stable and has the same material source.(3)The results of particle size measurement show that the sediment particles in different sections are obviously changed,but the particle characteristics of the sediments are consistent.The lower and upper part of the study is dominated by silty mudstone and argillaceous siltstone,and the middle is siltstone sandstone and sandstone.The samples of the conglomerate are subjected to a sieve with 2 mm before the particle size analysis.It shows that all the samples are mainly composed of silt particles,clay content is high,and contains a certain amount of sand.The results show that the sediments of the sediments are characterized by fine-coarse and fine-grained sediments,which are characterized by thick clastic rocks(71.5-66 Ma).The size of sediments in the sediments may vary from one source to another,and may reflect the characteristics of various sources,both the sand and the granite,and the clay.(4)The results of the petrological measurements of the system show that hematite is the dominant magnetism in the sediments,or the only magnetic minerals that can be detected.The total ? is very low and the maximum value is not more than 20×10-8 m3/kg which is much lower than that of the Quaternary loess-paleosol and Tertiary red clay.However,the relative content of hematite is much higher than that of the latter,suggesting that the climatic conditions of the Cretaceous-Early Paleocene strata are more high and less humid than the later Cenozoic.Hematite is characterized by high content of fine sandy siltstone,high magnetic susceptibility,low content of coarse gravel and low magnetic susceptibility.But the magnetic susceptibility value is still showing a high-low-high trend with depth,which corresponds to the change of the thickness change of the silt to the mudstone-gritstone-silty mudstone in the stratigraphic strata.The feature essentially reflects the change in controlled hematite content.(5)The variation of carbonate content in the section is between 0%and 17.1%,and the mean value is 6.5%.There is no obvious law with the depth of the section,and the pearson correlation coefficient is-0.117,|r| = 0.117.It Indicate that there is no correlation between the two,so that the main factor controlling the change in susceptibility is still hematite content changes.(6)Magnetic susceptibility and paleoclimatic changes:the variation of magnetic susceptibility in the study can be divided into three periods:1)The magnetic susceptibility of the main field group(72-71.5 Ma)is stable at high value,which corresponds to the deep ocean oxygen isotope value Negative zone.It reflect the relatively high temperature,pale soil calcareous nodules ?18O positive.Combined with the sedimentary facies,it indicates that this stage of this phase for the relative wet period.In the relatively humid climate conditions,the role of soil enhancement promote hematite formation;2)The magnetization rate of 71.5-66 Ma is greatly reduced,and the isotopic value of deep sea oxygen is relatively positive,which reflects the relative decrease of temperature.The ?18O of calcareous nodules in the paleosol is negative,which reflects the relatively dry characteristics of the climate.3)The magnetization rate of the upper-lake group(66-61.5 Ma)increased,but the fluctuation was larger.The magnetic susceptibility was lower than that in the Huaihu Formation(66-61.5 Ma)The?18O positive of calcareous nodules in the paleosol was higher than that in the paleocloaly,indicating that the dryness of the area was weakened and the wettability increased,and the temperature recovered,but it was unstable,which resulted in stronger soil formation.Eventually increasing the hematite content,the magnetic susceptibility increased. |
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