International Geologiical Congress - Oslo 2008

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HPS-05 Recent developments in the Geologic Timescale

 

A Middle and Late Permian time scale calibrated by cycles and radio-isotopic age determinations

 

Manfred Menning, GeoForschungsZentrum Potsdam (Germany)
James G. Ogg, Purdue University (United States)
Rolf L. Romer, GeoForschungsZentrum Potsdam (Germany)
 

 

Orbital-climate cycles interpreted from Middle through Upper Permian strata enable estimates of durations of Permian stages and polarity zones. These cyclostratigraphic estimates are consistent with recently published radio-isotopic age determinations, and are significantly different from some previous interpolations of durations.
Cyclic sedimentation in the Central European Basin has enabled estimates of the duration for these groups and subgroups and corresponding scaling of Triassic stages (Menning et al. 2005). Unfortunately, there is not yet an accurate correlation of the Late Rotliegend and Zechstein with global geological stages, and thus, their cycles can not be used for scaling the Permian.
The Upper Permian (Lopingian Series) in South China, the type area for the Wuchiapingian and Changhsingian stages, contains 25 parasequences (Chen et al. 1998). Chen (pers. com. 2006) estimates that Parasequence 1 corresponds to the Guadalupian/Lopingian boundary, the Wuchiapingian/Changhsingian boundary is at the lower part of Parasequence 19, and the top of Parasequence 25 is equivalent to the Permian-Triassic boundary. If the major 400 ky eccentricity cycle is assigned to these parasequences, then the Changhsingian (6 and 3/4 cycles) spans ∼2.7 my and Wuchiapingian (17?18 cycles) spans ∼6.9-7.3 my. Thus, the Late Permian (Lopingian) spans ∼9.8 my.
Combining radio-isotopic age determinations and cycle-scaling in Late Permian, the best estimate for the age of the Permian-Triassic boundary is 252.5 Ma (Mundil et al. 2001, 2004; Menning et al. 2005). Therefore, the cycle-scaled age for the base of the Changhsingian is 255.2 Ma, and the base of the Wuchiapingian is projected as ∼262.3 Ma.
For Middle Permian, Bowring et al. (1998) yielded an age of 265.3 ± 0.2 Ma for a tuff from the uppermost Wordian using multigrain U/Pb ID-TIMS age determination. In general, multigrain U-Pb ages are systematically offset by ∼1.5 Ma younger from single-grain U-Pb ages reported from Late Permian through Middle Triassic (Menning et al. in prep.). Applying this offset, we estimate a target age of ∼266.6 Ma for the base of the Capitanian Stage. We hope that this can be tested in the near future by further cyclostratigraphic investigations.
If one assumes that the durations of the Roadian and Wordian stages are shorter than the Capitanian Stage, then the base of Roadian is projected as 272-273 Ma. The interpretation of cycles from Central Europe (Middle Permian?Middle Triassic) and of South China (Late Permian) as of Milankovich duration is consistent with the 52 radio-isotopic age determinations analysed.
Age and duration of Middle and Late Permian stages are: base of Triassic 252.5 Ma; base of Changhsingian (∼ 2.7 my) ∼255.2 Ma; base of Wuchiapingian (∼ 6.9-7.3 my) ∼262.3 Ma; base of Capitanian (∼ 2.8-4.3 my) ∼266.6 Ma; base of Wordian (∼ 3 my?) ∼269.5 Ma; base of Roadian (∼ 3 my?) ∼272.5 Ma.

 

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