Finds Miocene

By Charles Suslavage, USA

Often quoted "Seek and Ye Shall Find" worked for this amateur microscopist. The result of effort, good fortune, and dumb luck, was to find a deposit of diatomaceous earth in the vicinity of Newport Beach, California. For effort I would actively examine rocky outcrops and road cuts any time I was in the vicinity of the beach. I was aware that fossil bearing layers were to be found in the area in and around Newport Beach from the Monterey Formation of Miocene age. Good fortune was recognizing what I was looking for. I had never seen diatomite before and was working from a description of 'chalky texture' and 'light weight', exactly what I found. Dumb luck was traveling to an estuary for the purpose of collecting living diatoms and being prevented from doing so by fences and keep out signs. Unable to reach my original goal I turned 180 degrees to some nearby rocky outcrops and eureka!

Once back at my lab, a cluttered dust covered bench in the garage, I pondered what to do with these chalky lumps of light weight material. I decided to do three things immediately, first was to clear off a section of the bench and cover this with nice fresh clean newspaper. Second was to place a small piece in a vessel with distilled water and third was to examine the material under a binocular microscope.

I had expected some of the outer layer to dissolve in water but I was surprised when it seemed the entire lump broke down immediately when immersed. The text books all indicated the use of strong acids. I now worried that I had only collected a lump of uninteresting clay! I hurried to my dissecting microscope which is now seated on the clean news print. Another new experience, I had read, somewhere, that the larger diatoms would be visible on the surface. So I scanned at 45x and at first not much of anything interesting was observed. As my initial disappointment passed I began to quietly and slowly scan the dull gray surface and occasionally I observed what looked like tiny disks or flying saucers. Are these diatoms, they don't really look like diatoms but they are something unusual. Some of my disappointment and insecurity was now passing, maybe I'm in luck after all. Then I found what looked like a clump of spicules, oh boy, definitely something of interest.

Turning to my vessel of what now looks like muddy water I took a drop of this and placed it on a slide and added several drops of distilled water diluting that ugly brown drop. Now into the house for a look under the microscope. I never take the microscope out to my dust shrouded lab, too hard to clean, I always take the sample to the microscope. When transitioning from lab, the garage, to microscope I usually try to avoid my wife. This time I ran into her and she asked seeing that I was carrying a slide "more pond water"? "No" I replied "just dirt". No further comment or show of interest from my wife so I proceed up the stairs to my desk where I keep my computer and microscope. My wife worries about things like bacteria and disease so I avoid any areas of food storage or preparation, always a good idea.

With slide on the microscope stage, take deep breath, focus, and happy happy I am. There amid a crowded field of quartz, little boulders, and undefined debris is one large less than perfect centric diatom. Scanning further I found additional centric diatoms, lots of fragments of centric diatoms, silicoflagellates, and even a foraminiferan. I was very excited and pleased.

Many months have now passed and I am still very pleased with my discovery and I have learned much about separating the wanted diatoms from the unwanted debris. A sieve is an essential tool in this process. I had some success with swirling and decanting to separate fossil diatoms but nothing worked as well as the sieve. An important first step is to place a small sample of diatomite into a container with distilled water and subject this to cycles of freezing and thawing, more cycles seem to be better, roughly 20 to 30, than fewer, 10 cycles or less. This cycling does an excellent job of breaking down the diatomite and freeing the fossil diatoms before sieving. I have also used hot acid, muriatic acid, to further separate and clean the frustules, silicious shells, after the freeze thaw cycles. Today I have about 10ml of cleaned material, about 10% of this is diatoms the remaining 90% is fragments of diatoms, spicules, silicoflagellates, fragments of radiolaria, but no foraminifera, the processing apparently destroys these. Of the 10% that I would describe as usable material 95% are centric diatoms and a large percentage of these are Cosinodiscus and the remaining fraction is a lot of fun to explore.

The following images are from the collected diatomaceous earth. The bar in the lower right corner is the standard, perhaps traditional, 0.010mm. The images were taken from strewn slides of my manufacture using ZRAX as a mountant.
The diatom images were cut out of their original frame and pasted onto the neutral background using Paint Shop Pro.

Genera Actinoptychus


Genera Asteromphalus


Genera Auliscus


Genera Cosinodiscus


Genera top to bottom Entopya, Rutilaria, Craspedodiscus


Genera left to right Triceratium, Actinocyclus, Stictodiscus

I am very fortunate to have a copy of "Miocene and Pliocene Marine Diatoms from California" by Walter W. Wornardt, Jr. A 1967 publication of the California Academy of Sciences. This 108 page paper has become well thumbed as it is the exact document needed by an amateur working with Miocene age fossil diatoms of California. My second best source for information on California marine diatoms is a book in pdf format currently available from the Scripps Institute of Oceanography "Marine Plankton Diatoms of the West Coast of North America" by Easter E. Cupp.
A third source that is invaluable to my current endeavor and in diatoms in general is "The Diatoms Biology & Morphology of the Genera" by F. E. Round, R. M. Crawford, and D. G. Mann. This book is currently available and for anyone interested in diatoms this is a must have addition to their personal library.

Now that I have some experience separating diatoms from the collected diatomite I wonder how to separate and collect the Foraminifera from this material? It seems there is always another interesting challenge just around the corner. As Holmes would say to Watson "The game is afoot".

Comments to the author are welcomed.


Editor's note: Thanks to Howard McPherson for providing a link to the Cupp reference.




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