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

October 23rd, 2015

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.

2 Responses to “Wooster’s Fossil (Maybe) of the Week: Kinneyia ripples”

  1. Howard Allenon 23 Oct 2015 at 12:37 pm

    Thanks for this! I’ve been puzzling over these things for about 8 years, after seeing and photographing pretty much identical structures in carbonate rocks (Carboniferous/Mississippian) in the front ranges of the Canadian Rockies (Alberta). They look superficially like current or oscillation ripples, but seem “wrong” in several respects. This interpretation seems “right”! I’ll have to hit the library and check out your references.

    Cheers
    –Howard

  2. Bruce L. Stinchcombon 01 Jul 2016 at 1:13 am

    Charles D. Walcott was an astute and competent field geologist with an early and extensive experience with outcrops, rocks and fossils. Many of his “Pre-Cambrian Algonkian algae” (see above references) like Kinneyia and Newlandia have recently been relegated to the status of pseudofossils by a number of geologists. As a geologist who has seen these in the field in outcrop, I believe that this is wrong. It’s been said that the best geologist is one who has seen the most rocks and outcrops and I think this is true. Walcott saw lots of rocks, outcrops and fossils and he knew what he was doing!

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