| 摘 要： | Isotopic determinations were made on basalts intercalated in the strata with abundant Upper Tertiary fossils. In order to satisfy the needs of K-Ar age determina.tions of younger basalts with lower potasium content, we have made some modifications on the China-made ZhT-1301 massspectrometer, Meanwhile, some improvements and refinements have been made as well on the mass-spectrometer and the argon-extraction system and argen-measureing technique. Our results are: 7.86---13.Sm.y. for the youngest basalts ; 20--24 m.y. for the Shanwang Group with abundant Miocene fossils;and: 44 m.y. for basalts from the lower part of the Shanwang Group. The chronological results are basically in agreement with the stratigraphic sequence.
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