The T/J boundary in shallow marine environments: the example of Mount Messapion section (Chalkida, Greece). Rivista Italiana di Paleontologia e Stratigrafia.

In the Mount Messapion area (Chalkida, Greece) a continuous and expanded section of Triassic/Jurassic (T/J) limestone outcrops. This section consists of a pile, 710 m thick, of the classic shallowing-upward peritidal cycles; the persistence of the facies and the lack of paleoenvironmental changes across the T/J boundary allowed studying the distribution of shallow water microfossils. The T/J boundary was placed in the upper part of the section in correspondence with (i) the last occurrence of Triasina hantkeni, (ii) the abrupt disappearance of megalodontid faunas and (iii) the presence of Lower Jurassic microfossil assemblages. This paleontological reorganization happens suddenly, it is not controlled by any facies change, and surprisingly, it seems to produce no evident modification in the vertical stacking pattern of the cycles. A detailed facies analysis, performed along a stratigraphic interval about 290 m thick (60 metres above the T/J boundary and 230 below), allowed the recognition of peritidal cycles: five different elementary cyclothemes are described and their distribution along the section is given. This integrated stratigraphic study represents an attempt to highlight the relationship between the changes of carbonate producers and sea level variations across the T/J boundary.