In a section near Pignola, Italy, conodont stratigraphy suggests that the Triassic-Jurassic boundary occurs in the Lagonegro units at or above the top of the exposed section, in the transition from the Calcari con Selce Formation to the Scisti Silicei Formation. A significant facies transition is exhibited in this interval as calcarenites and calcilutites of the Calcari con Selce grade vertically into the marl, chert, and radiolarite-dominated Scisti Silicei. Carbon (ä13C) and oxygen (ä18O) isotopes from the carbonate were measured in 50+ meters of section bracketing the transition zone. Several negative excursions of ä13C of significant magnitude occur in the section. The largest occurs slightly above the FO of Misikella posthernsteini, a conodont that marks the base of the Rhaetian stage. Another excursion, below the last in situ Triassic conodont, M. ultima, is consistent with previous reports of shortduration carbon isotope excursions below the system boundary. Notably, the carbon and oxygen isotopes display limited covariance, suggesting at least partial recrystallization of the carbonate from isotopically light formation waters.
Carbon isotope record of upper triassic strata of the Lagonegro basin, southern Apennines, Italy: preliminare results
Di Leo P
2006
Abstract
In a section near Pignola, Italy, conodont stratigraphy suggests that the Triassic-Jurassic boundary occurs in the Lagonegro units at or above the top of the exposed section, in the transition from the Calcari con Selce Formation to the Scisti Silicei Formation. A significant facies transition is exhibited in this interval as calcarenites and calcilutites of the Calcari con Selce grade vertically into the marl, chert, and radiolarite-dominated Scisti Silicei. Carbon (ä13C) and oxygen (ä18O) isotopes from the carbonate were measured in 50+ meters of section bracketing the transition zone. Several negative excursions of ä13C of significant magnitude occur in the section. The largest occurs slightly above the FO of Misikella posthernsteini, a conodont that marks the base of the Rhaetian stage. Another excursion, below the last in situ Triassic conodont, M. ultima, is consistent with previous reports of shortduration carbon isotope excursions below the system boundary. Notably, the carbon and oxygen isotopes display limited covariance, suggesting at least partial recrystallization of the carbonate from isotopically light formation waters.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
