In this paper, the basic characteristics of sedimentary tuff are introduced which has recently been discovered in Miyang Depression, Henan Province. The tuff consists of the basaltic debris, plagioclastics, hyaloclastic fragments, and silicated or chloritized interstitial materials, with the addition of minimal terrigenous quartzic and cherty clastics. Furthermore, the current cross lamination shown by abundant animal and plant remains contained in the rock indicates its transitional characteristics.
The plagioelase in the basaltic debris and crystalloclastic plagioclase are classified into the albite or oligoclase.They are products of the albitization of more basic plagioclase during diagenesis.The sedimentary tuff occurs in the fan deltaic depositonal system in the Tertiary faulted basin，while pyroclastics in the sedimentary tuff are the syndepositional basic effusion under water.The southwest faults of Miyang Depression are boundary faults which stretch to the upper mantle.It is shown that they can provide passages of the emplacment and eruption of basic magma at some extensional stage.
