The application of fission track analysis to the dating of barren sequences: examples from red beds in Scotland and Thailand

In continental red-beds facies, which often contain little or no organic material for biostratigraphic dating, fission track (FT) analysis of detrital zircon crystals represents one method by which a maximum stratigraphic age may be determined. In addition, FT analysis of detrital apatite provides a means of palaeotemperature estimation, especially in areas where there is insufficient, or unsuitable, organic matter for vitrinite reflectance. Two examples of the application of FT analysis to the solution of stratigraphic problems in redbed sequences are described. In Scotland, the age of the Tongue Outlier is disputed, previous studies having suggested either a Devonian or Permo-Triassic age. Comparison of FT data from both detrital apatite and zircon indicates a Permo-Triassic age. In Thailand, the 3 km thick continental clastic Khorat Group has a well-defined lithostratigraphy but is poorly constrained biostratigraphically. The lower Nan Phong Formation has a Rhaetic age whilst the Khok Kruat Formation at the top of the group has been assigned an Aptian age. In the absence of any biostratigraphic control, the intermediate Phu Kradung and Phra Wihan Formations have been assumed to be of Middle and Upper Jurassic age. FT data presented here for detrital zircons indicate a Lower Cretaceous age for Phra Wihan Formation of the Khorat Group