Backyard Trip

[Missourian]

A preliminary strat chart for the latest recon:

 

[Missourian]

As promised in the previous post ( http://www.thefossil...post__p__302034 ), I continued north up the big creek. At a point about a quarter mile upstream from the burrow-cast-bed exposure, the creek forks into two equal branches. The west fork was first on the agenda. After only a short hike through the thicket, I reached some bedrock:

 

 

There are two limestone beds with several inches of yellowish shale in between. At first, I couldn't tell which unit I was dealing with. Up close, I could make out some crinoidal debris in the fairly thick bed, which I tentatively identified as the upper Cement City:

 

 

There are also some cobbles and boulders containing modestly sized brachiopods and other fossils, as well as some erosional furrows that form a sort-of 'mini-karst':

 

 

These are similar to beds within the Cement City that I've seen elsewhere. As they are lying loose, they probably had slid down from the slope above.

 

Another chunk of the 'karst' with some nice brachiopods:

 

 

I didn't find any more outcrops as I followed the creek nearly to the freeway and an adjacent business. The flat and open terrain here was not conducive to exposures of bedrock.

[Missourian]

I returned to the fork and continued up the east branch. For a ways, the creek banks and floor were all mud. Much of this is probably loess and channel fill. After much bush-wacking and mud-sliding, I finally came across this:

 

 

Hmmm.... It looks like Paola Limestone with some Chanute Shale underneath. The slope may be all shale, but I couldn't tell with all the leaf litter. It wasn't possible to take a closer look, so I continued on. It couldn't have been much more that a hundred feet until I saw this:

 

 

Well, this looks like the Paola as well, but this time it's down at the water level. Confirming this as Paola is the small limestone above it, which is the crinoidal bed at the base of the Raytown Limestone. Up close, we can see how the beds form a nice little waterfall:

 

 

The beds are dipping upstream (i.e. to the northeast). In between the limestones, large sheets of Muncie Creek black shale can be seen beneath the water.

 

 

The dipping strata aren't as obvious in these images as they are in person. Here is the basic layout of the outcrop and the pools of the creek:

 

 

The angle of these beds struck me as bizarre, but I was recalling the dipping Cement City ledge that I had seen earlier. These are all likely part of the same structure, which could be a syncline or anticline, or dipping strata adjacent to a fault. Structures like this are fascinating in their own right, but they can be frustrating when you're trying to map the stratigraphy of an area with limited exposures.

 

A little further up, I came across more dipping limestone. Unlike at the last outcrop, the dip here is in the downstream direction (roughly southeast):

 

 

Note the bedding plane that has been exposed by stream erosion.

 

The limestone is full of large brachiopods:

 

 

I don't know yet if this is more Raytown or some of the overlying Argentine Limestone. The bedding, lithology and color remind me of the Argentine, but the rock and fossils within the two units are too similar to each other to notice any distinctions. It would help if the exposed sequence was thicker, or if any adjacent shales were present, but that is not the case here.

 

A little further up, I came to the main road and a barbed-wire fence across the creek, so that serves as the northern limit of my recon.

Again, there is something seriously interesting going on with the bedrock structure here. I’m having a hard time figuring out how there can be steep southeast and northeast dips in such a small area. I’ll have to return yet again to sort it out.

And here I include a slightly updated strat chart:

 

 

I’ve preliminarily assigned the last outcrop to the Raytown Limestone.

[jacob]

woah brilliant locations you have there but even better fossils, i like the Cephalopods you've found

[Missourian]

On 2/17/2012 at 5:38 AM, jacob said:

woah brilliant locations you have there but even better fossils, i like the Cephalopods you've found

 

Thanks. The nautiloid spots are exquisite when you hit them right. So far, no luck in my immediate neighborhood. The search continues....

[jimsherri]

Great pics... I wish i could take some like that....

[Wrangellian]

Despite your uncertainties on the Argentine vs Raytown, etc, I am continually amazed by your ability to identify formations based on such small outcrops - though I guess you are using other observations to infer these.

PS I assume when you post a pic of something like that loose chunk w/ brachs on it, you are taking these home?

[Missourian]

On 2/17/2012 at 5:45 PM, Wrangellian said:

Despite your uncertainties on the Argentine vs Raytown, etc, I am continually amazed by your ability to identify formations based on such small outcrops - though I guess you are using other observations to infer these.

PS I assume when you post a pic of something like that loose chunk w/ brachs on it, you are taking these home?

 

Fortunately, there are usually just enough markers to work with. On the other hand, these tilting strata are giving me headaches.

As for the brachiopod chunk, I can't take everything home. I only have room for the prettiest.

[Missourian]

Speaking of tilted strata.... So what's going on with the twisted bedrock?

 

First, a quick refresher on strike and dip:

 

 

Here are some hypothetical structures that fit the dipping in the observed outcrops:

 

 

I'm leaning toward the structure(s) being part of a fault system. Folding in the region is typically very gentle, if not imperceptible. On the other hand, there are a number of instances of significantly tilted strata near fault zones. Also, the change in direction of the dip and strike leads me to think that a fault block had rotated as it slid down.

 

There are many variations that are possible, but the available info is very limited. I'll have to poke around in the woods some more to see if I can flush out more bedrock.

[oldbones]

I've been reading stuff at FF just long enough to have some idea how good this. Bravo Mitch!

[Missourian]

On 2/17/2012 at 5:03 PM, jimsherri said:

Great pics... I wish i could take some like that....

 

1. The main thing is just to take many, many photos. At least a few will be winners.

2. I typically take about three or four photos of a subject, pick out the best one (or two), and discard the rest.

3. Also, the best photos are often those that are unintended.

[Missourian]

Next up on the agenda is a highway interchange that features about eighty feet of strata of the Lansing and Douglas Groups. Because one particular outcrop was behind a throng of small trees, I had to wait for an overcast sky to avoid all the little shadows crisscrossing the rock faces.

 

I'll start with a small exposure near the road:

 

 

This is the Little Kaw Limestone of the South Bend Formation. Many fossils are present, though none were collectable. Included in the mix are brachiopods, fusulinids and crinoid fragments.:

 

 

Below the limestone are some thin beds of calcareous sandstone. These are considered to be part of the Little Kaw:

 

 

These beds are intriguing, as they probably correlate with sandstone several miles to the west that produce some spectacular Asteriacites traces:

 

 

Both starfish and brittle stars appear to be represented here:

 

 

The other two members of the formation are fairly thin and were not exposed here. The next unit down is the Rock Lake Formation. It is a sandy shale.

 

Next, we'll climb down into a nearby creek bed to reach some limestone:

 

 

I spotted this while driving through a few days ago. Since this is about twenty feet below the road surface, I believe it is the top of the Stoner Limestone of the Stanton Formation. Note the slight dip in the beds. Because of this, I'm not entirely sure this isn't actually the Little Kaw.

 

I followed the creek a bit, but found only a few patches of limestone bedrock in the bottom. These are likely the same Stoner beds.

[Missourian]

Moving back up and above the South Bend, we come to the Stranger Formation:

 

 

The thirty-foot slope is the Weston Shale. It is capped by the brownish Tonganoxie Sandstone. The orange stuff near the bottom is an inch-thick bed of clay ironstone. Here is some up close:

 

 

And closer still:

 

 

I had to take one of these home with me. In addition, there is a second, thinner bed or lens of the same clay ironstone a few feet higher.

 

Moving along, we approach the Tonganoxie Sandstone:

 

 

The big gully was a pain to cross, but it nicely exposed the Weston right up to near the base of the sandstone. In another spot, there is some beautifully colored clay just under the contact:

 

 

As the base of the Tonganoxie is an erosional surface, this may be a paleosol. The color is likely due to oxidation as it was exposed to the air.

 

The Tonganoxie itself is a channel fill. Back in the Pennsylvanian, large valleys were cut into the previously deposited strata. Eventually, as sea level rose, sand and conglomerate filled the drainage. At this location, the erosion cut part way into the Weston. In some spots, it reaches well down into the Lansing Group. Large-scale cross-bedding are evidence of river deposition:

 

[Missourian]

The bottom part of the Tonganoxie shows some interbedding of sandstone and conglomerate. The rubbly stuff is conglomerate:

 

 

Most of the clasts appear to be made up of claystone:

 

 

A few appear to be the clay ironstone fragments we've seen earlier in the Weston:

 

 

These may have been derived from that shale.

 

This rock shows a transition from sand to gravel (or is it gravel to sand?):

 

 

The upper part of the ledge shows more of the same. Note the fine cross-bedding in the sand lenses:

 

 

Some thinner beds formed during quiet moments on the ancient river:

 

 

As did these graded laminae:

 

 

Above the ledge, there was about five more feet of sandstone, but it was poorly exposed. The rest of the hill above was covered with vegetation.

[Missourian]

So where are the fossils, you may ask? A few plant fragments were mixed into the conglomerate:

 

 

These are nothing compared to the fossil plants found in the Tonganoxie near Ottawa, Kansas....

 

Neuropteris:

 

 

Annularia:

 

 

Calamites:

 

 

Lycopod bark:

 

 

Rhabdocarpus:

 

 

Dolerotheca:

 

[Nandomas]

From the last serie, Neuropteris and Dolerotheca are my favourites

Edited February 21, 2012 by Nandomas

[Wrangellian]

Nice ones! The starfish traces are nice too, they're almost as good as a body fossil.

Should I assume these are the cream of years' worth of collecting?

[Missourian]

And a strat chart to cap the upper end of the column:

 

[cgodwin37]

see Feldman et al., 1995, Stratigraphic architecture of the Tonganoxie paleiovalley fill (Lower Virgilian) in northeastern Kansas, AAPG Bulletin, v. 79, no. 7, p. 1019-1043

I would attach it if I could figure out how....

Ah AH! there we go.

Feldman et al., 1995_Pennsylvanian_Virgilian_Tonganoxie Paleovalley_NE Kansas_p.pdf

Edited February 21, 2012 by cgodwin37

[Missourian]

On 2/21/2012 at 8:01 AM, cgodwin37 said:

see Feldman et al., 1995, Stratigraphic architecture of the Tonganoxie paleiovalley fill (Lower Virgilian) in northeastern Kansas, AAPG Bulletin, v. 79, no. 7, p. 1019-1043

I would attach it if I could figure out how....

Ah AH! there we go.

 

Thank you so much for that.

[Missourian]

On 2/21/2012 at 5:27 AM, Wrangellian said:

Nice ones! The starfish traces are nice too, they're almost as good as a body fossil.

Should I assume these are the cream of years' worth of collecting?

 

These do show the best detail. I have a few more buried somewhere.

[Missourian]

Changes of the names, ranks, and boundaries of a number of stratigrapic units within the Lansing and Douglas Groups have caused me some confusion. I found an updated chart and will place it here for your convenience (and mine):

 

[cgodwin37]

Stratigraphic and sedimentologic concepts/models continue to evolve, even in historically well-workd areas, which will keep me employed for years to come.

Cheers,

Cory

[cgodwin37]

Changes of the names, ranks, and boundaries of a number of stratigrapic units within the Lansing and Douglas Groups have caused me some confusion. I found an updated chart and will place it here for your convenience (and mine):

Feldman et al., 2005, Impact of longer-term modest climate shifts on architecture of high-frequency sequences (cyclothems), Pennsylvanian of midcontinent U.S.A., J. Sediment. Res., v. 75, no. 3, p. 350-368

Feldman et al., 2005_Pennsylvanian_Cyclothems_High Frequency_Midcontinent_p.pdf

[Missourian]

I returned to the city park described at http://www.thefossilforum.com/index.php/topic/25424-backyard-trip/page__view__findpost__p__285787 to see if I could find more strata downstream. Since the Cement City is well exposed here, I figured some Westerville Limestone shouldn't be too far away.

 

As I worked my way down the creek, I wasn't seeing any bedrock. The few cut banks present are made up of loess or alluvium. These old creek sediments caught my eye:

 

 

Perhaps these could have formed a nice sandstone in the distant future.

 

I did spot these limestone blocks:

 

 

There was no sign of bedrock anywhere. The chaotic jumble may be the weathered remains of a glacial morraine.

 

After a third of a mile or so, I reach the next road crossing the creek. The land beyond is posted, so that ended the exploration in that direction. Before I returned, I checked out a ravine that ran up the hill to the south. This proved to be little more than a dumping ground:

 

 

Wow. This junk included a discarded concrete culvert, carpet padding, some metallic stuff, some other stuff, and a lawnmower. I'm sure a kitchen sink was thrown in there somewhere. Also included in the drainage was some limestone bedrock:

 

 

The level, style of bedding and some pinkish chert nodules confirmed it as Westerville:

 

 

This is the top part of the unit. Note the subtle laminae:

 

 

These may be related to the tidal-flat deposits exposed near the golf course to the north, as shown at http://www.thefossilforum.com/index.php/topic/25424-backyard-trip/page__view__findpost__p__302032 .