Tuesday, February 9, 2016

Anastrophia grossa brachiopod from the Bois d'Arc formation of Oklahoma

The genus Anastrophia first becomes widely seen in the Silurian and it extends into the lower Devonian before disappearing from the fossil record. The specimens below are Anastrophia grossa from the Bois d'Arc formation of Oklahoma. The shell is subpentagonal in outline with coarse costae present on both valves. There is a shallow sulcus on the pedicle valve that becomes much more expressed at the anterior margin forming a "u" shape. The corresponding fold is also shallow. Both valves are convex with the brachial valve being more so than the pedicle valve.


Pedicle valve
Anterior
Brachial valve
Posterior
Profile

Specimen #2 - Brachial valve
Anterior
Pedicle valve
Posterior
Profile

I have not found any specimens of Anastrophia from the rocks of the Helderberg group in New York yet, but according to Amsden and Boucot, in their Bulletin 78 from the Oklahoma Geological Survey "Stratigraphy and Paleontology of the Hunton Group in the Arbuckle Mountain Region", 1958, there is a species, A. verenuili, known from there and they compare the Oklahoma species to it:
"A. grossa differs from A. verenuili in several respects, one of the most important differences being in the nature of the brachial umbo. This part of the brachial valve on the New York species is swollen and extends posteriorly well beyond the pedicle beak, whereas in A. grossa the umbo is not so enlarged and extends only slightly, if at all, behind the pedicle beak."
I found the specimens shown on this page in the Bois d'Arc formation (Cravatt Member) near Clarita, OK which is Devonian in age (Lockhovian stage). The Bois d'Arc overlies the Haragan formation but both are the same age (Devonian, Lockhovian stage). They are both roughly correlative to the Helderberg fauna of New York and thus are contemporaneous with the Coyemans, Kalkberg and New Scotland formations.

Compare these specimens to some from the Silurian rocks of the Waldron Formation of Tennessee, and the Wenlock formation of England.

References: 
"Stratigraphy and Paleontology of the Hunton Group in the Arbuckle Mountain Region, Part V - Bois d'Arc Articulate Brachiopods " Amsden, 1958, Oklahoma Geological Survey Bulletin 82

Saturday, February 6, 2016

The Bois d'Arc formation of Oklahoma

      While the majority of my vacation last fall was to Utah and Wyoming, I did a quick couple of days in Texas and Oklahoma. Texas was kind of a bonus for the visit as my primary goal was to collect in the prolifically fossiliferous exposures of lower Devonian aged rocks found around Clarita, Oklahoma. There are two main formations that are extremely productive, the Haragan formation and the Bois d'Arc formation. They are sequential formations, with the latter overlying the former conformably. The faunas of both formations are very similar with only minor differences usually seen as rare species unique to each formation. Both formations roughly correspond to the New Scotland and Kalkberg formations of New York and the trilobite fauna has affinities with that of similar aged rocks in Morocco.

      On this trip I was able to arrange a visit to a large exposure of the Bois d'Arc formation on land owned and operated by Leon Theisen. I met him and his wife at the Clarita post office and they led me to their property for the fossil hunt. They are nice people to spend a day in the field with and were helpful and generous during my visit. Here are some pictures of the nearly mile long exposure I was exploring.




      Leon owns and maintains the land and the rock exposure and also hunts for trilobite fossils which he then prepares and sells. As with any fee quarry, Leon has the right to keep any rare specimens that are found but he won't leave you with nothing. He often will make a trade with you so that you get maybe a lesser specimen or a host of more common species. I was not fortunate enough to find anything truly rare during my trip but Leon and his wife were very generous and gave me several fossils of somewhat uncommon or rare animals.

       The weather was good for late August in Oklahoma, temps in the upper 70's to low 80's (24 to 30 degrees Celsius), light cloud cover and lower humidity. After a short primer on what to look for Leon turned me loose on the exposure. Finds were plentiful and came fast as the ground was littered with fossils of brachiopods, trilobites and coral. Within the first hour I'd found three complete Paciphacops trilobite fossils loose in the road gravel and a partial Cordania trilobite along with pygidiums of the larger trilobite Huntonia.

An initial collection pile


      A little research informed a little more about the exposure I was collecting at. It was most likely the Cravatt member of the Bois d'Arc formation which is a marly limestone that weathers easily. Amsden and other workers feel that the rocks represent a shallow water, off shore community that was below wave base. There are no real reef building organisms present, for example algae, stromatoporoids or sponges while the corals and bryozoans that are present are generally smaller, solitary species or encrusters. The fact that there are no concentrated shell beds, or only very thin horizons, nor are there shells present that show wear, is indicative of a calm water environment that didn't have many storms rolling through. This is likely also the reason that many trilobite fossils usually are intact and represent species with many delicate spiny features. Were this a more turbulent environment those parts of the shells would be broken and scattered quickly.

    There was some wildlife that I saw while collecting, but luckily none of the snakes, wild boars or tarantulas that I'd heard about.

A metalmark butterfly drinking up the salts I was sweating out.

A small lizard that was staying cool under a rock.

      I spent most of the day at this site collecting anything I could find that piqued my interest. Brachiopod were the most abundant and diverse but I snagged a number or trilobites as well. Perhaps the best was this plate with three enrolled Paciphacops logani.


     After eight hours climbing over rocks and bending to inspect potential fossils my feet, ankles, back and neck ached. Leon was quite gracious and said I could hunt for longer if I liked but I was about exhausted.  I was happy with what I had found but would have loved to take more home with me. As it was I had to limit or trim down any larger pieces of rock since I was getting on a plane the next afternoon. The weight was going to be too much for my suitcases so I opted instead to mail my finds home via USPS flat rate boxes. This worked well although the boxes were quite beat up by the time they arrived at my house.

     Over the next few weeks I'll be posting pictures and descriptions of the fossils I found during my visit to the Bois d-Arc formation in Clarita, OK.  I'm very interested in comparing the fossils I found there to those I've found in New York in the Kalkberg formation.


References: 
"Stratigraphy and Paleontology of the Hunton Group in the Arbuckle Mountain Region, Part V - Bois d'Arc Articulate Brachiopods " Amsden, 1958, Oklahoma Geological Survey Bulletin 82

Wednesday, February 3, 2016

Spiriferellina ? or Punctospirifer? brachiopod from the Chainman formation of Utah

Here is another mystery brachiopod from the Chainman formation of Utah. It is a triangular shaped shell which is longer than wide. Both valves have coarse folds that extend from the hinge line to the anterior margins with a simple fold and sulcus. The hinge line is flat and runs the length of the anterior margin. A small triangular shaped delthyrium is present on the anterior of the pedicle valve but it is only 1/2 the length of the hinge line. My initial speculation as to the identity of this shell was that it is a Punctospirifer sp. But while reading through some publications concerning Mississippian faunas in Western US formations, I came across a similar looking shell called Spiriferellina sp. I want to lean towards the latter name because it would be more appropriate for the region I found it in.  Still, without a complete shell or multiple examples I probably can not truly identify this specimen.

Brachial valve
Anterior
Pedicle valve
Posterior
Profile

This specimen came from the Chainman formation at Conger Springs (west of Delta), Utah and is Carboniferous (Mississippian epoch, Visean stage of the ICS or Mississippian period, Chesterian stage in the US) in age.

Sunday, January 31, 2016

Reticulariina sp. ? brachiopod from the Chainman formation of Utah

I believe this next fossil is a Reticulariina sp. brachiopod but am not sure of the species. It comes from the Chainman formation of Utah which is lower Carboniferous in age (Mississippian epoch, Visean stage of the ICS or Mississippian period, Chesterian stage in the US). The shell is small, with a very convex pedicle valve and a flat to slightly convex brachial valve. It sort of resembles a Cyrtia sp. type brachiopod that occurred in the Devonian. Each valve has very coarse plications with 2-3 on each side of the median. There is a sulcus and fold structure present on the valves but it is only noticeable at the anterior margins. It is hard to see but it appears there are some sort of concentric growth lines decorating the shell surface as well. The posterior of the pedicle valve has a large triangular interarea under a beak that recurves back.

Brachial valve
Anterior
Pedicle valve
Posterior
Profile


This specimen came from the Chainman formation at Conger Springs (west of Delta), Utah and is Carboniferous (Mississippian epoch, Visean stage of the ICS or Mississippian period, Chesterian stage in the US) in age.

Thursday, January 28, 2016

Anthracospirifer sp. brachiopod from the Chainman formation of Utah

I believe this next brachiopod fossil is Anthracospirifer sp.. It comes from the Chainman formation at Conger Springs in Utah. The shell is missing part of a "wing" but enough is left to help identify it. The pedicle and brachial valves are equally convex, rectangular shaped and have coarse plications. A sulcus on the pedicle valve corresponds with a single fold on the brachial valve. The pedicle valve has a wide interarea with a recurved beak.

Brachial valve
Anterior
Pedicle valve
Posterior
Profile


There are a number of known species of Anthracospirifer but little literature on what specific forms occur in the Chainman formation. One resource, "Mississippian Stratigraphy of the Diamond Peak Area, Eureka County, Nevada", Brew, David, 1971, Indicates that A. occiduus, A. pellaensis, A. increbescens and A. bifurcatus are found in equivalent strata in Nevada but I can find no clear illustrations of those species or those I find do not match what I have here..

The reference "Brachiopoda of the Amsden Formation (Mississippian and Pennsylvanian) of Wyoming.", MacKenzie Gordon, Jr., 1975 lists multiple species of Anthracospirifer, including A. occiduus but none seem to match my specimen.

This specimen came from the Chainman formation at Conger Springs (west of Delta), Utah and is Carboniferous (Mississippian epoch, Visean stage of the ICS or Mississippian period, Chesterian stage in the US) in age.