The base of the Maastrichtian Stage is defined at level 115.2 on platform IV of the geological site at Tercis les Bains (Landes, France).
The Tercis les Bains Section is located 8 km from Dax in the Landes (SW France) between the Basque Region to the south and the Charente province to the north. The quarry is situated on the left bank of the Adour River. The quarry comprises 5 formerly worked “platforms”, each 5 to 7 m high, opening westwards between the south and north wall, about 100 m apart.
The section in the quarry is 165 m thick and is subdivided into the d’Avezac Unit below (without flint) and the Les Vignes Unit above (with flint). The d’Alvezac Unit can be subdivided into five subunits according to the presence of glaucony, a key sedimentary feature in this homogeneous succession; its thickness is about 100 m. The Les Vignes Unit has been subdivided into a pale flint-bearing (below) and a dark flint-bearing subunit above. The pale flint-bearing subunit is 31 m thick. A distinctive pycnodont-rich (comparatively deep-water oyster) horizon is located near the stage boundary (2.1 m above the GSSP). The homogeneous pithonellid-bearing limestone (95% carbonate) of the quarried portion of the section characterizes an open marine environment, the depositional depth of which probably fluctuated between 50 m and 200 m. The main lithologic variations are related to the amount of glaucony and the development of chert.
The first appearance of Pachydiscus neubergicus is considered as the guide-event for the base of the Maastrichtian Stage. The following table shows 12 biohorizons which characterise the boundary interval: (ka is the age difference between the GSSP level and the biohorizon).
|Ammonites||1 FO Pachydiscus neubergicus
2 LO Nostoceras hyatti and allied forms
3 FO Diplomoceras cylindraceum
≤ 111 ± 3
|Dinocysts||4 LO Corradinisphaeridium horridum
5 LO Raetiaedinium truncigerum
6 LO Samlandia mayii & S. carnarvonensis
|112.4 ± 2.4
118.6 ± 3.8
|Planktonic foraminifera||7 FO Contusotruncana contusa
8 FO Rugoglobigerina scotti
|116.5 ± 0.3
116.2 ± 0.5
|Benthic foraminifera||9 FO Bolivinoides 5 lobes > 4 on last chamber
10 LO Gavelinella clementiana
|107.4 ± 7.4
115.5 ± 0.7
|Inoceramids||11 FO genus Trochoceramus||≤ 97.7||≈ 700|
|Calcareous nannofossils||12 LO Quadrum trifidum||134.2 ± 2.7||≈ 750|
Arithmetic mean level of biological change: 115.2
Mean of 12 biostratigraphic criteria of equal importance. Closely above is FAD of ammonite Pachydiscus neubergicus. Boreal proxy is FAD of belemnite Belemnella lanceolata.
Correlation with the boreal German section at Kronsmoor is done indirectly through sections in Norfolk (England) and Poland. Poland and Tercis are correlated by using the LO of Nostoceras hyatti which is assumed to be below the FO of Belemnella lanceolata in that country. Tercis and Norfolk are correlated using echinoids ranges which suggest that the FO of P. neubergicus at Tercis would be contemporaneous (± about 0.1 Ma) with the FO of B. lanceolata in Norfolk. Dinocysts confirm this correlation.
Correlation with North Spain and the Apennines can be achieved by using calcareous nannofossils, planktonic foraminifera and magnetic signals.
Correlation to North America is achieved by using planktonic foraminifera, ammonites, inoceramids or the magnetostratigraphic record. Notes on Derivation of Age:
Estimated placement relative to Ar-Ar calibrated Sr-curve.