Study On The Late Cretaceous Paleoenvironment Indicative Significance By Red Beds In The Western Fujian Province

A set of Mesozoic Cretaceous broad and deep continental red strata has been deposited in southeastern China,which is composed of reddish-toned clastic sediments,also called as "red beds".The Late Cretaceous red beds in western Fujian are widely distributed,and has representive sedimentary.It is a good material for studying the paleoclimate and paleoenvironmental changes.At present,the continental Cretaceous red beds are generally regarded as terrestrial clastic sediments,and they are conventionally regarded as lacustrine-fluvial sediments in basin,whose paleoenvironmental implication is still in debate.In this paper,the late Cretaceous red beds in the west of Fujian is the main research object.Through field sampling analysis,and systematic analysis of 179 samples of the red beds of the Liancheng section(LC)and the Guanzhangshan section(GZS),such as systematic particle size analysis,environmental magnetism research,geochemistry,diffuse reflectance spectroscopy,and paleo-soil analysis,to explore the paleoenvironment indicative significance of the late Cretaceous red beds in western Fujian.At the same time,we can supplement the related study of late Cretaceous red beds in this paper.Based on the results of the samples,the following main conclusions are drawn:(1)Through field surveys and grain size experiments,it is shown that the grain size composition of the Late Cretaceous red beds in western Fujian is mainly composed of fine silt particles,with less clay and sand content,and the rock layer is silt and sand interbedded with thin layer of fine-grained gravel.The particle size parameters and particle size curves indicate that the dynamics of sediment handling power are complex.(2)The late Cretaceous red beds in western Fujian has low magnetic properties,and the main magnetic bearing mineral is hard magnetic mineral hematite.Geochemical parameters show that the western Fujian red beds has a higher degree of weathering.In addition,the rare earth elements(REE)of red beds show enriched light rare earth element(LREE),depleted heavy rare earth elements(HREE),which resembled that of average upper continental crust(UCC),thus indicating thoroughly mixing sediments.(3)Although the Late Cretaceous red beds in western Fujian developed some paleosols characteristics in the upper part of the Shaxian Formation,the degree of soil formation was not strong,and there was no obvious paleosols viscous layer(Bt)and calcium layer(Bk).But the strong weathering reflected by geochemistry is not coordinated with it.Therefore,the red beds sediments have undergone a considerable degree of weathering process in the source area before sedimentating,and then deposited by the hybrid power in the basin.After deposition,the red sediments were hardly chemically weathered.It should be explained that the red beds can not indicate paleoenvironment indirectly.Besides,the characteristics and changes of sedimentary environment of the red beds need to be determined in combination with the characteristics of paleosols development,which must take it into account.And it can provide an alternative prospect in studying Cretaceous red beds.(4)The late cretaceous paleoenvironment in western Fujian was suspected to be arid and semiarid.The hematite in red beds were mainly derived from source area,indicating well-drained dry oxidizing environment,rather than aqueous condition.