Closing the Mid- Paleocene gap: toward a complete astronomically calibrated Paleocene Epoch at Zumaia (Basque Basin, W Pyrenees)

Details Closing the Mid- Paleocene gap: toward a complete astronomically calibrated Paleocene Epoch at Zumaia (Basque Basin, W Pyrenees) Closing the Mid- Paleocene gap: toward a complete astronomically calibrated Paleocene Epoch at Zumaia (Basque Basin, W Pyrenees)

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmgp52a..02d&link_type=abstract

American Geophysical Union, Spring Meeting 2007, abstract #GP52A-02

Mathematics

Logic

1520 Magnetostratigraphy, 1535 Reversals: Process, Timescale, Magnetostratigraphy, 4910 Astronomical Forcing, 4944 Micropaleontology (0459, 3030), 4948 Paleocene/Eocene Thermal Maximum

Scientific paper

The ~10 Myr long Paleocene Epoch is bounded by two of the most popular and studied chronostratigraphic limits, the Cretaceous/Tertiary (K/T) boundary at its base and the Paleocne/Eocene (P/E) boundary at the top. The Paleocene time scale has relied on an age model for magnetic polarity chrons derived from a cubic-spline fit of marine magnetic anomaly pattern in the South Atlantic to two radiometrically dated calibration points (Cande & Kent, 1992, 1995). These include an age of 65 Ma for the K/T boundary (66 Ma in the CK92 time scale) and a derived age of 55 Ma for the P-E boundary (this age constrained from 40Ar/39Ar dated volcanic ash layers within a clay sequence in Denmark). An age of 65.5±0.3 Ma for the K/T and 55.8±0.2 Ma for the P/E are taken in the most recent time scale GTS2004 (Gradstein et al, 2004) which combines both isotopically (using a 28.02 Ma age for the Fish Canyon Sanidine FCT monitor standard) and astronomically derived ages in the Neogene. However, intercalibration of single crystal sanidine dates of primary ash layers in astronomically dated sections arrives at an astronomically calibrated age of 28.24±0.1 Ma for the FCT standard (Hilgen et al., 2006), which will suggest an ~1% underestimate in current Paleogene ages. Thus, the astronomically tuned chronology for the (hemi)-pelagic basal Paleocene succession at Zumaia (Dinarès-Turell et al, 2003) that arrives an estimated age of ~65.8 Ma for the K/T appears consistent. In that study an ~4 Myr long tuned chronology based on the R7 full numerical solution for the Solar System of Varadi et al. (2003) we presented. However, more recently a second solution has been proposed (La04, Laskar et al., 2004), which differs notably in the Paleocene with respect R7 (offsets between the ~2.25 Myr long-term cycles). The differences arise from the uncertainty due to the chaotic behaviour of the inner planets to some resonant argument that limits an accurate age determination of successive minima in this very long eccentricity cycle. It is interesting to note, however, that in the Paleocene both solutions share one of such nodes of reduced eccentricity amplitude at about 62.2 Ma, which was the feature used as starting point in our tuning at Zumaia. Recent tuning efforts of hyperthermal events within the lower Cenozoic greenhouse climate record documented in Ocean Drilling Program (ODP) core sediments (Lourens et al., 2005) have provided tuned ages for the P/E thermal maximum using both the La04 and R7 astronomical target solutions (~55.270 Ma and ~55.675 Ma respectively) and showed that hyperthermal events correspond to maxima in the ~405-kyr and ~100-kyr eccentricity cycles that postdate prolonged minima in the 2.25-Myr eccentricity cycle. Here, we present integrated magnetostratigraphy and calcareous plankton biostratigraphy for the Mid Paleocene interval at Zumaia and evaluate the lithologic cyclicity using spectral analysis on magnetic susceptibility and CaCO3 proxy records. Considering that a previous study in the uppermost Paleocene interval included the record of chron C25n (Dinarès-Turell et al., 2002), all Paleocene reversals have now been identified at Zumaia, and a complete tuned Paleocene record is possible, rendering Zumaia an exceptional section. Implications for the definition of the Selandian stage, the absolute ages of chron C26r and the Mid-Paleocene Biotic Event (MPBE)) will be also considered.

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