1995  Ruan, p.407: Lower subformation of Heishantou (or Donggulubastau) Formation is mainly composed of
         clastic rocks and tuff with some intercalations of tuffaceous sandstone and limestone lens.

         Age: Younger than Tn1, "Protocanites-Pericyclus zone", lower Tn3 (Tn2 b - Tn3c).