[N] 2006 The position of the Triassic-Jurassic boundary
Lucas, S. & Tanner, L. (2006) Fossil vertebrates and the position of the Triassic-Jurassic boundary. JVP 26(3) Abstracts pp.91
The working definition of the Triassic-Jurassic boundary (TJB) has long been taken as the LO (lowest occurrence) of the ammonite Psiloceras (usually P. planorbis). But, there is no direct way to relate the LO of P. planorbis to the fossil vertebrate record across the TJB. In the nonmarine Newark Supergroup of eastern North America, the TJB has been placed just below the oldest basalts of the Central Atlantic Magmatic Province (CAMP) based on palynostratigraphy, and most vertebrate paleontologists have long relied on this placement of the TJB. This boundary, however, is demonstrably older than the TJB defined in marine strata.
The palynological turnover cited as the TJB in the Newark most resembles a late Norian change in the European sections and does not correspond to any palynological event at the marine-defined TJB. Vertebrate footprint evidence (LO of Eubrontes) used to support the palynostratigraphic placement of the TJB in the Newark Supergroup is undermined by occurrences of Eubrontes in the Triassic of Europe and Australia and of bones of potential Eubrontes trackmakers in Triassic strata. Radioisotopic ages indicate the marine TJB is no older than 200 Ma, but the palynostratigraphically-defined TJB in the Newark Supergroup is older than 201 Ma, based on isotopic dates of the oldest CAMP basalts.
Magnetostratigraphic correlation to European marine sections also suggests that the palynostratigraphically- defined TJB in the Newark Supergroup is older than the marine TJB. Thus, all data indicate that the TJB in the Newark Supergroup is above the lowest CAMP basalt, probably in the extrusive zone or just above it. Therefore, the position of the TJB in nonmarine strata is actually higher than generally thought, and does not obviously correspond exactly to any bioevent in the fossil record of vertebrates.