The Cretaceous Period lasted approximately 80 million years, from 145 to 65 million years ago.

    The Cretaceous Period is divided into twelve chronostratigraphic stages. From oldest to youngest, these are the Berriasian, Valanginian, Hauterivian, Barremian, Aptian, Albian, Cenomanian, Turonian, Coniacian, Santonian, Campanian, and Maastrichtian Stages.  The historical significance of France and Switzerland is quite apparent from the graphic, as all of the names are derived from these two countries.  An excellent treatment of the historical origin and validity of these stage names can be found in:  Rawson, et al. (1978, ref below).

    Notice that all of the stages are of different time intervals.  That is because these boundaries have been arbitrarily defined based on the fossil evidence, such as mass extinctions (e.g., the J/K, Cenomanian/Turonian and K/T boundaries) and other significant events as interpreted from the rock/fossil record.  The arbitrary nature of these boundaries means that the corresponding absolute dates are also subject to interpretation. 

     A lot of work has been done in the past two decades on assigning universally accepted absolute values.  Such an exercise is not just useful but is very important, as it allows everyone to be on the "same page".  While integrated approaches that employ a combination of macrofossil, microfossil, and stable and radioactive isotope data have been published on several stage boundaries in the Cretaceous, the values still vary somewhat from paper to paper.  The values we use here are from somewhat dated sources (see refs below), but this is clearly not important.

     The terms, Senonian and Neocomian are older stage names and have been replaced by the following stages:  a) the Campanian, Santonian and Coniacian Stages for the Senonian, and b) the Hauterivian, Valanginian and Berriasian Stages for the Neocomian.  We've included them here to recognize their historical significance.  We also included a few older substage names (e.g., Clansayesian, Gargasian and Bedoulian Substages within the Aptian Stage) that have historical value.

     It is tempting to include other historical terms such a Vraconian and Urgonian on the time scale.  However, these are imprecise labels that have limited [geographic] utility and are therefore not universally accepted.  Vraconian in the strictest sense refers to latest Albian time (typically includes the Stoliczkaia dispar and Mortoniceras inflatum Zones).  However, the Vraconian in Madagascar also includes earliest Cenomanian age beds, so the term is not well defined (and consequently not included below).  The term Urgonian is derived from beds of Barremian to earliest Aptian (Bedoulian) age from Orgon, Bouches du Rhône (13) of southeastern France.  However since it specifically refers to a reef facies in the Marseille area (it's a facies term not a chronostratigraphic one), we've omitted it from the time scale.  The Urgonian (facies) is said to be present in Drôme and Vercors as well.

References

• We would like to thank Hannes Löser for clarifications/corrections on the geologic time scale
• We would also like to thank Emmanuel Pénagé and Cyril Baudouin for their help in making sure the information on this page is correct.
• Kauffman, E. G., special ed.  1977.  “Geological and Biological Overview:  Western Interior Cretaceous Basin”.  In:  Kauffman, E. G., ed.  North American Paleontological Convention II.  Cretaceous Facies, Faunas, and Paleoenvironments Across the Western Interior Basin.  The Mountain Geologist 14 (3-4), 75–100.

• Obradovich, J. D.; Cobban, W. A.  1975.  "A Time-Scale for the Late Cretaceous of the Western Interior of North America".  In:  Caldwell, W. G. E., ed.  The Cretaceous System in the Western Interior of North America.  Geological Association of Canada Special Paper 13, 31–54.

• Obradovich, J. D.  1992.  “A Cretaceous Time Scale”.  In:  Caldwell, W. G. E.; Kauffman, E. G., ed’s.  Evolution of the Western Interior Basin.  Geological Association of Canada Special Paper 39, 379–396.
• Palmer, A. R.  1983.  The Decade of North American Geology 1983.  Geologic Time Scale.  Geology 11, 503–504
• Rawson, P.F.; Curry, D.; Dilley, F. C.; Hancock, J. M.; Kennedy, W. J.; Neale, J. W.; Wood, C. J.; Worssam, B. C.  1978.  "The Cretaceous Stages and Zones in Britain.  Introduction."  In:  A Correlation of Cretaceous Rocks in the British Isles.  Geological Society, London, Special Report 9, pp. 8-30.
• Van Hinte, J. E.  1976.  A Cretaceous Time Scale.  American Association of Petroleum Geologists Bulletin 60 (4), 489–516.