Paleonet: Splitting of small samples

LIPPS, Jere H. jlipps at berkeley.edu
Thu Oct 11 21:04:25 UTC 2012



Michael: 

Even the professionals have questions about each other's
classifications, but as long as we know the basis of it, we can deal with
it. Loeblich & Tappan is certainly the best reference, since everyone knows
it and it is comprehensive (as of 1982) although it has a lot of
interpretation problems. But we all know that L border-left: #1010ff 2px
solid; margin-left: 5px; width: 100%;"> Jere,

 with the success of the
website (180 visits a day) we have a "little" problem, as we as amateurs
may provide wrong classifications and information. So we try to get
images/illustrations from professionals which rest on their hard-drives
useless. We also indicate if a classification is not reviewed and state the
source we used.

 Thanks for your great work on foraminifera, which we
frequently come across in JFOR, MP, PE ... .

 Michael

 Am 11.10.2012
21:40, schrieb LIPPS, Jere H.:  

Michael:  

You are most welcome.  

If
your aim is the practical matter of correlation, then the 300 specimen way
of decreasing the labor may be sufficient. Since the samples from the cores
are somewhat similar in collecting methods, I wouldn't worry about the
stats. Another simple method, used by many micro people is to simply pick a
sample until you think you have everything. Most of the time, you will be
close enough for that kind of work. If you have problems, just go back and
restudy the sample(s). Microsplitters are a handy way to cut the size of
the job to something easier. What i'd suggest is doing the 300-500
specimens, and then running quickly through the rest of the sample to see
if you spot any other species. Sometimes those very rare species are
important in correlation, age dating, paleoenvironmental analysis.  

Good
luck. 

Your website is really great. Anyone on PaleoNet that needs images
of forams or info on them should take a look. 

Jere 

On Thu, 11 Oct 2012
21:04:40 +0200, Michael Hesemann wrote:  Dear Jere,

 thanks for your
detailed and thoughtful answer. 

 On my way to study foraminifera I
started 2008 with the fun part by picking nice specimens, image them and
find literature on their classification. I brought first images online 2008
and after having hundreds I needed to somehow sort them. I collected and
studied a lot of literature on classification (US, German, Russian ...) in
order to build a searchable catalogue, now having 5500 illustrations (
www.foraminifera.eu/querydb.php [1] ) . A group of
hobby-foraminiferologists was built. In 2011 we were asked by the Hamburg
Geological Survey to correlate gamma logs of drill cores with its
foraminiferal content. We used the simple 300-500 specimens per sample
method, though sometimes having 5000 specimens to pick and count due the
lack of a micro-splitter. We came up with a result based on the total
amount per 100g sediment, benthic/planktonic ratio, a faunal distribution
count based on 15 groups and accompanying fauna + lithology. Driven by
getting at least some results we now enjoy analysing profiles. (Miocene and
Aptian) As you pointed out the 300 specimens method does not reveal too
much, so we are also searching for key-forams and accompanying fauna.
Rarefaction maybe too much for us as amateurs, though we have members, who
dedicate a lot of time picking every kind of object from just one sample
(see e.g. www.foraminifera.eu/weddell.html [2] ) We definitely need to
study according literature and I decided to buy a multiple dividers
micro-splitter. 

 Your answer thus was very helpful to get a broader view
on the subject and heat up the discussion in our team. 

 Thanks again


Michael Hesemann
 Foraminifera.eu Project
 Hamburg, Germany 

 Am
11.10.2012 18:04, schrieb Jere H. Lipps: It depends on what you want to do.
If, for example, you are only interested in diversity (number of species
and what they are), you might do just as well by scanning through different
size-fractions sorted by some kind of mesh. Such mesh is cheap in stores.
You just need to figure out what sizes you want and can get. We commonly
make reference slides of a set of samples this way so that we know what we
will encounter in more labor-intensive work. We can have a lot of fun with
forams without a lot of work and time.

 If you really want to do
statistically valid sorts to 300-500 specimens for quantitative studies,
then you should probably increase your number of specimens. The usual 300
or so specimens was something that came out of sedimentary geology where
people wanted to know the proportions of mineral and rock types in sand. In
sand there are seldom more than a few different types to look for and 300
specimens might be a valid sample size. But if you have a 100 different
species in a foram sample for example, then you need far more specimens to
get an valid sampling. Some key species may be very rare (I've looked at
samples wanting species that were 1 in 10,000 because of dominance of
others). The only way to deal with these is by rarefaction where you pick
or look until you see no more new species and at the same time keep track
of the numbers of specimens counted. This is plotted on a graph of newly
discovered species vs total number of specimens, and when the curve
flattens out, you can assume you have sampled enough. It is still an
assumption and a lot of work. 

 You can split samples, but I doubt that is
a truly statistically valid sampling of the original distribution of
species. A number of different kinds of splitters can be had, but each has
its own problems. The best ones are those that have multiple dividers that
send a sample to two bins. The fewer dividers, the more likely error will
be introduced since the foram shapes and sizes will influence how they are
arranged as introduced to the splitter and where they go. Biases exist at
every step from sampling through splitting to your selection of specimens.
All of that has to be considered in your work plan. If your original sample
is not good, then being rigorous later on is just a waste of time. You
might get, by splitting, a near-statistically valid sample of your original
sample, if you are careful about how you processed the sample and how you
introduced the sample to the splitter (I try to spread it more or less
evenly on a or tray piece of paper, then dump that in more or less evenly
across the splitter from one side to the other), and then being sure that
you examine every specimen. Also a lot of work. 

 A far simpler way is
just to start looking through a lot of sample to pick out the interesting
(defined any way you want) forams, and then draw whatever conclusions are
possible (not statistically based ones, obviously). Also what should be
obvious is that I don't like to pick samples, so I try to maximize my labor
(sounds good like that, but perhaps you might think a better word would be
"lazy"). A lot of good science or fun can be had without statistically
valid samples.

 There's a lot more to this, of course, than can be told on
PaleoNet, and if you really want to deal with statistically valid samples,
there's plenty of good books that would help.

 Jere

 At 06:25 AM
10/11/2012 Thursday, you wrote:
 Dear Paleonetters,

 how may I split a
foraminifera-rich sample-residue (>63µm) of about 20g into even portions of
about 0,5g ?

 So far I mix such a rich residue of about 20g in a small
container and quickly dump it onto a sheet of paper. Then I cut the residue
carefully with a knife into 4 parts and so forth until I end up with about
0,5g. The method doesn't seem very reliable for evenness and puts the whole
picking and counting into question. As I want to process many samples rich
in small forams counting of 5g with 5000+ specimens is not an option and I
need to count 300-500 specimens per sample.

 Will a common micro-splitter
do such a delicate job ? So far I didn't want to spend $400 on a
micro-splitter as I am an amateur :)

 Thanks for your advice.

 Michael
Hesemann
 Foraminifera.eu Project
 Hamburg, Germany
 www.foraminifera.eu
[3]

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[2]
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