Rhaetian
[13] The most comprehensive source of precise age data for the Late Triassic comes from astrochronologically-constrained terrestrial strata of the Newark basin in the eastern United States.
[19][20][21][22] Most recently, aspects of the "short-Rhaetian" hypothesis have been revived by radiometric dating of Peruvian bivalve extinctions and magnetostratigraphy at the Pignola-Abriola GSSP candidate.
[26][11][27][13] In the Tethyan domain (i.e. the area of the Tethys ocean), the Sagenites reticulatus and Paracochloceras suessi ammonite biozones begin at the base of the Rhaetian.
This sequence records a pronounced negative spike in δ13C just before the first appearance of Misikella posthernsteini (sensu stricto) and the Proparvicingula moniliformis radiolarian zone.
[29] The Norian-Rhaetian extinction may have been caused by the eruption of the Angayucham large igneous province in Alaska,[30] or the asteroid responsible for the Rochechouart impact structure in France.
It records many potential Norian-Rhaetian biostratigraphic events, such as the appearance of the conodonts Misikella hernsteini and M. posthernsteini (sensu lato) and the ammonoid Paracochloceras suessi.
It also record the extinction of large Monotis bivalves and the disappearance of ammonoids including Metasibirites and some Sagenites forms with lateral nodes.
The GSSP marking the beginning of the Hettangian (and the end of the Rhaetian) is located at Kuhjoch, a geological section near the base of the Kendelbach Formation in Austria.
[15] Gallet et al. (2007) explained this by suggesting that there was a missing period of time or "hiatus" at the end of the Newark sequence, which would have resembled part of Oyuklu had it not been eroded away.
The conchostracan Shipingia olseni, which in Europe is found in Norian rocks, occurs in the upper portion of the Passaic Formation, the last pre-CAMP section of the Newark basin.
When the International Commission on Stratigraphy updated their Geologic Time Scale in 2012, the "short Rhaetian" and "long Tuvalian" hypotheses were equated with each other.
The combined "short Rhaetian/long Tuvalian" hypothesis as described by Ogg (2012) was ultimately not chosen by the ICS when compared to its competition, which was supported by a more diverse array of methods.
This hiatus was presumed to lie within the normal polarity-dominated end of the Rhaetian, after a very short reverse polarity section (E23r) and just before the first CAMP eruptions.
In addition, the magnetic signature of at the end of Newark basin has been found worldwide, with sequences in Morocco, Nova Scotia,[34] Italy, the U.K., and possibly Turkey all preserving E23r-equivalent magnetozones underlying the Rhaetian-Hettangian boundary.
Kent, Olsen, & Muttoni (2017) additionally found convincing correlations between the magnetozones of the upper Passaic Formation and Rhaetian strata in England.
They suggest that the apparent delay between Newark and Europe fauna and flora may instead be biogeographic differences due to climatic variation over time and latitude, a factor which has manifested at other points in the Triassic.
[18] Ikeda & Tada (2014) provided an astrochronologically-constrained chert sequence in Japan which suggested that the Norian-Rhaetian boundary occurred 208.5 ± 0.3 Ma, based on the extinction of the Norian radiolarian Betraccium deweveri.
[11] Partially inspired by the work of Hüsing et al. (2011), the ICS's 2012 Geologic Time Scale utilized a tentative 208.5 Ma date for the Norian-Rhaetian boundary.
This date corresponds to "short-Rhaetian" predictions, but Wotzlaw et al. (2014) also agreed with "long-Rhaetian" proponents who argued that there was no good evidence for a hiatus in the Newark Basin sequence.
[23] Golding et al. (2016) utilized U-Pb dating at a part of the Black Bear Ridge section of British Columbia which is considered early Rhaetian based on its conodont fauna.
This section recorded the Norian-Rhaetian boundary as tracked by the first occurrence of Misikella posthernsteini, the base of the Proparvicingula moniliformis radiolarian zone, and a prominent negative δ13C anomaly.
[12] A recent update of Newark stratigraphy by Kent, Olsen, & Muttoni (2017) combined magnetostratigraphy with astrochronology to form the longest astrochronostratigraphic polarity time scale (APTS) known in the fossil record.
By tracing McLaughlin cycles backwards from the radiometrically-dated CAMP basalts, the boundaries between each formation and magnetozone in the Newark sequence could be assigned a precise age.
[41] The end date of the Rhaetian currently in use by the ICS (201.4 ±0.2 Ma) is based on a study by Schoene et al. (2010) involving ammonite-bearing strata in Peru.
The biostratigraphically-defined Triassic-Jurassic (Rhaetian-Hettangian) boundary is considered to lie approximately 60–140 thousand years after the extinction by most sources, and therefore the Rhaetian ended in the range of 201.5 to 201.4 Ma under the methodology of Blackburn et al.
