GSSP for Toarcian Stage
Definition:
The base of the Toarcian Stage is defined at the base of micritic limestone Bed 15e at Ponta do Trovão, Peniche, Lusitanian Basin, Portugal. The boundary coincides with the mass occurrence of the ammonite genus Dactylioceras (Eodactylioceras). The GSSP is marked in Bed 15e by the first occurrence of Dactylioceras (Eodactylioceras) simplex co-occurring with D. (E.) pseudocommune and D. (E.) polymorphum.
Location:The GSSP of the Toarcian Stage is located at Ponta do Trovão, Peniche (Portugal), Lusitanian Basin, Portugal at a latitude of 39°22’15"N, and a longitude of 9°23’07"W. The Peniche peninsula is located about 80km north of Lisbon. |
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Sedimentology:The Pliensbachian – Toarcian boundary section at Ponta do Trovão, Peniche is composed of hemipelagic deposits of marlstone – limestone alternations with abundant ammonites, belemnites, bivalves, brachiopods, crinoids and siliceous sponges. The GSSP lies in the uppermost part of the Lemede Formation, which is composed of bioturbated, cm–thick marlstones alternating with dm–thick limestones. The Lemede Formation is about 24m thick and ranges from the top of the margaritus zone to the lowermost part of the polymorphum zone. The uppermost part of the Lemede Formation shows a progression from carbonate– to marl–dominated sediments. These are the so–called "Couches de passage" (Transition Beds 15a – 15e). The overlaying Cabo Carvoeiro Formation consists of a thick carbonate–rich succession. This formation is subdivided into 5 members. The lowest member (CC1) is 11m thick and is dated as polymorphum zone and consists of dm-thick marls alternating with cm-thick limestones. |
Primary Markers:
Ammonites:The boundary coincides with the mass occurrence of the ammonite genus Dactylioceras (Eodactylioceras). The GSSP in Bed 15e coincides with of first occurrrence of Dactylioceras (Eodactylioceras) simplex, co- occurring with D. (E.) pseudocommune and D. (E.) polymorphum. The boundary ammonite assemblage also includes Protogrammoceras (Paltarpites) cf. paltum (Buckman), Lioceratoides aff. ballinense, and Tiltoniceras aff. capillatum.
Secondary Markers:
Nannofossils:The GSSP lies within the NJT5b Lotharingius sigillatus nannofossil subzone.
Ostracods:
The boundary interval is marked by the first appearance of Kinkelinella sp. 1 and Ektyphocythere knitteri.
Isotope Stratigraphy:
A prominent negative carbon-isotope excursion has been recognized in the marlstone/limestone succession across the Pliensbachian/Toarcian boundary.
Correlation Events:
Ammonite FAD of Dactylioceras (Eodactylioceras) simplex co- occurring with D. (E.) pseudocommune and D. (E.) polymorphumOther Locations around the World:
A reference section for the Toarcian Stage is located near Almonacid de la Cuba, 35km South of Zaragoza, Spain, (about 41°18’ N, 0°49’ W). A bed by bed correlation between Peniche and Almonacid de la Cuba is possible. In addition magnetostratigrapghy is available for this section. The Pliensbachian/Toarcian boundary is recorded in the Turmiel Formation in Bed CU35.2.Peniche Almonacid de la Cuba
Bed 16c = Bed 62
Bed 16a = Bed 46 and younger
Bed 15e = Bed 35.2 - 42
Bed 15d = Bed 29 - 35
Bed 15c = Bed 23 - 28
Bed 15a - 15b = Bed 15 - 22
Notes on Derivation of Age:
Duration of Aalenian-Toarcian from cycle stratigraphyOther Images:
References:
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