Need A Term For This Kind Of Occurrence, Deposit.

[RichW9090]

The following is a deposit of undetermined Pleistocene age from the eastern shore of Tiburon Island, Sonora, Mexico. It consists of many, many tubes of Vermes or a similar worm, along with some of the other invertebrates which would have lived with them, molluscs, etc, all in life position.

It isn't a coquina, which is a high energy deposit formed when shells are broken up and mechanically sorted and then consolidated. In true coquina, the pieces are all very nearly the same size, and there are no, or very rare, complete shells.

This is almost a reef-like structure, with everything in life position.

Have you inveterate invertebrate specialists ever seen a name for this type of deposit?

Edited September 8, 2013 by RichW9090

[rejd]

I can't help with your question but when i try to view the picture it says I don't have permission to view it. Anyone else?

[Indy]

I got the same message about not having permission to view the image

However, I wasn't signed in. I signed in and tried again and link to me

to a gallery page but the image was not visible.

[Auspex]

Probably not a "public gallery", since I cannot view it either.

[piranha]

On 9/8/2013 at 11:47 AM, RichW9090 said:

...This is almost a reef-like structure, with everything in life position. Have you inveterate invertebrate specialists ever seen a name for this type of deposit?

 

 

Following up on your observation of a reef-like structure; the term 'Vermetid Reef' shows up in this paper:

Quote

Many marine organisms with calcified shells or testae can accumulate through long periods of time to form a kind of lithic structures of different types and various sizes and colours, in which only the upper surface is alive. Vermetid reefs are one of such biogenic structures.

 

Al-Nimeh, M., & Elassafin, I. (1996)
Vermetid reefs (Gastropoda: Vermetidae) on the coast of Syria.
Zoology in the Middle East, 13(1):89-92

 

 

[piranha]

Searching through the various papers on vermetid reefs and the term 'Vermetid Biostrome' appears to be popular as well.

[Auspex]

Per Encyclopedia Britannica:

"A structure built by similar organisms that is bedded but not moundlike is called a biostrome"

("Autochthonous biostrome" is a particularly hefty term!)

[RichW9090]

It is in the same Gallery I always used, so unless you guys fiddled with the settings when you made the recent changes, I have no idea why you can't view it.

[Edit]. The image was a tif file - perhaps that was the problem. I have switched it out for a jpg.

Edited September 8, 2013 by RichW9090

[Auspex]

That's really strange looking; must have been a "no energy" deposit?

[piranha]

Digging a little deeper for the minutia and discovered 3 terms describing the elements of a vermetid reef:

 

Study of eroded reefs has shown that masses of vermetid tubes may have three distinctive growth habits.

These are termed heads, plates, and layers.

 

1) Heads are thick, solid masses of roughly parallel tubes which radiate upward and outward. Plate 1 shows a typical head which was formed during two growth episodes. Plate 2 shows a fragment of a head in which crowding was extreme. In order for heads to form, the vermetids of the nucleus must colonize substrate within the lower part of the intertidal zone; growth can then proceed upward for a distance of up to two feet. Another condition necessary for head development is a strong current; the current brings food and removes fecal products from a relatively dense population of vermetids. Heads are especially characteristic of reef edges which border deep tidal channels.

 

2) Plates form in the upper part of the intertidal zone where growth upward is limited by the length of time the orifice is exposed at low tide. Plates are typically a few inches in thickness and one to three feet in diameter. Growth is initiated on some firm substrate and advances radially outward, often growing over soft,muddy pockets. Where the edges of two plates meet, tubes bend upward almost vertically, forming a lip around the plate. In the central part of the plate's top, there are scattered tubes which form lax coils attached to the more or less parallel tubes below. Plate 3 shows a plate fragment. Plate 4 shows the surface of a reef consisting entirely of plates. Each plate is fused to underlying plates to form a solid framework.

 

3) Layers are formed in areas where the lower part of the intertidal zone has adequate substrate exposed, but tidal currents are not sufficient to support the large population necessary for head formation. Layers slope toward the water at angles of 10 to 30° and are laterally continuous for tens of feet. Each layer is several inches thick and has a slightly different aspect. Different layers show changes in tube density, tube growth (coiled or straight tubes), and percentage of interstitial silt and sand. Layers are shown in Plate 5.

 

Heads and layers were formed only at the edges of a reef and were mainly responsible for the lateral accretion of the reef framework. Plates formed in the upper part of the intertidal zone and built a cap over the layers and heads below. When sea level rose and vermetids colonized the tops of older reefs, most of the growth was in the form of plates. Plate growth has been mainly responsible for vertical reef accretion.

 

Shier, D.E. (1969)

Vermetid reefs and coastal development in the Ten Thousand Islands, southwest Florida.

Geological Society of America Bulletin, 80(3):485-508

 

 

 

[Ridgehiker]

Neat looking, never seen it before. Also a reminder that reefs were built of of various types of area isms throughout time.

General terms for some type of deposition can get nebulous. A geology paper would describe the specifics. One old paleo professor would give anyone the evil stare if the term 'crinoidal limestone' was used.

[RichW9090]

Piranha,

Much thanks! It will appear in print as "...dead, possibly fossil, intertidal Vermetid reefs....."

[Auspex]

Digging a little deeper for the minutia and discovered 3 terms describing the elements of a vermetid reef:...

[piranha]

Piranha,

Much thanks! It will appear in print as "...dead, possibly fossil, intertidal Vermetid reefs....."

Happy to assist and look forward to reading that paper!

[RichW9090]

Piranha: In looking through the two references you provided, and the references in their bibliographies, etc. It appears that such intertidal reefs have not been well studied. Especially neglected are the fossil examples. I was asking about this because that picture, or one like it, is going to appear in a book about the aboriginal use of molluscs in a large portion of the Gulf of California, which I am reviewing. The author wanted to call the depost a coquina, which it clearly is not.

I've now talked to the author, and she and I are going to see if we can do a paper describing this occurrence, after we get a date or two on the shells - although that is not the best materail to date, because shelled marine organisms are known to extract and incorporate into their shells fossil carbonates from the sea water, often giving anamolously old dates. I hope to make a trip down there at the end of the year to see if there is any stratigraphic, perhaps archaeological, way to more closely dte the deposits.

I'll post some more pictures when I can find my high res originals.

Rich

Edited September 9, 2013 by RichW9090