The age of the Tortonian/Messinian boundary

Abstract

The Tortonian/Messinian boundary is marked by the first occurrence datum (FOD) of Globorotalia conomiozea which is found all over Crete in open-marine marls with good palaeomagnetic properties. Within the framework of the MIOMAR project, the previously studied sections of Langereis et al. [1] have been extended and (partly) resampled. Here, we present new magnetostratigraphic and biostratigraphic results from sections on eastern Crete (Faneromeni), central Crete (Kastelli) and western Crete (Potamida and Skouloudhiana) supplemented by cyclostratigraphic data.The recently developed geomagnetic polarity time scale (CK92) of Cande and Kent [2] allows an unambiguous correlation of the polarity sequences on Crete. The FOD of G. conomiozea occurs in the reversed interval of anomaly C3Bn.lr. This leads to a new age determination of 6.92 Ma for the Tortonian/Messinian boundary and a duration of 1.76 Myr for the Messinian. A slightly modified version of CK92--if we use more recent age estimates--provides an age of 7.10 Ma and a duration of 1.78 Myr, respectively.Bipartite sedimentary cycles are distinctly present in the Cretan sections studied. Assuming that these cycles are precession-induced and using an average periodicity of 21.7 kyr enables us to independently estimate the duration of the successive individual polarity zones. The astronomically derived durations of the Cretan polarity zones are in good agreement with CK92, but are approximately 10% shorter.

The Abad composite (SE Spain): a Messinian reference section for the Mediterranean and the APTS

“…This event is immediately preceeded by the LO of the group of G. menardii 5 and is a well known event usually cited in the Mediterranean as the FRO of the G. conomiozea group (Zachariasse, 1975(Zachariasse, , 1979aD'Onofrio et al, 1975;Iaccarino et al, 1975;Bossio et al, 1976;Gonzalez Donoso and Serrano, 1977;Cita and Ryan, 1978;Glac Ëon et al, 1990;Sierro et al, 1993Sierro et al, , 1997Krijgsman et al, 1994Krijgsman et al, , 1995Krijgsman et al, , 1997. The FRO of the G. conomiozea group, with an astronomical age of 7.24 Ma , has been widely used as a biostratigraphic indicator for the Tortonian/Messinian boundary.…”

“…Unlike the Mediterranean, where these groups have never been found coexisting (with the exception of the Potamida section on Crete; Zachariasse, 1979b), the G. menardii group is clearly replaced by the G. miotumida group after a short period of coexistence in the Atlantic (Sierro, 1985;Sierro et al, 1993). Although the Lower Abad did not produce reliable magnetostratigraphic data, this event has been pinpointed in a reversed interval corresponding to subchron C3Br.1r in the Kastelli and Faneromeni sections on Crete and the Metochia section on Gavdos (Krijgsman et al, 1994. Moreover, the in¯ux of highly conical types of the G. miotumida group, located 1 1 2 cycles below cycle LA1 in the Abad composite, can be correlated with the in¯ux of G. conomiozea s.s., identi®ed below sapropel C18 at Monte del Casino (Northern Italy) and below the ®rst sapropel in the Potamida section (Crete) with an astronomical age of 7.19 Ma .…”

Extending the astronomical (polarity) time scale into the Miocene

“…In this study, we aim at extending the astronomi- [8] carried out a preliminary and partial astronomical tuning of GRAPE (Gamma Ray Attenuation Porosity Evaluation) records of ODP Leg 138 sites for the interval between 6 and 10 Ma, while Krijgsman et al [15] calculated an astronomical duration for a late Miocene polarity sequence on Crete by multiplying the number of sedimentary cycles with the average 2 1.7 kyr period of precession. The duration of the latter sequence is approximately 10% shorter than that of the correlative part in the geomagnetic polarity time scale (GPTS) of Cande and Kent [16].…”

Calcareous nannofossil biostratigraphy of the M. del Casino section (northern Apennines, Italy) and paleoceanographic conditions at times of Late Miocene sapropel formation

“…In 1993, radiometric dating of biotites obtained from volcanic ash layers in the Monte del Casino and Monte Tondo sections (northern Apennines) led to an age of 7.26 Ma for the T=M boundary (Vai et al, 1993). A re-evaluation of magnetostratigraphy including new data and cyclostratigraphic information from sections on Crete resulted in an age of 6.92 Ma for the T=M boundary according to the geomagnetic polarity time scale of Cande and Kent (1995) (Krijgsman et al, 1994). The radiometric age of Vai et al (1993) has subsequently been confirmed and refined -to 7.240 Ma -by the astronomical dating method which relies on tuning sedimentary cycle patterns to astronomical time series which describe the past variations in the Earth's orbital parameters (Krijgsman et al, 1995;.…”