Turritella/Elimia Agate and the Green River fm.

[JBkansas]

I was surprised to learn that turritellia(elimia) agate comes from the Green River fm. It seems surprising that such radically different matrices are present in the same formation.  Does anyone know the association, are there clumps of agate mixed in with green river fish/leaves/etc or are they isolated deposits that got lumped in together due to similar age and location?

 

*edit*: Also, Eden valley wood/algae and giant stromatolites. Truly a diverse formation

 

Edited January 27, 2023 by JBkansas

[Fossildude19]

I read somewhere that the Laney Member of the Green River Formation is the origin of the Elimia agate.

So I think it outcrops in different areas from the Fish layers.

[ClearLake]

53 minutes ago, JBkansas said:

It seems surprising that such radically different matrices are present in the same formation

Geologic Formations are generally not based on a single lithology type but rather a set of lithologic characteristics that distinguish it from other bodies of rock.  Meaning, it can have one type of lithology or many types (think alternating sand and shale sequence or alternating shale and limestone sequence, or a mixture of all of these) as long as that mix of lithologies is definably different from surrounding bodies.  There is also a time component, it occupies a certain range of geologic time ( we won't get into lithostratigraphic vs chronostratigraphic) and an areal component.  Formations can vary in rock type up and down the rock column as well as aerially across the formation.  So different matrices are quite common in formations, I would hazard a guess that a variety of lithologies is the norm in most formations, but I don't know that for certain.

 

Now, as to the Green River Formation specifically and your question, I am not an expert on it but I know that the formation deals with a lot of lacustrine (lake) deposits and as you might imagine if you think about the aerial extent of lakes, there could be quite a bit of variability within that type of setting.  Also, formations are often subdivided into Members (as @Fossildude19 pointed out) and from what I read, the Laney Member is different (area and age) than the Fossil Butte Member which is what you are most familiar with the fish, etc.  Here is a snapshot of one figure out of a publication (Bulletin 63 of the Wyoming Geological Survey) that displays the variability of the GR Formation across different basins and shows the various members contained within.   See the Laney Shale Member in the Bridger and Washakie Basins and the Fossil Butte Member in the (not surprisingly) Fossil Basin and slightly older.

 

 

Hope this helps.

[JBkansas]

Oddly enough, looking into the Laney member has even more lithography:

 

From classic green river type fish to the Blue forest of petrified wood/alge and even giant stromatolites. I never realized the Green River formation was so diverse (and this was only one member of the formation):

 

Blue forest: https://www.mdpi.com/2076-3263/9/1/35

 

Giant stromatolites: https://www.searchanddiscovery.com/pdfz/documents/2014/50984awramik/ndx_awramik.pdf.html

 

[jpc]

ClearLake explained it very well.  Most formations are a lot more than just one type of rock as we see here.  The Turritella agate comes from the Laney Shale which also has fish beds but it is almost all BLM land and the parts that are private, the landowners do not allow commercial sales of fossils.  So you never see those fossils for sale.  They Laney Shale fish are almost all different from the Fossil Lake fishes, including Erismatopteron, Amyzon, Goscuitichthyes and Hypisodoris.  The Turritella bed is separate from those fish beds but they are still part of the Laney Shale, as is the Blue Forest and Eden Valley petrified wood.  The LS was deposited in Lake Gosuite which was large and dynamic, so there are many different layers of different rocks in it.   There are other layers in the Laney that are rich in fresh water snails, including many other layers of Elimia in which the preservation is much sandier than the agate and therefore does not polish like the agate, but is just as rich.          

[JBkansas]

Thank you all for the education on a fascinating area.

Edited January 27, 2023 by JBkansas