Abstract:

According to the forming process and geological attributions, the volcanostratigraphical boundaries will be divided into 5 types. They are eruptive conformity boundary(ECB, typeⅠ), eruptive unconformity boundary (EUB, typeⅡ), eruptive interval unconformity boundary (EIUB, typeⅢ), tectonic unconformity boundary(TUB, typeⅣ) and intrusive nonconformity boundary (INB, typeⅤ). Except INB, the others unconformity boundaries can be divided into angular unconformity and paraconformity/angular unconformity. The time interval of ECB and EUB is from several minutes to years. There is chilling crust or fine pyroclastic layer above and below these surfaces. The two types’ boundaries maybe curve or netlike plane, coarse and small ranges distribution. The time interval of EIUB is from decades to thousands years. There is weathered crust underlying the EIUB, and sedimentary rock bed overlying the EIUB. In most time, the weathered crust and thin sedimentary bed associate together. The boundary is smooth curve plane. The characteristics of TUB are similar to EIUB’s. The interval time of TUB is from thousands to millions years, and the distribution scale is bigger than EIUB’s. The Mesozoic volcanic rocks of NE China reveal that there is high porosity zone(mainly contribute by the primary pore) near the EUB or EIUB, and the porosity decreases when it is apart from the boundary. Both porosity and the percentage of pore rich rock of netlike boundary are higher than the curved boundary’s. The wells in Songliao basin show that there is abundant secondary pore below the EIUB or TUB. Its porosity may be enhanced when the primary pores exit . On the other hand, it is difficult to predict the change of porosity.

Key words: volcanostratigraphical boundary, unconformity boundary, geological attributions, Northeast part of China, Mesozoic, volcanic rocks