Transatlantic d13C correlation and establishment of New-World reference curves for the potential d13C definition of stage/substage boundaries in the Turonian and Coniacian (Upper Cretaceous).
Zusammenfassung der Projektergebnisse
For the Cenomanian to Lower Coniacian, δ13C curves from Brazil (Nassau Quarry), NE Mexico (Iturbide I, Iturbide II, Puerto Pastores, Huasteca Canyon, El Rosario) and the Helvetic Alps (Burgberg quarry) were established. These were correlated with biostratigraphically well-dated reference sections from NW Germany (Salzgitter-Salder, Halle/Westfalen, Oerlinghausen) and Spain (Liencres) and other curves of Italy and Spain. The most relevant results are: i. Of the δ13C event correlation template of JARVIS et al. (2006), the OAE II peak, Hollywell, Lulworth, Round Down, Bridgewick, Hitch Wood and Navigation events were documented for the first time from NE Mexico. The stratigraphic advance aid a better understanding of the tectonosedimentary history of the early Late Cretaceous in NE Mexico. ii. The turnover from pelagic limestones (Cuesta del Cura Formation) towards black shales/limestones of the OAE II (Agua Nueva Formation), associated with a phase of tectonic activity, occurs isochronous in NE Mexico and Europe (“Facies Change”) at the base of the Metoicoceras geslinianum ammonite Zone. iii. The δ13C signature of the OAE II is ideally developed in the Iturbide area, easily correlatable with other sections and represented by an anomalously thick succession (ca. 70 m). iv. The increase of accumulation rate from 11 mm/ky (Cuesta del Cura Formation) to 160 mm in the Agua Nueva Formation in the Iturbide area might be due to pull-apart movements in the context of the C/T boundary event. v. The last occurrence (LO) of the planktonic foraminifera H. helvetica is diachronous in an interbasinal context. Early local LOs (e.g. Liencres, Spain) are situated at the Pewsey Event (base Upper Turonian by means of ammonites). Latest LO is located between Caburn and Bridgewick δ13C events (Burgberg in the Allgäu). Thus, the taxon is unusable for high-resolution stratigraphic subdivision and the definition of the Middle/Upper Turonian boundary by its LO. Instead, it is recommended here to take the Caburn Event as a possible boundary marker into consideration, which approximates the FO of the inoceramid bivalve Inoceramus perplexus. vi. A correlation of the δ13C curve from the proposed GSSP for the base of the Lower Coniacian Salzgitter-Salder (base Coniacian: FO of Cremnoceramus deformis erectus) with Liencres and NE Mexico and its calibration against inoceramid-stratigraphic data unequivocally confirms a significant hiatus or strong condensation at Salzgitter-Salder in the boundary interval: At Salzgitter-Salder, the FOs of Cr. waltersdorfensis and Cr. deformis erectus are bundled in a 1 m interval, around a negative δ13C event, interpreted as Navigation Event. In Liencres and NE Mexico, the FO of Cr. waltersdorfensis and the succeeding FO of Cr. deformis erectus are situated 30 and 20 m, respectively, below the inferred Navigation Event. Furthermore, in NE Mexico, the FO of Cr. deformis erectus is possibly situated well below Navigation event. As a conclusion it must be stated that Salzgitter-Salder is an inappropriate GSSP candidate and that the exclusive application of δ13C stratigraphy in this interval leads to diachronous miscorrelation.
Projektbezogene Publikationen (Auswahl)
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(2010): Stratigraphic re-assessment of the Seewen Formation in the classic Helvetic key locality “An der Schanz” quarry, Burgberg (Bavarian Alps; Turonian, Coniacian): biostratigraphy and δ13C correlations – Cretaceous Research 31: 130-146
Wiese F.
