Wooster’s Fossil of the Week: A common trilobite from the Upper Ordovician of Ohio

Mark Wilson December 11, 2015 12:28 am

Flexicalymene meeki cephalon view 585This beautiful specimen was collected by Wooster student Eve Caudill on this year’s College of Wooster Invertebrate Paleontology field trip to Caesar Creek Lake, Ohio. It is the iconic trilobite Flexicalymene meeki (Foerste, 1910) from a soft, “buttery” shale in the Waynesville Formation (Upper Ordovician). This is one of the most common trilobite species in the world, and it has been photographed thousands of times, so I posed it at an unconventional, rakish angle. We are looking here at the cephalon (head) of the animal. I like the way the remnants of the enclosing sedimentary matrix cling to the low places, highlighting the bumps and ridges. The center of the cephalon shows the distinctive glabella with its side lobes. The stomach of the trilobite was housed underneath it. The two eyes are visible on either side of the glabella, the one on the right split by the slightly-open facial suture used for dividing its exoskeleton during molting (ecdysis).

Flexicalymene meeki pygidium view 585This is a view of the pygidium (tail end) of the same Flexicalymene meeki specimen. It is tucked under the leading edge of the cephalon in the classic enrollment position. Trilobites likely enrolled for several reasons, but the primary one was almost certainly to affect a pill-bug-like defense against predators.

Flexicalymene meeki side view 585This is a side view of the enrolled trilobite. The articulated segments between the cephalon and pygidium constitute the thorax.foerste-1936We met the author of Flexicalymene meeki four years ago in this blog, so let’s visit him again. August F. Foerste (1862-1936) was one of the pioneers of Cincinnatian paleontology and stratigraphy. He grew up and worked in the Dayton, Ohio, area. Foerste went to Denison University where he was a very successful undergraduate, publishing several geological papers. He returned to Dayton after graduation with a PhD from Harvard, teaching high school for 38 years. When he retired he was offered a teaching position at the University of Chicago, but instead went to work at the Smithsonian Institution until the end of his life.

A final note from the Invertebrate Paleontology class this year: We were greatly assisted by two fantastic paleontological websites, one by Alycia Stigall at Ohio University called The Digital Atlas of Ordovician Life, and the other by Steve Holland at the University of Georgia titled The Stratigraphy and Fossils of the Upper Ordovician near Cincinnati, Ohio. Thank you to my most excellent and productive colleagues.

References:

Brandt, D.S. 1993. Ecdysis in Flexicalymene meeki (Trilobita). Journal of Paleontology 67: 999-1005.

Brett, C.E., Thomka, J.R., Schwalbach, C.E., Aucoin, C.D. and Malgieri, T.J. 2015. Faunal epiboles in the Upper Ordovician of north-central Kentucky: Implications for high-resolution sequence and event stratigraphy and recognition of a major unconformity. Palaeoworld 24: 149-159.

Esteve, J., Hughes, N.C. and Zamora, S. 2011. Purujosa trilobite assemblage and the evolution of trilobite enrollment. Geology 39: 575-578.

Evitt, W.R. and Whittington, H.B. 1953. The exoskeleton of Flexicalymene (Trilobita). Journal of Paleontology 27: 49-55.

Foerste, A.F. 1910. Preliminary notes on Cincinnatian and Lexington fossils of Ohio, Indiana, Kentucky, and Tennessee. Denison University Science Laboratories Bulletin 16: 17-87.

Frey, R.C. 1987. The paleoecology of a Late Ordovician shale unit from southwest Ohio and southeastern Indiana. Journal of Paleontology 61: 242-267.

 

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A True Liberal Arts Experience

mpollock December 9, 2015 8:21 pm

Guest Blogger: Mary Reinthal

If you were to poll the campus about their fall break, not many would say that they spent 20 hours over 2 days in an FTIR lab analyzing glass chips for volatile content. But if you were to ask geology senior Mary Reinthal and her advisor Dr. Meagen Pollock, that’s exactly what they would say. Fly in on a Monday; analyze samples at University of Massachusetts Amherst Tuesday and Wednesday; fly out Thursday. It was a lot of work, but somebody had to do it (for their Independent Study). The time was spent looking at the volatile spectra from individual, doubly polished glass chips collected from British Columbia, Canada.

Not a lot of windows in the FTIR lab, so Mary had to look at glass chips.

Not a lot of windows in the FTIR lab, so Mary had to look at glass chips.

After all that time in the lab, a lot of data were collected (yay!). These numbers will hopefully help us understand the evolution of glaciovolcanic tindars in British Columbia. Until then, however, these data will to be sifted through and looked at more closely as the semester continues.

Mary measuring thickness of glass wafers. To understand the bigger picture of volatile effects on eruptions you have to look small. Like micron-scale small.

Mary measuring thickness of glass wafers. To understand the bigger picture of volatile effects on eruptions you have to look small. Like micron-scale small.

Of course, the visit to U-Mass. Amherst wasn’t all science and glass chips. After finishing a 9-hour stint in the lab on Wednesday, Dr. Pollock and Mary ventured to Concord, Massachusetts to visit Walden Pond. In short, a truly liberal arts education was had by all.

Mary and Thoreau pondering life and science.

Mary and Thoreau pondering life and science.

 

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Wooster’s Fossils of the Week: Zig-zag oysters from the Middle Jurassic of southern Israel

Mark Wilson December 4, 2015 12:01 am

Actinostreon Matmor Jurassic 171 173 585These pretty little oysters are from the Matmor Formation (Middle Jurassic, Callovian) of Makhtesh Gadol in southern Israel. Because I regrettably missed going to Israel for fieldwork this summer, I thought I’d choose these exquisite fossils to be celebrated this week. The genus is Actinostreon Bayle, 1878. There may be more than one species here, so we’ll just leave the identification at the genus level.
Actinostreon single 585Actinostreon is very common in some units of the Matmor Formation. Hundreds can be found scattered through a single unit. They were epifaunal filter-feeders as all oysters, and like most attached to hard substrates. The Actinostreon in the Matmor Formation commonly settled on small shell fragments in marl, giving them the appearance of dwelling in mud. Their zig-zag commissures (their shells are formally called plicate) strengthened their shells with ribs and helped them maintain high water inflow for filter-feeding with a relatively small opening (gape).
bayle 300The French paleontologist and mineralogist Claude Émile Bayle (1819-1895) named the genus Actinostreon in 1878. Bayle was raised in the beautiful French coastal city of La Rochelle. His family was related to Alcide Dessalines d’Orbigny (1802-1857), one of the greatest French naturalists, so collecting and analyzing fossils and modern shells was encouraged. Bayle studied at the Ecole Polytechnique and then the Ecole des Mines. After his schooling he was employed as the Chief Engineer of the Corps des Mines. He assembled a large collection of fossils (about 185,000 of which were cataloged). In 1848 he began teaching paleontology and mineralogy at the Ecole des Mines, retiring in 1881. His paleontological specialties were mollusks (especially Jurassic and Cretaceous bivalves) and Cenozoic mammals. He had a fairly modest publication record until he produced his magnum opus, an 1878 fossil atlas to accompany a new geological map of France. It is here that he described Actinostreon, and many other new taxa.

References:

Alberti, M., Fürsich, F.T. and Pandey, D.K. 2013. Seasonality in low latitudes during the Oxfordian (Late Jurassic) reconstructed via high-resolution stable isotope analysis of the oyster Actinostreon marshi (J. Sowerby, 1814) from the Kachchh Basin, western India. International Journal of Earth Sciences 102: 1321-1336.

Bayle, E. 1878. Fossiles principaux des terrains: Explication carte geologique France. France Service Carte Geologique, vol. 4, pt. 1, pl. 132.

Hirsch, F. 1980. Jurassic bivalves and gastropods from northern Sinai and southern Israel. Israel Journal of Earth Sciences 28: 128-163.

Machalski, M. 1998. Oyster life positions and shell beds from the Upper Jurassic of Poland. Acta Palaeontologica Polonica 43: 609-634.

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Wooster’s Fossil of the Week: A fragmentary rostroconch from the Middle Devonian of Ohio

Mark Wilson November 27, 2015 12:15 am

1 Hippocardia 1Not all of our featured fossils are particularly beautiful, or even entire, but they are interesting in some way. Above is the broken cross-section of a rostroconch mollusk known as Hippocardia Brown, 1843. It was found somewhere in Ohio by the late Keith Maneese and kindly donated to the department by his widow Cameron Maneese. From its preservation and the kind of rock making up the matrix inside, we can tell that it almost certainly came from the Columbus Limestone (Middle Devonian, Eifelian).

In the top image it is apparent that this fossil has bilateral symmetry, a heart-shaped cross-section, and a ribbed calcitic shell. This is the dorsal view.
2 Hippocardia 2Flipping the specimen upside-down, we now have a view of the ventral portion. Again we see the ribs and bilateral symmetry.
3 Hippocardia side viewThis side view shows that the ribs extend from the dorsal to the ventral sides and are angled to the axis of the shell. That’s about all we can tell. (And this is the best specimen of a rostroconch we have! Thank you again, Cameron.)
4 CzechVirtualRostroThis diagram of a complete rostroconch (from the Czech Virtual Museum). This is a side view of a species that does not have the dorsal-ventral ribbing. The shell is superficially like that of a bivalve (clam), but the valves are fused together and their is a distinctive tube (rostrum) extending to the posterior. Much study and debate about the rostroconchs has at least confirmed that these are a class of mollusks separate from the bivalves. They lived semi-infaunally with the rostrum extending into the seawater to channel a flow of water into the body chamber for filter-feeding, much like infaunal bivalves today that have siphons. Rostroconchs and cephalopods appear to be sister groups, and some rostroconchs may have evolved into the scaphopods. Plenty of arguments to go around, though, on the evolution and diversification of mollusks
5 Thomas 1843 p 976 Thomas pl 8 fig 10 1843Captain Thomas Brown (1785-1862) named the genus Hippocardia in 1843. He was a Scottish naturalist who studied many topics, including mollusks. Above are the sections of his book The Elements of Fossil Conchology that describe and illustrate Hippocardia (considering it a bivalve). Captain Brown was born in Perth and went to school in Edinburgh. He joined the militia at 20, becoming a captain at 26. When he was transferred to Manchester, England, Brown acquired an interest in nature. He bought a flax mill after leaving the military, but it burned down while still uninsured. He thus turned to nature writing for support. He was became a Fellow of the Royal Society of Edinburgh in 1818, and in 1840 he was appointed curator of the Manchester Museum. He retained this position for the rest of his life. He was later a Fellow of the Linnean Society and a member, in classic 19th Century fashion, of several other groups, including the Wernerian, Kirwanian and Phrenological Societies. (I love the addition of phrenology to his interests!) The marine gastropod Zebina browniana d’Orbigny, 1842, was named after him. An interesting character, this Captain Brown, but I’ve been unable to find a single portrait of him.

References:

Brown, T. 1843. The elements of fossil conchology according to the arrangement of Lamarck; with the newly established genera of other authors. Houlston & Stoneman, London; 133 pages.

Hoare, R.D. 1989. Taxonomy and paleoecology of Devonian rostroconch mollusks from Ohio. Journal of Paleontology 63: 838-846.

Pojeta, J., Jr., Runnegar, B. 1976. The paleontology of rostroconch mollusks and the early history of the phylum Mollusca. United States Geological Survey Professional Paper 968: 1-88.

Pojeta, J., Jr., Runnegar, B., Morris, N.J. and Newell, N.D. 1972. Rostroconchia: a new class of bivalved mollusks. Science 177: 264-267.

Runnegar, B., Goodhart, C.B. and Yochelson, E.L. 1978. Origin and evolution of the Class Rostroconchia [and discussion]. Philosophical Transactions of the Royal Society B: Biological Sciences 284(1001): 319-333.

Wagner, P.J. 1997. Patterns of morphologic diversification among the Rostroconchia. Paleobiology 23: 115-150.

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Wooster’s Fossil of the Week: A tall brachiopod from the Devonian of western Russia

Mark Wilson November 20, 2015 12:01 am

1 Ladogia Nalivkin, 1941In the summer of 2009 I had a field adventure in Russia. It was an extraordinary time. I learned considerable amounts of Russian geology and paleontology, of course, and was immersed in the Russian geological culture. Along the way I collected the above unusual brachiopod. We are looking at its posterior (where the articulating hinge is), with the ventral valve below and dorsal valve above.
2 Ladogia Nalivkin, 1941This is the anterior view of the same specimen showing the junction between the valves (the commissure). The brachiopod is Ladogia Nalivkin, 1941, a rhynchonellid from the Upper Devonian (Frasnian) of the Central Devonian Field somewhere along the Syas River in the Leningrad Oblast of western Russia. We can immediately see that this brachiopod is very tall for its kind, with a strongly defined fold (the top part of the “anticline” in the dorsal valve) and sulcus (the lower folded surface in the  ventral valve). Note that the sulcus has several encrusting organisms, including eroded microconchids.
3 Ladogia Nalivkin, 1941The side view shows the dramatic upward sweep of the dorsal valve and the fine radiating ornamentation. The tall fold was effective in separating the incoming water for filter-feeding from the outflow of filtered water, essentially functioning like a chimney. Many brachiopods have such a fold and sulcus, but few have a set of such amplitude.
4 Nalivkin, Dmitrii VasilevichLadogia was described by Dmitrii Vasil’evich Nalivkin (1889-1982) in 1941. Nalivkin was a Soviet paleontologist and geologist born in 1889 in St. Petersburg. He graduated from the Institute of Mines in Petrograd (the name was changed from St. Petersburg) in 1915. In 1917 he joined the Geological Commission of Russia, staying a member through its many changes for over six decades. In 1920 he became a professor at the Institute of Mines after, we presume, the political situations from the Great War, the Bolshevik Revolution and the Russian Civil War calmed down. He is notable for giving the first lecture series on facies theory in the USSR in 1921. After World War II he was chairman of the Turkmen section of the Academy of Sciences. In 1954 he was made chairman of the Interdepartmental Stratigraphic Committee of the Academy of Sciences of the USSR. In 1954 he was appointed chairman of the Interdepartmental Stratigraphic Committee of the Academy of Sciences of the USSR. Nalivkin specialized in stratigraphy and paleontology of the Paleozoic, especially the Devonian and Carboniferous. He is best known for his geological maps of the USSR, for which he received the Lenin Prize in 1957. Here’s a man who saw a lot of history in his time.

References:

Nalivkin, D.V. 1941. Brachiopods of the Main Devonian field. Akademii Nauk SSSR Trudy 1: 139-226.

Sokiran, E.V. 2002. Frasnian-Famennian extinction and recovery of rhynchonellid brachiopods from the East European Platform. Acta Palaeontologica Polonica 47: 339-354.

Zhuravlev, A.V., Sokiran, E.V., Evdokimova, I.O., Dorofeeva, L.A., Rusetskaya, G.A. and Malkowski, K. 2006. Faunal and facies changes at the Early-Middle Frasnian boundary in the north-western East European Platform. Acta Palaeontologica Polonica 51: 747-758.

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Wooster’s Fossil of the Week: A striated brachiopod from the Silurian of New York

Mark Wilson November 13, 2015 12:04 am

6 StriispiriferCalebsSometimes it is a Fossil of the Week simply because it is new to me. The brachiopods above are abundant in a thin layer of shells within the Lewiston Member of the Rochester Shale (Silurian, Wenlockian) in western New York State. They are well exposed in the magnificent Caleb’s Quarry a few colleagues and I visited this past summer.
2 Striispirifer niagarensis Bed 9 Mbr D

3 Striations Sheinwoodian 585I find this spiriferid brachiopod fascinating because of the fine striations it shows on its fold and sulcus (where the shell bends at its middle). I’ve never seen these before on a brachiopod. The species is Striispirifer niagarensis (Conrad, 1842). I know of no functional interpretation of these fine lines other than that they might have provided some micro-topography to dissuade encrusting organisms. (I observed, in fact, no encrusters on these shells, but that may be coincidence.) The Striispirifer shell pavement consists mostly of isolated valves, but there are occasionally clusters of articulated shells in living position. It appears likely this is a storm lag of shells that was later colonized by the same brachiopods composing it.
4 Conrad description niagaraensisWe met the species author Timothy Abbott Conrad (1803-1877) earlier in this blog. He described this brachiopod originally as Delthyris niagaraensis in 1842 (above). (The third “a” in the species name was dropped by James Hall in his species lists.) This name held for over a century until G. Arthur Cooper and Helen Muir-Wood discovered that the genus was also in use for another brachiopod named in 1828 by Johan Wilhelm Dalman. This made “Delthyris” a homonym, or a name for a taxon identical in spelling to another such name for a different taxon. We can’t have that, of course, since every genus name must be unique (at least among the animals). Cooper and Muir-Wood (1951) gave the later genus (the junior homonym) the new name Striispirifer. Paul Taylor and I recently had our own adventure with a homonym we inadvertently created.
5 Helen Muir Wood 1955 Jill DarrellHelen Muir-Wood (1896-1968) was one of the most prominent brachiopod experts of the 20th Century. The image above may be the first one of her online. (Thanks to Jill Darrell of the Natural History Museum, London, for providing it. Come to think of it, the earlier image of Rousseau Hayner Flower in this blog is likely the first picture of him on the web.) Muir-Wood was born in Hampstead, England, and educated at Bedford College, University of London (a college for women at the time). She joined the professional staff at the British Museum (Natural History) in 1922 and spent the next 43 years of her career there. She was a systemacist to the core, apparently intolerant of any work with with fossils outside of describing and classifying them. Although she did no fieldwork of her own, from her position at the museum she was able to study brachiopods from around the world. She pioneered the techniques of describing brachiopod internal structures and eventually had to her credit hundreds of new and redescribed taxa. She was awarded the Lyell Medal in 1958 for her achievements, and in 1965 received the Order of the British Empire. She was remarkably successful and her work is still heavily cited to this day.

References:

Ager, D. 1969. Helen Marguerite Muir-Wood. Proceedings of the Geologists’ Association 80: 122-124.

Brett, C.E. 1983. Sedimentology, facies and depositional environments of the Rochester Shale (Silurian; Wenlockian) in western New York and Ontario. Journal of Sedimentary Research 53: 947-971.

Conrad, T.A. 1842. Observations on the Silurian and Devonian Systems of the United States, with descriptions of new organic remains. Journal of the Academy of Natural Sciences of Philadelphia 8: 228–280.

Cooper, G.A. and Muir-Wood, H.M. 1951. Brachiopod homonyms. Journal of the Washington Academy of Sciences 41: 195-196.

Dalman, J.W. 1828. Uppställning och Beskrifning af de i sverige funne Terebratuliter. Kongl. Svenska Vetenskaps Academiens Handlingar, für 1827, 1828; Stockholm, tryckt hos P.A. Norstedt & söner, pp. 93, 99.

Williams, A. 1969. Helen Marguerite Muir-Wood. Proceedings of the Geological Society of London 1655: 123-125.

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Wooster’s Fossil of the Week: Reptile tracks from the Lower Permian of southern Nevada

Mark Wilson November 6, 2015 12:02 am

1 Komodo on slab side viewAlways lead with your most interesting image. The fossil here is the thin orange slab of siltstone underneath my magnificent Komodo Dragon model.
2 Footprints slabHere is the slab itself. On the far right and the far left you can see two fossil footprints from both sides of some ancient reptile. The plastic Komodo Dragon just happens to fit these prints in size and shape, but they certainly weren’t made by an actual Komodo Dragon. I found this rock in the Spring Mountains of southern Nevada while doing my doctoral dissertation fieldwork decades ago. It is from the Lower Permian of the massive Bird Spring Formation (which is almost a mile thick). The footprints had nothing to do with my work (I was concentrating on the Carboniferous part of the formation), so I kept this little slab as a memento at home.
3 Back right track copyThese tracks, a kind of trace fossil, belong to the ichnogenus Dromopus based on the slender nature of the elongated toes. Dromopus has been attributed to an araeoscelid reptile, which looked and apparently lived very much like a modern lizard.
4 Araeoscelis grandis by Smokeybjb WikipediaAraeoscelis is one of the earliest diapsid reptiles, a group that has two distinctive holes (temporal fenestrae) on the sides of its skull. Diapsids are the most common type of reptile today, including crocodiles, lizards, snakes and dinosaurs. This genus was small, growing only to about 50 cm, and apparently predatory on insects and other arthropods. (Image from Smokeybjb via Wikipedia.)

5 Komodo top view on slabAgain, my friendly Komodo Dragon is only a stand-in for the Permian tracemaker, but he does have a nice pose to fit the tracks of his ancestral cousin!

References:

Haubold, H. and Lucas, S.G. 2003. Tetrapod footprints of the Lower Permian Choza Formation at Castle Peak, Texas. Paläontologische Zeitschrift 77: 247-261.

Hunt, A.P. and Lucas, S.G. 2006. Permian tetrapod ichnofacies. Geological Society, London, Special Publications 265: 137-156.

Hunt, A.P., Lucas, S.G., Lockley, M.G., Haubold, H. and Braddy, S. 1995. Tetrapod ichnofacies in Early Permian red beds of the American Southwest. New Mexico Museum of Natural History and Science Bulletin 6: 295-301.

Lucas, S.G. 2002. Global Permian tetrapod footprint biostratigraphy and biochronology. Permophiles 41: 30-34.

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Wooster’s Pseudofossils of the Week: Cone-in-cone structures from southern Ohio

Mark Wilson October 30, 2015 12:04 am

1 ShatterCones 585

Author’s note: James Chesire convinced me through the comments and later correspondence that what we actually have here are cone-in-cone structures, not shatter cones. I’ve thus changed the title but have left the post below in its original form. They are still pseudofossils. I’ll link here later for a full update. Thanks, James!

This complex rock was collected decades ago in Adams County, Ohio, by the late Professor Frank L. Koucky of The College of Wooster. He was at the time studying a strange geological feature in that part of the state known then as the Serpent Mound Cryptoexplosion Structure. He thought that the ring-like disturbance in the bedrock nearly 10 km wide was a place where “mantle gases” explosively erupted from below. The rock shown was going to be a key to deciphering the energy of these cataclysmic events. It is a set of shatter cones formed when enormous, high velocity pressures were applied to a micritic (fine-grained) limestone. Professor Koucky knew what these features represented, but they are still collected in that region and elsewhere as “fossils” by some because of their resemblance to corals. They are thus fine examples of pseudofossils, or inorganic features resembling fossils.

These shatter cones ended up showing conclusively that the event that caused the “bedrock disturbance” in southern Ohio was actually an ancient meteor impact, and the site is now known as the Serpent Mound Crater. This ancient crater (it may be as much as 320 million years old) has a central uplift surrounded by a ring graben (circular down-dropped rocks). It took a lot of clever geology to sort this out because known of it is now visible on the surface.
2 Shatter cones closerThe Serpent Mound shatter cones have a multiple long fractures running parallel to the cones, resembling hair or “horsetails”. The cones have horizontal step-like fractures on their broken surfaces. You can simulate this kind of structure by firing a BB or small rock at thick glass, which produces a conical fracture and perpendicular steps. To do this in a limestone requires between 20 and 200 kbar of pressure, which can only be achieved by a large meteorite impact or a nuclear explosion underground. More likely it was the former!
3 Shatter cones plan viewHere is what these shatter cones look like in plan view. The hole in the upper left is the tip of a cone that is not preserved.

So, shatter cones, despite their fine and repeatable details, are inorganic and not fossils of any kind. They represent enormous shock waves that left their marks as they passed through this limestone many millions of years ago.

References:

Carlton, R.W., Koeberl, C., Baranoski, M.T. and Schumacher, G.A. 1998. Discovery of microscopic evidence for shock metamorphism at the Serpent Mound structure, south-central Ohio: confirmation of an origin by impact. Earth and Planetary Science Letters 162: 177-185.

Kenkmann, T., Poelchau, M.H., Trullenque, G., Hoerth, T., Schäfer, F., Thoma, K. and Deutsch, A. 2012. Shatter cones formed in a MEMIN impact cratering experiment. Meteoritics and Planetary Science Supplement 75: 5092.

Milton, D.J. 1977. Shatter cones – an outstanding problem in shock mechanics. In: Impact and Explosion Cratering: Planetary and Terrestrial Implications 1: 703-714.

Sagy, A., Fineberg, J. and Reches, Z. 2004. Shatter cones: Branched, rapid fractures formed by shock impact. Journal of Geophysical Research 109: B10209.

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Nicolás Young (’05) receives a 2015 Blavatnik Award for his work measuring ice sheet response to past climate change.

gwiles October 29, 2015 9:45 am

nicolas-young-greenland-rocks-637x428

Congratulations Nicolás (now a researcher in the Cosmogenic Nuclide Group at Lamont-Doherty Earth Observatory ) – Read more about Nicolás’ work and his award here.

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Wooster’s Fossil (Maybe) of the Week: Kinneyia ripples

Mark Wilson October 23, 2015 12:01 am

1 Kinneyia_Grimsby_Silurian_Niagara_Gorge_585While hiking through the Niagara Gorge on a field trip in August, my friend Andrej Ernst of the University of Kiel found the above block of siltstone from the Grimsby Formation (Silurian) with unusual small-scale ripples in a patch. Carl Brett (University of Cincinnati) immediately identified it as a sedimentary structure/fossil known since 1914 as Kinneyia. This name was new to me. I had long called such features “elephant skin”, but I’ve now learned that these “sedimentary wrinkles” have a long and sometimes contentious history of study, and they have significant variability (see references).

Charles Doolittle Walcott (1850-1927) was one of the best known and productive invertebrate paleontologists. An American, he most famously discovered the Cambrian Burgess Shale in western Canada with its fantastic soft-tissue preservation. Walcott was especially fascinated with finding the earliest evidence of life, so he intently studied rocks older than the Cambrian (an interval we used to call the Precambrian). In 1914 he published a compendium of what we considered to be fossil algae, including Kinneyia. Below is his original description followed by his photographic image.
2 Walcott 1914 1073 Screen Shot 2015-08-22 at 6.42.01 PM4 Screen Shot 2015-08-22 at 6.42.57 PMWe now know that these curious structures are not fossilized algae, hence the name Kinneyia no longer has any biological use. (You may note that most authors do not italicize the name, emphasizing that it is no longer a valid taxon. I keep the style as a reminder of the name’s history.) These are ripples with sinuous, bifurcating, flat-topped crests. They are sometimes very complicated when the crests interfere with each other. Their flat tops (when well-preserved) suggest that there was something lying above them. Most workers on Kinneyia conclude that this was a microbial mat, so Walcott would be at least satisfied that life was involved. Did the Kinneyia ripples form as gas built up underneath a decaying mat? Are they made when the mat shrinks through desiccation? Experimental physicists have even gotten involved in the interpretations. Thomas et al. (2013) write: “Microbial mats behave like viscoelastic fluids. We propose that the key mechanism involved in the formation of Kinneyia is a Kelvin-Helmholtz type instability induced in a viscoelastic film under flowing water. A ripple corrugation is spontaneously induced in the film and grows in amplitude over time.”

Kinneyia is thus a sedimentary feature formed by physical processes mediated by life in the form of a microbial mat. What those processes were is the most interesting question now.

References:

Gerdes, G., Klenke, T. and Noffke, N. 2000. Microbial signatures in peritidal siliciclastic sediments: a catalogue. Sedimentology 47: 279-308.

Hagadorn, J.W. and Bottjer, D.J. 1997. Wrinkle structures: Microbially mediated sedimentary structures common in subtidal siliciclastic settings at the Proterozoic-Phanerozoic transition. Geology 25: 1047-1050.

Noffke, N., Gerdes, G., Klenke, T., Krumbein, W.E. 2001. Microbially induced sedimentary structures — a new category within the classification of primary sedimentary structures. Journal of Sedimentary Research A71: 649-656.

Porada, H., Ghergut, J. and Bouougri, E.H. 2008. Kinneyia-type wrinkle structures—critical review and model of formation. Palaios 23: 65-77.

Thomas, K., Herminghaus, S., Porada, H. and Goehring, L. 2013. Formation of Kinneyia via shear-induced instabilities in microbial mats. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 371(2004), 20120362.

Walcott, C.D. 1914. Cambrian geology and palaeontology III No.2 – Precambrian, Algonkian algal flora. Smithsonian Miscellaneous Collections 64: 77-156.

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