Studies of ~(40)Ar-~(39)Ar Isotopic Chronostratigraphy of the Sanjianpu Formation in the Hefei Basin, Anhui
WANG Dao xuan 1) , JIN Fu quan 1) , XIE Xian de 2) , and LIU Yin 1) ( 1)Hefei University of Technology, Hefei, 230009; 2) Anhui Petroleum Prospecting Company, Hefei, 230022)
Sequence and ages of the Mesozoic red beds on the southern margin of the Hefei Basin have been arbitrarily modified for several times. The 40 Ar 39 Ar dating of illite samples forming under the conditions of the deposition and diagnoses, from the mudstones of the Sanjianpu Formation red beds, gives plateau age of 157.7~159.5 Ma, as a isochron age of 157.2~159.9 Ma, and a K Ar age of 151.8~155.8 Ma, suggesting that the lower limit of the Sanjianpu Formation is latest Middle Jurassic (Callovian stage) in age and its upper limit is of earliest Late Jurassic (Oxford stage) age. The 40 Ar 39 Ar age spectrum also records a thermal event during the Late Jurassic to Early Cretaceous and cooling history of the parent rocks (mica schist, gneisse, etc.) of the terrigenous debris of the Sanjianpu Formation red beds.