Psiloceras spelae tirolicum. The "Golden Spike" was fixed at Kuhjoch East. The section displays a high and continuous sedimentation rate with a constant facies trend across the boundary level. Other bio-events include the FO of the aragonitic foraminifer Praegubkinella turgescens, and of diverse ostracod species 1.0-3.40 cm below the FO of P. spelae and 3.2 m below P. spelae occurs the continental palynomorph Cerebropollenites thiergartii. Because of the lack of other terrestrial microfloral events this is yet the FO event closest to the FO of P. spelae and allows a correlation with nonmarine sediments. The δ 13 C org record shows a strong initial negative excursion at the boundary between the Kössen and Kendlbach formations, 5.8 m (Kuhjoch W) below the T-J boundary, a shift to more positive δ 13 C org in the Schattwald Beds and a gradual decline to more negative values at the transition of the Schattwald Beds to the proximate Tiefengraben Mb. The stratotype point lies within a zone of smaller negative and positive δ 13 C org peaks, which is superimposed on a longer lasting main negative shift. According to recent investigations, the radiometric age of the T-J boundary is about 201,3 Ma.

Numerical calibration of the Late Triassic stages is arguably the most controversial issue in Mesozoic stratigraphy, despite its importance for assessing mechanisms of environmental perturbations and associated biologic consequences preceding the end-Triassic mass extinction. Here we report new chemical abrasion–isotope dilution– thermal ionization mass spectrometry zircon U-Pb dates for volcanic ash beds within the Aramachay Formation of the Pucara Group in northern Peru that place precise constraints on the age of the Norian- Rhaetian boundary (NRB) and the duration of the Rhaetian. The sampled ash bed–bearing interval is located just above the last occurrence of the bivalve Monotis subcircularis, placing this stratigraphic sequence in the uppermost Norian, perhaps ranging into the earliest Rhaetian. Zircon U-Pb dates of ash beds constrain the deposition age of this interval to be between 205.70 ± 0.15 Ma and 205.30 ± 0.14 Ma, providing precise constraints on the age of the NRB. Combined with previously published zircon U-Pb dates for ash beds bracketing the Triassic-Jurassic boundary, we estimate a duration of 4.14 ± 0.39 m.y. for the Rhaetian. This ends a prolonged controversy about the duration of this stage and has fundamental implications for the rates of paleoenvironmental deterioration that culminated in the end-Triassic mass extinction

[1] Constraining the carbon isotopic changes associated with the end-Triassic mass extinction is key to understanding the causes of the extinction and dynamics of recovery from it. Yet the pattern and timing of d 13 C variation surrounding the extinction remain poorly constrained. Here we present close to 1000 new d 13 C measurements from six newly sampled sections in Italy. We observe a sharp negative excursion in d 13 C carb coincident with the disappearance of the Triassic fauna, and two positive excursions above it. The negative d 13 C carb excursion in these sections does not occur in d 13 C org suggesting a possible diagenetic origin. In contrast, the interval of elevated d 13 C occurs in both carbonate and organic carbon, suggesting that it is likely to be a primary feature. The positive excursions in the Lombardy Basin (southern Alps) and Mt. Cefalo (southern Apennines) appear to be time correlative on the basis of their position above the disappearance of characteristically Triassic biota. However, it is less certain that they are time correlative with positive excursions in other sections worldwide, as few options exist that honor both bio-and chemostratigraphy. Nonetheless, similarity to other events that are interpreted as global, as well as carbon cycle considerations, suggest that the isotopic enrichment is best interpreted to reflect a shift in the isotope composition of the global surface carbon reservoir. Our data indicate that perturbation of the global carbon cycle was not confined to the immediate vicinity of the extinction interval, but rather persisted for substantial length of geologic time afterwards.

No abstract

No abstract