Late Cretaceous chalk in North America

[The Amateur Paleontologist]

Hey everyone  

I know I've been lately rather inactive on TFF; I was held back by fieldwork and other reasons (though do expect some posts about the fieldwork next weekend  ).

But anyway, onto what I came to talk about...

Would anyone know of some good exposures of Late Cretaceous chalk in Canada or USA? I'm thinking specifically about Campanian chalk or, even better, Maastrichtian chalk..

It would be great if the exposed chalk is very fossiliferous, of course.

Thanks for any help!

-Christian

[connorp]

There is of course the famous Niobara Chalk in Kansas/Nebraska. However, from what I've read (it hasn't been that much), most exposures are on private land.

[JarrodB]

Texas has plenty. 

[caldigger]

7 minutes ago, JarrodB said:

Texas has plenty. 

"Chalk" it up to Texas to have everything! 

[JarrodB]

Just now, caldigger said:

"Chalk" it up to Texas to have everything! 

When it's larger than some countries lol. 

[Heteromorph]

For Campanian chalk in Texas, the Pecan Gap formation would be my go-to. There are some lowermost Campanian Austin Chalk exposures in North Texas too, but in most places that horizon is missing.

 

Of course, if you’re talking about Coniacian-Santonian chalk, we have plenty of that too! 
 

Dan Woehr would be the one to know the most about the Pecan Gap, so his meanderings would be a great place to start.

 

EDIT: For more information on the Campanian stage of the Austin Chalk and its fossils, see: An integrated study (geochemistry, stable oxygen and carbon isotopes, nannofossils, planktonic foraminifera, inoceramid bivalves, ammonites and crinoids) of the Waxahachie Dam Spillway section, north Texas: a possible boundary stratotype for the base of the Campanian Stage

[siteseer]

4 hours ago, The Amateur Paleontologist said:

Hey everyone  

I know I've been lately rather inactive on TFF; I was held back by fieldwork and other reasons (though do expect some posts about the fieldwork next weekend  ).

But anyway, onto what I came to talk about...

Would anyone know of some good exposures of Late Cretaceous chalk in Canada or USA? I'm thinking specifically about Campanian chalk or, even better, Maastrichtian chalk..

It would be great if the exposed chalk is very fossiliferous, of course.

Thanks for any help!

-Christian

 

 

It's an interesting question because I'm not sure there is Maastrichtian-age chalk in North America.  Offhand, other than the Pecan gap Chalk as noted by Heteromorph, I know of only the uppermost layers of the Niobrara Chalk and the Selma Group (Alabama) as bearing Campanian-age chalk.  I would assume there may be spots in Mississippi.  I have only a few fossils from the Pecan Gap Chalk and have seen very little from it in other collections and at shows so I assume that outside of Uncle Siphuncle's determined hunting it's not very productive.

[FossilDAWG]

The Mooreville Chalk in Alabama and Mississippi is Campanian. Outcrops are mostly chalk glades on private property.  These glades mostly resulted from poor erosion control a century or more ago.  Once exposed, the chalk (which is very clay-like, not "white cliffs of Dover" type chalk) will expand when wet, then dry to a powder that blows away in the slightest wind, so soil development is very slow.  It has produced a fairly large fauna of marine turtles and mosasaurs, very rare dinosaurs, fish, shark teeth and vertebrae, and scattered invertebrates.  However these fossils are quite sparse on the ground, you can look for hours without finding much of anything other than worm tubes.  The sea floor was a soft ooze that wasn't very amenable to invertebrates except large flat inoceramids, and they crumble into a billion tiny pieces when the wet chalk swells up, then dries out.  Their abundance is indicated only by the broken pieces of thickened hinges with distinctive fibrous structure and teeth.  Other invertebrates are rarely found because the aragonitic shells dissolved leaving fragile steinkerns the same texture and softness as the chalk matrix.  In the summer, the reflective chalk acts like a solar oven, so temperatures in the glades easily get well over 100 degrees F.

[The Amateur Paleontologist]

@connorp @JarrodB @Heteromorph @siteseer @FossilDAWG

 

Thanks for your answers - I'll be sure to look up the sites and formations you all mentioned  

Would you guys happen to know about similar exposures in Canada?

[Heteromorph]

@The Amateur Paleontologist,

 

While I don’t have any information on Campanian - Maastrichtian chalks from Canada, I now know that there is exposed Maastrichtian chalk in North America, specifically the Prairie Bluff Chalk of Alabama and Mississippi. Information on it and other related formations can be found here and here.

[Uncle Siphuncle]

The Pecan Gap Chalk of Texas has a long ribbon of surface exposure from San Antonio to the North Sulphur River basin and perhaps farther into NE Texas.  It isn't rich in macrofossils everywhere, but more in isolated pockets and horizons.  In it I've found a handful of ammonite (Pachydiscus, Placenticeras, Didymoceras, Trachyscaphites) and echinoid (Echinocorys, Hemiaster, Coenholectypus) species, lots of bivalves and gastropods, several species of oysters, a few shark and fish teeth, one crab, other crustacean material, even some articulated fish material.  There were some big sites in Bexar County 10 years ago that are now built over, sad to say.  But stream bed and construction sites dot the 350 mile outcrop ribbon heading NE from San Antonio, including Austin, east of Waco, the NSR, etc., so maybe you'll bump into an underexploited outcrop.

[Uncle Siphuncle]

In the TX Maastrichtian, I've seen way more marl and clay than chalk.  Keep in mind that in areas where fossils are not abundant, Upper K outcrops begin looking pretty similar.  Many are tan to gray with conchoidal fracture.  Oysters are the fossils most resistant to weathering in these formations, and fortunately most are zone specific, helping you to decipher formation where oysters are present, especially when found bedded.  Of course an ammonites or fragments thereof used in conjunction with oysters will narrow the timeframe as best as possible.

[erose]

On 10/7/2019 at 11:00 PM, Uncle Siphuncle said:

The Pecan Gap Chalk of Texas has a long ribbon of surface exposure from San Antonio to the North Sulphur River basin and perhaps farther into NE Texas.  It isn't rich in macrofossils everywhere, but more in isolated pockets and horizons.  In it I've found a handful of ammonite (Pachydiscus, Placenticeras, Didymoceras, Trachyscaphites) and echinoid (Echinocorys, Hemiaster, Coenholectypus) species, lots of bivalves and gastropods, several species of oysters, a few shark and fish teeth, one crab, other crustacean material, even some articulated fish material.  There were some big sites in Bexar County 10 years ago that are now built over, sad to say.  But stream bed and construction sites dot the 350 mile outcrop ribbon heading NE from San Antonio, including Austin, east of Waco, the NSR, etc., so maybe you'll bump into an underexploited outcrop.

Back in 2008-9 there was tiny exposure of Pecan Gap just down the road from the museum's fabrication shop on the east side of Austin. It was exposed as they prepared for construction. I pulled a variety of decent fossils from the spot including lots of Baculites frags, a few small ammonites, Exogyras, gastropods and a few shark teeth.  But within the second year it was overgrown and had virtually disappeared.  Best thing I ever found there was a beautiful 4 foot Yellow Bellied Racer. He didn't come home with me...

 

[Norki]

On 10/2/2019 at 3:06 AM, The Amateur Paleontologist said:

Would you guys happen to know about similar exposures in Canada?

The northernmost exposures of the Niobrara formation occur in central Manitoba and Saskatchewan, though by the time it reaches that far north it's more of a chalky shale than a true chalk. More information can be found here.

 

I have a thread about some basal hesperornithine fossils that I found in the Pasquia Hills region of SK, from a formation which technically underlies the Niobrara*, but is essentially similar (though I see that you've already checked out the thread ). I also have a fair bit of experience with the Campanian Bearpaw shale which occurs further south in the province, so if you happen to have any questions about that I'd be happy to share what I know.

 

*Changed this to be more accurate, I mistakenly had it noted as equivalent with the Niobrara before.

[Mark Kmiecik]

On 10/1/2019 at 12:17 PM, JarrodB said:

When it's larger than some countries lol. 

It's actually larger than MOST countries. There's only 30-some that are larger. Really.

[The Amateur Paleontologist]

@Heteromorph @Uncle Siphuncle @erose @Norki Thanks for the extra information guys

[flyingpenut]

On 10/1/2019 at 12:17 PM, JarrodB said:

When it's larger than some countries lol. 

Texas is actually larger than most countries. In fact it would be the 39th largest country in the world if it chose to be one. 

[flyingpenut]

On 10/12/2019 at 2:30 PM, Mark Kmiecik said:

It's actually larger than MOST countries. There's only 30-some that are larger. Really.

Sorry, I just saw your response. Your trivia knowledge is quicker than mine.