Neophyte
Seeking Cretaceous Diatoms
By
Charles Suslavage
USA
Around 65 million years ago an asteroid
or comet slammed
into the
Searching the available literature
I was able to unearth
some pictures of Cretaceous diatoms, but pictures of diatoms no matter
how
excellent, do not compare to first hand observation. I
did discover the identities of several formations that may contain
diatoms from this period. Deposits of fossil diatoms from
the
late Cretaceous may occur in the Moreno shale and Panoche hills
formation
(Fresno, California),
Ananino, Simbirsk (Russia), Küsnetzk (Russia), Antillies
(Barbados, Hayti) and
Jutland. Cretaceous diatoms are also found in deep sea core samples
from
various locations. If an amateur diatomist had a really big boat,
drilling
rig, and unlimited funds, he could sail the high seas dredging and
drilling. With deep pockets he could travel the world sampling
exotic
foods and drinking fine wines while collecting diatomite. For the
remaining
amateurs it would be
more
practical to search for prepared microscope slides from the listed
locals as I
did.
Fig 1. Moreno
Shale. Top row, L to R. Actinoptychus packi, Glorioptychus
callidus.
Second row L to R Unidentified, Actinoptychus, Aulacodiscus pugnalis.
It was surprisingly easy to find slides
of fossil diatoms from most of the locations on my list and they were
all interesting. But was I examining diatoms from the Cretaceous
the last Period of the Mesozoic Era,
65.5 million years old or older, or were they from the later Cenozoic
Era,
less then 65 million years of age? Cenozoic is the era of new life that
began 65.5 million years ago (Ma) to the present. The early Cenozoic
would be the
Paleocene (65.5 - 55.8 Ma), Eocene (55.8 - 33.9 Ma), and Oligocene
(33.9 - 23 Ma) epochs. I needed to find
biostratigraphic marker
species. Stratigraphy is a branch of Geology that studies rock layers
and layering. Fossils big and small can be used to understand
chronologic sequence. All the slides examined were strews containing
diatoms,
Silicoflagellates, and radiolaria. If I could identify any of these I
could then correlate the identified species to geologic
time.
The first slides I examined were from
the Moreno shale. Mixed with the diatoms were broken radiolaria and
Silicoflagellates. The Silicoflagellates would be my first
time marker.
The Silicoflagellates of the Late
Cretaceous are interesting
and graciously simple in form making identification very easy. What
more could
a novice ask for? Before attempting identification I used very simple
identifiers,
horse shoe, wish bone, star, and windowed club. Later, after a bit of
research,
they acquired their more accurate identifiers, Lyramula simplex,
Lyramula
forcula, Vallacerta hortonil, and Corbisema geometrica. Secretly I have
a
decided preference for the names I first used and more confidence in
the
pronunciation.
Fig
2. Moreno shale. L to R. Vollacerta hortonil, Lyramula forcula,
Lyramula simplex, Corbisema geometrica.
My horse shoe, Lyramula simplex, and
wish bone, Lyramula
forcula, are very intriguing. What could they have
looked like as living
creatures? We
view only their skeleton, a skeleton so basic in design that surely in
life had
a chloroplast and most likely a flagellum like that of the extent,
living genus,
Dictycha. From which end would the flagellum radiate? Both are present
in the fossil record of the late Cretaceous
and
possibly became extinct as a result of environmental changes or the
hammer blow
from an asteroid along with the dinosaurs. Which ever the cause or
combination
of events, their extinction now makes their presents in
diatomite
deposits or
deep core samples an excellent easily identifiable stratigraphic marker
and both were abundant in the Moreno shale.
Vollacerta hortonil and Corbisema
geometrica have a plate of
hyaline silica. I was initially confused by the appearance of this
plate in V.
hortonil, was this a unique diatom? V. hortonil’s central plate of
punctate
hyaline silica is not unlike that observed on some diatoms. This plate
is
unusual and I had not observed it in Silicoflagellates from the
Cenozoic. The
lucky genus Corbisema survived the great extinction 65 million years
ago and
continued on into the Middle Miocene (15 Ma).
In the Panoche California slides, mixed
in with
numerous centrics, I found a friend, my wish bone Silicoflagellate, Vollacerta
hortonil, suggesting once again the Cretaceous period. This was not
surprising, both the Moreno shale and the Panoche hills are located in
Fresno county in northern California with the Moreno formation located
on the east flank of the Panoche Hills. What was a surprise and very
different from the Moreno shale were the large number and size of
coscinodiscus diatoms,
Coscinodiscus morenoensis, none this large, 200 to 240 micro meters,
were observed
in the Morano shale slides. Also present were the Coscinodiscus steinyi
but here they were generally smaller then those in the Morano shale.
Also present in quanity were Glorioptychus callidus and Aulacodiscus
pugnalis. A small number of Actinoptychus packi were found but in poor
condition. Finding similar unique diatoms in both groups of slides,
Moreno shale and Panoche, indicates that both formations
were laid down around the same time, possibly one continuous ancient
coastline. However, I wonder what environmental conditions would
account for the noted size differences or was this simply the result
of random sampling?
Fig 4. Ananino, Russia. L to R. Cheloniodiscus ananinensis, Actinoptychus simbriskianus, Aulacodiscus septus.
The slides I
examined identified as Ananino Russia were superising in that there
were few spicules no Radiolaria and no Silicoflagellates. The lack
of Silicoflagellates was a particular disappointment I was really
hopeing to find more wish bones and horse shoes. The
diatoms were plentyful and many were large centrics and there was a
verity of Triceratiums. I
was able to identify one centric diatom that
was of Cretaceous age Aulacodiscus
septus and a second Actinoptychus simbriskanus
is also of Cretaceous age if I have identified it correctly.
The third diatom picutured in Fig 4. Cheloniodiscus ananinensis appears
ancient
but was
listed as epoch unknown.
Fig 5. Simbirsk
Russia. Aulacodiscus ledebourii.
Simbirsk
Russia or as it is now called Ulyanovsk is not far from Ananino Russia.
Broken Radiolaria, spicules, and Silicoflagellates were abundantly
mixed with the diatoms. In amateur speak there was a plethra of three
sided diatoms more correctly called Triceratium or Trinacria but to add
to the fun some are being placed in a new genus Sheshukovia. One
Triceratium I
believe I have identified correctly is Triceratium abyssorum, Fig 6. My
research places this diatom according to one source in the late
Paleocene and a second source places it in the Eocene to lower
Oligocene. One Silicoflagellate Corbisema
bimucronata bimucronata, hopefully correctly identified by this
amateur, was well represented on the examined slides and is reported to
be from the Eocene to Oligocene. A second Silicoflagellate well
represented was Corbisema hastata, again hopefully correctly
identified, is found in layers dating from the Paleocene through the
Eocene into the Oligocene. Am I dissapointed at not finding any time
markers for the Cretaeous? No, not at all, it is an interesting
although sometimes a frustrating challenge to identify what I observe
and searching through the strews is just plain fun.
I was
surprised at the reference to Cretaceous diatoms and
Jutland. My experience, limited as it may be, placed the Jutland
diatoms in the Eocene epoch. One or two sample slides would not, could
not,
tell the whole story. Diatomite deposits can cover a great expanse of
land and measure hundreds of feet
in height with the lower deposits being an earlier age while those at
the top being a later age. Where in a given local or where in the
vertical column was a sample
collected? Which portion of the vertical column is exposed and
accessible? Geologic forces can twist invert and mix rock formations,
the earth is dynamic. My approach was 'B' cubed; beg, borrow, or buy
slides. This
may not
be the scientific approach but it has the advantage of allowing me to
work
from home with the smallest expenditure of capital and time but fails
to address these issues.
I examined
four strew slides from Jutland. On all four slides I found
examples of the somewhat square diatom, or an octagon with four horns,
Trinacria exculpta which is a
typical Late Paleocene and Early Eocene species of planktic diatom, Fig
8. Happy is the amateur
who can identify a fossil diatom with a measure of confidence. I also
found examples of the Silicoflagellate
Naviculopsis aspera which is another biostratigraphic
marker species for the Late Paleocene and Early Eocene. On three of the
slides Triceratiums were present in large numbers on the fourth slide
the Triceratiums were almost completely absent, only a few broken
fragments, and it was dominated by fragmented centric diatoms
resembling
Coscinodiscus. Fig 7. left strew is typical of Mors Jutland, three
slides, while the strew on the right is from Fur Jutland. If the forth
slide from Fur Jutland had been the only slide
examined I would have an incomplete picture of the diatoms
from Jutland. What caused this disparity, water depth, acidity, time?
Fig 8. Mors
Jutland. L to R. Trinacria exculpta, Trinacria, Triceratium
I am pleased
with the results of my quest for Cretaceous diatoms. I believe I was
successful and I have acquired an interesting collection of early
fossil diatom slides that I will treasure for years to come. While
sitting
at my desk, microscope before me, box of diatom slides to the right,
computer monitor on left, I imagine a Cretaceous diatom drifting in a
shallow warm blue green sea when suddenly an ugly segmented crustacean
larva,
mouth wide, gulps down my diatom. The crustacean is then eaten by a
juvenile fish which is eaten by a larger fish and yet a
larger
fish devours this. A sudden storm washes the big fish onto a Cretaceous
beach and a roaming Theropod dinosaur, flesh eater, devours the
stranded fish. A diatoms place in the natural order of things has not
changed much in 65 million years. Today we can
replace my imagined Cretaceous storm with a trawler net and the flesh
eating dinosaur with todays top predator, homo sapien.
I apologize to the reader in the event of errors in identification. My
command of the English language is OK but my German is not so good and
my French is almost nonexistent and two of my best sources for
identifying fossil diatoms happen to be in German and French. I
believe the Genus I have given is correct, possibly not up date, but am
less certain of the
family. I am an amateur and amateurs will make mistakes. I follow the
convention genus has a capital character for the first letter and
family is lower case.
Photography.
All images were recorded using the AMscope 6 mega pixel MD900
microscope
camera. Black and white images are preferred because I believe they
provide greater contrast. Each diatom was imaged through a
green filter and then converted to gray scale. Only one exception, Coscinodiscus
steinyi, Fig 3, was a color image converted to gray scale. The diatoms
and Silicoflagellates
were cut out using paint shop Pro and then pasted onto a colored
background.
Scale. Unless noted the black bar in the lower right cornor is 10 micro meters.
References:
Barker, P. F, Kennett, J. P.
Enigmatic Lower Albian Silicoflagellates From
OF THE ORDER
SILICOFLAGELLATA? Proceedings of the Ocean Drilling Program, Scientific
Results, Vol. 113. 1990
Barker, P. F, Kennett, J. P. Cenozoic
Silicoflagellates and Ebridians Ffrom
Dallas
Hanna, G,
Cretaceous Diatoms from California. Occasional
Papers of the California Academy of Sciences. 1927
Bolli,
H. M. Saunders,
J. B. Perch-Nielsen. Plankton Stratigraphy Volume
2.
Cambridge University Press. 1985
Van Heurck, Henri. Sysnopsis des Diatomees de Belique. 1885
Pantocsek,
Josef. Fossilen Bacillarien Ungarns. Berlin. 1903
Pedro M. Tapia and David M. Harwood. Upper Cretaceous diatom biostratigraphy of the