关键词: 老红砂, 环境演变, 晚第四纪, 闽东南沿海

Abstract: The old red sandy sediments are quite typical and widespread along the coast of Southeast Fujian Province. Based on the field investigations and lab studies (including the analysis of grain size, SEM, geochemistry, XRD and the datings of TL, ESR and ¹⁴C), this paper discussed the sedimentary characteristics, origin and the evolution of the "old red sands" in the coastal area of Southeast Fujian. The old red sandy deposits are mostly massive shaped with no beddings (partly develop some high angle cross beddings), but have several sedimentary boundary planes. The sedimentary characteristics of the "old red sands" are clearly different from those of beach sands, but similar to those of dune sands. The "old red sands" have mainly medium fine grain size with more silts and clays, good roundness and medium sorting, mostly positive skewness. By the SEM analysis, the surface textures have not only inherited and reformed the features of beach sands (e.g. rodent V shaped percussion pits and directive triangle shaped corrosion pitsetc.), but also accumulated or paragenerated typical features of aeolian environment (e.g. dish shaped pits, cresent shaped pits, pitted surfaces, etc.). Some trace elements and their ratios also indicate that the old red sandy sediments belong to terrestrial facies. The sedimentary characters mentioned above and the distribution forms indicate that the old red sandy sediments along the coast of Southeast Fujian are mainly ancient aeolian deposits. But there're also partly alluvial and aeolian slope washed old red sandy sediments. By the direct and indirect datings, the forming ages of the "old red sands" may be divided into two main stages as 60~45 ka BP and 30~10 ka BP. The two stages equal to the early Wüurm glacial substage of the medium period of late Pleistocene and the late Wüurm glacial substage of the late period of late Pl eistocene seperately. The formation and development of the old red sandy sediments along the coast of Southeast Fujian reflect the changes of plaeo geographic environment, specially the paleo climate, in some degree. The forming stage of the old sandy sediments corresponding to the glacial substage (the cold period) is the marker that the climate becomes cold and arid, and the fixing stage (grass growing, paleoso l developing or laterization stage) corresponding to the interglacial stage (the warm period) is the evidence of damp hot climate. The sea level fluctuations during the glacial and interglacial stages had controlled the sand sources and distribution of the old red sandy deposits to a certain degree.

Key words: The "old red sands", Environmental evolution, Late Quaternary, Coast of Southeast Fujian