Collecting fossil diatoms. #collecting


Rudi Venter
 

Hi everyone.

I live in a semi desert area (Karoo region in South Africa) that used to be an inland sea/lake. I have seen indications of fossils including shells and signs of Zoophycos. 

Since I have an interest in fossilized diatoms I wonder if anyone can give me advice on the best way of looking and collecting specimens. Would dry river beds be the best place or maybe the same places I have seen the Zoophycos? How would I collect them, maybe sifting the sand?

Any advice would be highly appreciated!
Thanks!
Rudi


 

Hi Rudi,

I can not really help you re fossil diatoms but I have a collection of diatoms but can not confirm if they are fossil diatoms. Just realised I do have phots of fossil diatoms somewhere.

Best regards

Mo Vaughan.

 

Kind Regards

Maurice (Mo) Vaughan

 

 

 

From: Rudi Venter
Sent: 24 January 2022 18:36
To: diatom-forum@groups.io
Subject: [diatom-forum] Collecting fossil diatoms.

 

Hi everyone.

I live in a semi desert area (Karoo region in South Africa) that used to be an inland sea/lake. I have seen indications of fossils including shells and signs of Zoophycos. 

Since I have an interest in fossilized diatoms I wonder if anyone can give me advice on the best way of looking and collecting specimens. Would dry river beds be the best place or maybe the same places I have seen the Zoophycos? How would I collect them, maybe sifting the sand?

Any advice would be highly appreciated!
Thanks!
Rudi

 


--
Best regards
Maurice (Mo) Vaughan.


Brian O
 

Hello Rudi,

First, I must tell you that I know nothing of the geology of South Africa.

I do not think that you will have any luck just 'randomly' sampling*- you need to find a deposit which has a significant diatom content. Very many of these sites are already known and described. Search online for 'diatomite', 'diatomaceous earth', 'kieselguhr'. These deposits are often of economic value and may be exploited commercially and therefore are listed and mapped by the national geological survey. There is a publication that would be of great value to you:
Diatomaceous deposits in the Union of South Africa : with special reference to Kieselguhr      L E Kent; A W Rogers (1947)  Memoir (Geological Survey of South Africa), no. 42.

Small non-commercial deposits may not be listed and it may be more difficult to find info. On this forum there is a fantastic world list of diatomite sites put together by Steve Gill. You can find it in the 'files' section - it is the last folder 'world diatomite' and the file 'world diatomite locations' will plot them out for you on Google Earth (unfortunately GE is not working for me so I cannot check it out for you).

Some general thoughts:
You are more likely to find freshwater diatomites than marine.
They are more likely in younger rocks. Say recent through to 20 million years old. Diatomites are very rare before the Miocene. Over geological time diatom frustules can dissolve or lose their distinctiveness and end up as a shapeless mass of 'amorphous silica'.
Unfortunately many diatomites are mainly made up of just one or a few diatom species and often the material is fragmentary.
Your nearest deposits are likely to be in your local supermarket or agricutural supplier! Diatomaceous earth is a common component of cat litter and among other uses is used to control parasites etc on poultry. However, in my experience the frustules are usually fragmentary and only one or two species are present.
Zoophycus would be a good indicator of environments where diatom frustules might initially accumulate on the sea bed (depending on the age and water depth - frustules dissolve slowly as they sink), but almost certainly they will have disappeared over the intervening geological time.

* Apart from studying diatoms, I am also interested in other micro-fossils. In all the samples (100s) I have taken over the years I have never come across a fossil diatom in a 'random sample' only where there is an obvious diatomaceous deposit. Not impossible but very very unlikely.

Good Luck with the hunt!

BrianO


Rudi Venter
 

Hi Brian.

Thanks for the very informative email, lots of useful information!

I am aware of a few deposits here in South Africa, some of them extremely rich and yes, I have had a look at what is available in the shops. Some of it is really interesting but because it is mostly processed/crushed there are very few complete diatoms, even so it makes for interesting hunting!

Maybe I should also look at more recent diatom "skeletons" and not just fossils, it might be easier to find these in the local, mostly dry riverbeds. I will go and collect a few samples from dried out waterholes and other places where I have seen standing water after rains.

Thanks for the reference material, I will go and check it out, especially the GE file would be interesting. I would be surprised if there is anything local to me, mostly because it is a rather neglected part of the country but you never know.

The other micro fossils also sound interesting, worth investigating as well.

If I find anything of interest I will post it to the group.

I really appreciate all the information!

Keep well,
Rudi

On Tue, Jan 25, 2022 at 6:16 PM Brian O <bottway@...> wrote:
Hello Rudi,

First, I must tell you that I know nothing of the geology of South Africa.

I do not think that you will have any luck just 'randomly' sampling*- you need to find a deposit which has a significant diatom content. Very many of these sites are already known and described. Search online for 'diatomite', 'diatomaceous earth', 'kieselguhr'. These deposits are often of economic value and may be exploited commercially and therefore are listed and mapped by the national geological survey. There is a publication that would be of great value to you:
Diatomaceous deposits in the Union of South Africa : with special reference to Kieselguhr      L E Kent; A W Rogers (1947)  Memoir (Geological Survey of South Africa), no. 42.

Small non-commercial deposits may not be listed and it may be more difficult to find info. On this forum there is a fantastic world list of diatomite sites put together by Steve Gill. You can find it in the 'files' section - it is the last folder 'world diatomite' and the file 'world diatomite locations' will plot them out for you on Google Earth (unfortunately GE is not working for me so I cannot check it out for you).

Some general thoughts:
You are more likely to find freshwater diatomites than marine.
They are more likely in younger rocks. Say recent through to 20 million years old. Diatomites are very rare before the Miocene. Over geological time diatom frustules can dissolve or lose their distinctiveness and end up as a shapeless mass of 'amorphous silica'.
Unfortunately many diatomites are mainly made up of just one or a few diatom species and often the material is fragmentary.
Your nearest deposits are likely to be in your local supermarket or agricutural supplier! Diatomaceous earth is a common component of cat litter and among other uses is used to control parasites etc on poultry. However, in my experience the frustules are usually fragmentary and only one or two species are present.
Zoophycus would be a good indicator of environments where diatom frustules might initially accumulate on the sea bed (depending on the age and water depth - frustules dissolve slowly as they sink), but almost certainly they will have disappeared over the intervening geological time.

* Apart from studying diatoms, I am also interested in other micro-fossils. In all the samples (100s) I have taken over the years I have never come across a fossil diatom in a 'random sample' only where there is an obvious diatomaceous deposit. Not impossible but very very unlikely.

Good Luck with the hunt!

BrianO


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