A New Late Neogene Time Scale: Application to Leg 138 Sites

Abstract

The sediments recovered during Leg 138 provide a remarkable opportunity to improve the geological time scale of the late Neogene. We have developed new time scales in the following steps. First, we constructed age models on the basis of shipboard magnetostratigraphy and biostratigraphy, using the time scale of Berggren, Kent, and Flynn (1985). Second, we refined these age models using shipboard GRAPE density measurements to provide more accurate correlation points. Third, we calibrated a time scale for the past 6 m.y. by matching the high-frequency GRAPE density variations to the orbital insolation record of Berger and Loutre (1991); we also took into account δ 18 θ records, where they were available. Fourth, we generated a new seafloor anomaly time scale using our astronomical calibration of C3A.n (t) at 5.875 Ma and an age of 9.639 Ma for C5n.ln (t) that is based on a new radiometric calibration (Baksi, 1992). Fifth, we recalibrated the records older than 6 Ma to this new scale. Finally, we reconsidered the 6-to 10-Ma interval and found that this could also be partially tuned astronomically.

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

“…The ages of all four reversals are considerably older than previously reported in the conventional time scales of Kent (1992, 1995), in the astronomical time scales of Hilgen et al (1995), Shackleton et al (1995) and Benson et al (1995). These considerable divergent ages in the different astronomical time scales can be explained by the fact that the ages of the Hilgen et al (1995) time scale do not represent true astronomical ages, but ages that were calculated on the basis of linear interpolation of seā oor spreading rates using astronomical ages for the next younger and older reversal as calibration points.…”

“…These considerable divergent ages in the different astronomical time scales can be explained by the fact that the ages of the Hilgen et al (1995) time scale do not represent true astronomical ages, but ages that were calculated on the basis of linear interpolation of seā oor spreading rates using astronomical ages for the next younger and older reversal as calibration points. The Shackleton et al (1995) time scale was a ®rst preliminary attempt to establish a partial astronomical tuning for ODP leg 138 records in the interval between 6 and 10 Ma. Detailed quantitative analysis of calcareous nannofossils, however, suggests that the preliminary astronomical tuning for leg 138 is not correct, but that revised ages are in perfect agreement with the results from our Spanish sections .…”

Integrated stratigraphy and astronomical calibration of the Serravallian/Tortonian boundary section at Monte Gibliscemi (Sicily, Italy)

“…6; Table 3). In our opinion, this correspondence cannot be explained other than that these biohorizons are (near-)synchronous between the tropical Atlantic and the Mediterranean and that the astronomical timescales independently es- Ages for equatorial Pacific events are based on the biostratigraphic data of and the time scales of Shackleton et al (1995;SCHPS95) and Cande and Kent (1995;CK95); ages for equatorial Atlantic (Ceara Rise) events are based on biostratigraphic data of Backman and Raffi (1997) and the astronomical time scale of Shackleton and Crowhurst (1997). The error in the ages is based on the uncertainty in the position of the events.…”

“…Firstly, the magnetostratigraphy of (parallel) sections, that were correlated cyclostratigraphically in detail to Gibliscemi A=B, was calibrated to the polarity timescales of Cande and Kent (1995;CK95) and Shackleton et al (1995;SCHPS95). Secondly, the ages of CK95 and SCHPS95 for the polarity reversals and especially for the youngest polarity reversal recorded in our sections were taken as starting point for the actual tuning.…”

Cyclicity and NRM acquisition in the armantes section (Miocene, Spain): Potential for an astronomical polarity time scale for the continental record

“…A major breakthrough in chronology -with a resolution and accuracy of several kyr -recently came from marine studies directed at establishing an astronomical polarity time scale (APTS) (Shackleton et al, 1990(Shackleton et al, , 1996Hilgen 1991a A magnetostratigraphic study of the Armantes section of Central Spain, a typical example of a cyclically bedded sequence, showed that sedimentation was continuous (from 17-12 Ma) and that no significant hiatuses are present (Krijgsman et al, 1994b). A large-scale (10 m) cyclic bedding of alternating reddish silts (red beds) and whitish limestones is very pronounced.…”