Wooster’s Fossils of the Week: Trepostome bryozoans, burrow systems, and bedding features in an Upper Ordovician limestone from southeastern Minnesota

August 12th, 2016

1 DSC_1322One of the little mysteries on the recent Minnesota research trip by Wooster students, faculty and staff is the origin of thin limestone beds in the middle of the thick shales of the Decorah Formation (Upper Ordovician). How did such accumulations of almost pure carbonate develop on such a muddy seafloor? Are they storm beds? Some sort of diagenetic feature? The records of brief sealevel changes? Brief interruptions in the supply of silicate sediments to the basin? Turbidites of carbonate material swept into a deeper basin? Above is a view of the top surface of such a limestone bed, this one found in the middle of the Decorah in Shop Quarry (N 43.97232°, W 92.38332°). The light-colored twiggy objects are broken colonies of trepostome bryozoans; the network of holes are burrows of a trace fossil called Chondrites.

3 Wangs carbonate bedAn outcrop view of one of these carbonate beds in the Decorah Formation, this one at Wangs Corner (N 44.41047°, W 92.98338°). These units are only a few centimeters thick, and have a variety of petrographic fabrics. This one appears to be an almost pure biosparite with Thalassinoides burrows penetrating from above carrying down a light brown sediment.

2 DSC_1325Back to our slab from the Decorah at Shop Quarry with a closer view of the trepostome bryozoans and round holes representing the trace fossil Chondrites.

3 DSC_1333Sawing a rock and then polishing a cut surface is always fun and profitable! This is a cross-section through the Shop Quarry slab, oriented with the top upwards. A little bit of iron oxide diffused through the sediments provides the touches of red in the fabric of the limestone.

4 DSC_1341This closer view of the cut surface shows the exquisite bedding features, along with the bryozoans (B) and trace fossils (T) in cross-section. The burrows pass through the bedding and pie down into the rock a brownish sediment from above. These burrows were made by some sort of deposit-feeding organism that was mining the sediment for organic material. The bedded sediment may be slightly graded in grain size, meaning the many beds may consist of thin fining-upwards sequences. Note how the beds are contorted around the bryozoans as if they were dropped into the sediment while it was still accumulating.

This slab of bryozoans, trace fossils and contorted laminae looks to me like a storm bed formed quickly during and after the seafloor was significantly disturbed by currents. When conditions returned to normal some worm-like deposit-feeders in the fine sediment above sent their mining tunnels down deep into the carbonate looking for food. We have a hypothesis to test!

The work begins

July 29th, 2016

1 Wangs Corner 072916Rochester, Minnesota — Today we started collecting specimens and data for the Team Minnesota student Independent Study projects. We began with a long drive south to Decorah, Iowa, to measure a thick section of our Upper Ordovician target units at the Decorah-Bruening Quarry (N 43.29036°, W 91.76558°), but a patch of persistent and heavy rain lingered over the area all morning. We gave up and headed back north to the Rochester, Minnesota, region, where it was dry and sunny. Our first stop was at Wangs Corner (N 44.41047°, W 92.98338°) to collect fossils from the Decorah Formation for a taxonomic and paleoecological assessment. Rachel Wetzel and Nikki Bell are the Team Paleontologists for this work.

Wangs signWangs is a little crossroads in this part of the Minnesota prairie. (Photo by Nick Wiesenberg.)

2 Dean on WangsDean Thomas has a role at this outcrop as well. He will be doing a conodont biostratigraphy and paleoenvironmental study of the Decorah and units above and below. At Wang’s Corner he found a thin biosparite bed in the midst of the calcareous shale that he can use to help stratigraphically position this section of the Decorah, which has no visible upper or lower contacts.

3 Wangs carbonate bedThis bed is a beautiful nearly pure, coarse, well-cemented biosparite/grainstone in contrast to the argillaceous beds above and below. The orange patches in the top of the rock are burrows (likely Thalassinoides) filled with sediment from above. The traditional interpretation of these units is that they were formed by storms. Why they are so clay-poor is a mystery.

4 Turkey Run 072916Our last stop was the Turkey Run locality (N 44.38441°, W 92.91199°). Here the Decorah Formation is just barely exposed through the weeds. The students gamely collected fossils as the bright sun made us forget the disappointing morning rain.

Team Minnesota visits the Upper Ordovician of Iowa

July 27th, 2016

1 Decorah Bruening QuarryRochester, Minnesota — Team Minnesota traveled south today to visit exposures of our three favorite formations: the Platteville Limestone, Decorah Shale, and Cummingsville Limestone. Where best to see the Decorah Shale than in Decorah, Iowa? Above the crew is scattered in the abandoned Decorah Bruening Quarry. They are walkinng on top of the Carimona Member of the Decorah, with the shaley units above topped by the Cummingsville Limestone.

2 Team with Deicke at Decorah BrueningWe began at the bottom with the Platteville and a bit of rare shade. Nikki Bell and Etienne Fang have their hands on the iconic Deicke Bentonite. A very handy time indicator, that volcanic ash deposit.

3 Andrew Decorah Cummingsville contactOur excellent guide Andrew Retzler of the Minnesota Geological Survey is examining the contact between the upper Decorah Shale and Lower Cummingsville Limestone. We found here several specimens of the “gumdrop” bryozoan Prasopora.

4 Rachel CummingsvilleRachel Wetzel gets a bit too close to the crumbly cliff of Cummingsville Limestone at the Decorah Bruening  Quarry.

5 Cummingsville limestoneWhere freshly exposed, the Cummingsville reveals itself to be a fascinating unit with alternating limestone lithologies. The darker layer here is a packstone with fine fossil debris. It is almost certainly a storm deposit.

6 Cummingsville ChondritesThis slab of Cummingsville is covered with beautiful Chondrites trace fossils.

7 Team at Golden HillIn the afternoon we returned to Minnesota and explored a very overgrown exposure of the Decorah Shale at the Golden Hill abandoned quarry along US 52 near Rochester. The main attraction here for us is the abundance of “iron ooids”, small spheres of iron oxides. Etienne Fang is studying their composition and origin for her Independent Study thesis. It’s a steep and muddy slope after a journey through head-high brush, but the bags full of samples made it worthwhile.

8 Golden Hill slabThe fossils here are gorgeous. This is the base of a crinoid calyx surrounded by brachiopod, crinoid and bryozoan debris.

It was a great day of exploration. Tomorrow we examine localities north of Rochester.

A Wooster Geologist visits the caves of Tel Maresha in central Israel

March 21st, 2016

1 Bell caves MareshaTEL AVIV, ISRAEL — My last day in Israel was spent with my friend Yoav Avni exploring some sites in the central part of the country before my flight left Tel Aviv late in the evening. The most geological place we visited was Maresha (which later became, in order, Beit Guvrin, Eleutheropolis, Bethgibelin, Bayt Jibrin, Kibbutz Beit Guvrin and Beit Guvrin National Park — you know there’s a long story there!). Maresha was an 8th Century BCE Israelite city in Judah that guarded several trade routes and access to the Judean hills from the coast. It thus had significant strategic value and was subject to just about every conqueror of the region since the Iron Age. The bedrock has a very thick section of the Maresha Formation (Eocene), a homogeneous soft chalk that is easily carved. This chalk has long been quarried for building stone and the main component of plaster and cement. The typical quarries are bell-shaped, with a small circular entrance from ground level and an expanding cone downwards. Above we see several intersecting quarries exposed by a roof collapse.

2 Bell caves signHere is a helpful diagram showing the construction of bell caves. The top geological layer is a hard calcrete (caliche) locally called nari. It provides a strong roof for the quarries.

3 Bell cave openingThe opening of a bell cave through the calcrete upper layer.

4 Bell cave carving marksThe sides of the quarries easily show the tool marks made by the workers as they spiraled down into the bedrock. This rock is soft enough to dig with your fingernails.

5 Columbarium Maresha

Residents of Maresha, especially in the diverse Hellenistic times (2nd-3rd centuries BCE), reused the quarries for living and working spaces, expanding several into new rooms. Above Yoav is standing in the largest columbarium, a place to raise doves for food and rituals. (Not for the storage of ancestral ashes or bones, as was once thought.)

6 Yoav in Columbarium MareshaI didn’t want to crop out Yoav’s happy face! He is standing in the bottom of a bell cave repurposed as a columbarium.

7 Olive cracker MareshaThere are several underground olive oil factories that were active from the 3rd Century BCE until modern times. This device was driven by a donkey to crush raw olives.

8 Large olive press MareshaThis is an underground olive press. Heavy stones were attached to the beams to press the juices out of olives cracked first by the donkey apparatus above.

9 Siddonian cavesThe Sidonian tombs (about 2nd Century BCE) are very impressive. All the carving is original, but the paint shown above is a modern reconstruction. This inscription on a tomb here is haunting:

Nothing else remains that I can do for you, or that will pleasure you. I am sleeping with someone else, but it is you I love, dearest to me of all.

In the name of Aphrodite, I am happy about one thing, that your cloak has been left to me as a pledge.

But I flee, and permit you expanses of freedom. Do anything you desire.

Do not strike the wall; it only makes noise. We will motion to each other; this will be the sign between us.

10 Maresha countrysideThe scenery above ground at Tel Maresha is lush and green. This region received more than the usual amount of rain this season, and it shows. We are looking here from the tel towards Hebron in the Judean hills. Note the herd of sheep in the middle ground distance.

11 Bedouin sheep MareshaLater in the day we met those sheep and their Bedouin shepherds.

12 Tel MareshaAnd here is Tel Maresha itself. Only 10% has been excavated, so much more remains to be discovered.


My tradition at the end of a field excursion is to include my most important GPS numbers and coordinates:

125: N29.99183°, E35.07680° Gerofit Junction Ora Formation
126: N30.94310°, E34.97972° SU62 below oolite; nice corals
127: N30.94323°, E34.99110° Top Zohar Cliff
128: N30.95774°, E35.00615° SU65 bedding plane
129: N30.94358°, E34.97828° SU65 in Matmor Hills
130: N30.94812°, E35.00099° Lowest exposed Zohar
131: N30.33491°, E34.92828° Road to Be’er Ada
132: N30.32229°, E34.90701° Be’er Ada
133: N30.32553°, E34.90683° Near Be’er Ada along fault
135: N30.32973°, E34.91417° Ada Canyon top view
136: N30.32001°, E34.97467° Wadi Paran cliffs

At some point you must start collecting data

March 18th, 2016

1 Acacia at Meredith SectionMITZPE RAMON, ISRAEL — Today my friend Yoav Avni (Geological Survey of Israel) and I returned to Makhtesh Gadol to pursue a project with Subunit 65 of the Matmor Formation (Callovian, Middle Jurassic). You may recall this limestone contains an extraordinary bedding plane of fossils preserved in near-life positions (as seen in a recent Fossil of the Week entry). Yoav’s job was to find additional exposures of this subunit in the area; mine was to map the distribution of fossils on the bedding plane. This area of the makhtesh, by the way, is called “Meredith’s Section” after IS student Meredith Sharpe, who did splendid work here. The acacia tree above is our traditional lunch spot (when the camels aren’t using it).

2 SU65 bedding plane 031816This is the bedding plane of Subunit 65. I went over every square centimeter of it photographically mapping and detailing it with a square-meter quadrat. It was hot work, and a bit of drudgery compared to the previous days of exploring new exposures.

3 SU65 quadrat 031816This is a typical quadrat, complete with my boot toes. I took 41 quadrat photos like this, and then detailed the fossils within and their positions. In the meantime, Yoav wandered the hills and found many excellent exposures of the same unit, although none with a bedding plane like this. We will be able to compare the fossils in the “traditional” exposures with what we see here.

That’s pretty much it for my day in the desert!

Last day of fieldwork in England: A working quarry and another great unconformity

June 26th, 2015

1 Doulting quarry sawBRISTOL, ENGLAND (June 26, 2015) — Tim Palmer has a professional interest in building stones, and a passion for sorting out their characteristics and historical uses. He thus has many contacts in the stone industry, from architects to quarry managers. This morning we visited the Doulting Stone Quarry on the outskirts of Doulting near Shepton Mallet in Somerset. Here a distinctive facies of the Jurassic Inferior Oolite is excavated for a variety of purposes. The rock has a lovely color, is relatively easy to work, and is durable. Above is a quarry saw that cuts out huge blocks from the natural exposure.

2 Thalassinoides layer DoultingSuch sawing produces great cross-sections for geologists to examine. We were particularly interested in that light-colored unit above with the irregular top and dark sediment-filled holes. The holes are part of a network of Thalassinoides burrows (tunnels made by Jurassic crustaceans) and reduce the value of the rock as a building stone. There is thus lots of it laying around the quarry yard for study.

3 Pinnid likely Trichites cross section DoultingOne impressive fossil exposed by the sawing is this pinnid bivalve, probably Trichites.

4 Burrow fill sediments DoultingThe Thalassinoides burrows are filled with a poorly-cemented sediment. It is full of little fossils, so we collected a bag of it for microscopic examination. It may give us clues as to what communities lived on the surface of this burrowed unit when it was part of the Jurassic seafloor.

5 shaping saw DoultingWe had a tour of the quarry shops, which included seeing these giant rock saws in action. Many of the saws are controlled by computers, so elaborate cuts can be made.

6 Medieval stone breaking marksThis rock has been quarried since Roman times, so there is over 2000 years of stone working here. The quarry owner set aside this rock face which shows chisel marks made in Medieval times. Wooden wedges were jammed into chiseled channels and then pulled over days to eventually crack the stone free.

7 Tedbury Camp wavecut surface along strikeAfter the quarry visit, Tim Palmer and I tromped through the woods and eventually found (with the help of several locals) an exposure known as Tedbury Camp. It is another Jurassic-on-Carboniferous unconformity like we saw at Ogmore-By-Sea earlier in the week. A century ago quarry workers cleared off this surface of Carboniferous limestone. It is a wave-cut platform on which Jurassic sediments (the Inferior Oolite) were deposited. The surface has many geological delights, including faults, drag folds, differentially-weathered cherts and carbonates, and Jurassic borings and encrusters. Beautiful.

8 wavecut surface foldingIn this view of the surface you may be able to see the odd folding of the dark chert layers in the right middle of the image. These seem to be drag folds along a fault. They clearly predate the Jurassic erosion of the limestone surface. The overlying Jurassic can be seen in the small outcrop on the left near Tim.

9 section view of wavecut surfaceIn this cross-section of the erosional surface you can clearly see we’re working with an angular unconformity.

10 filled borings wavecutTrypanites borings are abundant across this surface, most filled with lighter Jurassic sediment. There are other borings here too that deviate from the straight, cylindrical nature of Trypanites.

11 curved borings wavecutI don’t know yet how to classify these curved borings. They resemble Palaeosabella.

12 Encrusting bivalve wavecutHere is a Jurassic bivalve attached to the Carboniferous limestone at the unconformity. Most of the encrusters have been eroded away.

13 Tim on wavecut platformThere are many possibilities for further study of the Tedbury Camp unconformity. This was a productive site for our last field visit in England this year. Thank you very much to Tim Palmer, seated above, for his expertise, great companionship, and generosity with his time. It was a reminder of how much fun we had together in the field twenty years ago.

My month of geology in the United Kingdom has now come to an end. My next two days will be devoted to packing up and making the long train and then plane flights home. What a wonderful time I had, as did my students on the earlier part of the trip, Mae Kemsley and Meredith Mann. Thank you again to Paul Taylor for his work with us in Scarborough. I am very fortunate with my fine British friends.

For the record, the important locality coordinates from this trip —

GPS 089: Millepore Bed blocks N54.33877°, W00.42339°

GPS 090: Spindle Thorn Member, Hundale Point N54.16167°, W00.23326°

GPS 091: Robin Hood’s Bay N54.41782°, W00.52501°

GPS 092: Northern limit of Speeton Clay N54.16654°, W00.24567°

GPS 093: Northern limit of Red Chalk N54.15887°, W00.22261°

GPS 094: South section Filey Brigg N54.21674°, W00.26922°

GPS 095: North section Filey Brigg N54.21823°, W00.26904°

GPS 096: Filey Brigg N54.21560°, W00.25842°

GPS 097: D6 of Speeton Clay N54.16635°, W00.24520°

GPS 098: C Beds of Speeton Clay N54.16518°, W00.24226°

GPS 099: Lower B Beds of Speeton Clay N54.16167°, W0023326°

GPS 100: Possible A Beds of Speeton Clay N54.16129°, W00.23207°

GPS 101: A/B Beds of Speeton Clay N54.16035°, W00.22910°

GPS 102: C7E layer of Speeton Clay N54.16447°, W00.24043°

GPS 103: Lavernock Point N51.40589°, W03.16947°

GPS 104: Triassic deposits, Ogmore-By-Sea N51.46543°, W03.64094°

GPS 105: Sutton Stone Unconformity N51.45480°, W03.62609°

GPS 106: Sample of lowermost Sutton Stone N51.45455°, W03.62545°

GPS 107: Nash Point N51.40311°, W03.56212°

GPS 108; Devil’s Chimney N51.86402°, W02.07905°

GPS 109: Fiddler’s Elbow N51.82584°, W02.16541°

GPS 110: Doulting Stone Quarry N51.18993°, W02.50245°

GPS 111: Tedbury Camp unconformity N51.23912°, W02.36515°


Wooster Geologist in England (again)

June 25th, 2015

1 old quarry face cotswoldsBRISTOL, ENGLAND (June 25, 2015) — Our little geological exploration of southern Britain now passes into England. Tim Palmer and I crossed the River Severn and drove to the Cotswolds to examine old quarry exposures and Medieval stonework. We are parked above in Salterley Quarry near Leckhampton Hill.

2 devils chimney leckhamptonOur theme again is Jurassic. At Leckhampton Hill we examined exposures of the Middle Jurassic Inferior Oolite. It is not, of course, inferior to anything in the modern sense. The name, originally from William Smith himself, refers to its position below the Great Oolite. This is Devil’s Chimney, a remnant of stone left from quarrying in the 19th Century.

3 fiddlers elbow hdgd and Pea GritWe stopped along a bend in a Cotswold road called Fiddler’s Elbow and found an old carbonate hardground friend in the Inferior Oolite. Borings are evident in this flat, eroded surface. Next to the hammer are pieces of the Pea Grit, a coarser facies. I want to examine the grains for microborings and encrusters.

4 Dogrose leckhamptonThis is the gorgeous dog-rose (Rosa canina, not surprisingly), which is common in the Cotswolds. It is the model for the Tudor Rose in heraldry.

5 Fiddlers elbow orchidsThese tall orchids were also abundant near our outcrops.

6 fiddlers elbow orchids closeA closer view of the orchids. When I learn the name for this plant, I’ll amend this post. [And we have one! Caroline Palmer identified the flowers as Dactylorhiza sp. Thanks, Caroline!]

7 Painswick church and yewsAt the end of the day we stopped by St. Mary’s Church in Painswick, with its distinctive churchyard and variety of building stones. The sculptured trees are English yews.

8 Tim and Painswick gravestonesThe gravestones date back to the early 18th Century, with older ledger stones inside the church.

9 Painswick church pyramid markerThe unique pyramidal tomb of the stonemason John Bryan (1716-1787). He was apparently responsible for most of the 18th Century ornate monuments in this churchyard.

10 copper markers killing lichen PainswickMany of the gravestones have copper plates affixed to their upper faces. The rain washes copper ions out of the metal and over the limestone, killing the lichens and other encrusting organisms. This leaves the lighter patch of bare limestone. Somewhere in this is a study of microbiome ecological gradients!

11 St Marys church Painswick shot divot 1643The Painswick church was the site of a 1643 battle during the English Civil War. There are numerous bullet and shot marks on the exterior stones. Tim commented on the remarkable resilience of this stone to stay coherent after almost 400 years of weathering of these pits.

A great unconformity in South Wales

June 24th, 2015

1 Dinantian Sutton unconformity wide viewBRIDGEND, WALES (June 24, 2015) — Today Tim Palmer and I visited a famous unconformable rock plane in South Wales. I last saw it thirty years ago, when I knew a lot less about eroded, bored and encrusted surfaces. It is an unconformity between a Carboniferous limestone (High Tor Limestone, Dinantian in age) and an overlying Jurassic limestone (Sutton Stone, Hettangian, Lower Jurassic) exposed on the coast near Ogmore-By-Sea. It was most thoroughly described in 2004 by Johnson and McKerrow (Palaeontology 38: 529-541). You can see it as the surface above, with the Jurassic rocks on top of it to the right. (I know, gray rocks on gray rocks. It takes close examination to tell them apart after they both have been subjected to coastal weathering.)

2 Dinantian Sutton close viewHere is a closer view with part of the Lower Jurassic Sutton Stone broken away to show fresh material. (We didn’t do this, despite the guilty-looking hammer. The hammer is Paul Taylor’s, by the way. Thanks, Paul!) Note the pebbles in the Sutton Stone. They are made of the Carboniferous limestone beneath. Classic unconformity.

3 Dinantian Sutton borings wide viewThe Carboniferous limestone is punctured by numerous small borings (Trypanites) drilled by filter-feeding worms of some kind when the Early Jurassic sea covered this surface. They are the clusters of small black dots shown above.

4 Dinantian Sutton borings closeIn this closer view of the borings you can see that they are filled with a lighter Jurassic sediment. The openings have been somewhat enlarged by weathering.

5 Dinantian Sutton reliefThis erosion surface shows some relief, probably formed by cobbles and pebbles washing over it during the Early Jurassic. This matches what we see on modern wave-cut rocky platforms.

6 Triassic Dinantian unconformityOn the same stretch of shoreline there is a small section where Triassic wadi deposits cut down into the Carboniferous limestone — another even more dramatic unconformity, but without marine fossils.

7 Triassic wadi deposits Ogmore by seaComing from a desert myself, I have an affinity for wadi sediments. They are coarse, angular and poorly sorted. These grains are entirely from the underlying Carboniferous limestone. They were likely generated from steep rocky canyons through which intermittent streams flowed.

8 Nash Point viewAt the end of the day Tim and I visited Nash Point, again on the coast of South Wales. Here the Lias is brilliantly (and dangerously!) exposed as a series of alternating limestones and shales.

9 Nash Point CliffWe didn’t get too close to these unstable cliffs. The limestone blocks fall often as the interbedded soft shales holding them in place weather away.

10 Nash PointA view of Nash Point at low tide. Tim always wears that red jacket, so he’s easy to spot. (Classic Redcoat!)

11 Nash Point cobblesWe didn’t find much to paleontologically interest us at this last outcrop, but it was beautiful on another stunning coastal day. These cobbles, all made of Lias limestones, are pretty to look at, but tiresome to walk through. We were ready for a slow dinner after this excellent day.


Wooster Geologist in Wales

June 23rd, 2015

1 Triassic Lavernock Point Penarth GroupBRIDGEND, WALES (June 23, 2015) — My train journey yesterday was successful. It was close, but I made the four tight connections and arrived in Aberystwyth, Wales, from Thurso, Scotland, on schedule. It took 15 hours. My friend Tim Palmer was there to greet me as I stumbled out of my carriage. I went from rainy, cold Scotland to warm and sunny Wales. The top image is of the Triassic/Jurassic transition at Lavernock Point in south Wales (see below).

2 Tim Caroline houseMy first Welsh night was with Tim in his great country home (with is wife Caroline) on the outskirts of Aberystwyth. It is called The Old Laundry because of its function on a previous manorial estate. I had my best sleep here for the entire trip. Quiet and beautiful.

4 Talley Abbey ruinsOne of Tim’s passions is the study of building stones in England and Wales. As we drove to southern Wales for our geological work, we stopped by interesting stone structures, including the ruins of Talley Abbey, a 12th Century monastery.

5 Tim at Talley AbbeyTim is here examining the dressing stones on a corner of this pillar in the Talley Abbey ruins. I learned that these dressings are usually made of stone that can be easily shaped, is attractive, and will hold sharp edges. In many cases these are called “freestones”.

6 Lower Lias Lavernock dinosaur siteOur first geological stop was at Lavernock Point on the southern coast of Wales. We looked here at the boundary section between the Upper Triassic and Lower Jurassic (Lias). In this view we see an alternating sequence of limestones (buff-colored) and shales (dark gray) of the lower Lias. These are marginal marine units with oysters and ammonites. On the left side of the image you can see a broad niche cut back into the cliff. This is the site where the first carnivorous dinosaur in Wales was recently excavated. It is also one of the oldest Jurassic dinosaurs since it was discovered just above the Triassic/Jurassic boundary. More on this dinosaur later.

7 Lower Lias pseudo mudcracksWe wandered across broad intertidal wave-cut platforms at Lavernock Point looking at the limestones and shales of the lower Lias. I was intrigued by these features on some bedding planes. They are not desiccation cracks, but rather some combination of jointing and weathering.

8 Liostrea hisingeri LavernockThe oyster Liostrea hisingeri is very common in this part of the Lias. In the limestones it is sectioned by erosion, resulting in these shelly outlines.

9 Liostrea hisingeri shale LavernockWhen Liostrea hisingeri is present in the shales, it is preserved three dimensionally.

10 Tonypandy street viewAfter our geologizing was done for the day, Tim and I drove up into the Rhondda Valleys just north of our hotel. This was at one time a very busy coal mining and industrial region, but the mines are closed and most of the heavy industry has moved elsewhere. Above is a view down a street in Tonypandy, one of the more famous towns of The Valleys. There were massive riots here in 1910 which eventually a minimum wage for miners in 1912.

A beautiful day for Wooster Geologists in the Silurian of Ohio

April 18th, 2015

aDSC_5072FAIRBORN, OHIO–It’s field trip season at last for the Wooster Geologists. Several geology classes have now been out in Ohio, taking advantage of windows of spectacular weather. Today was one of those days for 25 students in the Sedimentology & Stratigraphy class. We returned to the Oakes Quarry Park exposures in southwestern Ohio (N 39.81472°, W 83.99471°). Three years ago here in April it was 37°F and raining. This year the conditions were perfect. We studied outcrops of the Brassfield Formation (Early Silurian, Llandovery) in the old quarry walls. The students measured stratigraphic columns of these fossiliferous biosparites as part of an exercise, and then explored the glacially-truncated top of the unit.

bDSC_5079The Brassfield is intensely fossiliferous. Large portions of it are virtually made of crinoid fragments. In the random view above you can see columnals, as well as a few calyx plates. This is why this unit is very popular among my echinodermologist friends at Ohio State.

DSC_5056Kevin Komara, Brian Merritt and Dan Misinay (Team Football) are here contemplating the quarry wall, planning how to measure their sections.

DSC_5063One of our Teaching Assistants, Sarah Bender, is here pointing out one of the many thin intercalated clay units in the Brassfield biosparites.

DSC_5065Fellow Californian Michael Williams directed the action. No, actually he’s doing the time-honored technique of following a measured unit with his finger as he finds a place he can safely climb to it and the units above. He is holding one of our measuring tools, a Jacob’s Staff. Why do we call them “Jacob’s Staffs”? Read Genesis 30:25-43. (Yes, today’s students are mystified by Biblical references.)

DSC_5066Here’s Rachel Wetzel, giving me a heart attack. Don’t worry, insurance companies and parents, she’s fine.

DSC_5068Rachel is again on the left. Team Ultimate Frisbee (Meredith Mann and Mae Kemsley) are in the front, and Sharron Ostermann is above. This is the recommended way to get to the top of the exposure!

DSC_5070We carried our lunches in “to go” boxes from the dining hall. Our Teaching Assistants Sarah Bender and Kaitlin Starr enjoyed a sunny picnic on the rocks.

yDSC_5077The top level of the quarry was cleared of soil and brush many years ago to expose a glacially truncated and polished surface of the Brassfield. Looking for glacial grooves and fossils here are (from the left) Tom Dickinson, Jeff Gunderson (another Californian!), Andrew Conaway, and Luke Kosowatz (who seems to also be making a little pile of rocks as a memorial to a great day).

zDSC_5074One of the many corals we found in the top of the Brassfield was this halysitid (“chain coral”), an indicator fossil for the Late Ordovician and Silurian.

Everyone returned safely to Wooster with their completed stratigraphic columns, lithological descriptions, and a few fossils. Thank you to Mark Livengood, our bus driver. Good luck to the other field trip groups later this month!

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