Niobrara coprolite with marks

[doushantuo]

[Ramo]

Wow,  I was pleasantly surprised to this back up and some new ideas presented.  This could be getting us somewhere.  For the record though, I don't think I've ever collected a gastropod from the chalk.   That doesn't mean they were not there though.

 

Ramo

[GeschWhat]

12 hours ago, Ramo said:

For the record though, I don't think I've ever collected a gastropod from the chalk.   That doesn't mean they were not there though.

I haven't been able to find any evidence of gastropods from the Niobrara either. However, many gastropods don't have shells...like sea slugs. Do you happen to know what unit these were found in?

[GeschWhat]

23 hours ago, doushantuo said:

This is really interesting. I have been thinking about whether or not these traces and other traces would have been produced pre- or post fossilization. It seem many of the traces from modern species are etched into hard surfaces. I wonder if gastropods with unmineralized radulae would be more likely to graze on algae forming on fecal surfaces. Does anyone know anything about how common it is for fossiliferous exposures to be exposed and reburied? Just pondering out loud 

[doushantuo]

Common.

[GeschWhat]

3 minutes ago, doushantuo said:

Common.

So what do you think the likelihood is that these traces were left when the fecal matter was fresh? Is there anyway to tell?

[doushantuo]

*Mumbles*Buried karst,hiatus concretions,stratigraphic mixing,unconformities,transgressive lags,non-homotaxiality.etc.

looking at some stuff now

 

[ynot]

9 minutes ago, GeschWhat said:

So what do you think the likelihood is that these traces were left when the fecal matter was fresh? Is there anyway to tell?

That information should be detectable under a microscope, as rock will ebrate different than a soft poo would.

My guess would be that it is more likely done to relatively fresh droppings.

[doushantuo]

Tony could be (partly) on the right track: some radular morphologies might be distinctive enough ,at least underneath the microscope.

It is not beyond the realms of possibility that molluscan detritivores grazed coprolites covered with algae or cyanobacteria/(microbial mat).

meanwhile:

steneckwatlingMARBIOL1982.pdf

 

 

 

 

 

 

 

[GeschWhat]

I might have to break out the digital scope tomorrow and take some 100x images of those in my collection to see what they reveal. This 20x image of the traces on the coprolite I got from Ramo doesn't really show anything. I think the chips on the edges were likely happened during shipping when it rubbed against other coprolites. More fun!

 

[doushantuo]

might be fun/useful to investigate possible depth and shape changes along the traces.

U-shaped,V-shaped?

Do the endings coincide,if so how often?

Are the shallowest scratches in the middle of an average set,or on the outside?

Do the superposed ones differ from the "primal ones"?

Man-made scratches*(prehistoric OR recent),as Abyssunder pointed out,is still a possibility.

*from prehistoric forks?.((***they looked edible,Mom**))

 

[doushantuo]

afterthought(bit of threadjacking): why a random piece of Cretaceous chalk is intrinsically interesting for those interested in past life of ANY size:

 

Chalk nannofossils(coccoliths/image from Covington/JNRes./1994:New taxa from the Niobrara/lowermost:Kita et al: "Helicolithus from the Santonian of the Western Interior Seaway")

basically, chalk is made up of the skeletons of these organisms

magnification: x 2300

[kerrimarie805]

Niobrara chalk of western Kansas, would that be the area we called "the pyramids?" I lived in Scott City, Kansas for a few years in high school and we loved going out there on the weekends. Now I wish I'd known to take my Monday through Friday brain along and keep my eyes peeled!

[Ramo]

These are in the "lower chalk"  Very common to find, and not uncommon to find these lines in them.  I can testify for certain that the lines are not put into these during modern times.  The large one in the first picture of this thread was eroding out of a vertical chalk wall.  Some of the lines were in the portion that was still underground when I found it.  No way it was re-worked recently, and etched. 

 

Ramo

[MarcoSr]

Maybe this will help someone sort out a pattern for the different groups of lines.  The arrow heads could be in the opposite directions.  There does seem to be groups of lines going in the same direction (in the same color ellipses).

 

 

Marco Sr.

[sagacious]

As doushantuo suggested above, a large gastropod, may have grazed epiliths from exposed coprolites. 

 

Later, other gastropods graze the same coprolites as the epiliths regrow/recolonize, and (as Marco Sr observed) groups of overlapping or differently oriented grazing traces are left. 

 

Subsequent regrazing would suggest that the coprolites were mineralized and provided a durable, hard surface to (re)grow on. 

 

 

 

 

[GeschWhat]

On 12/12/2017 at 11:54 PM, doushantuo said:

might be fun/useful to investigate possible depth and shape changes along the traces.

U-shaped,V-shaped?

I looked at these under higher magnification, but couldn't really tell if they were U- or V-shaped. But I think I could just make out the individual radula marks in a few places. I outlined the start and stop points I could make out. What do you think?

[abyssunder]

I don't think there is any reliable evidence for gastropod grazing traces, also there were no fossil gastropods found in the same or adjacent layers. I think, the closest match might be chiton grazing marks after deposition of the coprolites and before sediment burial.

 

[GeschWhat]

I sent a quick email to Mike Everhart (Oceans of Kansas). He said that he had found a shark tooth that was possibly etched by an invertebrate, but has not seen gastropods in the chalk either. He said that the ocean bottom was "generally anoxic and devoid of most things that we would expect to see in a warm water ocean...Even the inoceramids appear to be specially adapted for a low oxygen environment (large gills)." So if these marks were left on the fecal matter prior to fossilization, whatever created them would have to be able to survive in a low oxygen environment or they were left by nibblers on their journey to the bottom.

[doushantuo]

"The ocean bottom" meaning?

[ynot]

9 minutes ago, doushantuo said:

"The ocean bottom" meaning?

Where it stops being water and starts being sand or rock.

[GeschWhat]

3 minutes ago, doushantuo said:

 

"The ocean bottom" meaning?

 

Sea floor. Doing a quick check, Nudibranchia known to exist in deep ocean environments, but like all deep sea dwellers, not much is known about them.

[doushantuo]

And was the seafloor below the Calcite Compensation Depth(more or less "lysocline)"?

I assume we're talking about the Western Interior Seaway?

In the Cretaceous,but which part of it?

BTW: anybody familiar with sea floor topography and its hypsometrical pecularities wouldn't poke fun at some questions I pose

BTW two :Seafloor lithification isn't a simple process.

Lithification involves such various processes as loss of water while pores were occluded by cement, the wet transformation of aragonite to calcite, recrystallisation of calcite, dissolution of small supersoluble particles, transfer of Mg2+, the production of secondary voids, influx of allochthonous CaCO3 and pressure-solution. Some micrites have been lithified on the seafloor as hardgrounds during prolonged exposure to seawater, supersaturated for CaCO3, for hundreds of thousands of years.

Of course,aragonitic mollusc can dissappear from the fossil record.... 

[westcoast]

On 12/12/2017 at 4:34 AM, Ash said:

What a fantastically interesting thread this has been

Agree 100%

[fifbrindacier]

5 minutes ago, westcoast said:

  On 12 décembre 2017 at 5:34 AM, Ash said:

What a fantastically interesting thread this has been

Agreed too.