Abstract:

The Jurassic/Cretaceous is the only Phanerozoic boundary that does not yet have an accepted global boundary definition. In contrast to most geological systems, there are nearly no “global events” within the uppermost Jurassic and lowermost Cretaceous. It has been difficult to find any significant widespread biostratigraphic, geochemical or other markers for interregional correlation within this interval. The ammonite definition for the base of the Cretaceous appears to fall within the middle of relatively long ammonite zones. The current markers tend to integrate regional calpionellid zones, calcareous nannofossil datums, ammonite zonations, and magnetostratigraphy. The J/K boundary is at the base of Calpionella alpina zone and FAD of Nannoconus steinmannii minor and N.kamptneri minor. It is in the Chron M19n.2n and of 145 Ma age. The international stratigraphical division and correlation are based on marine standard. The Jurassic and Cretaceous strata in northern China are mostly of terrestrial origin. It appears a difficulty to define the boundary. In the previous biostratigraphic work, the J/K boundary was referred to a higher position of much younger age, which caused a big controversy between local biostratigraphy and international age. The pronounced provincialism of terrestrial fauna and flora obstructs global correlation. The solution of persistent debates on the J/K boundary in China should be the integrated stratigraphic markers which might provide the most useful global correlation. Owing to the obscure of terrestrial fossil evidences to indicate the boundary, the macro biotic evolution is suggested as a potential workable J/K boundary indicator. The Yanliao Biota and Jehol Biota are two big fossil groups representing Jurassic and Cretaceous respectively. If it is the case, the transition beds of two biotas would be down to the Tuchengzi Formation. The boundary age could alternatively be 139 Ma on the top or 145 Ma in the middle of the formation. Only accurate indicators or markers would be obtained from the Tuchengzi Formation and/or GSSP being accepted, the J/K boundary in China tends to be completely located.

Key words: J/K boundary, terrestrial strata, boundary definition, international correlation