More Evidence for Long Norian and Rhaetian Stages

This is a new paper looking at Triassic magnetostratigraphic correlations between Europe and North America.  The findings essentially support the early conclusions of Muttoni et al. (2004; 2010) arguing for long Norian and Rhaetian stages.  Correlations between the Steinbergkogel sections in Austria and the Newark Supergroup in the eastern U.S.A., suggest the following timescale revisions:

Carnian-Norian boundary: ~226.6 Ma;
Lacian-Alaunian boundary: ~216.4 Ma (fairly equivalent to the old Carnian/Norian boundary);
Alaunian-Sevatian 1 boundary: 211.8 Ma;
Norian Rhaetian boundary: ~209.8 Ma.

Thus according to these data the early Norian is approximately 10 million years long, the middle Norian is 4.5 million years old, and the late Norian is 2 million years old for an approximately 17 million year long Norian stage.  The Rhaetian is approximately 9 million years long.

Proposed biostratigraphic data from palynomorphs and conchostracans suggesting a shorter Norian are refuted.

Hüsing, S. K., Deenen, M. H. L., Koopmans, J. G., and W. Krijgsman. 2011. Magnetostratigraphic dating of the proposed Rhaetian GSSP at Steinbergkogel (Upper Triassic, Austria): Implications for the Late Triassic time scale.  Earth and Planetary Science Letters 302: 203-216

Abstract - The Global Stratotype Section and Point (GSSP) for the Rhaetian Stage has recently been proposed at Steinbergkogel in Austria. We re-sampled the Steinbergkogel sections (STK-A and STK-B + C) in high-resolution to establish a robust magnetostratigraphy that allows global correlation. The palaeomagnetic signal at Steinbergkogel is composed of three components, which can be separated by thermal demagnetization. The highest temperature component, revealed between 280/300 and maximum 600 °C is of dual polarity and is interpreted as primary. Rock magnetic experiments showed that the signal is carried by magnetite. Our results allow correlation between the two individual Steinbergkogel outcrops. Subsequently, we correlate the two key biostratigraphic horizons for the base of the Rhaetian, the FO of M. hernsteini and the FAD of M. posthernsteini to other sections of the Tethys domain. The correlation to the astronomically dated continental successions of the Newark basin indicates that these positions for the base of the Rhaetian are most likely determined in chrons E16n and E16r, respectively. This correlation is confirmed by cyclostratigraphic control on the marine Pizzo Mondello (Italy) section, where a combination of long period Milankovitch cycles (~ 175-Myr) and short-eccentricity cycles (~ 100-kyr) provide additional correlation constraints, respectively supporting a long duration of the Rhaetian. Our study implies that the Norian and Rhaetian Stages have durations of ~ 17 and ~ 9 Myr.


REFERENCES

Muttoni, G., Kent, D.V., Jadoul, F., Olsen, P.E., Rigo, M., Galli, M.T., and A. Nicora. 2010. Rhaetian magneto-biostratigraphy from the Southern Alps (Italy): constraints on Triassic chronology. Palaeogeography, Palaeoclimatology, Palaeoecology 285: 1–16.

Muttoni, G., Kent, D.V., Olsen, P.E., Di Stefano, P., Lowrie, W., Bernasconi, S.M., and F. M. Hernandez. 2004. Tethyan magnetostratigraphy from Pizzo Mondello (Sicily)and correlation to the Late Triassic Newark astrochronological polarity time scale. Geological Society of America Bulletin 116: 1043–1058.