A New 40Ar/39Ar Analysis Method of Volcanoclastic Strata to Determine Eruption Periods—Example of Xintaimen, China

The Jehol Biota is famous for its diversity of Early Cretaceous fossils preserved under large amounts of pyroclastic materials. However, the precise determination on the ages of volcanoclastic strata is challenging, because of their complex provenance. The solution to this problem may lie in the greatly improved geochronological methods, such as the 40Ar/39Ar geochronology. In this study, we use the laser fusion 40Ar/39Ar dating method to date volcanoclastic samples and apply statistical analyses of the acquired apparent ages to determine the volcanic eruption periods. From the 12 volcanoclastic samples analyzed in this study, we obtained 262 apparent ages that vary from 85.5 to 153.6 Ma. By fitting these apparent ages with a Gaussian mixture distribution model, we find three age clusters that are normally distributed, with each cluster statistically representing an eruption period. The mean values of the three normal distributions are 90.37±2.72 (1σ), 109.89±4.94, and 125.26±10.01 Ma. A comparison of our results with a statistical analysis of literature data indicates that volcanic activities occurred over a wide spatial scale across western Liaoning Province during the two older periods, whereas during the last time period, eruptions occurred more locally and belonged to the final stage of volcanic eruptions in the basin. The method and results reported in this study provide a good example of (1) dating volcanoclastic materials using the 40Ar/39Ar method to determine the time periods of volcanic activities and (2) investigating the stratigraphic correlation in complex volcanoclastic basins.