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North America Dinosaur Formations


Nanotyrannus35

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Why are there so many late Cretaceous dinosaur fossil bearing formations in the western usa? In just Montana alone, there is the Hell Creek fm, the Lance fm, the Judith River fm and the Two Medicine fm. The fauna in these different formations are also similar, it's kind of confusing. 

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I'm sure it seems like North America has more late Cretaceous deposits than most places but it doesn't really. Here is a map from https://macrostrat.org/ with all known cretaceous formations shown.

image.thumb.png.92974aeccdd22f42ca3ffd3345ad72c2.png

 

Hollywood has made the North American formations more famous by making dinosaurs like T. rex, Triceratops and others famous. There may be other reasons for the popularity of the western US cretaceous but can't think of any at the moment. I'm sure others will talk about those shortly.

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Alberta has lots of cretaceous deposits.   All beneficiaries of the inland seaway which drastically changed ecosystems along the center of north america 

 

Screenshot_20190406-191847.thumb.jpg.17000e1364a3bf1516c9b91a6a02d4bd.jpg

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Oh yeah, because in the cretaceous, part of North America was separated from the rest of it.

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1 minute ago, Nanotyrannus35 said:

Oh yeah, because in the cretaceous, part of North America was separated from the rest of it.

 

484778955_therLateCret92withBigWaterandlabels.thumb.jpg.d1eaf3e56575944c3cf2e75094c0b845.jpg

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So there's a lot of fossils there because the ecosystem of the beach was good?

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couple of other important factors:

 

1. the deposits of the mountain west are pretty extensively exposed in dry badlands, so you can really prospect for fossils across long distances. 

 

2. there is a lot of money for research in Canada and the US, and has been for ~150 years, meaning that these rocks not only are easy to prospect but they have been prospected

 

3. these badlands are in politically stable regions with good infrastructure (roads, services)

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Let me add

A lot of the bonebeds are from inland rivers like the one I just posted on my last trip.   Also a good amount of what you see sold in open markets (not skeletons) come from channel deposits which are from fresh water rivers.   

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I have to say that map of the Cretaceous deposits of the world is pretty "approximate".  It shows a band of Cretaceous where the Appalachian Mountains are located, and they are definitely not Cretaceous.  In British Columbia it shows the whole of the Coast Range as Cretaceous, which it is not (except in a few limited areas), and it shows no Cretaceous at all on Vancouver Island where there is a fair bit of Cretaceous.  Also it doe not show any Cretaceous in Belgium and southern Holland, where the type section for the latest Cretaceous (Maastrichtian) is located.

 

Besides the points jdp made, most of the good dinosaur-yielding rocks in the North American West were deposited on the eastern side of Laramidia (i.e. the Western side of the seaway).  This area had a wide area of lowlands with numerous large meandering rivers, ideal for burying and preserving animal carcasses.  At the time the Rocky Mountains has scarcely started to form, so Laramidia was relatively flat.  There are relatively few outcrops of the right age along the Eastern side of the seaway, or in other world the Western shore of Appalachia, and so few dinosaurs.  Te Appalachians were much higher in the Cretaceous than they are today, so rivers coming off the Southern or Eastern side of Appalachia were steeper and faster, and did not create large meanders or areas of deposition.  Most known dinosaurs were from marine or mixed marine/terrestrial deposits.  In other words, they are from carcasses that floated downstream, were carried out to sea, then sank and were buried offshore or washed back onshore and rolled around with the waves.  Either way there are few skeletons that are anywhere near complete, as most fell apart bit by bit or were torn apart by scavengers.  Basically decomposition gasses made them float like a balloon for a while, as the head/tail/legs decayed and fell off (or scavengers tore them off) until the body ruptured and whatever was left sank to the bottom.  Either that, or the bloated carcass washed into nearshore lagoons or got smashed by waves on the shore.  A few 1/2 complete skeletons have been found, but the overwhelming majority of East Coast/Gulf Coast dinosaurs are isolated bones.  Most come from sites that also yield bones of mosasaurs, shark teeth, and other marine fauna.

 

Probably Appalachia was just as good as Laramidia environmentally for dinosaurs, but the conditions for preserving them as fossils were much worse.

 

Don

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10 minutes ago, FossilDAWG said:

I have to say that map of the Cretaceous deposits of the world is pretty "approximate".  It shows a band of Cretaceous where the Appalachian Mountains are located, and they are definitely not Cretaceous.  In British Columbia it shows the whole of the Coast Range as Cretaceous, which it is not (except in a few limited areas), and it shows no Cretaceous at all on Vancouver Island where there is a fair bit of Cretaceous.  Also it doe not show any Cretaceous in Belgium and southern Holland, where the type section for the latest Cretaceous (Maastrichtian) is located.

The band is south of the Appalachians and is where the cretaceous dinosaurs from Georgia and Alabama are found. The map doesn't only highlight fossiliferous or sedimentary formations, most of the highlighted portion in British Columbia is Mesozoic granite. Zooming out to encompass the whole world sacrifices detail. If you zoom in you will see there are cretaceous exposures on Vancouver Island. Same with Belgium and the Netherlands. The map is just to show other areas have Cretaceous deposits which it does even without detail. If the OP wishes he can use the link to see higher resolution images of certain areas.

“If fossils are not "boggling" your mind then you are simply not doing it right” -Ken (digit)

"No fossil is garbage, it´s just not completely preserved” -Franz (FranzBernhard)

"With hammer in hand, the open horizon of time, and dear friends by my side, what can we not accomplish together?" -Kane (Kane)

"We are in a way conquering time, reuniting members of a long lost family" -Quincy (Opabinia Blues)

"I loved reading the trip reports, I loved the sharing, I loved the educational aspect, I loved the humor. It felt like home. It still does" -Mike (Pagurus)

“The best deal I ever got was getting accepted as a member on The Fossil Forum. Not only got an invaluable pool of knowledge, but gained a loving family as well.” -Doren (caldigger)

"it really is nice, to visit the oasis that is TFF" -Tim (fossildude19)

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