T241 Late Jurassic through Early Cretaceous Geologic Time Scale

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Sagamore Ballroom 7

AGE MODEL FOR LATE JURASSIC THROUGH EARLY CRETACEOUS USED IN THE GEOLOGIC TIMESCALE 2012/2016 REFERENCE SCALES

Paper number: T241-1
Program: Technical Sessions
Time: 8:00 AM – 8:15 AM

Authors

Abstract

The Geologic TimeScale 2012/2016 had age assignments for all biozones, geochemical excursions and magnetic polarity chrons and for the derived geologic stage boundaries according to the calibrations of their GSSPs to these other chronostratigraphic events. For the Late Jurassic through Early Cretaceous, the age model was based on a merger of astronomical cycle-scaled durations for biozones and polarity zones to produce a semi-smoothed M-sequence spreading model for the Pacific Ocean. This was placed on an absolute age framework using the few available constraints of Ar-Ar and U-Pb dates from ODP boreholes (e.g., basalts of ODP Site 801 of Bajocian/Bathonian, Shatsky Rise of basal Berriasian and Ontong Java Plateau of early Aptian) and from volcanic ash beds near the base-Cenomanian (Japan), base-Albian (north Germany) and reported dates on levels in Lower Cretaceous from the Great Valley successions that had calcareous nannofossil biostratigraphy.

Post-2012 published cyclostratigraphy studies have largely verified the assigned durations for the geologic stages/substages, biozones and/or polarity chrons within the Bajocian through Albian stages; however, the radiometric dates from some ODP sites seem inconsistent with some new radiometric dates from bentonites in Argentina, Italy and Svalbard. The main challenges are to identify and verify which of the cycle-scaled reference sections have been mis-interpreted, to avoid anomalous jumps in oceanic spreading rates, and to test the previous datings of the ODP basalts and volcanic ash beds.

Ogg, J.G., and Hinnov, L.A. (with contributions by Huang, C.), 2012. Jurassic, and Cretaceous chapters. In: The Geologic Time Scale 2012 (Gradstein, F.M., Ogg, J.G., Schmitz, M.D., and Ogg, G.M., editors), Elsevier Publ.: pg. 731- 792 and 793-854.

Ogg, J.G., Ogg, G.M., Gradstein, F.M., 2016. A Concise Geologic Time Scale 2016. Elsevier Publ., 234 pp.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-322883

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