Talk:Graneros Shale

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Graneros Group

While I have made a practice of merging redundant geology unit pages, there seems here a reason here to speculate about introducing a separate Graneros Group page. (mind you this is a very early thought, based on knowing more about the Dakota than the alternate Graneros Group)

South of the Dakota states, the Graneros Formation is a widely used datum unit, but other than the X Bentonite, and its function as defining the top of the Dakota, it seems a relatively small unit.

As noted in the Description, there is another classification (Collier, A.J., 1922); however, what is understated there is that this other classification is quite different, with, in some places, the unit having a sub-unit carrying the same name (i.e., the Graneros Shale Formation unit of the Graneros Group unit). The first paragraph states that the unit lies on the Dakota Group, but the second paragraph reflects that the Graneros Group embraces the same sequences as the Dakota Group.

See South Dakota Stratigraphic Correlation Chart.

From this correlation chart, the Graneros Group correlates with the Colorado/Wyoming Dakota Group. But, the correlation is not precise; the base of the Graneros Group is at the conformal shale/sandstone facies change at the base of the Skull Creek Shale, rather than the major discontinuity at the sandstone base of the Skull Cycle. So, in contrast to the usage south of the Dakotas where the Graneros is generally assigned to the first transgression of the Greenhorn Cycle, this SD usage assigns the Graneros to the high stand of the Skull Creek Cycle, the entirety of the Mowry(Dakota) Cycle, and then the transgression of the Greenhorn Cycle (maybe, have to read the SD publications).

I'm not saying the SD classifications are "wrong", I'm just saying their may be a lot of complication in trying to expand the article, and I clearly have only scratched the surface of the Graneros Group.

IveGoneAway (talk) 13:54, 10 March 2021 (UTC

Well, in 1965, Hattin in polite terms confirmed that the "Graneros Group" is not at all the same as the type definition. On the other hand, "Graneros Group" is sufficiently depreciated as to not warrant a separate page. IveGoneAway (talk) 04:31, 14 March 2021 (UTC)