A wet cave and the Mighty Mississippi River

August 1st, 2016

1 Niagara Cave 1Rochester, Minnesota — Since Team Minnesota efficiently finished its fieldwork yesterday, we have two days before the students fly out of the Minneapolis-St. Paul airport. The good weather has given us a gift of time, so we’re using it like enthusiastic geologists.

This morning we drove down to Harmony, Minnesota, near the Iowa border to visit Niagara Cave. This cave is unusual because it has a stream with a 60-foot waterfall and (a new term to me) active vadose canyons. The cave is entered down a sinkhole into the Dubuque Formation, and then it descends through the Stewartville Formation and reaches its lowest level in the Prosser Formation. These are Ordovician units above the Platteville-Decorah-Cummingsville sequence we did our work with. The cave passages follow joint patterns inn these limestones. It is plenty wet down there.

2 Cave joint NiagaraMy cave photos are not the best with my small flash. Here at least we can see a vertical joint passage and flowstone structures.

3 Cave StreamThe fast-moving stream running through Niagara Cave.

4 Waterfall top Niagara CaveThe top of the 60-foot waterfall.

5 Cave stratThis view up into a dome shows the internal stratigraphy visible in the limestones.

6 Ceiling gastropodsPlenty of fossils are exposed in the cave. These are sections of gastropods in the ceiling of one section. They were high up so I have little idea of their sizes. I’m just amazed the photo worked out.

7 Queens BluffIn the afternoon we drove northeast to Great River Bluffs State Park on the Mississippi. We had spectacular views of the river and its opposite bank in Wisconsin. Above is a view eastward of Queen’s Bluff overlooking the river.

8 Black River DeltaThe main navigation channel of the Mississippi is in the foreground, with the Black River Delta in the middle ground. In the distance are the bluffs on the Wisconsin side, about 4-5 miles away.

9 Team Minnesota 080116Team Minnesota is ready to answer any geological questions!

 

Team Minnesota finishes its work (in Iowa, funny enough)

July 31st, 2016

1 Decorah outcrop 073116Rochester, Minnesota — We returned to Decorah, Iowa, today to measure and sample the Decorah Shale (Upper Ordovician) in its type locality. It was much drier here than on our last attempt! Above is the gray Decorah Shale topped by the brown Cummingsville Formation.

2 Dean sampling 073116We started below the quarry exposure along the road to get the top of the Platteville Formation. This is the main locality for Dean Thomas (above) who is sampling these three units for conodonts and their associated carbonate petrographic facies. You may see tiny red ribbons on the outcrop that mark where we removed small blocks of limestone for lab analysis back in Wooster.

3 Decorah sampledHere are some of Dean’s sampled strata in the Decorah. He also collected a few samples from the base of the overlying Cummingsville.

4 Etienne collecting 073116While Dean measured section and took samples, Etienne Fang (pictured), Rachel Wetzel and Nikki Bell worked through the Decorah Shale collecting fossils, with special concentration on the beautiful “gumdrop” bryozoan Prasopora.

5 Minnesota lunch 073116It was a sunny day, so we took shade where we could find it!

6 Cummingsville blocksAt the end of the day we explored the richly-fossiliferous Cummingsville in blocks fallen from the face of the old quarry wall.

7 Traces and brachsThe Cummingsville is rich with both body fossils (brachiopods, crinoids, gastropods, bryozoans, especially) and trace fossils. A future Senior IS project?

8 Team Minnesota signTeam Minnesota has now completed its fieldwork! From the left, Etienne Fang (Bethesda, Maryland), Nikki Bell (Santa Monica, California), Rachel Wetzel (Sewickley, Pennsylvania) and Dean Thomas (Montpelier, Virginia). These students did fine work, setting themselves up for several months of lab analyses back in Wooster. I’m proud of this group!

We still have a couple of days in Minnesota before the students fly to their homes and Nick Wiesenberg and I make the long drive back to Wooster with our samples and equipment. We plan to see the geological and historical sights within range of Rochester, which will, of course, be duly reported here.

Paleontological fieldwork in southeastern Minnesota

July 30th, 2016

1 Nikki brachs 073016Rochester, Minnesota — It was a good day for fossil collecting on the Minnesota prairie. Above you see a handful of articulated orthid brachiopods collected by Nikki Bell at the Shop Quarry exposure near Rochester.

2 Shop Quarry 073016Shop Quarry (N 43.97232°, W 92.38332°) has long been abandoned and is quickly reverting back to woodlands except for the steepest parts of the old walls. The grey streak visible through the trees is our site where the Decorah Shale is exposed.

3 Shop Quarry 073016 closeAs usual, we worked on steep slopes with plenty of foliage. The fossils, though, were easy to find.

4 HCS at Shop QuarryThe shale has thin limestone beds penetrated thoroughly by the trace fossils Chondrites (the small holes visible in the slab above). This particular rock shows hummocky cross-stratification on its top surface (the dips and ridges), almost certainly an indication it was deposited during an Ordovician storm.

6 Rachel 073016Rachel Wetzel (Pennsylvania) is working with the fossils from this quarry and our other Decorah outcrops to put together a general paleoecological reconstruction and then explore in detail the bryozoans. She is particularly adept at effortlessly clinging to steep slopes!

5 Nikki 073016Nikki Bell (California) is working on the Decorah fossils with Rachel. Her specialty will be the brachiopods.

7 Etienne 073016Etienne Fang (Maryland) is studying the “iron ooids” found in the Decorah Shale at Shop Quarry and several other sites.

8 Dean 073016Dean Thomas (Virginia) will be assessing the carbonate petrology and conodonts of the Decorah Shale, along with the underlying Platteville and overlying Cummingsville Formations. His main outcrop will be in Iowa, but he’s also collecting limestone specimens within the Decorah at other locations for biostratigraphic correlation. All four student projects are integrated, with the whole team collecting data and samples for each individual project.

9 Nick 073016Our superb geological technician Nick Wiesenberg has also been collecting fossils for us.

10 Lunch 073016A typical lunch in the woods for us. We’ve had surprisingly few mosquitoes, and very patchy interactions with parasites. Dean is a tick magnet, and I’ve been badly chiggered!

11 Golden Hill 073016Our last stop of the day was the annoying Golden Hill roadcut (N 43.98788°, W 92.47962°). It is next to an off-ramp of US 52/63 so we have to reach it by descending through a bouldery, overgrown culvert from above. The students did their jobs, though, and did good sampling.

12 Wild Parsnip bushThis spindly green bush is wild parsnip (Pastinaca sativa), a plant we’re careful to avoid despite its abundance in some very inconvenient places. It is often referred to as poison parsnip for good reasons. These plants contain “furocoumarins, chemicals that when combined with skin and ultraviolet light can cause what’s known as a phytophotodermatitis”. You have to contact the sap of the plant and then be exposed to the sun, so brushing against it is not a problem. We worry about grabbing a stalk and breaking it in our hands while clinging to slippery slopes.

13 Wild parsnip closeHere’s a closer view of the wild parsnip. We also deal with poison ivy, stinging nettles, thistles and other sticker bushes. Sometimes I miss my desert fieldwork!

14 Yellow flower 073016Of course, most plants here are benign and often beautiful. These yellow flowers were abundant today at Shop Quarry. I suspect this is Lotus corniculatus (Birds-foot Trefoil). Unfortunately the description of this flower says, “This is a terrible pest plant …”

It was a successful day for Team Minnesota, especially since we were able to end our work just before a bout of thunderstorms. Tomorrow we return to Iowa, which we hope will be much drier than it was yesterday.

 

Wooster’s Fossil of the Week: A new Late Ordovician bryozoan from Oklahoma

July 29th, 2016

1 Color brach Zigzagopora encrustedI am very pleased to introduce a new bryozoan genus and species recently described in the First View section of the Journal of Paleontology. Paul Taylor (Natural History Museum, London) and I present: “A new runner-like cyclostome bryozoan from the Bromide Formation (Sandbian, Upper Ordovician) of Oklahoma and its phylogenetic affinities”. The bryozoan is shown above encrusting the interior of an orthid brachiopod identified as Multicostella sulcata (thanks, Alycia Stigall!) in the Lower Echinoderm Zone of the Mountain Lake Member of the Bromide Formation near Fittstown, Oklahoma. We are particularly proud of its new scientific name. Here’s the abstract:

Zigzagopora wigleyensis n. gen. n. sp. is an Upper Ordovician (Sandbian, early Caradoc) cyclostome bryozoan from the Arbuckle Mountains of Oklahoma, USA. It has runner-type colonies characterized by a mostly uniserial, geniculate arrangement of monomorphic zooids that bud alternately left and right, producing a zig-zag pattern of growth. This new genus has calcified interior walls and non-pseudoporous exterior walls. It is thus most likely affiliated with the paleotubuliporine Family Sagenellidae, despite superficial similarities with the corynotrypid cyclostomes with which it co-occurs.”

You’ve got to love a job where you can coin a name like Zigzagopora wigleyensis. The fortuitous species name, by the way, refers to the Wigley Quarry in Oklahoma (below).

Slide08_052815Here is a pictorial guide to Zigzagopora wigleyensis, featuring Paul’s excellent Scanning Electron Microscope images:
2 Good zigs 0p20This is what we mean by a “uniserial, geniculate arrangement of monomorphic zooids that bud alternately left and right”. The zooids are the little skeletal tubes, each of which housed an individual bryozoan connected by soft tissue to the rest of the colony. Uniserial means that most series of zooids have just one branching from another. Geniculate means “bent abruptly” like a knee joint. Monomorphic refers to the shape of each zooid being about the same. The scale bar is 0.20 mm.

3 Zig zooid shape 0p10

It is this zig-zag shape that makes Zigzagopora distinctive. Scale bar is 0.10 mm.

4 Zig over Cory 0p20The abstract ends with “… superficial similarities with the corynotrypid cyclostomes with which it co-occurs.” In this scene Zigzagopora (Z) has overgrown a branch of the encrusting cyclostome bryozoan Corynotrypa (C). These bryozoans are obviously similar, but the geniculate (our new word!) nature of Zigzagopora sets it apart. This is significant beyond just the shape of the colony: it indicates a different kind of budding of one zooid from another. The scale bar is 0.20 mm.

5 Ancestrula Zig 0p06All bryozoans start from an initial zooid called the ancestrula. It is not always easy to find, but is critical for identification and systematics. The arrow points to the protoecium, the first chamber. The scale bar is 0.06 mm.

6 Pore in zooecium 0p03Inside a broken zooid we can see an interior wall surface and a tiny pore. Really tiny. This is likely an interzooidal pore connecting the soft parts of the zooids. Scale bar is 0.03 mm.

7 Extended zig 0p60Here, then, is Zigzagopora wigleyensis, new to science. It is a tiny new piece for the puzzle that is the evolution of cyclostome bryozoans. It is one of countless billions of species in the history of life, but unique nonetheless.

References:

Taylor, P.D. and Wilson, M.A. 1994. Corynotrypa from the Ordovician of North America: colony form in a primitive stenolaemate bryozoan: Journal of Paleontology 68: 241–257.

Wilson, M.A. and Taylor, P.D. 2016. A new runner-like cyclostome bryozoan from the Bromide Formation (Sandbian, Upper Ordovician) of Oklahoma and its phylogenetic affinities. Journal of Paleontology 90: 413-417.

UPDATE: Zigzagopora wigleyensis made the cover!

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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.

Wooster’s Fossil of the Week: A bored rhynchonellid brachiopod from the Middle Jurassic of France

July 22nd, 2016

1 Kutchi dorsal 585Another beautiful brachiopod this week from our friend Mr. Clive Champion in England. His donations to our collections have considerably enriched our teaching program, especially for brachiopods! This specimen is the rhynchonellid Kutchirhynchia morieri (Davidson, 1852) from the Middle Jurassic (Upper Bathonian) of Luc-sur-Mer, France. This is a view of the dorsal side with the dorsal valve on top with the ventral valve (containing the round opening from which the stalk-like pedicle extended) seen below it. Like most rhynchonellids, the valves have distinct plicae (thick ridges) where the shell is tightly folded.
2 Kutchi ventral 585This is the ventral view showing only the exterior of the ventral valve. Note the curved serpulid worm tube attached near the center, and the squiggly borings. These were likely sclerobionts (hard substrate dwellers) that occupied the brachiopod shell when the animal was still alive, since the dorsal and ventral valves are still articulated. The borings are probably of the ichnogenus Talpina, but I would have to grind down the shell to know for certain.
SSBuckmanThe genus Kutchirhynchia was named by Sydney Savory Buckman (1860-1929) in 1917. We met Buckman earlier in this blog when looking at another of his Jurassic rhynchonellid genera, Burmirhynchia. We learned a lot more about Buckman this summer during our expedition to the Jurassic of Dorset, where he did much of his work. He is best known there as an ammonite worker and stratigrapher (and massive taxonomic splitter).
3 Thomas DavidsonThe species Kutchirhynchia morieri was named by the Scottish paleontologist Thomas Davidson (1817-1885), who originally placed it in the large genus Rhynchonella. Buckman acknowledges Davidson in an ammonite monographs as one of his “earliest geological friends”. (Davidson was 43 years older than Buckman.) Davidson was born in Edinburgh to wealthy parents. He studied at the University of Edinburgh and then in France, Italy and Switzerland, where he made many long geological tours. He was convinced by the German paleontologist Christian Leopold von Buch (1774-1853) to work on fossil brachiopods. (Von Buch was 43 years older than Davidson. Nice to see the older generation having an effect on those kids!) Davidson stayed with brachiopods his entire career, producing massive monographs on both fossil and recent forms. He engraved his own plates on stone, and there are more than 200 of them. Davidson was elected a fellow of the Geological Society of London in 1852, awarded the Wollaston medal in 1865. In 1857 he was elected a Fellow of the Royal Society, receiving their Royal medal in 1870. Upon his death in Brighton, England, in 1885, his entire collection of fossil and recent brachiopods went to the British Museum.
4 Elizabeth GrayThis is a good place to mention Elizabeth Anderson Gray (1831-1924), an important fossil collector in Scotland who supplied Thomas Davidson and many other paleontologists with critical specimens for their work. She is one of the many unnoticed heroes of paleontology, being rarely acknowledged publicly and then overshadowed by her husband. She worked primarily in the Ordovician and Silurian and so did not give Davidson Jurassic rhynchonellids, but she provided hundreds of brachiopods from the early Paleozoic. I love this image of her knocking out fossils with a hammer, just like we do today. Trowelblazers has an excellent biographical page on Elizabeth Anderson Gray.

References:

Buckman, S.S. 1917. The Brachiopoda of the Namyau Beds, Northern Shan States, Burma. Palaeontologia lndica 3(2): 1-254.

Gilman, D.C., Thurston, H.T. and Colby, F.M., eds. 1905. Davidson, Thomas (paleontologist). New International Encyclopedia (1st ed.). New York: Dodd, Mead.

Shi, X. and Grant, R.E. 1993. Jurassic rhynchonellids: internal structures and taxonomic revisions. Smithsonian Contributions to Paleobiology, Number 73, 190 pages.

Wooster’s Fossils of the Week: A molluscan assemblage from the Miocene of Maryland

July 15th, 2016

1 Calvert Zone 10 Calvert Co MD 585Earlier this month a gentleman stopped by The Department of Geology and donated the above beautiful slab of fossils to our program. Dale Chadwick of Lancaster, Pennsylvania, is an avid amateur fossil collector with a very useful website and considerable generosity. His gift to the department makes an excellent Fossils of the Week entry. Later I’ll show you the equally-impressive other side of this specimen!

We have here a fine sandstone from the famous Calvert Formation (lower to middle Miocene) exposed at the Calvert Cliffs, Plum Point, Calvert County, Maryland, in the stratigraphic Shattuck Zone 10. As you can see, some horizons are densely fossiliferous with large numbers of gastropods and bivalves. This is what we refer to us a death assemblage, meaning these shells are not preserved in their life positions but how they accumulated just before final burial. These rocks and their fossils were the initial basis of Susan Kidwell’s important work on taphonomic feedback, or how shell accumulations affect the succeeding living communities.

So what are the prominent fossils in this slab? Dale has the answers on his website. I’ve annotated the image and made a list below:

2 Calvert Zone 10 Calvert Co MD 585 labeledA Turretilla variabilis (a turritellid gastropod)
B Stewartia sp. (a lucinid bivalve)
C Turritella plebia (a turritellid gastropod)
D Cardium laqueatum (a carditid bivalve)
E Siphonalia devexa (a buccinid gastropod)

So how did several of these animals die on that seafloor long ago? You’ve probably guessed predation by looking at that round hole in specimen B, a lucinid bivalve.

3 Naticid borehole Calvert 585The beveled nature of this round drillhole tells us it was made by a predatory naticid gastropod, which used its radula (a tongue-like device with sharp teeth) to penetrate the calcareous shell and damage the muscles holding it tight against the attack. About half the specimens in this slab show similar predatory penetrations. Wooster alumna Tricia Kelley did critical work on predation styles, intensities and evolutionary patterns with Calvert specimens like these.

Thank you again to Dale Chadwick for his gift!

References:

Kelley, P.H., 1983, Evolutionary patterns of eight Chesapeake Group molluscs: Evidence for the model of punctuated equilibria: Journal of Paleontology 57: 581–598.

Kelley, P.H. 1988. Predation by Miocene gastropods of the Chesapeake Group: stereotyped and predictable. Palaios 3: 436-448.

Kidwell, S.M. 1986. Taphonomic feedback in Miocene assemblages: Testing the role of dead hardparts in benthic communities: Palaios 1: 239–255.

Kidwell, S.M., Powars, D.S., Edwards, L.E. and Vogt, P.R. 2015. Miocene stratigraphy and paleoenvironments of the Calvert Cliffs, Maryland, in Brezinski, D.K., Halka, J.P. and Ortt, R.A., Jr., eds., Tripping from the Fall Line: Field Excursions for the GSA Annual Meeting, Baltimore, 2015: Geological Society of America Field Guide 40, p. 231–279.

Wooster’s Fossil of the Week: An ammonite from the Middle Jurassic of southern England

July 8th, 2016

Leptosphinctes microconch Jurassic Dorset 585We’re featuring just a workaday fossil this week because of other summer activities. This is the ammonite Leptosphinctes Buckman 1929 from the Inferior Oolite (Middle Jurassic) at Coombe Quarry, Mapperton, Dorset, southern England. Cassidy Jester (’17) and I collected it last month during our 2016 England research expedition. Our friend Bob Chandler generously identified it. It popped out of a rock we were pounding into submission, providing a direct application of ammonite biostratigraphy to our work. As with many ammonites, the group is well known but the names are still a bit dodgy.

This specimen is a microconch, meaning it is the smaller version of a species pair, the larger being the macroconch. It is presumed that this is sexual dimorphism and that the microconch is the male because it didn’t need to carry resources for egg-laying. This is one reason why the taxonomy of these ammonites is in perpetual revision.

References:

Buckman, S.S. 1909–1930. Yorkshire Type Ammonites & Type Ammonites. Wesley & Son, Wheldon & Wesley, London, 790 pl.

Chandler, R B., Whicher, J., Dodge, M. and Dietze, V. 2014. Revision of the stratigraphy of the Inferior Oolite at Frogden Quarry, Oborne, Dorset, UK. Neues Jahrbuch für Geologie und Paläontologie-Abhandlungen 274: 133-148.

Galácz, A. 2012. Early perisphinctid ammonites from the early/late Bajocian boundary interval (Middle Jurassic) from Lókút, Hungary. Geobios 45: 285-295.

Pavia, G. and Zunino, M. 2012. Ammonite assemblages and biostratigraphy at the Lower to Upper Bajocian boundary in the Digne area (SE France). Implications for the definition of the Late Bajocian GSSP. Revue de Paléobiologie, Vol. spéc, 11: 205-227.

Wooster’s Fossils of the Week: Iron-oxide oncoids (“snuff-boxes”) from the Middle Jurassic of southern England

July 1st, 2016

1 Snuffbox colection BBThese fossils (in the broad sense!) are inevitable for our weekly feature considering how much time we spent studying and collecting them during last month’s fieldwork in Dorset, southern England. “Snuff-boxes” are the subject of Cassidy Jester’s (’17) Senior Independent Study project, so here we’ll just broadly cover what we think we know about them.

These discoidal objects are called “snuff-boxes” because their carbonate centers (usually a bit of limestone or shell) often erode faster than their iron-oxide exteriors, making them weather a bit like boxes with lids.
2 Quote from Buckman 1910 67This quote from Buckman (1910, p. 67) is the earliest reference I can find to the snuff-box term. Snuff-boxes were sometimes works of art in the 18th and 19th centuries, although quarrymen probably had more homespun varieties in mind.
1 Snuffbox serpulidssWe’re counting these snuff-boxes as fossils here because they formed through biotic and physical processes. The cortex of a snuff-box has layers of serpulid worm tubes, as shown above.
4 Palmer Wilson Fig 3There are also cyclostome bryozoans embedded within the iron-oxide layers, as shown in this image from Palmer and Wilson (1990, fig. 3).
3 Snuff-box horn 061716We believe the snuff-boxes grew by accretion of microbially-induced layers of iron-oxide formed on their undersides, which would have been gloomy caverns on the seafloor. They then would have occasionally turned over and grew layers on the other side. Many snuff-boxes have extensions on their peripheries that look in cross-sections like horns, as seen above. The layers are separate from those that formed around the nucleus. They may have grown after the snuff-box became too big to be overturned by currents or animals.
6 Platy minerals pdt19573Paul Taylor and I looked at the cortex of a snuff-box with Scanning Electron Microscopy (SEM) and had the above surprising view. The odd platy materials may be limonite, an iron-oxide that is amorphous (non-crystalline).
7 Hebrew letters pdt19572Sometimes the plates look like they’ve partially evaporated, leaving remnants that resemble Hebrew letters!
8 iron ooid pdt19576Associated with the snuff-boxes are small “iron ooids” that are about sand-size. They too have the platy materials, and so their origin may be similar to that of the snuff-boxes.

Cassidy has an interesting project ahead of her testing various origin hypotheses and sorting out the paleontology, mineralogy and geochemistry.

References:

Buckman, S.S. 1910. Certain Jurassic (Lias-Oolite) strata of south Dorset and their correlation. Quarterly Journal of the Geological Society 66: 52-89.

Burkhalter, R.M. 1995. Ooidal ironstones and ferruginous microbialites: origin and relation to sequence stratigraphy (Aalenian and Bajocian, Swiss Jura mountains). Sedimentology 42: 57-74.

Gatrall, M., Jenkyns, H.C. and Parsons, C.F. 1972. Limonitic concretions from the European Jurassic, with particular reference to the “snuff-boxes” of southern England. Sedimentology 18: 79-103.

Palmer, T.J. and Wilson, M.A. 1990. Growth of ferruginous oncoliths in the Bajocian (Middle Jurassic) of Europe. Terra Nova 2: 142-147.

Wooster’s Fossils of the Week: Encrusting cyanobacteria from the Upper Ordovician of the Cincinnati region

June 24th, 2016

1 pdt19598 D1253Deep in the basement of the Natural History Museum in London, Paul Taylor and I were examining cyclostome bryozoans encrusting an Upper Ordovician brachiopod with a Scanning Electron Microscope (SEM). This is one of our favorite activities, as the SEM always reveals tiny surprises about our specimens. That day the surprises were the smallest yet – fossils we had never seen before.

2 Infected brachWe were studying the dorsal exterior surface of this beat-up brachiopod from a 19th Century collection labelled “Cincinnati Group”. (Image by Harry Taylor.) We knew it was the strophomenid Rafinesquina ponderosa, and that the tiny chains of bryozoans encrusting it were of the species Corynotrypa inflata. We’ve seen this scene a thousand times. But when we positioned the SEM beam near the center of the shell where there was a brown film …

3 pdt16920 D1253… we saw that the bryozoans were themselves encrusted with little pyritic squiggles. These were new to us.

4 pdt19580 D7139In some places there were thick, intertwining mats of these squiggles. We later found these fossils on two other brachiopod specimens, both also Rafinesquina ponderosa and from 19th Century collections with no further locality or stratigraphic information.

5 pdt19578 D7139Last week Paul and I scanned these specimens again and began to put together an analysis. We believe these are fossil cyanobacteria. They are uniserial, unbranching strands of cells that range from 5 to 9 microns in length and width. Some of individual strands are up to 700 microns long and many are sinuous. The cells are uniform in size and shape along the strands; there are no apparent heterocysts. They appear very similar in form to members of the Order Oscillatoriales.

6 CyanobacteriaCyanobacteria are among the oldest forms of life, dating back at least 2.1 billion years, and they are still abundant today. The fossils are nearly identical to extant forms, as seen above (image from: http://www.hfmagazineonline.com/cyanobacteria-worlds-smallest-oldest-eyeball/).

7 pdt19599 D1253Paul made this remarkable image, at 9000x his personal record for high magnification, showing the reticulate structure preserved on some of the fossil surfaces. Note that the scale bar is just 2 microns long. These are beautiful fossils in their tiny, tiny ways.

We have not seen these cyanobacteria fossils before on shell surfaces, so we submitted an abstract describing them for the Geological Society of America annual meeting in Denver this September. We are, of course, not experts on bacteria, so we are offering our observations to the scientific community for further discussion. Here is the conclusion of our abstract —

“We suggest the cyanobacterial mats developed shortly before final burial of the brachiopod shells. Since the cyanobacteria were photosynthetic, the shells are inferred to have rested with their dorsal valve exteriors upwards in the photic zone. That Cincinnatian brachiopod shells were occupied by cyanobacteria has been previously well demonstrated by their microborings but this is the first direct evidence of surface microbial mats on the shells. The mats no doubt played a role in the paleoecology of the sclerobiont communities on the brachiopods, and they may have influenced preservation of the shell surfaces by the “death mask” effect. The pyritized cyanobacteria can be detected with a handlens by dark squiggles on the brachiopod shells, but must be confirmed with SEM. We encourage researchers to examine the surfaces of shells from the Cincinnatian and elsewhere to find additional evidence of fossilized bacterial mats.”

References:

Noffke, N., Decho, A.W. and Stoodle, P. 2013. Slime through time: the fossil record of prokaryote evolution. Palaios 28: 1-5.

Tomescu, A. M., Klymiuk, A.A., Matsunaga, K.K., Bippus, A.C. and Shelton, G.W. 2016. Microbes and the Fossil Record: Selected Topics in Paleomicrobiology. In: Their World: A Diversity of Microbial Environments (pp. 69-169). Springer International Publishing.

Vogel, K. and Brett, C.E. 2009. Record of microendoliths in different facies of the Upper Ordovician in the Cincinnati Arch region USA: the early history of light-related microendolithic zonation. Palaeogeography, Palaeoclimatology, Palaeoecology 281: 1-24.

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