Question on Conservat Lagerstätten

[Misha]

I have had this question for some time now and recently had it come up again. I was wondering does anyone know if there are particular conditions that affect the number of Conservat Lagerstätten we see on the earth at any given time?

I got this question because in my time collecting and learning about fossils it seemed to me that times like the Cambrian seem to have quite a number of these sites, and the type of preservation in them seems fairly consistent and similar, as we go into the Ordovician I know if fewer but still a few and they also have pretty similar preservation. The Silurian and Devonian on the other hand, seem to have much fewer, off the top of my head I can probably only think of a couple, but then you get into the Carboniferous and it once again seems like there are much higher numbers of these sites. The Carboniferous is especially interesting because a number of these sites have more usual nice preservation like Bear Gulch, Kinney Quarry, Hamilton Kansas, etc but also a number of sites have Siderite concretions with exceptional preservation like a few sites in the US including Mazon Creek and some in the UK I believe, a type of preservation I have not seen in any other time periods. I am not sure if this patchy record of sites with good quality preservation continues further outside of the Paleozoic, but this is where I noticed it occuring due to mostly focusing on that time span. Is all of this down to the different conditions on earth during these different times? Is there a degree that our sampling bias or just how much attention each of these gets that plays into how many we know from each time?

I have been curious about this for some time and thought maybe someone here would know more about the subject.

Thanks for looking!

Misha

Edited May 1, 2023 by Misha

[Dean Ruocco]

From my experience, a lot of the of fossil faunas are still out there to be found collected and documented especially in the Silurian and Devonian. So I think it’s a sampling bias, those are my thoughts.

[Missourian]

Exploring the concept of megabiases, particularly taphonomic megabiases, should provide much insight in this area.

 

https://www.google.com/search?q="taphonomic+megabiases"

 

I should do a deep dive into this myself.

[Misha]

36 minutes ago, Dean Ruocco said:

From my experience, a lot of the of fossil faunas are still out there to be found collected and documented especially in the Silurian and Devonian. So I think it’s a sampling bias, those are my thoughts.

I certainly agree that a lot if not most of it is likely down to bias, but the example of Siderite concretions with great preservation only occurs during the Carboniferous to my understanding, so I'd assume at least that has to be resultant from some kind of special conditions, right?

[Missourian]

Just now, Misha said:

I certainly agree that a lot if not most of it is likely down to bias, but the example of Siderite concretions with great preservation only occurs during the Carboniferous to my understanding, so I'd assume at least that has to be resultant from some kind of special conditions, right?

 

I believe so. I've long been intrigued how Mazon-Creek-type concretionary preservation occurs in widely separated locations (north America and Europe, at least) in the Middle Pennsylvanian. Other examples are Ediacaran fauna in the latest Precambrian, Burgess Shale-type deposits in the Cambrian, and chalk in the Cretaceous.

[Oxytropidoceras]

Your question is discssed in several papers. For example:

 

Gaines, R.R., 2014. Burgess Shale-type preservation and its distribution in space and time. The Paleontological Society Papers, 20, pp.123-146.

 

Muscente, A.D., Schiffbauer, J.D., Broce, J., Laflamme, M., O'Donnell, K., Boag, T.H., Meyer, M., Hawkins, A.D., Huntley, J.W., McNamara, M. and MacKenzie, L.A., 2017. Exceptionally preserved fossil assemblages through geologic time and space. Gondwana Research, 48, pp.164-188.

 

Orr, P.J., 2014. Late Proterozoic–early Phanerozoic ‘taphonomic windows’: the environmental and temporal distribution of recurrent modes of exceptional preservation. The Paleontological Society Papers, 20, pp.289-313.

 

Retallack, G.J., 2011. Exceptional fossil preservation during CO2 greenhouse crises?. Palaeogeography, Palaeoclimatology, Palaeoecology, 307(1-4), pp.59-74.

[Doctor Mud]

Interesting question! I’d always assumed that given enough time there is an equal opportunity for there to be exceptional preservation through time.

 

But I can think of reasons that at particular times and places the chances of exceptional preservation might be higher or lower. 
 

- High sedimentation rates and rapid burial are important for preservation

- Rapid formation of structures (concretions) that protect fossils from scavenging is also important.

 

What can affect these things? Sediment supply? Ocean and sediment chemistry? 
 

- Large scale changes in ocean chemistry may affect concretion formation or the type of concretion. I was thinking along these lines for siderite concretions vs say calcium carbonate. Things like high CO2 in the atmosphere and ocean acidification would affect ocean chemistry. 
 

- Times of increased mountain building (orogenies) and the buildup and breakup of supercontinents can erase past deposits. 
 

- Then we need to think about terrestrial and freshwater. Mussel and green river. I know that recent (Pleistocene) lake sediments are easily lost. Lakes have a limited lifespan (they fill in) and can be subsequently eroded by rivers or glaciers. Or even dry up and “deflate” loose sediment. Think desert lakes. 
 

interesting to think about this. The chances of any fossil surviving the journey it has to go through for us to see it is amazing. When you see soft tissue etc it’s like winning the fossil lottery. 
Mind boggling! 

Edited May 2, 2023 by Doctor Mud

[doushantuo]

a (fortuitous)combination of strike slip deformation->rhombic basin formation,tephra** (volcanic ash) deposition, and more or less permanent euxinia/anoxia(these are NOT synonyms) ,clay mineral authigenesis,catastrophic or anastrophic burial ,limited vadose/meteoric diagenesis,microbial mat involvement("death mask") ?

** e.g.: West Lothian,Scotland, Wuda Tuff,Permian of China

Non black shale :Laminated finegrained (micritic)carbonates(Lebanon,Solnhofen)

 

Volcanic lakes(maars) host a number of lagerstatte,eg.

Ninots(Spain)

Bauzile(France)

Foulden(New Zealand)

Enspel(Germany)

 

 

 

edit: a lot of lagerstatten were discovered and analyzed because of economic incentives:

e.g.

 

all lignites/Browncoals 

Franceville (Proterozoic) Sandstone- hosted uranium 

Paleogene of Northern Africa: phosphates(oceanographic cause:probably upwelling)

Jurassic of Svalbard(Slottsmoya): hydrocarbons

Alum Shale: Uranium

Orcadian(Scotland): hydrocarbons

Green River: Hydrocarbons

Messel: hydrocarbons(it turned out that its prospectivty was too low

San Giorgio: bitumen

Rupelian of Germany: equigranular well sorted shallow marine sands(useful in e.g. beach fortification,cement manufacture,Carbon dioxide sequestration)

Cenozoic diatomites(Germany,France,Czech Republic): fertilizer, filter manufacture( because of excellent porosity and permeability)

generally speaking,black shales/mudstone make good reservoirs and have a  good search envelope for well preserved fossils(e.g.Posidonia shale)

edit: some of you may like

https://doc.rero.ch/record/16411/files/PAL_E3595.pdf

 

 

Edited May 3, 2023 by doushantuo