Short papers for the 8th international congress on the jurassic system. Marine and non-marine jurassic / Краткие заметки 8-го международного конгресса по юрской системе. Морские и континентальные юрские отложения

For decades, the base of the Hettangian (the Triassic-Jurassic system boundary) in the terrestrial succession of the Newark Supergroup of eastern North America has been placed incorrectly at a stratigraphic level that coincides with a modest palynological turnover immediately beneath the lowest basalt flow of the Central Atlantic Magmatic Province (CAMP), e.g. the Orange Mt. Basalt in the Newark basin or the North Mountain Basalt in the Fundy basin (see review in Whiteside, et al., 2007). According to numerous studies (reviewed in Whiteside, et al., 2007), the system boundary can be defined on the basis of the following: (1) last appearances of certain Triassic species (Ovalipollis ovalis, Vallasporites ignacii, and Patinasporites densus); (2) a dramatic increase in the abundance of Corollina spp. (= Classopollis and Gliscopollis); (3) and a bloom of trilete spores (fern spike), considered as the expression of a palynofloral recovery after the end-Triassic mass extinction. Consequently, all the strata overlying and interlayered with the CAMP lava flows have been assigned to the Jurassic, and the ages of the oldest CAMP basalts considered basal Jurassic. Calculations based on the cyclostratigraphy of the Newark basin strata suggest that the onset of CAMP volcanism should postdate the system boundary in the Newark basin by 20-40 ky and the entire basalt pile in these basins should have then been erupted during the Early Jurassic normal polarity chron E24n (e.g. Kent and Olsen, 2008). 
Apparent validation for this definition of the system boundary came from the magnetostratigraphy of the Newark basin. Hounslow, et al. (2004) attempted to make a palaeomagnetic correlation to the Newark of the Upper Triassic-Lower Jurassic marine section at St. Audrie’s Bay, England, where the system boundary is in the upper part of the Penarth Group. They suggested that either their SA5r reversal, which is the stratigraphically highest short reversed interval, or one of the stratigraphically lower reversals, SA5n.3r or SA5n.2r, correlate to the E23r reversal that corresponds to the palynofloral turnover event in the Newark section. Notably, these correlations indicate that the E23r  reversal is older than the currently proposed definition of the Hettangian base in the marine (lowest occurrence of Psiloceras spelae), and correlation of the E23r reversal to the two lower reversals at St. Audrie’s Bay would make E23r older than the stratigraphically highest conodonts. Whiteside, et al. (2007) similarly correlate the E23r reversal to one of the brief reversals (chrons SA5n.3r and SA5r) of the St. Audrie’s Bay section (England) <...>