The Taphonomy Thread

[Missourian]

I posted a couple things here in another thread. I thought it would be good to have 'one-stop shopping' for this fascinating subject.

 

So what is taphonomy? It is the study of the processes (as burial, decay, and preservation) that affect animal and plant remains as they become fossilized. It can be used to discern the paleoecology of the organisms as well as the sedimentary processes that led to their preservation.

[Missourian]

Some definitions....

 

Taphonomy can be divided into necrolysis, biostratinomy, and diagenesis.

 

Necrolysis - Death and decomposition of an organism.

 

Biostratinomy - The 'sedimentary history' of a fossil. This basically includes everything that happens from the moment of death until final burial.

 

Diagenesis - Chemical and mechanical alterations within the sediment. This includes everything that occurs from final burial until the fossil is exposed.

 

Bioturbation - Is the reworking of soils and sediments by animals or plants. Its effects include changing texture of sediments (diagenetic), bioirrigation and displacement of microorganisms and non-living particles. This can have a profound effect on sediments and organic remains contained within.

 

Time-averaging - The temporal mixing of fossils due to bioturbation or other processes. Unlike live-collected organisms, fossils found together within a single stratum need not be contemporaneous with one another, but may represent mixed remains of organisms that lived at different times and never interacted with one another. Fossilized shells, bones, and other skeletal remains collected from the same sediment layer or the same bedding plane may represent individuals that lived centuries or even millennia apart.

 

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I may edit definitions and add more terms in the future....

[Missourian]

Some rules of taphonomy, transcribed from 'Taphonomy: A Process Approach' by Ronald E. Martin:

 

1. Organisms are more likely to be preserved if they have hardparts.

 

2. Preservation is greatly enhanced by rapid burial, especially in fine-grained sediment (low turbulence) or in the absence of decay and scavenging.

 

3. During the transition from biocoenosis to thanatocoenosis, disarticulation and chemical alteration resulting from decay, abrasion, transportation, predation, scavenging, or dissolution cause loss of information about species abundances and community diversity and structure.

 

4. Fossil assemblages consist of a) autochthonous remains, which represent organisms that lived in the community and may have been preserved in life positions; parauthochthonous remains, which are autochthonous components that have been moved (disarticulated, reoriented, concentrated) from their original position by bioturbators, predators, or scavengers, but not transported from another community; and c) allochthonous or foreign remains that have been derived from other communities.

 

5. Taphonomic loss, especially through dissolution and bioerosion, is typically most severe in shallow-water marine environments. Perhaps this "rule" also results from the attention these enviroments have received from "actuopaleontologists" because of their greater accessibility: salt-marshes, for example, are largely characterized by autochthonous remains, whereas complete unmixed deep-sea marine records are by no means the norm, despite the "optimistic assessments" of many biostratigraphers and paleoceanographers.

 

6. Information loss in terrestrial and fluvial biotas results largely from transport, disarticulation, sorting, and breakage by water, predators, scavengers, and trampling.

 

7. Bioturbation and physical reworking also cause time-averaging (temporal mixing) of different communities and may lead to increased diversity and variation in morphological features of fossil lineages. Temporal mixing often goes unrecognized in fossil assemblages.

 

8. Thus, false First and Last Appearance Datums (FADs and LADs) may result from bioturbation and physical reworking. False LADs are most serious because bioturbation and reworking preferentially mix sediment upward.

 

9. Nevertheless, information gain about taphonomic settings and long-term community dynamics may result from the actions of taphonomic agents (this point remains largely unappreciated by those outside the field).

 

10. Furthermore, catastrophic burial or smothering (obtrusion) may result in Lagerstätten that serve as "snapshots" of population dynamics. These "fossil censuses" may not, however, be truly representative of the long-term dynamics of the population, and so multiple snapshots of a fossil biota probably better represent the temporal variation in populations.

 

In case you're interested in the book: http://www.amazon.com/Taphonomy-Process-Approach-Cambridge-Paleobiology/dp/0521598338

[Missourian]

To me, the concept of bioturbation is particularly significant. Some thoughts:

 

- Bioturbation can degrade or destroy remains that would otherwise become fossilized. This process can be quite extensive and pervasive -- far more than I imagined before becoming aware of it.

 

- On the flip side, the lack of bioturbation may spare delicate remains.

 

- Finely laminated bedding is an indication of a lack of bioturbation. Many, if not most lagerstätten tend to be in extremely even, laminated strata.

 

- Laminae by themselves do not necessarily guarantee delicate fossils; the depositional environment may have not been conducive to life or any subsequent preservation.

 

- If fossils are present, it may be worth searching for rare and unusual specimens.

 

- It may be possible to 'predict' the presence of lagerstätten to some degree, particularly if diagnostic sedimentary structures -- especially those visible from a distance, i.e. from a cursory glance -- can also be taken into consideration. To date, I haven't had much success on this front....

[xonenine]

thanks Missourian, fascinating topic, and I am still enamoured of (with?)Kidwells models:

Models for Fossil Concentrations: Paleobiologic Implications

Susan M. Kidwell

aside from the fact that it has dagrams for tyros like myself

Edited December 13, 2014 by xonenine

[Missourian]

On 12/13/2014 at 7:27 AM, xonenine said:

thanks Missourian, fascinating topic, and I am still enamoured of (with?)Kidwells models:

Models for Fossil Concentrations: Paleobiologic Implications

Susan M. Kidwell

 

Thanks much for the link. Kidwell's 1986 paper tends to show up a lot as a reference.

[Missourian]

On 12/13/2014 at 7:27 AM, xonenine said:

Models for Fossil Concentrations: Paleobiologic Implications

Susan M. Kidwell

 

Speaking of Kidwell's studies, it is fascinating how similar-looking shell beds can vary tremendously in origin:

 

The shell beds in my profile pic probably formed in storm deposits in a tidal channel. A little closer:

 

 

 

The complete lack of bioturbation indicates an extremely short timescale for the entire deposit.

 

Shell beds can also form:

-- As shoals, built up by waves and current, as those sometimes associated with oolitic deposits.

-- During periods of reduced sedimentation, as indicated in Kidwell's 1986 paper.

-- As concentrations due to erosion of preexisting deposits.

 

Note: shell beds can potentially result as a combination of two to all of the above scenarios.

[Ludwigia]

Thanks for starting this informative thread. I'm not all that up on taphonomy, so I'm learning as I go here.

[Missourian]

Regarding:

 

 

Note the complete lack of bioturbation. Any burrowing would have disrupted the intricate bedding. This indicates either rapid formation and burial of the bedding, or an environment that is not conducive to burrowing organisms. The fossils present indicate a favorable environment, so I conclude the sedimentation was rapid.

 

Edit: I noticed that I mentioned the lack of bioturbation in a previous thread. This reflects an extremely important concept regarding the quality of fossils found in a deposit. I.e. there may be really nice fossils to be found if nothing messes it up.

[Auspex]

Are the shell bed layers in your example composed of ground up bits?

[Missourian]

Regarding:

On 12/13/2014 at 4:55 PM, Auspex said:

Are the shell bed layers in your example composed of ground up bits?

 

No. The shells are quite well preserved. Another example showing a weathered surface of the shell-bed stringers:

 

 

Edit: There may be ground up bits, but with well-preserved shells mixed in as well.

[Auspex]

It does rather seem like gentle wash and flow then, doesn't it?

[Missourian]

On 12/13/2014 at 5:32 PM, Auspex said:

It does rather seem like gentle wash and flow then, doesn't it?

 

One thing that I noticed is that the shell beds were present in the entire outcrop along one side of the road cut, while they were completely absent on the other side. This indicates to me that they filled something of limited extent -- probably a tidal channel.

[Auspex]

Incoming depositing shells, and outgoing adding silt?

[Missourian]

On 12/13/2014 at 6:28 PM, Auspex said:

Incoming depositing shells, and outgoing adding silt?

 

Or the 'silt' (micrite) represents quieter moments. There may be two populations of fossil debris: 1) relatively unabraided mollusks, and 2) worn bryozoans, brachiopds, etc. (present at the tops and bottoms of the blocks). I think the mollusks came from nearby, and the bryozoans, etc. came from further offshore. There are also Cordaites leaves occasionally mixed in.

[Missourian]

Some books on taphonomy.....

 

A good introduction to paleoecology, with a chapter on taphonomy:

 

Palaeoecology: Ecosystems, Environments and Evolution

http://www.amazon.com/Palaeoecology-Ecosystems-Environments-Evolution-Brenchley/dp/0412434504/ref=sr_1_1?s=books&ie=UTF8&qid=1418240371&sr=1-1&keywords=palaeoecology

 

If you really want to dive in deep:

 

Taphonomy: A Process Approach

http://www.amazon.com/Taphonomy-Process-Approach-Cambridge-Paleobiology/dp/0521598338/ref=sr_1_7?s=books&ie=UTF8&qid=1418240459&sr=1-7&keywords=taphonomy

 

This second book can be really dense at times, but there are many insightful concepts to be found.

 

I just found this one. It appears to be a 'symposium' of sorts:

 

Taphonomy: Process and Bias Through Time

http://www.amazon.com/Taphonomy-Process-Through-Topics-Geobiology/dp/9400734034/ref=sr_1_1?s=books&ie=UTF8&qid=1419066903&sr=1-1&keywords=taphonomy

 

This one will be a Christmas present to myself.

[Lmshoemaker]

Great thread! Are you planning on adding to it any more?

[Missourian]

On 12/29/2014 at 3:20 PM, Cryptidsaurian said:

Great thread! Are you planning on adding to it any more?

 

Thank you. Yes, I plan to add to it from time to time. There are a couple posts that I'm 'working on' (i.e. trying to figure out how to word in a concise way ). I'm still just a noob though....

[Lmshoemaker]

Thank you. Yes, I plan to add to it from time to time. There are a couple posts that I'm 'working on' (i.e. trying to figure out how to word in a concise way ). I'm still just a noob though....

Well thank you for posting, there is a lot of good information here!

[Auspex]

This is a very illuminating topic, revealing complexities which seem subtle, but have a profound impact on "seeing" a sites paleoecology. It is clear that anything I might add from my own meager knowledge-base will serve only as fodder for more detailed clarification.

I'm diggin' it!

[Missourian]

Some more definitions....

 

Autochthonous assemblage - An assemblage that is in the place that it should be (in situ), representing the biofacies or paleocommunity (also known as a biocoenosis).

 

Parautochthonous assemblage - An assemblage that is in place but has been moved (disarticulated, reoriented, concentrated) by bioturbators. These may resemble allochthonous assemblages.

 

Allochthonous Assemblage - An assemblage that is out of place, representing a biofacies that has been transported (e.g. shelf community transported by turbidites into deep water). Can be derived either from reworking of deposits or a thanatocoenosis.

 

Thanatocoenosis - The localized accumulation of the remains of dead organisms. The cause, time, and place of death of the individual are not important. A thanatocoenosis occurs, for example, when the remains of organisms that have perished at various times and in various places are deposited in a central location by flowing water. Bone beds are a notable example.

[Auspex]

...Allochthonous Assemblage - An assemblage that is out of place, representing a biofacies that has been transported (e.g. shelf community transported by turbidites into deep water). ..

As in the Burgess Shale, for example?

[Missourian]

On 1/3/2015 at 7:14 AM, Auspex said:

As in the Burgess Shale, for example?

 

Yes. The Burgess is a good example of the sedimentary & stratigraphic context being critical in determining the allochthonous nature of the assemblage. The shale beds occur as turbidites at the base of a carbonate reef (Cathedral Formation). Otherwise, the excellent quality of the fossils may lead one to assume that the animals were in life position.

 

Plus, I'm sure paleontologists have noted this sedimentary context to search for Burgess-type lagerstätten in other localities.

[xonenine]

Parautochthonous assemblage - very interesting terminology, thanks, there was a paper I read about 2nd and third order reworkings (regarding Buffalo to Canada and number of possible Eurypterids) that I'd like to find again, what's the terminology for multiple instances of reworking like this, still Parautochthonous assemblage ?

[Missourian]

On 1/3/2015 at 8:05 PM, xonenine said:

Parautochthonous assemblage - very interesting terminology, thanks, there was a paper I read about 2nd and third order reworkings (regarding Buffalo to Canada and number of possible Eurypterids) that I'd like to find again, what's the terminology for multiple instances of reworking like this, still Parautochthonous assemblage ?

 

An eurypterid assemblage would probably not be parautochthonous, since disruption of the exoskeletons by critters would likely destroy them.

 

My knowledge is quite limited on the New York/Ontario eurypterids, but I would think the deposit would be autochthonous if the mass-moult scenario that I've heard about is correct. It is also possible the exoskeletons were flushed from another location and were somehow concentrated where found, which would make it allochthonous. To find out which one, the depositional conditions (and paleoecology, if possible) would have to be determined.

 

Finally, what did the paper mean by 2nd and 3rd order reworkings? Now I'm intrigued....