An integrated calcareous plankton biostratigraphy allowed a very detailed biostratigraphic subdivision for the pre-evaporitic Tortonian-Messinian segments at Falconara, at Monte Gibliscemi and at Site 654 (ODP, Leg 107). Quantitative analysis on the planktonic foraminiferal assemblages pointed out a sequence of relative abundance fluctuations in the Globigerinoides spp. population. On the assumption that in this stratigraphic interval, as in the overlying Pliocene interval, the abundance fluctuations have a periodicity of 21 kyr, correlatable to the precession astronomical cycles, the age of every fluctuation has been estimated. At Site 654 correlation of the abundance fluctuations with the magnetostratigraphic boundaries, reinterpreted according to the magnetic polarity reversals record proposed by Cande and Kent (1992, 1995), made it possible to identify the ages of these boundaries. They are older than the ages proposed by Shackletori et al. (1995) and by Cande and Kenty (1995). The same procedure in the Upper Miocene segment of DSDP Site 552, on the base of the nannofossil abundance fluctuations published by Beaufort and Aubry (1990), allowed to obtain for the palcomagnetic boundaries of Chron 3An ages totally comparable to The ages proposed by Benson et al. (1995) and slightly older than the ages proposed by Shackleton et al. (1995) and Cande and Kent (1995). The re-interpretation of the magnetostratigraphy at Site 654 recently proposed by Kastens (1992) was not adopted since it introduces too large diachroneities for the biostratigraphic events within the Mediterranean basin. The data coming from the quantitative analysis on the planktonic foraminifera in the three Mediterranean sequences together with quantitative data on the nannofossil assemblage published by Beaufort and Aubry (1990) for the Late Miocene segment of the Northeastern Atlantic Site 552 provide a complete sequence of abundance fluctuations, forced. by the astronomical precession cycles, from the middle Late Tortonian to the base of the Zanclean. They allow an accurate correlation of the sedimentary and biostratigraphic events recorded in the Mediterranean basin with the paleoceanographic events recorded in the North Atlantic. The age of each sedimentary and/or biostratigraphic event could be estimated by comparison with the sequence of abundance fluctuations. The base of the Tripcoli Formation is estimated at 6.93 MA and its top at 6.08 MA. By correlation with Site 552, the top of the Tripoli Formation at Falconara predates the Messinian older glacial maximum by about 0.34 myr.
High resolution chronology for Late Miocene Mediterranean stratigraphic events
Sprovieri Mario
1996
Abstract
An integrated calcareous plankton biostratigraphy allowed a very detailed biostratigraphic subdivision for the pre-evaporitic Tortonian-Messinian segments at Falconara, at Monte Gibliscemi and at Site 654 (ODP, Leg 107). Quantitative analysis on the planktonic foraminiferal assemblages pointed out a sequence of relative abundance fluctuations in the Globigerinoides spp. population. On the assumption that in this stratigraphic interval, as in the overlying Pliocene interval, the abundance fluctuations have a periodicity of 21 kyr, correlatable to the precession astronomical cycles, the age of every fluctuation has been estimated. At Site 654 correlation of the abundance fluctuations with the magnetostratigraphic boundaries, reinterpreted according to the magnetic polarity reversals record proposed by Cande and Kent (1992, 1995), made it possible to identify the ages of these boundaries. They are older than the ages proposed by Shackletori et al. (1995) and by Cande and Kenty (1995). The same procedure in the Upper Miocene segment of DSDP Site 552, on the base of the nannofossil abundance fluctuations published by Beaufort and Aubry (1990), allowed to obtain for the palcomagnetic boundaries of Chron 3An ages totally comparable to The ages proposed by Benson et al. (1995) and slightly older than the ages proposed by Shackleton et al. (1995) and Cande and Kent (1995). The re-interpretation of the magnetostratigraphy at Site 654 recently proposed by Kastens (1992) was not adopted since it introduces too large diachroneities for the biostratigraphic events within the Mediterranean basin. The data coming from the quantitative analysis on the planktonic foraminifera in the three Mediterranean sequences together with quantitative data on the nannofossil assemblage published by Beaufort and Aubry (1990) for the Late Miocene segment of the Northeastern Atlantic Site 552 provide a complete sequence of abundance fluctuations, forced. by the astronomical precession cycles, from the middle Late Tortonian to the base of the Zanclean. They allow an accurate correlation of the sedimentary and biostratigraphic events recorded in the Mediterranean basin with the paleoceanographic events recorded in the North Atlantic. The age of each sedimentary and/or biostratigraphic event could be estimated by comparison with the sequence of abundance fluctuations. The base of the Tripcoli Formation is estimated at 6.93 MA and its top at 6.08 MA. By correlation with Site 552, the top of the Tripoli Formation at Falconara predates the Messinian older glacial maximum by about 0.34 myr.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
