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Ordovician ichnofossils


Wrangellian

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More ichnofossils, this time from the Ordovician of the Georgian Bay Fm (Lower member) in Toronto ON. @JUAN EMMANUEL sent them to me. In particular we got wondering about the little bumps all over the 2 pieces in the first pic, and the large 'mound' (or infilled hole) in the last pics. Anyone have any IDs for these or suggestions as to the nature of their formation?59c43b363b107_DSC_0328cro.thumb.jpg.c8154be603ab5e4bf5c13472d4e38038.jpg

 

 

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Here is the 'mound', with 3 side views.

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Stanley, D.C.A., & Pickerill, R.K. (1998)
Systematic ichnology of the late Ordovician Georgian Bay Formation of southern Ontario, eastern Canada.
Royal Ontario Museum - Life Sciences Contributions, 162:1-56  LINK

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In my thought the last specimen might be Bergaueria-like mound or related structure.

 

" We have divided the referred specimens into three informally termed categories; Bergaueria-like mounds, cupcake mounds, and tentacles-like structures. The Bergaueria-like mounds are simple to complex structures that are generally rounded to elliptical in outline. Specimens may have thin constrictions or sloped expansions at the bedding plane. Mound diameters range from 39 to 250 mm and height from the bedding plane ranges from 9 to 55 mm. Surface textures are rough and some show small bulges. Ornamentation or linings are not seen. Distal terminations lack a central depression. Pectinacean valves (Aviculopecten) sometimes occur as inclusions in Bergaueria like mounds.
Cupcake-type mounds are less abundant than Bergaueria-like mounds and generally smaller. They also differ by having rounded outlines, inwardly tapered sides, and flattened tops. Cupcake-type mounds are generally perpendicular to the bedding plane in orientation. Rarely, specimens may show dense, small invertebrate trails on their surfaces.
Tentacle-like structures appear as raised ridges in association with a Bergaueria-like mound or separately on shallow ripple slopes. These structures have rounded tops and are 1 mm wide or less. Both branched and unbranched forms occur. Tentacle-like structures are generally straight along their length, but may also curve or follow vertical contours on the slab surface. Some of the tentacle-like structures are covered by small invertebrate grazing trails at their base. " - description from here

 

Bergaueria-Mod-200-combined.thumb.jpg.9d35e3143b6b5351da228ed3527411a3.jpg

picture from here

 

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picture from here

 

 

 

 

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Those are some very nice ichnofossils. I sometimes pick cool looking specimens like that up but don't really give them a second thought. Glad to see that @piranha found a paper that will help with the ID's. 

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Yes, it's nice to have so much literature like they seem to have for the Toronto area! Thanks, all.

So far I can surmise that the trackways are some kind of Trichophycus, and the mound might be a Bergaueria or Bergaueria-like, which may or may not be biogenic. That's as far as I've gotten right now, will come back later. Still wondering about those little bumps...

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20 hours ago, Wrangellian said:

Still wondering about those little bumps...

It's a teenage rock and those are pimples. Nice job embarrassing it in front of it's friends!

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I'm pretty sure that in some areas of the surface the little bumps are arranged in a circular or semicircular manner, like it is shown in Fig. 6 - 10&12 of this document.

Considering that the ichnofacies might have a resemblance in appearance, character, or quantity, with similar ichnofacies of a different location and geological time, but having similar ichnogenera as constituent elements, I would like to compare the 'little bumps' with faecal pellets.

 

" Faecal pellets. Fig. 6(10, 12) and Fig. 8(1d).
Material: Numerous specimens preserved as full relief, and as concave semireliefs, in siltstone and fine-grained, micaceous sandstone. Among them, nine items are given the references MPZ 2002/773, 803, 881-883, 885-887 and 901.
Description: Pellets can be found either grouped or scattered on the rock. Scattered pellets range from 0.2 to 4.7 mm in diameter. MPZ 2002/881, 883 and 901.
Groupings are either linear or in circles. Linear groups are either straight and simple or curved and double (MPZ 2002/886; two parallel lines are 5 mm apart), accounting for a few pellets from 0.8 to 1.8 mm in diameter each. Total length reaches up to 30 mm.
Circular groupings show 5–15 pellets each, reaching up to 14.7 mm in diameter. Diameter of pellets range from 0.3 to 1.4 mm. MPZ 2002/773, 803, 882, 885 and 887.
Interpretation and discussion: The material is interpreted as faecal pellets after its morphology, arrangement patterns and mode of preservation. Prefossilization processes (Seilacher, 2002) should be invoked for preservation of primary morphologies.
Stratigraphical distribution and biochronology: Middle part of the Puente de Hierro section; Arroyo de Pedroche 1 section, levels 9 (upper part, above the Pedroche event) and 11. Lower Ovetian. "

 

 

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Interesting idea, abyssunder. I take it Ovetian is Cambrian - that's not too far off from the Late Ordovician.

So you don't think it's likely that we are looking at the negative side, here, and the bumps were originally indentations?

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campy.jpg

Let's not confound bio- and chronostratigraphy!

(The Ovetian is a biostratigraphical unit(with some correlation problems attending,see e.g. Geyer & Landing 2005)

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12 hours ago, doushantuo said:

campy.jpg

Let's not confound bio- and chronostratigraphy!

(The Ovetian is a biostratigraphical unit(with some correlation problems attending,see e.g. Geyer & Landing 2005)

This figure says "Litho- and chronostratigraphic units of the Cambrian sediments in the Iberian Chains." and it includes the Ovetian.

Anyway my point was it pertains to the Cambrian and not the Ordovician or any other perion/system.

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16 hours ago, Wrangellian said:

Interesting idea, abyssunder. I take it Ovetian is Cambrian - that's not too far off from the Late Ordovician.

So you don't think it's likely that we are looking at the negative side, here, and the bumps were originally indentations?

I think we are looking at the positive side.

The Ovetian stage is in the Lower Cambrian. Not that is important, but a similar ichnofacies with similar tracefossils, like Bergaueria, Cochlichnus, Monocraterion, Palaeophycus, Phycodes, Planolites, Rusophycus, Skolithos, as well as faecal pellets, meniscate trace fossils and others. If the figured 'bumps' in Gamez et al., 2006 are indeed faecal pellets, as it is supposed, than that would be the case with the specimens in question. It looks to me that the resemblance might be good.

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It does look pretty good... Thanks again. I'll amend the labels to include this possibility.

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On ‎2017‎-‎09‎-‎23 at 6:52 PM, abyssunder said:

I'm pretty sure that in some areas of the surface the little bumps are arranged in a circular or semicircular manner, like it is shown in Fig. 6 - 10&12 of this document.

Considering that the ichnofacies might have a resemblance in appearance, character, or quantity, with similar ichnofacies of a different location and geological time, but having similar ichnogenera as constituent elements, I would like to compare the 'little bumps' with faecal pellets.

 

" Faecal pellets. Fig. 6(10, 12) and Fig. 8(1d).
Material: Numerous specimens preserved as full relief, and as concave semireliefs, in siltstone and fine-grained, micaceous sandstone. Among them, nine items are given the references MPZ 2002/773, 803, 881-883, 885-887 and 901.
Description: Pellets can be found either grouped or scattered on the rock. Scattered pellets range from 0.2 to 4.7 mm in diameter. MPZ 2002/881, 883 and 901.
Groupings are either linear or in circles. Linear groups are either straight and simple or curved and double (MPZ 2002/886; two parallel lines are 5 mm apart), accounting for a few pellets from 0.8 to 1.8 mm in diameter each. Total length reaches up to 30 mm.
Circular groupings show 5–15 pellets each, reaching up to 14.7 mm in diameter. Diameter of pellets range from 0.3 to 1.4 mm. MPZ 2002/773, 803, 882, 885 and 887.
Interpretation and discussion: The material is interpreted as faecal pellets after its morphology, arrangement patterns and mode of preservation. Prefossilization processes (Seilacher, 2002) should be invoked for preservation of primary morphologies.
Stratigraphical distribution and biochronology: Middle part of the Puente de Hierro section; Arroyo de Pedroche 1 section, levels 9 (upper part, above the Pedroche event) and 11. Lower Ovetian. "

 

 

59c6e4c15e2f9_Gmez_et_al_2006.thumb.jpg.b753c7e02bfc94cdb3b0201cafb4dcc3.jpg

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I just want to point out that these round dots are similar in colour to the matrix they are in. @Wrangellian, I believe if you look at the undersides of these specimens there are also negative imprints of these dots. 

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Actually there are mostly positives on the underside, though the larger ichnos appear to me mostly negative... strange. I guess I have more photo'ing to do when we get some sunlight over here.

They are about the same color as the matrix but should they necessarily be different if they are fecal pellets? (that's a question for everybody)

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