New magnetostratigraphic data have been obtained from the Norian/Rhaetian boundary section of Pignola-Abriola (Southern Apennines, Italy), which consists in 60 m of basinal cherty limestones. A total of 10 magnetozones have been identified and calibrated with conodont and radiolarian biostratigraphy. The Pignola-Abriola section was correlated to the Newark APTS with a statistical method under the assumption that stratigraphic depth is a linear proxy of time. The section was slid aside the Newark APTS producing a total of 19 possible correlation options that were evaluated by linear regression of the agedepth tie points. Then, a student t-test was applied to the linear regression coefficients to isolate the most reliable correlation options. According to our best correlation option, the Pignola-Abriola section covers the interval from E13r (~217 Ma) to E20r (~205 Ma) in the Newark APTS. The Norian/Rhaetian boundary based on the FAD of conodont Misikella posthernsteini and the base of the Proparvicingula moniliformis radiolarian Zone 1 at Pignola-Abriola (Giordano et al., 2010: Lethaia 43, 573-586) falls on the Newark APTS at ~205.4 Ma within magnetozone E20r. The magnetostratigraphy of the Pignola-Abriola section has been successfully correlated to other Late Triassic magnetostratigraphic sections from the literature spanning the Norian/Rhaetian boundary (Steinbergkogel, Oyuklu, Brumano and Pizzo Mondello) . Our magnetostratigraphic correlation reveals an apparent discrepancy in the first appearance of conodont M. posthernsteini between Pignola-Abriola and Steinbergkogel/Oyuklu. However, we infer that the forms attributed to M. posthernsteini at Steinbergkogel/Oyuklu are more similar to what we refer to as M. hernsteini/posthernsteini transition at Pignola-Abriola, a solution that virtually eliminates the discrepancy. Considering the taxonomic complexity of the M. hernsteini/posthernsteini lineage, we propose to place the Norian/Rhaetian boundary in correspondence of a marked negative shift of d13Corgobserved at Pignola-Abriola at ~41.5 m (close to the FAD of M. posthernsteini),which, according to the correlation with the Newark APTS, would have an age of ~205.6 Ma. According to this new definition of the Norian/Rhaetian boundary, the Rhaetian is ~4.5 Myr-long.
|Titolo:||Magnetostratigraphic data from the Pignola-Abriola section (Southern Apennines, Italy): new constraints for the Norian/Rhaetian boundary|
MUTTONI, GIOVANNI (Secondo)
|Settore Scientifico Disciplinare:||Settore GEO/02 - Geologia Stratigrafica e Sedimentologica|
|Data di pubblicazione:||mag-2014|
|Appare nelle tipologie:||01 - Articolo su periodico|