CENOZOIC-MESOZOIC TIME SCALE 2004

The geologic time scale is the framework for deciphering the history of the Earth. The Geologic Time Scale 2004 (GTS2004) program under the International Commission on Stratigraphy of IUGS had three components: (1) Status of international definitions (“Global boundary Stratotype Section and Point” or GSSP) of divisions of geologic time, (2) High-resolution integrated stratigraphy, and (3) Numerical age scale for both boundaries and all major events within each stage. The Paleozoic-Precambrian portion of GTS2004 is summarized in a companion GSA presentation by Alan Smith.

Half of the 20 Cenozoic stages are fixed by GSSPs, but only 8 of the 30 Mesozoic stages are officially defined. Therefore, the summary scale has selected the most probable boundary definitions being considered by the subcommissions of ICS.

The Neogene Period (Holocene through Miocene) time scale has an ultra-high-resolution scaling from astronomical (Milankovitch) cycles. Astronomical cycles tied to radiometric ages also scale portions of the early Paleogene, middle Cretaceous, and early Jurassic-late Triassic. Depending on the time interval, other portions merge selected high-resolution radiometric ages, seafloor spreading models, strontium-isotope segments, and geomathematical interpolation methods.

Computed ages (rounded) for the BASES of geologic epochs are:

Holocene -- 11.5 ka, Pleistocene -- 1.8 Ma, Pliocene -- 5.3 Ma, Miocene -- 23 Ma (base of Neogene Period)

Oligocene -- 34 Ma, Eocene -- 56 Ma, Paleocene -- 65.5 Ma (base of Cenozoic Era)

late Cretaceous -- 100 ±1 Ma, early Cretaceous -- 145 ±4 Ma

late Jurassic -- 161 ±4 Ma, middle Jurassic -- 176 ±2 Ma, early Jurassic -- 200 ±1 Ma

late Triassic -- 237 ±2 Ma, middle Triassic -- 245 ±2 Ma, early Triassic -- 251 Ma (base of Mesozoic Era)

The compilation of GTS2004 involved a large number of specialists, and is summarized in A Geologic Time Scale 2004 (~600 pages with summary poster, Cambridge University Press, www.cambridge.org). Summary diagrams and tables of GSSPs can be downloaded from the ICS website (www.stratigraphy.org). The source data will eventually be accessed through the CHRONOS system. Coordinators for the Cenozoic-Mesozoic time scales include Felix Gradstein (GTS2004 chair), FritsAgterberg Phil Gibbard, Luc Lourens, Hanspeter Luterbacher, and John McArthur.