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Should the International Commission on Stratigraphy divide the Cretaceous into three different periods?


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Although the Cretaceous period lasted from 145 to 66 million years ago, geologic units from the Berriasian to Albian stages and several terrestrial units of Albian to Maastricthian age are not chalky in terms of geologic composition. I remember that the Cretaceous at one time was divided into the Neocomian, Gallic, and Senonian epochs, so one day International Commission on Stratigraphy should divide the Cretaceous into the Neocomian, Gallic, and Senonian periods, since the Cretaceous lasted longer than either the Triassic or Jurassic. This is similar to the fact that American geologists divide the Carboniferous in North America into the Mississippian and Pennsylvanian due to Mississippian deposits being marine and Pennsylvanian deposits being formed from coal.

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It's important to remember that such generalizations as "the Mississippian is marine" and "the Cretaceous is chalky" are just that, generalizations. There's many terrestrial Mississippian deposits just like there's many marine Pennsylvanian ones, and non-chalk Cretaceous ones. Likewise, the Mississippian-Pennsylvanian split is more a historical holdover amongst North American geologists as opposed to a strict international convention, as you'll rarely hear the two used in places like the British Coal Measures or Spain. 

 

Length of a period usually isn't much of a factor. The Silurian only lasted about 25-40 million years, depending on who you asked. The Ordovician lasted about 50-70 million, and the Devonian well over 40. Faunal/floral differences and other factors are far more important. 

 

I can't really speak to any big differences in faunal/floral succession in the Mesozoic, but out of habit I'd say the periods are fine as they are. There's some arguments to be made about the positioning of flowering plants/ammonite species to mark the Jurassic-Cretaceous border, but it won't substantially move it one way or the other. I'm not very knowledgeable about either, though, so I'll let it at that. 

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FossilDAWG

I don't see a compelling reason to divide the Cretaceous into periods, and much potential for confusion.  Dividing based on chalk/non-chalk makes as much (or as little) sense as restricting the Jurassic to rocks exposed in the Jura Mountains.  For finer-scale divisions I think the stages work well.  They are well constrained biostratigraphically, at least in the marine environment.  The Turonian, as one example, can be recognized worldwide based on ammonites, inoceramids, foraminiferans, etc.  The same is true of the other stages.  Reviving old names, long abandoned, cannot be helpful.

 

Don

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Mississippian and Pennsylvanian are Epoch-level subdivisions, effectively equivalent to "Lower" and "Upper". They are not elevated to Period in any current stratigraphic system.

 

What matters is consistency of marker beds and, typically, some sort of meaningful faunal change. Cretaceous currently meets those criteria so it would be crazy to subdivide it just for the sake of evenness. I will note that there is some discussion of whether the J-K boundary may correctly be placed at the Berriasian-Valangian boundary, in which case the Jurassic gets a bit longer and the Cretaceous gets a bit shorter.

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DPS Ammonite
6 hours ago, DD1991 said:

International Commission on Stratigraphy should divide the Cretaceous into the Neocomian, Gallic, and Senonian periods

 

5 hours ago, FossilDAWG said:

I don't see a compelling reason to divide the Cretaceous into periods

A correction, the Cretaceous is a Period and is divided into Late and Early Epochs.

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DPS Ammonite
3 hours ago, jdp said:

Mississippian and Pennsylvanian are Epoch-level subdivisions, effectively equivalent to "Lower" and "Upper". They are not elevated to Period in any current stratigraphic system.

Per the ICS, the Mississippian and Pennsylvanian are Subperiods (time units) that are divided into Early Middle and Late Epochs. The Mississippian Subperiod is roughly equivalent to the “early”Carboniferous. The current non interactive ICS chart does not make it clear about the Subperiods.

 

https://www.britannica.com/science/Mississippian-Subperiod/images-videos

 

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FossilDAWG
4 hours ago, DPS Ammonite said:

 

A correction, the Cretaceous is a Period and is divided into Late and Early Epochs.

The first post in this thread suggests dividing the Cretaceous Period into three new Periods.  I am perfectly aware that the Cretaceous is a Period.  I disagree with the idea of eliminating the Cretaceous Period and substituting three new Periods, I argued for leaving things as they are.  Period.

 

Don

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DPS Ammonite
1 hour ago, FossilDAWG said:

The first post in this thread suggests dividing the Cretaceous Period into three new Periods.  I am perfectly aware that the Cretaceous is a Period.  I disagree with the idea of eliminating the Cretaceous Period and substituting three new Periods, I argued for leaving things as they are.  Period.

 

Don

I see his proposal more clearly; thanks Don. He suggested elevating former epochs and one age, Senonian, into periods. Thus the Cretaceous would dissappear as a period. Recycling three names to become new periods that had various definitions would be very confusing. The Cenonian has been an epoch and an age; making it a period would be too much. Eliminating the Cretaceous because it is too long is near heretical and probably a non starter. I agree with others; keep the Cretaceous as it is

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8 hours ago, DPS Ammonite said:

Per the ICS, the Mississippian and Pennsylvanian are Subperiods (time units) that are divided into Early Middle and Late Epochs. The Mississippian Subperiod is roughly equivalent to the “early”Carboniferous. The current non interactive ICS chart does not make it clear about the Subperiods.

 

https://www.britannica.com/science/Mississippian-Subperiod/images-videos

 

 

The subperiod-epoch distinction is not really precise and I'm not entirely sure how formal it even is. However, it is important to recognize that historically these sequences were regional rather than global, so you had a European Carboniferous system that was organized into local series like the Silesian (Namurian-Westphalian-Stephanian) or the Dinantian (Tournaisian-Visean) in Europe and the Mississippian (Kinderhookian-Osagian-Meramacian-Chesterian) and Pennsylvanian (Morrowan-Atokan-Desmoinesian-Missourian-Virgilian). The international scale keeps some of the European stages (Tournaisian-Visean) then transitions to the Russian sequence for the remainder of the Carboniferous (Serpukhovian-Bashkirian-Moscovian-Kasimovian-Gzhelian) through the remainder of the early Permian, but keeps the North American epoch/sub-period division between lower and upper Carb with the Mississippian-Pennsylvanian North American nomenclature. This is the sort of sausage that gets made when you're trying to reconcile sequences from across the globe into a single timeline.

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DPS Ammonite
46 minutes ago, jdp said:

The subperiod-epoch distinction is not really precise and I'm not entirely sure how formal it even is.

The ICS did less than a stellar job in describing what units the Mississippian and Pennsylvanian are. See interactive ICS chart.

 

The ICS charts and guides are guidelines and do not have the force of law. They are however, the best attempt at internationally recognized  geological time charts and stratigraphy guidelines. The designation of Pennsylvanian and Mississippian as Subperiods are as close to a formal designation as you are going to find anywhere.

 

0F767F53-4142-4591-8384-3B966ED702DC.jpeg.99648bb54397e494b65e66271b3b5a46.jpeg
 

clicked on Mississippian in above chart.

 

B7C3B03A-9602-4DDF-A685-A0F25EFF9BC7.png


Old ICS chart as mentioned by Encyclopaedia Brittanica

F7F284A8-AC2B-4CF3-B9B8-F26DD9E24BA3.jpeg
 

 

The USGS 2018 time chart suggests that Mississippian and Pennsylvanian are Subperiods since they are in a column labeled Periods/Subperiods.

 

https://pubs.usgs.gov/fs/2007/3015/fs2007-3015.pdf

 

 

ECE0B4D5-CB8B-44E6-8238-D3E42F88109C.png

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All my labels are color coded by period. If I have to change them I am going to hunt you down and give you a nuggy that you will feel for the next ten epochs...

 

Years ago I had to learn to sort out chronostratigraphy from lithostratigraphy.  The stratigraphic record isn't always perfect.  I don't expect the division of geological time to be either.

 

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DPS Ammonite
22 minutes ago, erose said:

All my labels are color coded by period.

We’re you aware prior to this thread that according to the ICS the Mississippian and Pennsylvanian are Subperiods?

 

Do you have a different color for the Carboniferous, Mississippian and Pennsylvanian?

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41 minutes ago, DPS Ammonite said:

We’re you aware prior to this thread that according to the ICS the Mississippian and Pennsylvanian are Subperiods?

 

Do you have a different color for the Carboniferous, Mississippian and Pennsylvanian?

Yes, But so far my collection only includes Pennsylvania material. It's all North American and I have defaulted to using Pennsylvanian Period for my labels.  Nice thing is  that in my data base I can easily do a replacement and swap "Pennsylvanian Period" for Pennsylvanian Subperiod"

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2 hours ago, DPS Ammonite said:

The ICS did less than a stellar job in describing what units the Mississippian and Pennsylvanian are. See interactive ICS chart.

 

The ICS charts and guides are guidelines and do not have the force of law. They are however, the best attempt at internationally recognized  geological time charts and stratigraphy guidelines. The designation of Pennsylvanian and Mississippian as Subperiods are as close to a formal designation as you are going to find anywhere.

 

0F767F53-4142-4591-8384-3B966ED702DC.jpeg.99648bb54397e494b65e66271b3b5a46.jpeg
 

clicked on Mississippian in above chart.

 

B7C3B03A-9602-4DDF-A685-A0F25EFF9BC7.png


Old ICS chart as mentioned by Encyclopaedia Brittanica

F7F284A8-AC2B-4CF3-B9B8-F26DD9E24BA3.jpeg
 

 

The USGS 2018 time chart suggests that Mississippian and Pennsylvanian are Subperiods since they are in a column labeled Periods/Subperiods.

 

https://pubs.usgs.gov/fs/2007/3015/fs2007-3015.pdf

 

 

ECE0B4D5-CB8B-44E6-8238-D3E42F88109C.png

 

Yeah so I frequently use the Miss/Penn (or Lower/Upper Carb) distinction and I've effectively never used the "lower/Middle/Upper Miss/Penn" distinction, especially since each effectively translates to a single stage (except upper Penn, which translates to two). Contrast with Lower/Middle/Upper Devonian which correspond to 3/2/2 stages each, Cisuralian-Guadalupian-Lopingian, which correspond with 4/3/2 stages each in the Permian.

 

So again this is what I mean about sausage-making: these specific divisions of time and of the rock record are often imprecise on some level and are effectively meant to make it clear what is being discussed when two scientists have a conversation. Thus, it can make perfect sense to switch back and forth between terms like "Langsettian" or "Atokan" or "Bashkirian" depending on the specific context, particularly when the use of these terms grants accuracy (when referring to a specific local sequence) or precision (when talking about inter-basinal correlations). But, as far as Miss/Penn I use those terms routinely and I have never to my memory actually referred to what "level" of stratigraphic classification these fall into because it is understood they are above the level of Stage and below the level of Period and that's all that matters.

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