The Triassic time scale is poorly constrained due to a paucity of high-precision radiometric ages. We present a 206Pb/238U age of 230.91 0.33 Ma (error includes all known sources) for zircon from an ash bed in the upper Carnian (Upper Triassic) of southern\ud
Italy that requires a major revision of the Triassic time scale. For example, the Norian stage is lengthened to more than 20 m.y. The section containing the ash bed is correlated with other Tethyan sections and, indirectly, with the Newark astronomical polarity time scale (APTS). The dating provides also a minimum age for some important climatic and biotic events that occurred during the Carnian. We note a coincidence between these\ud
events and the eruption of the large igneous province of Wrangellia, but the possible link between volcanism and climatic and biotic events requires further scrutiny
Four stratigraphic sections belonging to Lagonegro succession (Southern Apennines) at Mt S. Enoc, Pignola-Abriola, Sasso di Castalda and Mt Volturino have been studied in detail under to provide a new micro-palaeontological data set based on conodonts and radiolarians for the characterization of the Norian⁄Rhaetian interval. The studied sec- tions represent the different settings of the Lagonegro Basin (from proximal to distal facies) and permit a detailed, integrated, biostratigraphy of the Calcari con Selce (cherty limestones) and Scisti Silicei formations (bedded cherts with radiolarians) to be drawn up. The upper portion of the Calcari con Selce Formation, exhibits intermediate charac- teristics between the Calcari con Selce and Scisti Silicei Formation, in particular the pro- gressive decrease in carbonate content against an increase in shales and cherts. Within the four sections studied, the Norian ⁄ Rhaetian interval has been documented both with conodonts and radiolarians. Because of the continuity and the absence of condensed facies, it has been possible to recognize the morphocline between species Misikella hern- steini and Misikella posthernsteini, here represented by all the transitional forms charac- terized by common features between the two species, gathered in three evolutionary steps. Moreover, the morphocline between M. hernsteini and M. posthernsteini has been involved in the definition of the Norian ⁄ Rhaetian Boundary, recognizing thus the FAD of M. posthernsteini, one of the possible biomarkers proposed for the boundary. The rich, well-preserved, radiolarian associations of Pignola-Abriola, Sasso di Castalda and Mt Volturino permit the correlation of Tethyan and American conodont successions, high- lighting the importance of the mostly coincident occurrences of M. posthernsteini and Epigondolella mosheri morphotype A, which correspond to the base of Proparvicingula moniliformis A. Z. and the disappearance of bivalve Monotis. These coincident bioevents are used here to define the base of the Rhaetian stage
A detailed magnetostratigraphic investiga-\ud
tion of the Pignola-Abriola section of Norian\ud
to Rhaetian age permits the identification of\ud
22 magnetic polarity reversals grouped in 10\ud
magnetozones. We correlate the magneto-\ud
stratigraphy of the Pignola-Abriola section\ud
with the Newark astrochronological polarity\ud
time scale (APTS). In total, 19 correlation\ud
options were tested, and only one (option 7)\ud
yielded a statistically significant correlation\ud
that was consistent with the available infor-\ud
mation on the stratigraphic age of the Newark\ud
APTS. After some adjustments to minimize\ud
erratic variations in sediment accumulation\ud
rates, a final correlation (option 7.1) was used\ud
to generate an age model of sedimentation\ud
for the Pignola-Abriola section. The Pignola-\ud
Abriola section has been correlated with\ud
Rhaetian sections from the literature, notably\ud
the current global boundary stratotype sec-\ud
tion and point candidate for the base of the\ud
Rhaetian at Steinbergkogel, Austria, where\ud
the Norian-Rhaetian boundary is proposed\ud
to be placed at a stratigraphic level contain-\ud
ing the first appearance datum (FAD) of\ud
conodont Misikella posthernsteini, traced on\ud
the Newark APTS to ca. 209–210 Ma. Issues\ud
regarding the taxonomy of M. posthernsteini,\ud
a species characterized by transitional forms\ud
with its ancestor Misikella hernsteini, lead us\ud
to propose the alternative option of placing the\ud
Norian-Rhaetian boundary at a prominent\ud
negative δ13C spike observed in the Pignola- org\ud
Abriola section at meter 44.5, 50 cm below the level containing the FAD of M. posthernsteini sensu stricto and close to the base of radiolarian Proparvicingula moniliformis zone. This level has been magnetostratigraphically cor- related to Newark magnetozone E20r.2r at ca. 205.7 Ma. Assuming an age of ca. 201.3 Ma for the Triassic-Jurassic boundary, the Rhaetian Stage would have a duration of ~4.4 m.y
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