Jump to content

Microfossil Mania!

  • entries
    16
  • comments
    41
  • views
    11,477

Another Method for Studying Microfossils

Rumi

412 views

 

One of the problems I experience in studying microfossils is that of orienting a specimen so that crucial characters are visible.  An example: for identification it is often necessary to check the shape of the tooth in the aperture of taxa in the family Hauerinidae.  The tooth can be long or short, plain or bifid, present or missing, etc.  The aperture is on the end of the test, so it isn't possible to look into it when the test is lying flat -- which it always does when the test is lying in a tray under the scope.  Of course, it is possible to use a little glue on the opposite end and manipulate it into a vertical position: but this is a lot easier said than done!  However, there is a much easier way to look at such things -- use a mechanical two-axis stage, which will allow you to turn a specimen to literally any position under the stereo 'scope.  One of my holiday gifts this year was just such a stage, of the type most commonly used by entomologists to examine pinned insects.

 

To use the stage, I have a size 0 insect pin from which I removed the head with side-cutter pliers.  I put a small drop of gum tragacanth on the resulting blunt end of the pin, and touch it to the side of the specimen I wish to examine, where it quickly dries.  I stick the sharp end of the pin into the soft rubber plug of the rotating arm of the stage, and I'm set to go.  I can alter the orientation of the specimen by rotating either of the two axles of the stage; by rotating the whole stage around its vertical axis I get the third "axle".  The pin is not too distracting, and only the little area under the glue is not visible.  This works quite well!

 

Snap1.thumb.jpg.f08bf0acf1c63705bf15510722b96c8e.jpg

 

In this image, the aperture is at the upper end, toward the top.  (Oops, mispelled "hauerinid", drat...)  Two chambers are visible on this side, and there are three chambers visible on the opposite side.  One can't see the tooth in the aperture, par for the course when the test is lying flat.  Let's look at another specimen, mounted on the mechanical stage:

 

Snap2.thumb.jpg.bc17b461c4397ad490037f61f0b8e94b.jpg

 

I rotated this specimen by 90 degrees from its "flat" position, and now the aperture is perfectly placed for inspection.  The long tooth in the aperture is clearly visible, as is the thickening of the lip.

 

Another example using different orientations: here the specimen is perched on top of the pin.

 

Lent_1.thumb.jpg.80bb7fc5a50bdf284f1f1e4823fdf0c0.jpg

 

The genus Lenticulina is planispiral and involute, and the aperture is at the upper end of the exposed face of the final chamber.  The aperture is radiate; i.e., composed of several thin slits in the shape of an asterisk.  This can be difficult to see.  In this image the position of the aperture is marked by the arrow, but the nature of the aperture is not at all clear.  Rotating the test by 90 degrees to get a profile view gives us a better look, and this profile view is also most useful in species identification:

 

Lent_2.thumb.jpg.b9b1a3fc6785c138e7e0f0a41dbc106c.jpg

 

 

In this image, the test is mounted on the pin, which is glued to the underside of the specimen.  So why is the pin not visible?  To light specimens under the 'scope I use a two-arm fiber optic illuminator -- careful adjustment of the twin light heads can "eliminate" the pin with shadows.  (Any remaining reflections from the pin are easily removed with image processing software.)  If the pin were visible, it would extend downward to the lower edge of the image.  Eliminating the pin makes the specimen appear to "float in midair", but at the expense of a weakly illuminated underside.

This image shows the involute structure nicely, the apertural face, the swollen center of the test, the thin peripheral keel, and the pale aperture area at the right end.  The aperture itself is still not well revealed, however.  Let's adjust the orientation a little more:

 

Lent_3.thumb.jpg.d9059662f6dd6ff96366247cf9be9f96.jpg

 

Turning the right end of the test upward toward the objective lenses, and boosting the magnification a bit, brings the radiate aperture into better view.  Three of the radial slits, filled with contrasting matrix, are fairly clearly shown.  Further rotation upward toward the objectives would provide a fuller view of the aperture, but this view is sufficient to demonstrate that the aperture is indeed radiate in structure. 

 

This method of mounting a specimen on a pin is totally non-destructive: to remove the specimen from the pin one just immerses it in a drop of water, where the gum tragacanth will quickly dissolve, leaving the specimen completely undamaged.

 

Hopefully this blog entry will encourage others to explore ways to alter the orientation of their specimens, whether for identification purposes or photo-imaging.

 



11 Comments


Recommended Comments

Hi Rumi,   That’s a great solution to an issue that many of us have! After seeing your first example with the foram’s aperture, two-axis stage is now on my wish list! :-)

On eBay, there are a number of x-y stages. I would think that you would need a stage with tilt to manipulate the pin.  Would you please post a photo of the stage that you use?

If I can find one to integrate with my Z  axis stage micrometer, then I would also be able to use both to create photo stacks from nearly any orientation.

Share this comment


Link to comment

@Acryzona  Glad to add photos, and explain my 2-axis stage a little better:

 

thumbnail.jpg.161c7270d7b23a589837657b4e15f5ea.jpg

 

The base is heavy metal, very stable, and the footprint is 1.5 x 3 inches, so it sits quite comfortably on the fixed stage of my stereo 'scope.  The knob for axis 1 is soft rubber, and rotates the horizontal axis that bears the L-shaped brass arm.  The knurled brass knob for axis 2 rotates the pin on its own long axis.  The following image shows the effect of turning axis 1.  As the caption suggests, it is best to cut the pin so that its blunt end is on line with axis 1 -- this keeps the observed object in fairly good focus, no matter how the two axes are adjusted.  I leave the pin long only because of my manual spasticity: I need all the size I can get to manipulate anything.  I pay the price of having to constantly make large changes in focus, and may end up cutting the pin short, and suffering the occasional consequences!

 

thumbnail4.jpg.d626191e3655f3325ed80a34c694903c.jpg

 

Here is the image with the brass arm turned toward the observer by about 90 degrees.  It will turn a full 360 degrees, of course, as will the knob for axis 2.  If you need further adjustment, you can turn the entire stage around its vertical pillar, giving you a further rotational axis.

 

Hope this helps!

 

Share this comment


Link to comment

Thanks for the photos- I understand much better how it works now.  Great idea to apply something from entomology to microfossils!

 

I’m thinking of using 00 or 000 size insect pins.  Do you think they would be too thin for ostracods?

Share this comment


Link to comment

@Acryzona

 

I would worry about the springiness of such fine pins, rather than their diameter.  Brush against it, and the specimen is likely to go flying across the room.  I'm using a size 0, and it works well for paleozoic ostracodes.  However, I'd like to get something with a lesser diameter for Holocene forams and smaller ostracodes.  Possibly a sewing needle point, or reversing the insect pin so the thin end is up.  With the head of the pin cut off, it should insert into the soft foam "cork" of the stage.  I'd like something finer to work on small forams, like globigerinids.  I'm currently working on a sample dredged from 700 feet depth in the Caribbean -- full of planktonic forams, as well as a lot of fascinating benthic taxa that I have not encountered before.  Cretaceous samples typically contain a LOT of tiny planktonic species, as well.  I collected a bit of Mancos Shale at Durango, CO, last year, which contains nothing but tiny planktonic forms -- the helicinids are especially hard to work with!  It's hard to attach these to the end of a size 0 -- the diameter of the pin is almost the same as that of the specimen.

 

Some advice, if you would?  I'm thinking of just stopping this microfossil blog, as very few people seem to be interested.  I'm not sure it's worth the trouble.  And I'd like to share Holocene material, as well as fossil, but I'm afraid that others might object to non-fossil specimens appearing on a Fossil Forum.  I would value your opinion!

Share this comment


Link to comment
doushantuo

Posted

I would definitely continue this blog .

Microfossils are beautiful,ecologically/oceanographically/biostratigraphically tremendously useful,and the calcareous ones they draw down CO2

douvcalcitlptttrymjjpwillist.jpg

douvcalcitlptttrymjjpwillist.jpg

douvcalcitlptttrymjjpwillist.jpg

douvcalcitlptttrymjjpwillist.jpg

Share this comment


Link to comment
3 minutes ago, Rumi said:

 

Some advice, if you would?  I'm thinking of just stopping this microfossil blog, as very few people seem to be interested.  I'm not sure it's worth the trouble.  And I'd like to share Holocene material, as well as fossil, but I'm afraid that others might object to non-fossil specimens appearing on a Fossil Forum.  I would value your opinion!

If you quit this blog, I would hope you continue to post photos of your microfossils on the regular forum. I think it will be fine to post modern specimens.

Share this comment


Link to comment

Hi,

 

We speak too rarely about microfossils on this forum, then you have to continue ! And it would not disturb me to see current species. Often they allow to understand better fossils ! ;)

 

Coco

Share this comment


Link to comment

Hi Rumi,  

regarding your blog, I hope you would continue - I’ve learned a lot from your blog, seen micros from formations that I don’t have the opportunity to collect and your photos are exquisite.  It may not have many followers but micros are a speciality within paleo and this is one of the few places on the web to meet and share our collections and learn from each other.

 

I’m going to order a package of 0 and 00 pins as I have some small ostracods.  Would you like some? (there is 100 per package - more than enough). I’d be happy to send you some.

 

Share this comment


Link to comment

@Acryzona

 

Thanks very much for the offer!  How about if you send me a few 00, and I'll send you some size 0 -- I have two packages of that size.  That would save you a bit of money, and me, too.

 

Rumi

Share this comment


Link to comment

Thanks to all who commented on my request for feedback!  Since no one complained, I'll continue to write the occasional blog entry -- and in keeping with the principle of Uniformitarianism, I'll add the occasional entry on Holocene forams and ostracodes.

Share this comment


Link to comment

@Rumi  Thanks.  We can exchange addresses  (don’t know if I still have your address) when the 00 pins arrive next week.

 

looking forward to your next blog post...

Share this comment


Link to comment
×