Archive for the ‘Paleoecology’ Category

An Uncommon Lichid

November 8, 2010

Upon returning to Lexington, one of the first outcrops that I looked forward to collecting was a relatively small outcrop of the Millersburg member of the Lexington Limestone. I worked the outcrop for 8 years back in the 80s, and it produced some stunning fossils.

The Millersburg is a nodular unit of shales and limestones that was deposited on a shallow carbonate bank. The depositional environment was one of relatively high energy as evidenced by the broken and abraded fossils found within the member. For that reason, it is often overlooked by paleo geeks

But, I have found some spectacularly preserved inverts from the member. I pulled a well preserved example of coprophagious(poop eating) symbiosis among the gastropod Cyclonema varicosum and a crinoid from the member 25 years ago, but even better, I found an undescribed lichid trilobite from the same locality!

And, that is what bring me to this post.

That wonderful outcrop, with all of its rare fossils, is no more.

Yep, they paved paradise and put up a parking lot…

So, I moved on to an outcrop farther down the road. I found my first complete trilobite there! It too was gone- The outcrop, not the fossil( I thought that I had written a blog entry about evil civil engineers, but I guess that I didn’t; maybe in the future?)

I then moved on to the next outcrop that wasn’t destroyed, and it was a good one. Other than most of the Pychnocrinus that I have displayed on the blog, I also found a partial pygidium from a lichid trilobite.

Usually, I would pass on something as insignificant as a partial pygidium, but it was from a lichid. Too remember, I pulled an undescribed lichid up the road a bit.

The undescribed trilobite consists of 11 cephalons, two pygidia(is that the plural?), and one hypostome.

Anyway, here it is. It doesn’t look like much, but it sure got my heart racing.


The box is about 1cm

Ouch!

August 20, 2010

Year ago while working an outcrop that has produced some stunning asasphids, I found this little Isotelus gigas. It appears that the little guy had a bite taken out of his cephalon, enrolled and died. I found it in a bed of the Clays Ferry Fm(early Late Ordovician) in Anderson Co. Kentucky. The bed is comprised of, almost entirely, I. gigas molts and orthocerid cephalopods.

EDIT: the bar at the bottom is 1 inch(2.54cm)

Trilobite Molts-Up Is Down, And Down Is Up

July 1, 2010

A while back, Chris over at Ediacaran put up a post in his “Paleoporn” series describing the environment and sedimentology of two sites, in the same formation, where the same Cambrian trilobite is found. His post is a description of the orientation of the molts in the two different environments. In the comments, we discussed the curious habit of finding inverted cephalons, ie, ventral up cephalons while the rest of the critter is found in its normal position(dorsal up).

In a thin bed of the Clays Ferry Formation in Anderson Co. Kentucky, I find numerous partial molts from the trilobite Isotelus gigas. Some of the bedding planes are almost entirely composed thoracic segments, cephalons and cranidiums, and pygidiums from this large asasphid. Occasionally, one comes across the curious preservation described above.

During ecdysis, the cephalic sutures of the trilobites rupture allowing the critter to escape from the front of its carapace. Sometimes during the egress, the critter will push the cephalon upside down. Hence, what we have here.

When I found this one, it didn’t appear that much was there.

But, I brought home anyway. While hitting it with a scribe, I noticed the ventral, but I thought that it was trash and nearly blew through it… as more became apparent, I slowed up a bit(word to the wise).

I have found several more from the same locality, but those are all that I have photographed. However, here is a nice juvenile that appears to have had a bite taken out it.

More on that later.

Sponge Encrusting Worm Tube Encrusting Bryzoa

June 10, 2010

At a crinoid garden that I have been working for a couple of years, I found this curious example of an epibiont on an epibiont.

First, a trepostomate bryozoan found its home, then some cornulites worm tubes found the bryozoan inviting.

Finally, the sponge.

When it was alive, it had to have been pretty cool looking with the worms sticking out of the sponge.

Width of photo about 3cm

Mag x10

You know the scale

Since, it was found at one of my crinoid “gardens”, here is a double from the same locality. I have pulled about 50 crinoids from this site(too lazy to check my notebook), and the Archaeocrinus sp. out number Pychnocrinus sp. by a substantial majority(again, too lazy to check my notebook), So these are probably Archaeocrinus sp.

Many of the crinoids at this site appear to be weathered, but they are from fresh exposures??? They are found in a thin lens of mudstone within a calcarenite/calcirudite. They are early Late Ordovician. Some researchers postulate that the abrupt changes in facies in the Central Kentucky region is due to weird structural crap associated with tensional forces at the close of the Taconic Orogeny to the east.

So, that leaves me wondering… were these critters left high and dry in their shallow lagoon/inlet by a regression, and then covered by a transgression??? It seems plausible. They could have laid there for months, or longer, since there were no land critters to pick at the carapaces.

Do you have another scenario??? Let me know.

Anyway, here is the double.

Width of photo about 10cm

Here is one that I have shown before. It is from a fresh exposure, so it can’t be weathered.
Width of photo about 6cm

Structural Inversion and the Origin of a Late Ordovician Carbonate Buildup:

The Ordovician Earth System

Correlations Across A Facies Mosaic…

Sponges

June 3, 2010

Dave, over at Views Of The Mahantango, put a post up yesterday describing some sponges(stromatoporoids) that he had found from Devonian rocks of New York and Kentucky, and some Silurian rocks of Pennsylvania.

This post will add to his description.

Stromatoporoids are peculiar, and poorly understood, sponges(Porifera) that evolved in either the Cambrian or Ordovician. Some experts classify some Cambrian archaeocyathids as stromatoporoids, but that classification is tenuous. They became extinct during either the Devonian or Mississippian… then re-appear in the Mesozoic forming reef building communities, again.

The Paleozoic forms lacked spicules-common to other types of Porifera.

I said that they were peculiar.

As Dave noted in his post, they formed massive reefs in the Devonian. Sometimes, tens of meters thick. Though, in the Ordovician, the reefs are less massive. Also, they were restricted to warm tropical waters near the equator. The Late Ordovician glaciation on Gondwana appears to have substantially reduced the numbers; since they lived in the shallow tropical seas, their habitat was decimated by the regression associated with the ice advances.

Sometime around Devonian/Mississippian time, they became extinct… but then re-appeared in the Jurassic with spicules.

Confused? Well, that makes two of us.

Most of the uncertainty is the result of very little research on stromatoporoids other than their paleoecological relationships. For the most part, their phylogenetics is unknown.

A few photos of some Ordovician stromotoporoids. All are from the Millersburg member of the Lexington Limestone, and found in Fayette Co. Kentucky(though, from two different localities). As always, click on image for bigger version.

All of these, with the exception of one, were left in the field-they are too big to lug around, and take up too much space.

Some that had fallen from the outcrop.

One that I have brought home.

Same as one above showing the concentric layering.

Another peculiar sponge that I find in the local rocks is Solenopora. Like the stromatoporoids, it was also mis-classified for years. Originally, the chaetetids were classified as tabulates.

Recently, Solenopora was re-classifed as a chaetetid, again no spicules. Solenopora aren’t common in the rocks of the Lexington, so when I find them, they find a new home in the cabinets(too, they are smaller).

Again, these were collected from the Millerburg mb of the Lexington Lm in Fayette Co. Ky.

This first I re-sized for some reason??? But you can get an ideal of what it looked like.

Width of photo about 10 cm.

Close up showing an orthogonal view of the pillars(mag x50)

To learn more about these peculiar critters, here are some good links.

Paleos Metazoa: Porifera -follow the links.

Systematics of Porifera– again, follow the links.

Or, you could ask Mr. Google.

Deep Water Stuff

May 17, 2010

The Ordovician of New York has been a fascination of mine since reading of C.D. Walcott’s discoveries, there, many years ago. A couple of years ago, I was granted the opportunity to visit a newly discovered lagerstatten in the Lorraine Group of Upstate New York.

The site was discovered by an amateur paleontologist from the region. In his quest to better understand the geology and paleontology of New York, he found the site that we visited, and several others that have produced stunning soft-tissue preservation of annelids and arthropods.

The Martin Quarry is located in the Whetstone Gulf Formation of the Lorraine Group in New York about 60 or 70 km north of Beecher’s Trilobite Beds. The rocks were deposited in a deep foreland basin that formed as a result of the Taconic Orogeny during the early Late Ordovician. The Late Ordovician was a time of intense tectonic activity on the Laurentian continent. As a result, the rocks of the Lorraine are characterized by sequences of turbidites.

It is within the turbidites that the exceptional preservation of the fossils are found. Bedding planes reveal hash plates with numerous partial trilobites-among other critters, but within the beds, whole critters can be found. And, if one is in the right horizon, the critters soft parts are preserved in pyrite.

Some photos:

After picking up a prep guy(one of the best in the field) at JFK, we got stuck in a traffic jam on the Tappan Zee… at 03:00!

Curiously, crinoids are absent from the locality, but they were somewhere, nearby.

The first thing that I saw when walking up to the outcrop was this lovely cephalon. The site is known for its Triarthrus fauna, and I was expecting it, but… this was the first Triarthrus that I had seen in the field! I was stoked!
photo about 15cm wide

A photo of me chopping away.

A photo of My Good Friend Who Is A Dog chillin in the creek.

A cutie(photo about 10 or 12 cm wide)

photo about 2cm wide

photo about 1.5 cm wide

Some kind of reptile… I might add, this guy shouldered(literally) a couple of tons of shale in an attempt to protect his finds, only to put on the gloves for this critter.

Probably, 75-100 partials on the slab.

Lots of partials and some other things, too. It appears that there is at least one calymenid free cheek, and a Sowerbyella brack. width of photo about 25cm

A nice ventral that is now part of the Peabody Museum collection

The guy that found this quarry developed a revolutionary an innovative technique in the preparation of pyritized soft tissue recovery… his methodology, at first, seems counter-intuitive, and maybe destructive, but his results are telling.

Further reading and references:


Beyond Beecher’s Trilobite Bed: Widespread pyritization of soft tissues in the Late Ordovician Taconic foreland basin

Farrell, et. al. 2009

Pyritization of soft-bodied fossils: Beecher’s Trilobite Bed, Upper Ordovician, New York State
Briggs, et, al. 1991

\Turbidite depositional influences on the diagenesis of Beecher’s Trilobite Bed and the Hunsrück Slate; sites of soft tissue pyritization
Raiswell, et. al. 2008

EDIT: to add photos

In the “Garden”

May 8, 2010

Upon returning to the Bluegrass region of Central Kentucky a couple of years ago, the first outcrop that I planned to visit was the type section for the Millersburg mb. of the Lexington Lm.

Generally, though out the Late Ordovician, most of the Laurentian margins were experiencing transgressive sequences, but here, regressive shoal complexes associated with deep-seated tectonics produced the carbonate clastics common to the area.

The Lexington Lm. is a complex assemblage of limestone and shale facies where the changes can be abrupt-both laterally and vertical. The formation is generally a transgressive sequence that grades upwards into the deeper water limestone and shales. However, in the inner-bluegrass region, the Tanglewood and Millersburg members are an exception to the transgressing sea sequences.

The Tanglewood is a thick sequence of coarse-grained calcarenites with local unconformities and tidal influenced structures; many of the beds are cross stratified(The header for the blog is one of those sequences).

The Millersburg is typical of the complex facie relationships of the region. It inter-tongues with the other members of the Lexington above and below, and in some places, it is absent; it isn’t even consistent within its own framework. Drive a few kilometers down the road, or climb/ descend a few meters in the column, and the fauna/lithology changes. The Millersburg is nodular limestone and shale that was deposited above the wave base.

But, I love it! The Millersburg is one of my favorite members of the Lexington Limestone. It is the unit in which I found my first trilobite, and one of my first crinoids. While, it is more known among local invert geeks for the common fossils found in its beds, there are some beds that produce spectacular finds(if you read this blog, you will notice that most of the stuff contained in it is from the Millersburg).

So, back to the start of the post. Driving out Main Street, I noticed that those nefarious engineers had widened the road. It used to be a nice drive in the country; now it is a four lane highway with a median and shoulders to park your vehicle if it decides to quit working. That sent shudders up my spine! Then, as I approached the type section, my heart fell out. It was gone!

The type section gone? How could it be? Perhaps it was ignorance; maybe the reason was economic? Who knows? But, It was gone!

Unfortunately, the destruction of significant geologic treasures is common. I have to assume that the reason is ignorance… how many engineers could know the significance of what they are destroying when they plan their construction projects?

My favorite outcrop was no more. Oh well! One has to move on, and so, I did. About a kilometer down the road, and a 10 or so meters down in the column, there was a tongue of Millersburg sandwiched between some shallower stuff of the Tanglewood mb.

On one of my first visits to the site, I found a nice Pychnocrinus sp., but I didn’t find the bed that it came from. It was located in the float at the base of the outcrop.

width of photo about 10cm

With this clue, my latter visits to the site were spent in the area where I found that little cutie. At first, I wasn’t having a lot of luck locating the bed in which the crinoid was from, but then I climbed a little up in the column, and perched at the edge of a ledge, I found this large pinnate structure.

width of photo about 12cm

Just above the ledge was a bed of clay that pinched out a couple of meters in both directions. That small bed has produced over 40 crinoids in just the face of the bed.

Curiously, a lot of the crinoids appear to be severely weathered… even when pulled fresh from the rock. The rapid changes in lithology-vertically- is thought to be a result of changes in sea level due to tectonic forces related to the Taconic Orogeny. The bed might represent a paraconformity where a small uplift drained the area resulting in the bed’s exposure.

Pychnocrinus (?)

This is one that I found recently. microscope stage for scale

Calyx encrusted by a bryozoan(I’ve never seen this before)
width of photo about 20 cm

Lots of partials(you know the scale by now)

Some are hard to recognize, at first

I have prepped a lot of the crinoids, and some have turned out, nicely. I’ll put some of those up in the future.

Further reading and references:

Contributions To The Geology of Kentucky: Ordovician System

From the Cincinnati Arch to the Illinois Basin: geological field excursions

LITHOSTRATIGRAPHIC FRAMEWORK OF THE TANGLEWOOD BUILDUP, LEXINGTON LIMESTONE (UPPER ORDOVICIAN) OF THE BLUE GRASS REGION, CENTRAL KENTUCKY

Sequence stratigraphy and long-term paleoceanographic change in the Middle and Upper Ordovician of the eastern United States

Extinction, invasion, and sequence stratigraphy: Patterns of faunal change in the Middle and Upper Ordovician of the eastern United States

Unknown Critter/Flora

May 3, 2010

I have encountered this strange structure a few times in my quest to understanding the Ordovician of Kentucky. It is rarely seen, and I always ignored the thing since it didn’t seem relevant to what I was studying. Though recently, I found a few of these, intimately associated, in what might be a lagoonal environment???*

That grabbed my attention, and I submitted photos of this thing to several well known paleo-researchers. Most had no ideal, but Dr. Young clued me in! Probably, algal balls. He suggested a thin section would be determinate, but I still haven’t cut the thing.

When informed of Dr. Young’s opinion, another researcher concurred, but he hadn’t seen any, this large, from the local biota; one other was skeptical.

So, have you seen anything similar?

mag x20

These were found in a mud bed, of limited lateral extent(a few meters), interbedded within the calcarenites of the Tanglewood mb. of the Lexington Limestone.

*perhaps, that is my familiarity with the barrier islands???

Too, why can't I figure out the code of wordpress?

I’m not a ‘puter geek, but I thought that the site was HTML??? Any suggestions?

Hiding in the Bushes?

April 11, 2010

Kevin Bylund’s last post over at Ammonoidea included a photograph of some very small gastropods(<1mm). It had me wondering… were they proto-gastropods(juveniles), or were the critters adult forms? I'm not much on that new stuff(well, kind of new, they are early Mesozoic).

Similarly sized proto-gastropods are common in some beds of the Lexington Lm(late Middle Ordovician-early Late Ordovician). They are usually found intimately associated with sponges and corals. Apparently, the little critters were seeking protection from larger predators or currents???

Any thoughts? Have you found similar associations?

The tabulate Foerstephyllum sp. on which two species of proto-gastropods were found.

Platycerid and murchisoniid proto-gastropods-mag x30(most of the gastropods from the unit are Cyclonema varicosum and Loxonema sp., though an occasional eotomarid or tergomyid will show up). Close up of above.

A Solenopora sp. sponge with murchisoniid proto-gastropods(see above).

Again, a close up of the above(note the probe for scale).

Worm Tubes Find A Home

April 7, 2010

Cornulites are generally found on sessile critters, but recently, I found a colony of worm tubes attached to partial carapace from the trilobite,  Isotelus gigas. It appears that the epibionts found their home on a molted carapace, rather that on the living critter.

(click on photo to enlarge)

Ordovician

Lexington Limestone

Millersburg Mb

Franklin Co. Ky.