Posts Tagged ‘bryozoa’

Ordovician Trepostomate

August 30, 2010

While visiting a friend’s(Herb) house, I noticed a stone that he had placed at the down spout of his gutter. Well, actually his father had placed it there many years ago in an attempt to inhibit erosion by allowing the energy from the falling water to dissipate at the surface of the stone.

The stone was placed in its location in the 50s or 60s, and the falling water, over the years, had exposed multiple “tips” of some kind of stony bryozoan. The bryozoan had been preserved as silica replacement in a bed of a muddy carbonate.

Herb knew of my enthusiasm for inverts, and when he noticed my pre-occupation with the “dissipation stone”, he ask if I wanted it!

Upon getting the rock home, I treated it with multiple baths of HCl to reveal the colony within… and a splendid colony, it was.

Trepostomate bryozoans can be particularly hard to ID without a thin section and intimate knowledge of the subject. And, I don’t have either, but the results are stunning.

It is probably some kind of calloporid.

Sorry, I don’t have a before pic and the finish is out of focus, but you get the ideal.

Since the rock was retrieved from the Kentucky River Valley near Frankfort, it is probably from the High Bridge Group; more than likely the Oregon Fm or Tyrone Fm.

EDIT:I am experiencing some kind of scripting error, so this is an off-site link.

Photobucket

EDIT: The scale is in inches(2.54cm/inch). Its a whopper!

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…

More Seismites, and some fossils, too

April 13, 2010

North of Frankfort Ky, some outstanding outcrops of Ordovician rocks are exposed in road cuts along U.S. 27. The outcrops represent an accumulative sequence of sedimentation spanning several millions of years, and the fauna represented in the rocks are typical of Mid.-Late Ordovician shallow tropical seas-brachiopods, partial trilobites, bivalves, gastropods,… ect. All of the usual stuff.

I want to show you a few more photos of some seismites, but first, let me regress. I was in the area to work an outcrop that has been producing large numbers of crinoids, and other interesting oddities(like this and this). But, that morning I wasn’t having much luck finding anything. Though, as I was packing up to leave, I noticed some pinnate structure in a small stone.

Normally, I would pass on something so insignificant, but as this was a second species of crinoid at the outcrop, I picked it up and threw it in the backpack to further document the fauna at the site. When I started working this outcrop, I found a couple of pinnate arms from some kind of crinoid. Until this trip, I hadn’t seen any other crinoids other than the Reteocrinus sp. that are found in abundance in a small talus pile at the base of a small outcrop.

This is the insignificant pinnate structure after a little prep! I haven’t identified the critter yet, but I have an ideal.

A few other photos from the outcrop.

A big ol’ ambonychiid bivalve.

A hypostome from the trilobite Isotelus gigas. The critter that molted this would have been a monster… probably about 25cm!

Rynchonellids litter the ground at this outcrop.

A nice Hebertella frankfortensis.
anterior view

posterior of above

Strophomenids are nearly as common(Rafinesquina sp. in the lower center left).

A trepostomate bryozoan exposing the “tubes” of the zooecia.

A change in lithology from the Millersburg to the Tanglewood members of the Lexington Lm.

Cross bedding in the Tanglewood (a few centimeters from the contact).

On to the Owenton Rd.

A photo of the outcrop along the Owenton Rd. after turning from the bypass. I pulled this photo from Graham Young’s wonderful blog-Ancient Shore. He was in the region for the North American Paleontological Convention, last summer.

As the day was getting hot and humid, I didn’t spend much time at the outcrop looking for fauna, but I did find a few crinoid holdfasts(apparently, I have deleted them from my hard drive. I will re-photograph, and put them up in the future). But, I did save photos of the thick sequence of seismites.

close up of above