GSSP for Ladinian Stage
The Base of the Ladinian Stage (Middle Triassic) is defined at the base of a 15 - 20cm thick limestone bed overlying a distinctive groove ("Chiesense groove") of limestone nodules in a shaly matrix, located about 5m above the base of the Buchenstein Beds in the Caffaro River bed (45°49'09.5"N, 10°28'15.5"E), south of the village of Bagolino (Province of Brescia, Northern Italy). The lower surface of the thick limestone bed has the lowest occurrence of the ammonoid Eoprotrachyceras curionii. Secondary global markers in the uppermost Anisian include the lowest occurrence of conodont Neogondolella praehungarica and a brief normal-polarity magnetic zone recognized in closely correlated sections. The GSSP level is bracketed by U-Pb single zircon age data from volcaniclastic horizons, indicating a boundary age of ca. 241 Ma.
GSSP is located at Bagolino (Province of Brescia, Northern Italy) in the
eastern Lombardian Alps, in Valle del Caffaro between Val Camonica and Valli
Giudicarie. The Anisian/Ladinian boundary succession is well exposed at three
sites (A - C) in the bed of the river Caffaro, in the surroundings of the
Romanterra Bridge, south of the village of Bagolino. The GSSP Site is situated
close to the eastern end of Site B and its coordinates are 614.276 / 5075.118
(UTM-grid) and Long./Lat. 45°49'09.5"N, 10°28'15.5"E respectively.
Bagolino, the pelagic succession consists from bottom to top of the Angolino
Limestone. the Prezzo Limestone, the Buchenstein Beds and the Wengen Beds.
The GSSP at Bagolino is located at the top of a distinct 20-25cm-thick interval of limestone nodules in a shaly matrix. The Anisian - Ladinian Boundary is defined by the first appearance of the ammonoid genus Eoprotrachyceras, i.e. with the species Eoprotrachyceras curionii at the lower surface of the overlying thick limestone bed.
The appearance of Neogondolella praehungarica and its co-occurrence with Paragondolella fueloepi in the upper part of the Neogondolella secedensis zone, just below the GSSP level, seems at present to be the only suitable marker for conodont-based correlations.
Ammonite FAD Eoprotrachyceras curionii (base of the E. curionii zone). Conodont FAD Budurovignathus praehungaricus is in the uppermost Anisian.
Other Locations around the World:
Representatives of the genus Eoprotrachyceras have been reported from numerous places including the Triassic successions in North America (Nevada, British Columbia) and Eoprotrachyceras is therefore a suitable marker for trans-Panthalassan correlation.
Notes on Derivation of Age:
array by Mundil et al. on levels near Nevadites (= Secedensis) ammonite zone in
Dolomites, plus placement relative to magnetostratigraphy correlations to
cycle-scaled Newark magnetic polarity pattern. However, revised correlations
and zircon processing suggest 240.5 Ma
Brack, P., Rieber, H., Nicora, A., and Mundil, R., 2005. The Global boundary Stratotype Section and Point (GSSP) of the Ladinian Stage (Middle Triassic) at Bagolino (Southern Alps, Northern Italy) and its implications for the Triassic time scale. Episodes 28/4, p. 233-244.