In the Pietrasecca section (central Apennines, Italy) the first occurrences (FOs) of Globorotalia conomiozea and Amaurolithus delicatus, which define the Tortonian/Messinian (T/M) boundary, were found in a reverse magneto-zone (R2) together with the FO of Amaurolithus primus. Assuming that this bioevent was isochronous, as suggested by the correlation of the biochronology of the equatorial Pacific Ocean with that of the tropical Indian Ocean (Raffi et al. 1995), and taking into account the results from ODP Leg 138 (Eastern Equatorial Pacific), which show the FO of Amaurolithus primus within C3Br.2r (Raffi 1992; Raffi et al. 1995), it is possible to correlate the magneto-zones recognised in the Pietrasecca section with Cande & Kent's (1992) Geomagnetic polarity time scale (GPTS) (CK92). Although in the Crete sections (Krijgsman et al. 1994) and in the northern Apennine sections (Vai, in press) the T/M boundary falls within chron C3Br.1r, the sedimentation rates calculated considering different magnetostratigraphic solutions show that for the Pietrasecca section the identification of R2 with C3Br.2r is the only realistic correlation to the CK92 GPTS. In particular, the T/M boundary recognised in the Pietrasecca section occurs in the uppermost part of C3Br.2r. According to the CK92 GPTS its age is 7.0 Ma while the modified GPTS of Baksi (1993) provides an age of 7.1 Ma, These ages are slightly older than that calculated for the Crete section (6.92 Ma) by Krijgsman et al. (1994). Finally, using Cande & Kent's (1995) GPTS (CK95) as a reference, the age of the T/M boundary is 7.12 Ma for the Crete sections, as suggested by Krijgsman et al. (1995) considering the T/M boundary within chron C3Br.1r, and 7.18 Ma for the Pietrasecca section. In addition, the Ar-40-Ar-39 radiometric information obtained on plagioclase separated from a volcaniclastic level occurring at the T/M boundary (FO of G. conomiozea) in the Pietrasecca section (less than or equal to 7.17 Ma) is in good agreement with the age of 7.15 +/- 0.04 Ma obtained from a biotite sample at the T/M boundary at the Monte del Casino section in the Northern Apennines (Laurenzi et al., in press).
Integrated stratigraphy of the Tortonian/Messinian boundary: The Pietrasecca composite section (central Apennines, Italy)
Laurenzi MA;
1997
Abstract
In the Pietrasecca section (central Apennines, Italy) the first occurrences (FOs) of Globorotalia conomiozea and Amaurolithus delicatus, which define the Tortonian/Messinian (T/M) boundary, were found in a reverse magneto-zone (R2) together with the FO of Amaurolithus primus. Assuming that this bioevent was isochronous, as suggested by the correlation of the biochronology of the equatorial Pacific Ocean with that of the tropical Indian Ocean (Raffi et al. 1995), and taking into account the results from ODP Leg 138 (Eastern Equatorial Pacific), which show the FO of Amaurolithus primus within C3Br.2r (Raffi 1992; Raffi et al. 1995), it is possible to correlate the magneto-zones recognised in the Pietrasecca section with Cande & Kent's (1992) Geomagnetic polarity time scale (GPTS) (CK92). Although in the Crete sections (Krijgsman et al. 1994) and in the northern Apennine sections (Vai, in press) the T/M boundary falls within chron C3Br.1r, the sedimentation rates calculated considering different magnetostratigraphic solutions show that for the Pietrasecca section the identification of R2 with C3Br.2r is the only realistic correlation to the CK92 GPTS. In particular, the T/M boundary recognised in the Pietrasecca section occurs in the uppermost part of C3Br.2r. According to the CK92 GPTS its age is 7.0 Ma while the modified GPTS of Baksi (1993) provides an age of 7.1 Ma, These ages are slightly older than that calculated for the Crete section (6.92 Ma) by Krijgsman et al. (1994). Finally, using Cande & Kent's (1995) GPTS (CK95) as a reference, the age of the T/M boundary is 7.12 Ma for the Crete sections, as suggested by Krijgsman et al. (1995) considering the T/M boundary within chron C3Br.1r, and 7.18 Ma for the Pietrasecca section. In addition, the Ar-40-Ar-39 radiometric information obtained on plagioclase separated from a volcaniclastic level occurring at the T/M boundary (FO of G. conomiozea) in the Pietrasecca section (less than or equal to 7.17 Ma) is in good agreement with the age of 7.15 +/- 0.04 Ma obtained from a biotite sample at the T/M boundary at the Monte del Casino section in the Northern Apennines (Laurenzi et al., in press).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
