Show Your Strata

[Caleb]

Here is a picture of the contact between the Ordovician age Decorah Formation and Galena Formation in Southwest Wisconsin. The Galena is dolomitic in SW Wisconsin so the preservation of small fossils is not very good. The Decorah fm however has great preservation and a very diverse fauna.

[Missourian]

On 4/25/2012 at 7:44 AM, Caleb said:

Here is a picture of the contact between the Ordovician age Decorah Formation and Galena Formation in Southwest Wisconsin. The Galena is dolomitic in SW Wisconsin so the preservation of small fossils is not very good. The Decorah fm however has great preservation and a very diverse fauna.

 

I'm amazed how the Galena became dolomitized, while the Decorah was left alone.

[Auspex]

I'm amazed how the Galena became dolomitized, while the Decorah was left alone.

I'd like to understand what "dolomitization" is, in as close to plain English as possible...

[Missourian]

On 4/25/2012 at 1:33 PM, Auspex said:

I'd like to understand what "dolomitization" is, in as close to plain English as possible...

 

I'm not sure what it is myself. I'll have to dust off that textbook at some point....

 

I do know I hate dolomitization because it destroys fossils.

[piranha]

:startle: Topics like Dolomitization make me dizzy... almost as bad as Dynamic Palaeoredox :phew:

I'm happy counting axial rings and tergites

[Caleb]

I'd like to understand what "dolomitization" is, in as close to plain English as possible...

Hmm, as plain as possible... From wikipedia: "Dolomitization is a process by which dolomite is formed when magnesium ions replace calcium ions in calcite."

When this happens the shell material is destroyed leaving only internal molds of fossils. Often only internal molds of larger fossils, such as gastropods and cephalopods are preserved, and usually poorly. Rarely are fossils such as trilobites preserved. One exception would be the Silurian age dolomites in eastern Wisconsin and northern Illinois where the Calymene trilobites are common.

Edited April 25, 2012 by Caleb

[Auspex]

That works; thanks!

Now, armed with this, to explore the question of "why one formation, and not the other?".

[Missourian]

Hey, one of my favorite strata, the Cement City Limestone, was shown on national TV (arrowed, on left):

 

 

There was also mention of an all-star game or something.

 

A close-up of the beds, courtesy of Google Street View:

 

[Missourian]

Since I didn't find anything worth writing home about, I'll place this here....

 

While poking through Google Maps, I spotted an amazingly large road cut in Leavenworth County, Kansas. Even with the low resolution Street View images (which looked like someone had smeared Vaseline on the lens of the camera used), I could tell that a large portion of the Lawrence Formation and the lower Oread Formation, were exposed. Up to this point, I'd never examined any of these strata. The Oread interests me, but the Lawrence has been known to produce some nice plant fossils. Eventually, I made my way out there.

 

The whole cut must have exposed 50-60 feet of strata:

 

 

I started at the bottom and worked my way up.

 

Near the bottom, there is a thin, ferruginous limestone about 2 or 3 inches thick:

 

 

I think this is the Amazonia Limestone Member of the Lawrence, but I'm not sure. There are a few fossils:

 

 

I spotted the bryozoan Tabulipora (in the image), crinoid fragments, the brachiopod Punctospirifer, and the pelecypod Aviculopecten.

 

Above the thin limestone are some thin beds of sandstone. Trace fossils are present:

 

 

I climbed over shale and two zones of thin-bedded sandstone to reach the first bench cut into the shale:

 

 

Even though the cut was fresh, gullies were already forming in the shale.

 

After climbing another thick section of shale and sandstone, I reached the second bench:

 

 

The yellowish ledge is the Toronto Limestone. It contains crinoid fragments, fusulinids, and brachiopods. Here are some fusulinids:

 

 

In the upper part, some root molds are present in the rock:

 

[Missourian]

Above the Toronto is the Snyderville Shale, the Leavenworth Limestone, and the Heebner Shale, which is the black, blocky stuff at the very top:

 

Since the Snyderville seemed to be barren, I made my way up to the next bench:

 

 

The very top of the bedrock sequence is capped by some Plattsmouth Limestone. This limestone is normally 15-30 feet thick, but it is mostly missing here. Instead, there is some Kansan glacial drift overlain with loess:

 

 

The upper part of the drift is oxidized. In places, erratics and outwash deposits can be seen:

 

 

I had limited time at this cut. I think I'll have to return to see if I missed anything....

[Missourian]

Well, these aren't quite 'my' strata, but they can be seen in my home state of Missouri.....

 

For a family memorial service, we drove from Kansas City to a spot near Belgrade in southeast Missouri. In many spots along US 50 and US 63 from Sedalia to Rolla via Jefferson City, there are a number of large exposures of limestone and dolomite with several spectacular filled sinkholes. I wanted to stop, but we were pressed for time. Upon our return, I did stop at a couple cuts on US 63 near the Gasconade River.

 

The book 'Roadside Geology of Missouri' mentioned Pennsylvanian strata near the entrance of the parking area of a scenic overlook. I didn't see any rocks, but I did get some good photos of the vista:

 

 

As we continued on our way, we encountered several impressive road cuts. We stopped at the first one:

 

 

I examined the rocks up close, but I didn't find any fossils. Here is how they appeared near road level:

 

 

About a half mile down the road, a larger cut enticed me:

 

 

This one has one of the better examples of a filled sinkhole:

 

 

The angled surface on the left may be one of the ring faults formed around the sink. When I walked to the left, the faults became quite apparent:

 

 

The other side of the road also displays a sink-fill:

 

 

This may be part of the sink across the road, or it could be different altogether.

 

This Virginia creeper was displaying its seasonal finest:

 

 

The beds in these two cuts are all dolomite belonging to the lower Ordovician Jefferson City Formation. As is the case today, there was extensive karst development on the Ozark dome at various periods in the Paleozoic. A number of sinks are topped with undeformed Devonian and Pennsylvanian beds.

 

In the vicinity of the cemetery near Belgrade, Cambrian and Precambrian rocks are present. No outcrops were apparent, but I did find chunks of Precambrian rhyolite:

 

[Auspex]

A filled sink hole cross section, with ring faults; thanks for posting and interpreting these pics!

[Missourian]

The Westin Crown Center is a hotel in downtown Kansas City. For some reason, they incorporated the local bedrock into the design.

 

Outside the main lobby, the Cement City (bottom) and Iola Limestones are worked into the landscaping:

 

 

I was pleased to see how the asphalt 'flows' around the natural joint breaks in the limestone. They very well could have blasted the rock away in a straight line. The only fossils I saw were a couple large crinoid stems in the Cement City.

 

Inside, they have planted a large tropical garden around the beds:

 

 

The catwalks among the plants is always closed. I've always wanted to check out that path.

 

The centerpiece is a waterfall over the Cement City:

 

 

The bottom 1/8 or so of the rock face is made up of limestone blocks from somewhere else, but they did a good job:

 

 

Historically, this site was known as Signboard Hill:

 

I wonder if they left the bedrock exposed as a sort of tribute.

[Missourian]

During a road trip from Kansas City to Branson, Missouri, I spotted some interesting layering near Osceola:

 

 

This is the Mississippian-Pennsylvanian boundary. At this spot, the Pennsylvanian shale and sandstone has collapsed into a sinkhole in the Mississippian limestone, or perhaps were deposited within an existing pit.

 

These clastic beds are typical of the mid-Pennsylvanian Cherokee Group:

 

 

The abutting limestone is the Burlington-Keokuk, which is essentially a mass of crinoid debris:

 

 

The rubble zone between the two units is a chaotic jumble.

[Bullsnake]

OK, I hunted near Osceola, but thought I was well into the Mississippian! Oy vey!!!

I'm pretty sure I was, but you always have me second guessing.

[Missourian]

On 11/19/2012 at 5:14 PM, Bullsnake said:

OK, I hunted near Osceola, but thought I was well into the Mississippian! Oy vey!!!

I'm pretty sure I was, but you always have me second guessing.

 

You figured it correctly. If you hunted in thick limesetone, it almost certainly is Mississippian. There may even be some Ordovician exposed in low spots nearby. The Pennsylvanian of the area is almost exclusively shale, sandstone and coal. There are limestones too (eg. Seville, Tiawah), but they are few in number and are only a foot or so in thickness.

 

Do you have any posts with Osceola finds?

[redleaf101]

Typical Carboniferous strata in the Maritime provinces of Canada. With luck, you'll find a tree through the different stratum. Typical alternating sandstone, mudstone, coal seems, dark grey siltstone, some conglomerate, and black shelly limestone.

[Missourian]

On 11/19/2012 at 6:00 PM, redleaf101 said:

Typical Carboniferous strata in the Maritime provinces of Canada. With luck, you'll find a tree through the different stratum. Typical alternating sandstone, mudstone, coal seems, dark grey siltstone, some conglomerate, and black shelly limestone.

 

Good stuff.

[Bullsnake]

You figured it correctly. If you hunted in thick limesetone, it almost certainly is Mississippian. There may even be some Ordovician exposed in low spots nearby. The Pennsylvanian of the area is almost exclusively shale, sandstone and coal. There are limestones too (eg. Seville, Tiawah), but they are few in number and are only a foot or so in thickness.

Do you have any posts with Osceola finds?

Yes sir!

http://www.thefossilforum.com/index.php/topic/30316-a-day-trip-back-in-time/page__hl__%2Bday+%2Btrip+%2Bback+%2Bin+%2Btime

[Missourian]

Branson, Missouri is known for country music, Silver Dollar City, go carts, 'ducks', and excellent and abundant exposures of Paleozoic carbonates. The 'hills 'n hollers' of the area are made up of the 350-foot Ordovician Cotter Dolomite capped with various, more-or-less cherty Mississippian limestones.

 

We were there for two full days and three nights, but I didn't have many opportunities to stop and hunt. I did check out a couple road cuts on the way back.

 

In Branson, when they decide they want an interchange at a certain spot, they don't mess around:

 

 

When I stepped back a bit, I could see the immensity of the road cut:

 

 

I have no idea if this is upper or lower Cotter. These structures in the rock may provide a clue:

 

 

They look like stromatolites, but one publication interpreted similar features in the Cotter as tidal channels.

 

Several miles up US 65, I reached what is said to be the highest road cut in Missouri:

 

 

I backed off quite a distance, but I couldn't quite capture the 170 feet of rock face. The three-tiered wall in the foreground is all Cotter. Just visible on the top are a few 'towers' of Mississippian Reeds Spring Formation.

 

The Cotter does have fossils, but they seem to be pretty sparse. Years ago, I found some low-spired gastropods in some rubble next to a Branson motel parking lot. I don't know what I did with them. This time, I found some poorly preserved gastropods at the high road cut:

 

[smokeriderdon]

Hmmmmm, wondering who Paleoc is as I know that mine in Florida and the individuals in the pic. I was on the next hill over...

And he pretty much posted the stuff I was going to. Glad I read the whole post first. LOL

[Missourian]

Tryst Falls is the centerpiece of a small park near Excelsior Springs, Missouri:

 

 

The Pennsylvanian Bethany Falls Limestone provides the foundation for the waterfall.

 

When we visited earlier this month, the falls were completely dry. The drought had taken its toll:

 

 

The full twenty feet of the limestone is exposed here:

 

 

The hallmark of the Bethany is the ridiculously large chunks that break away and slide downslope:

 

[Missourian]

The most significant fossils of the unit are the Eowaeringella ultimata fusulinids that can be found in the shaly limestone in the middle part (near grass level):

 

 

Years ago, I collected several loose and in matrix:

 

 

 

This species is found only in the Bethany, making it useful for stratigraphic correlation throughout the Midcontinent, especially in the subsurface.

 

Other fossils include the usual assortment of brachiopods, crinoid fragments, etc.

 

The upper half of the limestone is barren of body fossils, but trace fossils appear to be abundant:

 

 

 

Apparently, the waterfall ledge was used for a mill at one point:

 

 

On the other side of the pool, an abandoned quarry serves as a picnic area:

 

[Wrangellian]

Here is a little Upper Pennsylvanian age roadcut I visited on a field trip a few weeks ago (Mt. Mark Fm, Lake Cowichan, Vancouver Isl.) Consists of alternating beds of limestone (dolomite?) and chert. Not much in the way of fossils, the only things I picked up were a couple pieces with cavities that used to be crinoid stems, bryos, etc. I didn't have a camera with me so I had to go to Google for these..

Edited November 23, 2012 by Wrangellian

[redleaf101]

Very nice Wrangellian =P