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Re: Public Database of Geologic Formation Ages?
Quoting Ogg et al. (2004): Upper Maastrichtian zones (J. nebrascensis
through B. clinolobatus) are assigned 0.45 myr durations, which is
average of the lower Maastrichtian spline-scaled zones.
Speaking of K-Pg boundary and cyclostratigraphy, I saw no mention of
this paper on the DML ;-)
Husson D., Galbrun B., Laskar J., Hinnov L.A., Thibault N., Gardin S. &
Locklair R.E. 2011. Astronomical calibration of the Maastrichtian (Late
Cretaceous). Earth and Planetary Science Letters, 305 (3-4): p.328-340.
Recent improvements to astronomical modeling of the Solar System have
contributed to important refinements of the Cenozoic time scale through
astronomical calibration of sedimentary series. We extend this
astronomical calibration into the Cretaceous, on the base of the 405 ka
orbital eccentricity variation thanks to the recovery of well preserved
Maastrichtian sedimentary series from ODP (Ocean Drilling Program) Holes
1258A (Leg 207, Equatorial Atlantic), 1267B (Leg 208, South Atlantic),
762C (Leg 122, Indian Ocean) and DSDP (Deep Sea Drilling Program) Hole
525A (Leg 74, South Atlantic). Cyclostratigraphic analysis is performed
on high resolution measurements of magnetic susceptibility on sediments
cored during Legs 207 and 208, and gray level variations of sediment
color obtained from core photographs from Legs 122 and 74. Astronomical
control on sedimentation is evident at every site, with the presence of
cycles corresponding to forcing by precession, obliquity and orbital
eccentricity variations. Identification of these cycles leads to the
definition of a detailed cyclostratigraphic frame covering nearly 8 Ma,
from the upper Campanian to the Cretaceous/Paleogene (K/Pg) boundary.
Durations of each magnetochron from C32r.2r to C29n are inferred by
cycle counting. Astronomical calibrations of Maastrichtian sedimentary
series are proposed, based on the 405 ka eccentricity variation
according to the most recent astronomical solution La2010a. Two
different ages are suggested for the K/Pg boundary, considering the
uncertainty of the long-term variation of the 405 ka eccentricity cycle.
The first proposal provides a Cretaceous/Paleogene boundary age of 65.59
± 0.07 Ma and the second an age of 66 ± 0.07 Ma, which is coherent with
the most recent radio-isotopic datings. Magnetochron boundaries and the
Campanian/Maastrichtian boundary are dated relative to these numerical
ages of the K/Pg boundary.
Le 24/08/2011 10:21, David Marjanovic a écrit :
from Fowler (in prep):
Lower Maastrichtian: top: 69.23
That's an extremely precise date. How did you get it? If by
cyclostratigraphy, why isn't the K-Pg boundary as precisely dated? ~:-|