Episodes 2023; 46(2): 281-307
Published online June 1, 2023
Copyright © International Union of Geological Sciences.
Andrzej Wierzbowski1, Marcin Barski1, Angela L. Coe2*, Mark W. Hounslow3, Bronisław A. Matyja1, Gregory D. Price4, Hubert Wierzbowski5, John K. Wright6, with contributions from Francois Atrops7, Jacek Grabowski5, Emanuela Mattioli7, Nicol Morton8, James G. Ogg9, Federico Olóriz10, Kevin Page11, Horacio Parent12, Piotr Przybylski13, Guenter Schweigert14, Anna Bertha Villaseñor15
1 Faculty of Geology, University of Warsaw, Warszawa, Poland
2 School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes, MK7 6AA, UK
3 Lancaster Environmental Centre, Lancaster University, Lancaster, LA1 4YQ, UK and Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, L69 3GP, UK
4 School of Geography, Earth and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK
5 Polish Geological Institute–National Research Institute, Warszawa, Poland
6 Department of Earth Sciences, Royal Holloway, Egham, TW20 0EX, UK
7 Laboratoire de Geologie, Université de Lyon 1, F-69622 Villeurbanne, France
8 07200 Vogue, France
9 Department of Earth and Atmospheric Sciences, Purdue University, Indiana, USA and State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Institute of Sedimentary Geology, Chengdu University of Technology, Chengdu 610059, China
10 Facultad de Ciencias, Universidad de Granada, Granada, Spain
11 Camborne School of Mines, University of Exeter, Penryn, Cornwall, TR10 9FE, UK
12 Universidad Nacional de Rosario, Rosario, Argentina
13 BP America Inc. Southern Performance Unit, Houston, USA
14 Staatliches Museum für Naturkunde, Stuttgart, Germany
15 Departamento de Paleontologia, Instituto de Geologia, Ciudad México, Mexico
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Following voting by the Kimmeridgian Working Group, the International Subcommission on Jurassic Stratigraphy and the International Commission on Stratigraphy, the Global Stratotype Section and Point (GSSP) for the base of the Kimmeridgian Stage (Jurassic System) was ratified by the executive of the International Union of Geological Sciences. The boundary is placed in the upper part of Bed 35 of the Staffin Shale Formation, 1.25±0.01 m below the base of Bed 36 in block F6 in the foreshore at Flodigarry, Staffin Bay, Isle of Skye, Scotland. The coordinates for the middle part of the two adjacent sections (sections F6N and F6S) are 57°39'39.5''N, 6°14'43.9''W and 57°39'40.5''N, 6°14'45''W; UK National Grid Scheme NG 4687 7139 and NG 4687 7142±5 m. This stratigraphic point coincides with the appearance over a short stratigraphic interval of several new ammonite taxa that delineate the base of the Subboreal ammonite Baylei Zone, the base of the Densicostata Subzone marked by the base of the flodigarriensis horizon, and, independently, the base of the Boreal ammonite Bauhini Zone. The main advantages of this locality are: the presence of a dual ammonite zonation marked by two extensively studied, well-preserved and very abundant groups of ammonites, and their preservation within a continuous section of ~120 m of open marine, fossiliferous, thermally immature mudrocks with no evidence of condensation or stratigraphic gaps. Dinoflagellate cysts, magnetostratigraphy and stable isotope data from the same section provide secondary markers. The stratigraphic point is located 0.17–0.65 m below the boundary interval between the dinoflagellate cyst zones DSJ 26 and DSJ 27 (equivalent to the boundary between subzones c and d of the Scriniodinium crystallinum (=Scr) Zone). The point is located 0.02–0.24 m above the base of reversed magnetozone F3r. This magnetozone probably correlates with marine magnetic anomaly M26r but may correlate to the younger anomaly M25r. The point coin cides with a well-marked broad minimum in δ13C values and a calculated low Sr-isotope value of 0.70687. The section has yielded nannofossils that show that the potential last occurrence of Octopodorhabdus decussatus that marks the lower part of the NJ15 zone occurs about 1.09 m below the boundary. The thermal immaturity and unweathered nature of the strata in the Flodigarry section has permitted a direct Re-Os radio-isotopic age of 154.1±2.2 Ma to be obtained from the mudrocks 0.05 m below the Kimmeridgian GSSP. Sequence stratigraphic analysis indicates that the GSSP lies within the lower part of a highstand system tract. The corresponding stratigraphic level in the Submediterranean-Mediterranean successions is close to the boundary between the Hypselum and Bimammatum ammonite zones. The change in ammonite groups noted at this level provides biostratigraphic markers for further global correlation.