GSSP for Induan Stage
Definition:
The base of the Mesozoic Era, Triassic System and Induan Stage is defined at the base of Bed 27c in the Meishan Section, Changxing County, Zhejiang Province, China. It coincides with the first occurrence of the conodont species Hindeodus parvus in the evolutionary lineage Hindeodus latidentatus - Hindeodus parvus - Isarcicella isarcica.
Location:
Base of Bed 27c at the Meishan Section, Changxing County, Zhejiang Province, China. The longitude and latitude of the section are 119°42"20.9’ E and 31°4"47.28’ N respectively.
The strata of Bed 24 consist of dark-gray medium-bedded wacke- and packstones. Bed 25, "White Clay" is a light bluish grey illite-montmorillonite claystone. Bed 26 "Black Clay" is a dark grey montmorillonite-illite claystone. The GSSP Bed 27 consists of a light grey medium-bedded silty limestone, overlayed by grayish clay and medium-bedded dolomitic, argillaceous calcimicrite (Beds 28, 29).
Primary Markers:
First occurrence of the conodont species Hindeodus parvus in the evolutionary lineage Hindeodus latidentatus - Hindeodus parvus - Isarcicella isarcica at the base of Bed 27c in the Meishan Section
Secondary Markers:
Radiometric Dating:
Zircon dating of the "White Clay" (Bed 25) using SHRIMP (ion-microprobe) dating gave a 206PB/238U age of 251.2 ±
3.4 Ma.
Using incremental-heating 40Ar/39Ar analysis of sanidine grains (100-150m across) extracted from the "White Clay", obtained a plateau date of 249.91 ± 0.15 Ma, and a mean date by individual total-fusion analyses of 249.62Ma. The top of the "White Clay" is 0.14m below the level at which the GSSP is proposed, hence an unknown, but probably small number of years should be subtracted from the above determinations in order to approximate the age of the basal Triassic.
Stable Carbon Isotopes:
δ13C and δ18O minima (-1.9‰ and -8.3‰, respectively have been shown in the lower part of Bed 27, dropping from highs in beds below of +2.5 - 3.5‰. A similarly abrupt drop in δ13C within the Permian-Triassic Boundary interval has been detected elsewhere in South China, throughout the Tethyan region and in Greenland.
Correlation Events:
Conodont FAD Hindeodus parvus
Other Locations around the World:
The evolutionary lineage Hindeodus latidentatus - Hindeodus parvus - Isarcicella isarcica has been recognized in Iran, the Salt Range, and at the Gartnerkofel in the Carnic Alps.
Notes on Derivation of Age:
Average of U-Pb constraints from Bowring et al. (1998). However, revised processing for U-Pb ages suggest 252.5 Ma
References:
Yin, H., Sweet, W. C., Glenister, B. F., Kotlyar, G., Kozur, H., Newell, N. D., Sheng, J., Yang, Z., and Zakharov, Y. D., 1996. Recommendation of the Meishan Section as Global Stratotype Section and Point for basal boundary of Triassic System. Newsl. Stratigr. 34/2, p. 81 - 108.
Yin, H. (ed.), 1996: The Paleozoic-Mesozoic boundary, candidates of Global Stratotype Section and Point of the Permian-Triassic Boundary. China University of Geosciences Press, Wuhan, 137pp.