Constraints On The Clay Minerals From Lacustrine Sediments,in Western Qaidam Basin

In the lake sediments,the formation and transform of clay minerals are closely related to the environment.Clay minerals must be affected by high salinity,cold and arid.Study on the change of clay minerals not only have important mineralogical significance,but also for paleoclimate.The study seclected clay minerals from sediments in brackish,saline and playa lakes,in western Qaindam Basin.The examples were examined for the changes of contents,structure,illite crystralinity and?18O-?D of interlayer waters.These changes of clay minerals are possible driven by temperature,salinity and sources.The main conclusions are following as:Clay minerals in the area contains illite and illite/smectite mixed layer with minor chlorite,kaolinite and smectite.Illite has high crystallinity with the average value of0.35.Both low temperature and high salinity cause high illite crystallinity,because(a)illite will be well kept in cold conditions,and(b)more K ions enter illite interlayer and in saline lake.The content of illite layer in the mixed-layer illite/smectite is about 85%?90%,and the mixed-layer illite/smectite is highly ordered R3I/S.Both high temperature and high salinity can promote the transformation from smectite to illite.The contents in saline condition are higher than those in brackish conditions,while the contents in warm conditions are higher than those in cold conditioins.The clay mineral interlayer water range from-90‰?0‰with average-46.4‰,while the?¹⁸O range 2‰to 40‰with average 19.57‰.Both of them are higher than those of modern saline lake water in Qaidam Basin.The transformation from smectite to illite can result in high isotopic values.The?D and?¹⁸O also soucred from meteoric water,paleolake water and oilfield brine.