Archive for the 'Uncategorized' Category

Toward an Isopach Map of the Cedar Creek Mastodon Bog

August 27th, 2014

tooth Wooster’s Climate Change class is starting the semester by  coring a bog adjacent to a recent Mastodon find in Morrow County, Ohio. The Mastodon work and related excavation is being led by Nigel Brush, University of Ashland.  Above is a photo (courtesy of Nigel Brush) of the original mastodon tooth find.

probe3After a fairly extensive theoretical conceptualization – theory was successfully brought to practice and in some cases the probe was sunk over 20 feet into the soft mud of the bog. The 20+ feet of mud is a record of environmental change over the last ~15,000 years.

probe2The lead probe team – one taking notes, one operating the GPS, one on the blunt end of the probe, and two others reflecting on the experience.

total_station                     The survey team shares a humorous moment while setting up the total station.

probe1

Sharing another humorous moment as an interdisciplinary (Archaeology/Spanish/ Geology) tile probe team – note the Mastodon Excavation Site in the background.

bog_map

The Google earth map above shows the tile probe points taken for the construction of the isopach map. The area of the tight spacing of data points in the northwest is the excavation site. Now for the contouring of the map and the determination of where the team will extract sediment cores.

tall

The auger team sampled down to almost 18 feet and discovered that the stratigraphy is blue glacial lake clays overlain by a marl (with snail shells), which is overlain by organic-rich mud. This sequence and its details will become clearer when the site is cored on 6 September.

washing_upWashing up and wondering about how the Mastodon may have met its fate along the shore of a muddy lake during the Pleistocene.

Wooster’s Fossils of the Week: Remanié fossils in the Lower Cretaceous of south-central England

August 22nd, 2014

Faringdon ammonite smThe last two editions were about a bryozoan and borings from the Faringdon Sponge Gravels (Lower Cretaceous, Upper Aptian) of south-central England. This week we have some Jurassic fossils from the same unit. That sounds a bit daft at first — Jurassic fossils in a Cretaceous unit? — until it becomes obvious that these are older fossils reworked into a younger deposit. In this case underlying Jurassic ammonites have been unearthed and tossed around with sediment in Cretaceous high-energy tidal channels. These older fossils in a younger context are called remanié, meaning they have been “rehandled” in a fancy French way.

The above image is an example of remanié in the Faringdon Sponge Gravels. It is a partial internal mold of a Jurassic ammonite. Drilled into it are several holes attributed to Early Cretaceous bivalves and called by the trace fossil name Gastrochaenolites. The ammonite fossil was eroded out of an outcrop of Jurassic rock and then bored while rolling around in what would become the Faringdon Sponge Gravels.
Ammonite frag 2 072014This is another Jurassic ammonite internal mold. The jagged lines are the sutures of the ammonite (remnants of the septal walls). This mold was phosphatized (partially replaced with phosphate) before it was reworked into the Cretaceous gravels. Many remanié fossils are phosphatized because of long exposure on the seafloor.
Ammonite frag 1 072014Finally, this is a fragment of another Jurassic ammonite internal mold in the Faringdon Sponge Gravels. It has an odd shape because it has disarticulated along the sutures. We are looking at the face of one of the septa, or at least where this septum would have been if it hadn’t dissolved. You can see some tiny borings that were made by Cretaceous polychaete worms.

In one of the cobbles in the Faringdon Sponge Gravels I found an identifiable ammonite. It was Prorasenia bowerbanki, which indicated that the cobble was derived from the Lower Kimmeridge Clay or Upper Oxfordian clays. The above ammonites are likely from the same Jurassic sequence. This means these fossils were roughly 45 million years old when they were reworked into the sponge gravels. Today it would be as if Eocene fossils were eroding out of a cliff and being incorporated within a modern sediment. When you think about it, this is a relatively common occurrence.

References:

Murray-Wallace, C V. and Belperio, A.P. 1994. Identification of remanié fossils using amino acid racemisation. Alcheringa 18: 219-227.

Pitt L.J. and Taylor P.D. 1990. Cretaceous Bryozoa from the Faringdon Sponge Gravel (Aptian) of Oxfordshire. Bulletin of the British Museum (Natural History), Geology Series, 46: 61–152.

Wells, M.R., Allison, P.A., Piggott, M.D., Hampson, G.J., Pain, C.C. and Gorman, G.J. 2010. Tidal modeling of an ancient tide-dominated seaway, part 2: the Aptian Lower Greensand Seaway of Northwest Europe. Journal of Sedimentary Research 80: 411-439.

Wilson, M.A. 1986. Coelobites and spatial refuges in a Lower Cretaceous cobble-dwelling hardground fauna. Palaeontology 29: 691-703.

From the Russian wilderness to the big city!

August 15th, 2014

Guest Blogger: Sarah Frederick (’15)

Arriving in Moscow was a sharp return to reality. Suddenly all of the things that had come to feel normal while we were in Kamchatka – the winding gravel roads and little towns with random meandering livestock that would peek in your windows – were replaced by traffic jams and the overwhelming immensity of the city!

Russia Blog Pics - 09One unique experience in Kamchatka was shopping. Shopping, like everything else in Russia is a very long, arduous process that takes hours longer than it should. Above is shown a typical store in Kamchatka. All of the goods are located behind the counter, so each item had to be individually requested from the shopkeeper. However, in all likelihood the first shop you visited would not have half of the items you required, so you would have to visit two or three additional establishments to find everything you needed. Even so, simple necessities like bread or beer were not always available. Also, take note of the high tech abacus being used!

The items we purchased were also completely foreign to me. While I was initially pretty skeptical, everything was quite tasty if you had an expert cook like Tatiana to prepare it!

Russia Blog Pics - 13Cow-in-a-can anyone? More commonly referred to as Tushonka.

Russia Blog Pics - 15There are a variety of culinary influences present. Lots of Uzbek cuisine, but we also encountered Georgian, Russian, and Ukrainian dishes. A common afternoon meal with borscht, beat soup of Ukranian origin, is pictured above.

While in Moscow we toured the Institute, a towering majestic building, one of seven built around the city, which houses several departments of Moscow State University, a museum, faculty and students.

Russia Blog Pics - 16An apartment in the wing to the right was actually our home for the duration of our visit.

 While in Moscow we of course visited the touristy section of the city.

DSCN2787The Kremlin

Russia Blog Pics - 17Dr. Wiles with our two hosts, Olga and Vladimir in front of St. Basils.

DSCN2794One of the prominent monuments on the Red Square is Lenin’s tomb. He has been on public display since shortly after his death in 1924.

Russia Blog Pics - 03One last picture from Kamchatka. Thanks for following us through our journey! We look forward to reporting on our findings from the lab soon!

Wooster’s Fossils of the Week: Abundant borings in Early Cretaceous cobbles from south-central England

August 15th, 2014

Faringdon cobble in matrix 071714Last week I described a cyclostome bryozoan on the outside of a quartz cobble from the Faringdon Sponge Gravels (Lower Cretaceous, Upper Aptian) of south-central England near the town of Faringdon. This week I’m featuring a variety of heavily-bored calcareous cobbles from the same unit. One is shown above in its matrix of coarse gravel. The holes are bivalve borings known as Gastrochaenolites. As a reminder, these gravels are very fossiliferous and were deposited in deep channels under considerable tidal current influence (see Wells et al., 2010).

Faringdon cobble 1 071714The large and medium-sized flask-shaped borings are all Gastrochaenolites. In the suite of cobbles described in Wilson (1986), there are three ichnospecies of bivalve borings: G. lapidicus, G. cluniformis and G. turbinatus. It is thus likely, although not necessarily, an indication that at least three bivalve species were boring the soft calcareous claystone to make secure homes for their filter-feeding. The thin, worm-like borings are Maeandropolydora, which were probably made by polychaete “worms”.

Faringdon cobble 3 071714Some of the Gastrochaenolites lapidicus borings have remarkably spherical chambers, a testament to the uniform lithological character of the rock.

Faringdon cobble 5 071714Occasionally bivalve shells are found still preserved in their crypts, along with nestling brachiopods. Some shell bits are visible in the borings above.

FaringdonCobble 585 071714Some of the cobbles are so heavily bored that they fall apart quickly on removal from the matrix. On the Cretaceous seafloor this intensity of boring must have reduced many cobbles to bits before burial — a classic example of bioerosion.

Diagram 071714What is very cool about these Faringdon cobbles is that the borings often overlapped inside, creating a network of tunnels and small cavities that hosted dozens of bryozoan, foraminiferan, sponge, annelid worm, and brachiopod species. This is a diagram from Wilson (1986) showing the combination of external encrusters in a high energy, abrasive world, and coelobites (cavity dwellers) in the protected enclosures. A diverse community can be found on each cobble, inside and out. In a future post I will describe some of these coelobite fossils.

References:

Pitt L.J. and Taylor P.D. 1990. Cretaceous Bryozoa from the Faringdon Sponge Gravel (Aptian) of Oxfordshire. Bulletin of the British Museum (Natural History), Geology Series, 46: 61–152.

Wells, M.R., Allison, P.A., Piggott, M.D., Hampson, G.J., Pain, C.C. and Gorman, G.J. 2010. Tidal modeling of an ancient tide-dominated seaway, part 2: the Aptian Lower Greensand Seaway of Northwest Europe. Journal of Sedimentary Research 80: 411-439.

Wilson, M.A. 1986. Coelobites and spatial refuges in a Lower Cretaceous cobble-dwelling hardground fauna. Palaeontology 29: 691-703.

The power of hand-held x-ray fluorescence analysis comes to Wooster

August 13th, 2014

1DSC_4341WOOSTER, OHIO–Dr. Meagen Pollock, our mineralogist-petrologist and instrument scientist extraordinaire, should be writing this post, but she was off campus during this event. It is left to the paleontologist, of all people, to file this report. Despite my technological naïveté and more biological than chemical orientation, I quite enjoyed myself. I certainly learned a lot.

Today we had a training session to learn how to use our new Bruker Tracer III-SD portable X-Ray Fluorescence instrument (pXRF), which is shown in the above image. The resemblance to a hand phaser from Star Trek is no accident. The legend is that the inventor developed the casing directly from a Star Trek toy. The fact that it really does shoot radiation out of the front makes it über cool (and a bit more dangerous than the toy!).

We have this wonderful instrument through the leadership of Dr. Melissa Schultz in the Chemistry Department and our own Meagen Pollock. They wrote a successful proposal to the Pittsburgh Conference Memorial National College Grant program for seed money, and then the Geology and Chemistry departments, along with the Dean’s Office, provided the remaining funds needed for the purchase. This handy instrument will not only be used by the geologists and chemists, but also our archaeologists and art department. This is an excellent example of the kind of collaboration possible at a small school that makes large acquisitions possible. As with all our instruments, this one is intended to further our faculty-student research programs.

I’m not the one to provide a tutorial on how x-ray fluorescence (XRF) analysis works, so you have a link for the details. In short, the instrument fires a beam of x-rays through an oval window about 3-4 mm in width. The x-ray photons strike a target intended for analysis, penetrating into the very atoms with energy high enough so that some are ionized by having electrons ejected from their orbitals. When electrons from lower orbitals are removed, higher orbital electrons “fall” into their places, releasing photons (thus “fluorescence”). These photons are collected by a detector in the instrument. The energy of the photons released by the target is characteristic of the type of elements the atoms represent, thus diagnostic of composition. (Really, visit the linked page!) That we can now hold such analytical power in one hand is a scientific dream come true. This device is a superb complement to our excellent X-Ray Analysis lab in the Geology Department.

2DSC_4344Our two excellent trainers, Mike and Zach, spent the better part of a day taking us through the conceptual background for XRF analysis, safety issues, and then practical use. Despite the ray-gun look to the device, much of our use of it is likely to be in a lab hooked up to a laptop computer, as shown above. This is a very easy arrangement for doing non-invasive analyses of various small objects and liquids. We also received a complex tripod to use for scanning large items, such as paintings or other artworks. The pXRF is placed in an acrylic holder and pointed upwards. For some analyses, especially for light elements, a vacuum pump can be attached.

3DSC_4347Dr. Nick Kardulias, our senior archaeologist, provided the first and it turned out only specimen for analysis today.  This is a piece of obsidian from the western United States. Obsidian is a superb target for XRF analysis because it is a glass with smooth surfaces and a complex composition. There is already a set of settings and filters available for obsidian analysis. Archaeologists (and geologists) can use chemical compositions to “fingerprint” particular obsidian deposits for provenance analysis of isolated fragments. (Provenance is the history of origin and place of an object or material.) That obsidian arrowhead in Illinois, for example, may be made of obsidian gathered in California. Above you see the obsidian being placed on the detector window.

4DSC_4348A metal cap is placed over the specimen to shield us from scattered x-rays. The radiation is not high, but we take all the precautions we can. The instrument is then controlled through the computer interface.

5DSC_4350This is an example spectrum produced by the pXRF instrument and associated software. (It is of the above obsidian sample after four runs for those of you scrutinizing the details.) The peaks represent emitted photons, and thus particular elements. Spectral analysis here is complex, but the software has many built-in routines to ease the process.

6DSC_4352When the pXRF is hand-held and directed at a target, the data is summarized and displayed on this attached PDA screen. This is the kind of analysis I like — point and shoot! You’re looking here at data from an included standard, a piece of stainless steel, hence the high amount of iron, chromium and nickel. This is how I want to use the pXRF: in the field shooting various rocks like in the last image on this 2011 blog post by Meagen. It is nothing short of magic to get an elemental analysis of a stone in front of you in real time.

Thank you again to Melissa and Meagen, as well as our leaders in the administration, for managing the purchase of this superb tool for the community!

Coring Across Kamchatka

August 12th, 2014

Guest Blogger: Sarah Frederick (’15)

After traversing every stretch of road within Kamchatka at least twice, 5 bear sitings, and becoming intimately familiar with Kamchatka mosquitoes (they come in three sizes!), we are on our way to Moscow. All in all we cored over 500 trees! So I am sure that everyone back in the lab can hardly wait for our return…

Russia Blog Pics - 05

Russia Blog Pics - 10Coring larch trees in the mountains of the Eastern Range.

Coring took us to every reach of the Kamchatka Peninsula. We made our way as far north as Ust-Kamchatsky, a port city that was strategically important during the Cold War when the entire peninsula was closed to nonresident Russians and foreigners alike. Then we drove all the way west to the Sea of Okhotsk before returning east to Petropavlovsk, a large port city on the Pacific.

During our travels we have explored a variety of environments. While the most pervasive by far was the taiga, swampy coniferous forests, we also appreciated the beauty of spring in the tundra.

Russia Blog Pics - 18Spring blossoms.

The devastation caused by the frequent volcanic eruptions was also evident. We frequently came across open ash fields and even pyroclastic flow deposits!

Russia Blog Pics - 08The desolate remains of a pyroclastic flow (fast moving current of hot gas and rock) produced by the adjacent volcano.

Besides collecting cores, we also learned a bit about the local culture and history. In Esso, we visited the museum where we learned about the traditional practices of the indigenous peoples and how they survived Kamchatka’s harsh climate.

Russia Blog Pics - 01

The main building of the museum exhibits the beautiful woodwork typical of the region.

Russia Blog Pics - 02

A reproduction of a traditional home of the Koryak people. In order to optimize heat retention, the structure is built partially underground and in the shape of an oven. It even has an escape hatch out of the top for when snow buries the structure.

Esso is also significant as the starting point of the Beringia, Kamchatka’s traditional dog sled race, which in the 1990s held the record for the longest dogsled race, rivaling Alaska’s Iditarod.

Back in Petropavlovsk we visited Kamchatka’s Institute of Volcanology and Seismology, scientists from which have most generously hosted and guided us on our journey. Along with several visiting Japanese geologists, we were given a tour of the museum of Volcanology. Here we learned about Kamchatka’s most active volcanoes and the work of the volcanologists in the region. They were most excited about a recent discovery of diamonds in the ash of the Tolbachik Volcano, which made me re-evaluate the goals of our expedition to that site. Had I known, I would have been far more interested in sifting through the sediment for diamonds than in the trees…

Russia Blog Pics - 14

Finally, for those have been asking about the bears. Here is a cutie that we came across on one of our last days in the field. These Kamchatka brown bears are very large, though not a big threat to humans, particularly in the summer when food is plentiful.

Volcanoes, Mosquitoes, and Bears, Oh My!

August 9th, 2014

Guest Blogger: Sarah Frederick (’15)

After three weeks in Russia it sure feels great to be back on US soil! Since we didn’t have internet access during this expedition, our blog posts come a bit delayed. Here is a bit about our first week in Kamchatka: If, like me, you have never played the board game Risk, you likely have never heard of Kamchatka. So to give you some context of where we are, below is a map of the North Pacific. As you can see, this peninsula, part of the Pacific Ring of Fire, is further east than Siberia and it is not far from Alaska. However, since flights between Alaska and Kamchatka are extremely limited, we were forced to fly the long way around. map

After our nearly 40hr journey, crossing 16 time zones, it was a relief to arrive in Petropavlovsk, Kamchatka.

Untitled

Above is a picture taken on top of an extinct volcano that overlooks the city. From L to R, Tatiana Kuderina (Senior Researcher at Moscow University), Sarah Frederick (’15), Vladimir Matskovsky (Researcher at Moscow University) and our lovely host Tatiana. This picture is an achievement, because as you will notice, it is the only picture in which all of the Russians are smiling!

eruption We were greeted in Kamchatka, the land of many mosquitoes, bears, and volcanoes, by scientists from the Volcanology Institute. And after a day of recovery we headed north into the great wild. While there have been no bear attacks, just three sitings so far, we were lucky enough to witness a small volcanic eruption during one of our expeditions!   Though described in the literature as ‘pristine’ and ‘untouched,’ over the past week we have found much of Kamchatka far from that with the forests along the single main road (unpaved dirt and gravel) having been clear cut. Even so, with a lot of help from our driver, Vasily, and his mighty passenger truck, we managed to locate old growth larch in the north. truck While our quest for trees has required us to spend extensive time in the swamps being devoured by millions of mosquitoes, we also made it to some of the more picturesque parts of Kamchatka as well. The highlight thus far was our trekup the Tolbachik volcanic complex where we were greeted by unseasonably clear weather. Not only could we see the majestic glacier topped volcanoes of the Eastern Range, but to the west, the towering volcanoes of the Median Range were also visible! tobal We are now heading south for our last few days of tree hunting. It is our hope that the tree ring data that we are collecting will help to connect the extensive network of tree ring chronologies developed for the Gulf of Alaska with those from the West Pacific. Helping to develop a better understanding of North Pacific climate.

Stuck in Girdwood

August 9th, 2014

DSC_0067

Kaitlin, Nick and Dr. Wiles.

GIRDWOOD, ALASKA – The College of Wooster Tree Ring team set off for Columbia Bay Glacier this past wednesday. After arriving in Anchorage with no troubles we drove down to Girdwood to hopefully catch a helicopter with a company called Alpine Air. Unfortunately for us the Alaskan weather had some other plans in mind. Due to a storm in the Prince Williams Sound area the rain and high winds made it impossible to fly to the glacier and forced us to be grounded in Girdwood. Thanks to the hospitallity of USGS glaciologist Shad O’Neel the College of Wooster Tree Ring team was able to stay in a condo owned by his family at the base of the local ski resort in town. The group is currently on standby waiting for any break in the weather to fly to Columbia Glacier.

DSC_0090

Devils Club along the trail in Girdwood.

The storm may have prevented us from traveling to Columbia via helicopter but it did not slow us down from collecting samples. Yesterday the group hiked up in the surrounding trails around Girdwood testing out our rain gear, exploring the beautiful Alaskan area and most importantly collecting some living tree ring samples. The group plans to travel to the intertidal later today to collect some samples from  the 1964 Great Alaskan Earthquake.

DSC_0064

Kaitlin extracting a core sample from a Mountain Hemlock in Girdwood.

DSC_0116

Girdwood, Alaska.

Wooster’s Fossil of the Week: An Early Cretaceous cobble-dwelling bryozoan

August 8th, 2014

Faringdon quartz 071714One of my formative experiences as a young paleontologist was working in the Faringdon Sponge Gravels (Lower Cretaceous, Upper Aptian) of south-central England while on my first research leave in 1985. (I was just a kid!) These gravels are extraordinarily fossiliferous with sponges, brachiopods, corals, vertebrate bones, and a variety of cobbles, both calcareous and siliceous. These coarse sediments were deposited in narrow channels dominated by tidal currents with significant energy reworking and sorting the fossil and rock debris. Above is a cobble of very hard vein quartz from the Sponge Gravels. On the left end you see an encrusting bryozoan with an unusual morphology.
LhwydThe fossils of the Faringdon Sponge Gravels have been studied for a very long time. The first formal notice of them is a museum catalogue compiled by Edward Lhwyd (image above) and published in 1699. Lhwyd (1660-1709) was a Welsh natural philosopher better known by his Latinized name Eduardus Luidus. He had an unfortunate childhood being the illegitimate son of what has been reported as a “dissolute and impractical” (and poor) father. Still, he was better off than most and had schooling all the way up to Oxford (but he could not afford to graduate). In 1684 he became an assistant to Robert Plot, the Keeper of the Ashmolean Museum in Oxford. He became a great scientific traveler and collector, specializing in plants and fossils and (eventually) ancient languages of Britain. In 1691 he was appointed Keeper at the Ashmolean. His book detailing fossils of Britain (Lithophylacii Britannici Ichnographia) was published with financial assistant from his good friend Isaac Newton.
Corynella in Lhwyd plate 18This is plate 18 from Lhwyd (1699). The fossil in the upper right is the sponge Corynella from the Faringdon Sponge Gravels.

Lhwyd’s views on the origin of fossils are with describing. This is a summary from Edmonds (1973, p. 307-308):

He suggested a sequence in which mists and vapours over the sea were impregnated with the ‘seed’ of marine animals. These were raised and carried for considerable distances before they descended over land in rain and fog. The ‘invisible animacula’ then penetrated deep into the earth and there germinated; and in this way complete replicas of sea organisms, or sometimes only parts of individuals, were reproduced in stone. Lhwyd also suggests that fossil plants known to him only as resembling leaves of ferns and mosses which have minute ‘seed’, were formed in the same manner. He claimed that this theory explained a number of features about fossils in a satisfactory manner: the presence in England of nautiluses and exotic shells which were no longer found in neighbouring seas; the absence of birds and viviparous animals not found by Lhwyd as fossils; the varying and often quite large size of the forms, not usual in present oceans; and the variation in preservation from perfect replica to vague representation, which was thought to represent degeneration with time.

What is most interesting about these ideas is that they have no reference to Noah’s Flood or other divine interventions.

In 1708, Lhwyd was elected a Fellow of the Royal Society in 1708. He didn’t enjoy this privilege long for he died of pleurisy the next year at age 49.
Reptoclausa hagenowi Cretaceous England 071714Now back to the bryozoan on the Faringdon cobble. It is the cyclostome Reptoclausa hagenowi (Sharpe, 1854). It has an odd form of irregularly radiating ridges of feeding zooids (autozooids) separated from each other by structural zooids (kenozooids). I like to think (although I have no evidence) that this morphology was resistant to abrasion in the rough-and-tumble life of living on a cobble in a high-energy channel. There are few other encrusters on the outer surfaces of the Faringdon cobbles.

The next two Fossils of the Week will also be from the fascinating Faringdon Sponge Gravels.

References:

Edmonds, J.M. 1973. Lhwyd, Edward, p. 307-308. In: Gillespie, C.C. (ed.). Dictionary of Scientific Biography, 8. Charles Scribner’s Sons, New York, 620 pp.

Lhwyd, E. 1699. Lithophylacii Britannici Ichnographia. London, 139 pages.

Meyer, C.J.A. 1864. I. Notes on Brachiopoda from the Pebble-bed of the Lower Greensand of Surrey; with Descriptions of the New Species, and Remarks on the Correlation of the Greensand Beds of Kent, Surrey, and Berks, and of the Farringdon Sponge-gravel and the Tourtia of Belgium. Geological Magazine 1(06): 249-257.

Pitt L.J. and Taylor P.D. 1990. Cretaceous Bryozoa from the Faringdon Sponge Gravel (Aptian) of Oxfordshire. Bulletin of the British Museum (Natural History), Geology Series, 46: 61–152.

Wells, M.R., Allison, P.A., Piggott, M.D., Hampson, G.J., Pain, C.C. and Gorman, G.J. 2010. Tidal modeling of an ancient tide-dominated seaway, part 2: the Aptian Lower Greensand Seaway of Northwest Europe. Journal of Sedimentary Research 80: 411-439.

Wilson, M.A. 1986. Coelobites and spatial refuges in a Lower Cretaceous cobble-dwelling hardground fauna. Palaeontology 29: 691-703.

Wooster’s Fossils of the Week: An Ordovician hardground with a bryozoan and borings — and an unexpected twist

August 1st, 2014

1 Hardground Bryo Large 071514aThe view above, one quite familiar to me, is of a carbonate hardground from the Upper Ordovician Grant Lake Formation exposed near Washington, Mason County, Kentucky. We are looking directly at the bedding plane of this limestone. The lumpy, spotted fossil covering about half the surface is a trepostome bryozoan. It looks like a dollop of thick pudding plopped on the rock. In the upper left are round holes that are openings of the trace fossil Trypanites, a common boring in carbonate hard substrates.
2 Closer hdgd bryo 071514bThis closer view shows the bryozoan details in the right half. You can barely pick out the tiny pin holes of the zooecia (the tubes that contained the individual zooids) and see the raised areas called maculae, which may have assisted in directing water currents for these colonial filter-feeders. Without a thin-section or peel I can’t identify the bryozoan beyond trepostome, but I suspect it is Amplexopora. The Trypanites borings in the hardground surface are also visible.
3 Hardground oblique Ordovician sm 071514cThis oblique view brings all the elements together. The bryozoan has closely encrusted the microtopography of the hardground surface. The Trypanites borings are shown cutting directly through the limestone of the hardground. Both of these observations confirm that the hardground was cemented seafloor sediment when the encrusters and borers occupied it.
4 Cross section hdgd 071514dHere is a full cross-section view showing the borings and the draping nature of the bryozoan. Now for the twist — I’m showing the specimen upside-down! It was actually found in place with the bryozoan down, not up. This is the roof of a small cave on the Ordovician seafloor. The bryozoan was hanging down from the ceiling, and the boring organisms were drilling upwards. The true orientation of this specimen is thus —
5 Cross section hdgd right side up 071514dThe cave was apparently formed after the carbonate hardground was cemented on the seafloor. Currents may have washed away unconsolidated muds underneath the hardground, forming a small cavity then occupied by the borers and the bryozoan: an ancient cave fauna. Brett & Liddell (1978) showed similar cavity encrustation in the Middle Ordovician, and I recorded a nearly identical situation in the Middle Jurassic of Utah (Wilson, 1998). Other detailed fossil marine caves are described from the Jurassic by Palmer & Fürsich (1974) and Taylor & Palmer (1994).

I should write up this Ordovician story someday!

References:

Brett, C.E. and Liddell, W.D. 1978. Preservation and paleoecology of a Middle Ordovician hardground community. Paleobiology 4: 329– 348.

Bromley, R.G. 1972. On some ichnotaxa in hard substrates, with a redefinition of Trypanites Mägdefrau. Paläontologische Zeitschrift 46: 93–98.

Palmer, T.J. 1982. Cambrian to Cretaceous changes in hardground communities. Lethaia 15: 309–323.

Palmer, T.J. and Fürsich, F.T. 1974. The ecology of a Middle Jurassic hardground and crevice fauna. Palaeontology 17: 507–524.

Taylor, P.D. and Palmer, T.J. 1994. Submarine caves in a Jurassic reef (La Rochelle, France) and the evolution of cave biotas. Naturwissenschaften 81: 357-360.

Taylor, P.D. and Wilson. M.A. 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1–103.

Wilson, M.A. 1998. Succession in a Jurassic marine cavity community and the evolution of cryptic marine faunas. Geology 26: 379-381.

Wilson, M.A. and Palmer, T.J. 1992. Hardgrounds and hardground faunas. University of Wales, Aberystwyth, Institute of Earth Studies Publications 9: 1–131.

« Prev - Next »