An Astronomically Tuned Neogene Time Scale (ATNTS2012) is presented, as an update of ATNTS2004 in GTS2004. The new scale is not fundamentally different from its predecessor and the numerical ages are identical or almost so. Astronomical tuning has in principle the potential of generating a stable Neogene time scale as a function of the accuracy of the La2004 astronomical solution used for both scales. Minor problems remain in the tuning of the Lower Miocene. In GTS2012 we will summarize what has been modified or added since the publication of ATNTS2004 for incorporation in its successor, ATNTS2012. Mammal biostratigraphy and its chronology are elaborated, and the regional Neogene stages of the Paratethys and New Zealand are briefy discussed. To keep changes to ATNTS2004 transparent we maintain its subdivision into headings as much as possible.

The Neogene Period

Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of ∼1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40 Ar/ 39 Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40 Ar/ 39 Ar geochronology. This calibration results in a more precise older age of 28.201 ± 0.046 million years ago (Ma) and reduces the 40 Ar/ 39 Ar method9s absolute uncertainty from ∼2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of ∼65.95 Ma for the Cretaceous/Tertiary boundary.

https://science.sciencemag.org/content/sci/320/5875/500.full.pdf

Synchronizing Rock Clocks of Earth History

Joint determination of 40K decay constants and 40Ar∗/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology

ArArCALC-software for 40 Ar/ 39 Ar age calculations

On the ages of flood basalt events

A test for systematic errors in 40Ar/39Ar geochronology through comparison with U/Pb analysis of a 1.1-Ga rhyolite

Response to the comment by W.H. Schwarz et al. on “Joint determination of 40K decay constants and 40Ar∗/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology” by P.R. Renne et al. (2010)

Ar/ 39 Ar and K-Ar geochronology have long suffered from large systematic errors arising from imprecise K and Ar iso- topic data for standards and imprecisely determined decay constants for the branched decay of 40 K by electron capture and b � emission. This study presents a statistical optimization approach allowing constraints from 40 K activity data, K-Ar isotopic data, and pairs of 238 U- 206 Pb and 40 Ar/ 39 Ar data for rigorously selected rocks to be used as inputs for estimating the partial decay constants (ke and kb )o f 40 K and the 40 Ar*/ 40 K ratio (jFCs) of the widely used Fish Canyon sanidine (FCs) standard. This yields values of jFCs = (1.6418 ± 0.0045) � 10 � 3 , ke = (0.5755 ± 0.0016) � 10 � 10 a � 1 and kb = (4.9737 ± 0.0093) � 10 � 10 a � 1 . These results improve uncertainties in the decay constants by a factor of >4 relative to values derived from activity data alone. Uncertainties in these variables determined by our approach are moderately to highly correlated (cov(jFCs, ke )= 7.1889 � 10 � 19 , cov(jFCs, kb )= � 7.1390 � 10 � 19 , cov(ke, kb )= � 3.4497 � 10 � 26 ) and one must take account of the covari- ances in error propagation by either linear or Monte Carlo methods. 40 Ar/ 39 Ar age errors estimated from these results are significantly reduced relative to previous calibrations. Also, age errors are smaller for a comparable level of isotopic measure- ment precision than those produced by the 238 U/ 206 Pb system, because the 40 Ar/ 39 Ar system is now jointly calibrated by both the 40 K and 238 U decay constants, and because ke( 40 K) < k( 238 U). Based on this new calibration, the age of the widely used Fish Canyon sanidine standard is 28.305 ± 0.036 Ma. The increased accuracy of 40 Ar/ 39 Ar ages is now adequate to provide

for the Fish Canyon sanidine standard, and improved accuracy for 40 Ar/ 39 Ar geochronology

[1] Cretaceous and Cenozoic reactivation of the Triassic Qinling-Dabie orogen between the north China and Yangtze cratons resulted from the combined effects of Pacific subduction–back-arc extension in east China and collisions in west China. We report new apatite fission track and apatite and zircon (U-Th)/He data from east Qinling along a >400-km-long N-S transect from Huashan through the Qinling orogen to Huangling. The ages show a general pattern of younging northward. Three major cooling phases are defined by modeling the multiple thermochronologic data sets. The first phase occurred locally in the North and South Qinling during the late Triassic to early Jurassic, following heating associated with the Triassic Yangtze subduction and exhumation of the Wudang metamorphic core complex on the cratonal edge. A second phase represents regional exhumation between 100 and 60 Ma, coeval with rifting marked by the Late Cretaceous–Eocene (K2–E) red bed deposition in eastern China and possibly indicating a link with Pacific subduction–back-arc extension in eastern China; however, it may also have been superimposed by eastward tectonic escape resulting from the Lhasa–West Burma–Qiangtang-Indochina collision. The third cooling phase was initiated at ∼45 Ma exclusively in the north Qinling and in the footwall of the graben-bounding normal fault of the Weihe graben in the Lesser Qinling. We suggest the third phase was related to reactivation of the Qinling fault system as a result of eastward tectonic escape imposed by the India-Asia collision at ∼50 Ma.

http://users.clas.ufl.edu/kmin/publications/Hu%20et%20al.%20%282006,%20Tectonics%29.pdf

Late Mesozoic and Cenozoic thermotectonic evolution along a transect from the north China craton through the Qinling orogen into the Yangtze craton, central China

Kyoungwon Min

Papers

Joint determination of 40K decay constants and 40Ar∗/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology

A test for systematic errors in 40Ar/39Ar geochronology through comparison with U/Pb analysis of a 1.1-Ga rhyolite

Response to the comment by W.H. Schwarz et al. on “Joint determination of 40K decay constants and 40Ar∗/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology” by P.R. Renne et al. (2010)

for the Fish Canyon sanidine standard, and improved accuracy for 40 Ar/ 39 Ar geochronology

Late Mesozoic and Cenozoic thermotectonic evolution along a transect from the north China craton through the Qinling orogen into the Yangtze craton, central China