Looking for fossils in volcanic rocks?

[marguy]

During our explorations in search of fossils, we obviously favor sedimentary rocks; I invite you to follow me with my wife in search of fossils… in volcanic rocks! (only observation without sampling)

In the center of the volcanic massif of Cantal (central France), we explored a not very accessible valley where outcrop deposits of breccias of dense pyroclastic flows, in search of fossil woods of Villafranchian age (upper Pleistocene).

According to an old reference (conference , 1969) one can find: “sometimes tree trunks inclined in all directions and sometimes branches. They are black, it is charcoal, produced by combustion in the absence of oxygen. After their reduction in carbon, certain woods underwent a strong fumarolic activity with silicification in opal cristobalite, generally respecting the vegetal structures.” By anatomical study in microscopy, 5 genera have been identified: Cedroxylon, Piceoxylon, Cornoxylon, Fagoxylon, Ulmoxylon. They suggest a temperate or mountain type climate.

The conservation of carbonized organic matter indicates that the rock emplacement temperature must have been relatively lower than at the volcanic magma exit point estimated at 900°C according to mineralogy. The pyroclastic flow therefore destroyed a forest by descending the slope of the volcano while cooling.

Let us now see in some photos what we discovered with wonder: 2 fossiliferous sites, the first with only one vertical trunk in an overhanging cliff, the second with multiple trunks preserved or hollowed out and branches on the bank of the river (without signs of silicification on these 2 sites found about 300 meters apart). There must therefore still be other nearby sites, but the difficult access to the site probably keeps them out of sight.

 

Edited July 11, 2022 by marguy

[Meganeura]

That's really neat! I was under the impression that fossils were just about never found in volcanic rock due to the nature of how hot lava is. Makes sense that in certain, rare cases, some stuff would be preserved!

[Fossildude19]

Very interesting trip report!

Thank you for posting it here.   

[nala]

Great report!nice pictures!Thanks 

[FossilNerd]

Very interesting! I’ve never heard of preservation like this. We learn something new everyday it seems. Thanks for sharing! 

[Coco]

Nice report !

 

Coco

[Oxytropidoceras]

On 7/11/2022 at 3:03 PM, FossilNerd said:

Very interesting! I’ve never heard of preservation like this. 

 

Fossils in lava can be even weirder:

 

Climbers find basalt mold and bones of a 15-million-year-

old rhinoceros at Blue Lake, Grant County (July 1935)

Rhino Resource Center

 

Blue Lake Rhino Cave, Coulee City, Washington, Atlas Obscura

 

There's a Rhino-shaped Cave in Washington State, How Stuff Works

 

Some papers are:

 

Beck, G. F. (1937) Remarkable west American fossil,

the Blue Lake rhino [Washington]. Mineralogist.

vol. 5, pp. 8, pp. 7-8. (Oregon Agate and Mineral

Society. Portland, OR, United States)

 

Chappell, W. M., J. W. Durham and D. E. Savage (1949)

Rhinoceros mold in basalt. Geological Society of America

Bulletin. vol. 60, no. 12, Part 2, pp. 1949.

 

Chappell, W. M., J. W. Durham and D. E. Savage (1951)

Mold of a rhinoceros in basalt, Lower Grand Coulee,

Washington. Geological Society of America Bulletin.

vol. 62, no. 8, pp.s 907-918.

 

Yours,

 

PAul H.

[marguy]

thank you all for your feedback and comments.

[hemipristis]

On 7/12/2022 at 2:16 AM, Meganeura said:

That's really neat! I was under the impression that fossils were just about never found in volcanic rock due to the nature of how hot lava is. Makes sense that in certain, rare cases, some stuff would be preserved!

Under the impression, lol. Ya made a funny!  

Fossils in volcanic tuff aren't exactly common, but are known

[DPS Ammonite]

In Hawaii, recent lava flows have created exterior molds of trees. Assuming they don’t erode away, they may become fossils 10k years after their formation. Has anyone seen tree molds in lava that are at least 10k years old? 
 

https://www.nps.gov/havo/learn/nature/lava-trees.htm

[JimB88]

2 hours ago, DPS Ammonite said:

In Hawaii, recent lava flows have created exterior molds of trees. Assuming they don’t erode away, they may become fossils 10k years after their formation. Has anyone seen tree molds in lava that are at least 10k years old? 
 

https://www.nps.gov/havo/learn/nature/lava-trees.htm

 

Yep, check out the Ginko petrified forest in Washington. Where pillow lava (in a lake) encased many logs that were at the bottom. Its a state park.

 

A good talk about it by Nick Zentner:  https://youtu.be/nfbMxrPnYcc

[Castle Rock]

I have come to the conclusion that the ONLY place you are GUARANTEED NOT to find fossils is anyplace that you NEVER LOOK!

[Oxytropidoceras]

On 7/16/2022 at 5:56 AM, DPS Ammonite said:

In Hawaii, recent lava flows have created exterior molds of trees.

 

Lava tree casts have been found all over the  world.

 

Some examples:

 

Antarctica – lava tree casts – Jurassic

 

Siders, M.A. and Haban, M.A., Jurassic trees engulfed by 

lavas of the Kirkpatrick Basalt Group, northern Victoria 

Land. Mineralogy and Petrology, 73, pp.89-104.

 

Cameroon – lava tree casts – Cenozoic

 

Hyde, H.P., 1951. Tree trunks preserved in a volcanic flow 

in the northern Cameroons. American Journal of Science, 

249(1), pp.72-77.

 

New Zealand – lava tree casts - 140,000 BP

 

Allen, S.R. and Smith, I.E., 1991. The lava flows north of 

Takapuna Beach. Tane (Journal of the Auckland University 

Field Club), 33, pp.49-58.

 

Scotland – lava tree casts – Paleocene

Bell, B.R. and Williamson, I.T., 2016. Fossil trees, tree

moulds and tree casts in the Palaeocene Mull Lava Field, 

NW Scotland: context, formation and implications for 

lava emplacement. Earth and Environmental Science 

Transactions of the Royal Society of Edinburgh, 107(1), pp.53-71.

 

Direct link to PDF of paper's preprint

 

General lava tree casts

 Bella, P. and Gaál, L., 2007. Tree mould caves within

the framework of cave genetic classification. Nature 

Conservation, 63, pp.7-11.

 

Papers by Pavel Bella

 

A paper about the formation of lava trees casts.

 

Chevrel, M.O., Harris, A., Ajas, A., Biren, J., Gurioli, L.

and Calabrò, L., 2019. Investigating physical and thermal

interactions between lava and trees: the case of Kīlauea’s

July 1974 flow. Bulletin of Volcanology, 81(2), pp.1-19.

 

Yours,

 

Paul H.

Edited July 20, 2022 by Oxytropidoceras
grammar

[marguy]

some more, jurassic fossil trees in Mongolia

(french language, but great pictures) :

https://planet-terre.ens-lyon.fr/ressource/Img751-2022-06-13.xml