Based on high-resolution correlation of condensed pelagic successions of the Carnic Alps (northern Italy), Graz Palaeozoic (Austria), Montagne Noire (southern France), and French Pyrenees, conodont stratigraphy, extinctions, and biofacies changes were studied around the Devonian/ Carboniferous boundary and compared regionally and internationally. Th e new and previous results allow us to distinguish 11 conodont biozones from the Lower expansa Zone (upper Famennian) to the quadruplicata Zone (= Upper sandbergi Zone, top of lower Tournaisian). Fifty-six conodont taxa are documented and assigned to conventional platform element genera. Th eir relative distribution is used to describe the vertical biofacies evolution. Th e ranges of several species are extended and, in comparison with previous investigations, many new local records are added. Some new ammonoid data from the Carnic Alps allow a correlation of cephalopod and conodont zones. Th e latter are partly (e.g., Lower and Middle expansa zones) diffi cult to recognize because the defi ning index species are rare or locally absent; a revision of the zonal scheme is desirable. New evidence confi rms that the disappearance of Palmatolepis gracilis gonioclymeniae Müller, 1956, is locally very diachronous and not a meaningful level for correlation. Hence, the Middle praesulcata Zone is abandoned. Some additional conodont species disappear gradually before the main extinction of the Hangenberg event. Palmatolepis and some dominant Famennian lineages of Bispathodus and Pseudopolygnathus died out in all sections at the base of the Hangenberg Shale equivalent, at the same level as most ammonoids and benthic faunas of the pelagic realm. Th e global pelagic conodont extinction rate was ca. 38%, but locally much higher rates are observed in the Prototethys realm. We suggest using the signifi cant conodont extinction as a zonal boundary; the main part of the Hangenberg Event interval falls in a Bispathodus costatus – Protognathodus kockeli Interregnum (CKI) that locally can have common Polygnathus inornatus Branson, 1934, or some Protognathodus meischneri Ziegler, 1969. Th e former Upper praesulcata Zone is renamed the Protognathodus kockeli Zone. Due to the episodic rarity or absence of siphonodellids close to the boundary, the base of the Carboniferous is alternatively drawn with the entry of Protognathodus kuehni Ziegler & Leuteritz, 1970.
High-resolution conodont stratigraphy, biofacies, and extinctions around the Hangenberg Event in pelagic successions from Austria, Italy, and France / Kaiser S.I.; Becker R.T.; Spalletta C.; Steuber T.. - STAMPA. - 63:(2009), pp. 99-143. (Intervento presentato al convegno Studies in Devonian Stratigraphy: Proceedings of the 2007 International Meeting of the Subcommission on Devonian Stratigraphy and IGCP 499 tenutosi a Eureka, Nevada nel 7-17 September, 2007).
High-resolution conodont stratigraphy, biofacies, and extinctions around the Hangenberg Event in pelagic successions from Austria, Italy, and France.
SPALLETTA, CLAUDIA;
2009
Abstract
Based on high-resolution correlation of condensed pelagic successions of the Carnic Alps (northern Italy), Graz Palaeozoic (Austria), Montagne Noire (southern France), and French Pyrenees, conodont stratigraphy, extinctions, and biofacies changes were studied around the Devonian/ Carboniferous boundary and compared regionally and internationally. Th e new and previous results allow us to distinguish 11 conodont biozones from the Lower expansa Zone (upper Famennian) to the quadruplicata Zone (= Upper sandbergi Zone, top of lower Tournaisian). Fifty-six conodont taxa are documented and assigned to conventional platform element genera. Th eir relative distribution is used to describe the vertical biofacies evolution. Th e ranges of several species are extended and, in comparison with previous investigations, many new local records are added. Some new ammonoid data from the Carnic Alps allow a correlation of cephalopod and conodont zones. Th e latter are partly (e.g., Lower and Middle expansa zones) diffi cult to recognize because the defi ning index species are rare or locally absent; a revision of the zonal scheme is desirable. New evidence confi rms that the disappearance of Palmatolepis gracilis gonioclymeniae Müller, 1956, is locally very diachronous and not a meaningful level for correlation. Hence, the Middle praesulcata Zone is abandoned. Some additional conodont species disappear gradually before the main extinction of the Hangenberg event. Palmatolepis and some dominant Famennian lineages of Bispathodus and Pseudopolygnathus died out in all sections at the base of the Hangenberg Shale equivalent, at the same level as most ammonoids and benthic faunas of the pelagic realm. Th e global pelagic conodont extinction rate was ca. 38%, but locally much higher rates are observed in the Prototethys realm. We suggest using the signifi cant conodont extinction as a zonal boundary; the main part of the Hangenberg Event interval falls in a Bispathodus costatus – Protognathodus kockeli Interregnum (CKI) that locally can have common Polygnathus inornatus Branson, 1934, or some Protognathodus meischneri Ziegler, 1969. Th e former Upper praesulcata Zone is renamed the Protognathodus kockeli Zone. Due to the episodic rarity or absence of siphonodellids close to the boundary, the base of the Carboniferous is alternatively drawn with the entry of Protognathodus kuehni Ziegler & Leuteritz, 1970.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
