Jump to content

Microfossil Mania!

  • entries
    9
  • comments
    26
  • views
    9,851

About this blog

An ongoing account of additions to my burgeoning collection of Foraminifera and Ostracoda.

Entries in this blog

Rumi

Some Centric Fossil Diatoms

Diatoms are monocellular organisms which contain chlorophyll, and manufacture their own food in the same manner as plants, through the process of photosynthesis.  They are one of the major producers of the Earth's oxygen.  Their long geological history makes them very useful in the correlation of sedimentary rocks, and they are of equal value in reconstructing paleoenvironments.  They are remarkably common everywhere there is any water at all!  I have studied fossil marine diatoms for many years, as they are my primary interest in the microfossil world.  Many of them are quite beautiful, and they are a favorite subject with many persons who enjoy photomicrography.  My primary interest is in diatom taxonomy and evolution, not photography, so I'm afraid my images don't really do them justice.  Centric diatoms exhibit radial symmetry, from circular to triangular, and all points between.  Oval shapes are not uncommon.

 

Az_morenoensis.jpgP_fausta.jpg

 

The oldest specimens of essentially modern diatom types are from the Cretaceous, and one of the very best localities is the Moreno Shale, which crops out in the Panoche Hills of California.  Many diatomists have worked on this flora, and it is fairly well understood.  Here we see two of the common taxa from this source.  (The bar across the top of the Azpeitiopsis is a sponge spicule, not part of the diatom!)  Diatom frustules are composed of secreted silica -- hence they are brittle, but can be virtually indestructible by chemical or diagenetic change in the right sort of environment.  (One exception is a highly alkaline environment, which corrodes and ultimately dissolves biogenetic silica.)  Other siliceous microfossils include some types of sponge spicules, silicoflagellates (another blog entry coming up perhaps), radiolarians, and ebrideans.  At least one family of the foraminifera uses siliceous cement to form their tests.

 

Diatom floras changed radically across the KT boundary, but they are still abundant in the Paleocene.  Arguably the world's most famous locality for fossil diatoms is the region around Oamaru, New Zealand, and all collectors have many specimens from there.  The age is Late Eocene - Early Oligocene.  Somewhat earlier are the many great localities in Russia.  Here is a Paleocene specimen from Simbirsk, Ulyanovskaya, Russia.  Note that it deviates from pure centric form in that it is slightly ovoid.

 

R_oamaruensis.jpg

 

My own specialty is the diatoms of the Miocene.  The United States is blessed with superb Miocene localities on both coasts, many well-known to members of this forum, because most of them can also produce superb shark teeth.  The earliest known Miocene flora in the US comes from sites in Maryland: near Dunkirk, Nottingham, and other lesser known localities along the Patuxent River.  All of these sites began to be explored in the mid-19th Century, because the diatoms are so perfectly preserved, to say nothing of abundant!  These sites are in the lowest part of the Calvert Formation; indeed, there is an unconformity above them that lasted for a considerable period of time, and the diatom flora exhibits considerable changes across it.  This part of the Miocene section belongs to the Burdigalian Stage, and age-equivalent diatoms are found also in bore holes and artesian wells at Atlantic City, New Jersey.  An index fossil for the East Coast Burdigalian is the following taxon:

 

A_heliopelta.jpg

 

This species of Actinoptychus evolved relatively quickly, and became extinct at the end of the Burdigalian.  It is remarkably beautiful under the microscope, especially in color images, as fine structures in the silica serve as diffraction gratings.  I regret that I have no color image in my photo library: I need to make a few!  The Calvert Cliffs are rich in fossil diatoms, also, from the later, Middle Miocene.

 

C_coscinodiscus.jpg

 

The above is but one example of the many marvelous specimens that can be found in the Calvert.  If you're walking the beach for shark teeth, and have access to a microscope such as that used in microbiology or pathology labs, or even the type used in high school biology labs, grab a sample of the sediment.  Soak it in water until it disaggregates into mud, let it settle until the water is just a bit cloudy, and put a drop on a microscope slide with a coverslip.  A magnification of 100X should reveal diatom frustules (or fragments thereof) among the remaining, unsettled particles of silt.  Diatomists all have their own protocols to get such specimens almost perfectly clean, and permanent slides made with a mountant of high refractive index can be utterly gorgeous.

 

I am currently working most intensely on samples from the somewhat later Choptank Formation, that outcrops at Richmond, Virginia.  This is another locality that produces excellent specimens:

 

A_senarius_N.jpg

 

This is one of the most enduring taxa in the geological record, appearing from the early Paleogene right up until the present day, and it can be very abundant.

 

T_condecorum.jpg

 

A common triangular form.  There are many genera of triangular centric diatoms.  And other radial shapes are possible, too:

 

T_pentacrinus.jpg

 

So far as I am aware, this unique specimen is the earliest known example of this taxon, which is still found today in tropical waters.  The breakage in the top "arm" is unfortunate, but what can I say: the specimen is, thus far, unique.  One might expect modern contamination of the sample, were it not for the fact that the Richmond localities occur far from the contemporary ocean coast -- they are not "watered" by modern waves!

 


That's it -- the 3.95 MB limit..............................

 

 

 

Rumi

In 1958, Louis S. Kornicker and John Imbrie wrote a brief paper on the holothurian sclerites of the Florena Shale in which they described four species.  I have found 3 specimens of one of these, Microantyx permiana Kornicker and Imbrie, 1958.  Two of these  specimens were badly broken, but one is in fair condition.

 

M_permiana1.jpg

 

The sclerites are wheel-shaped with short spokes, and the openings between the spokes are roughly triangular.  In this dorsal view we can see a distinctive trait of this taxon: the central area has four deep depressions.  (The upper one in this view is largely filled with matrix, unfortunately.)  The dorsal surface is virtually flat.  Individual specimens are typically very close to circular, but this one seems to have a marginal chip that disturbs the symmetry.

 

M_permiana2.jpg

 

The ventral surface is slightly cup-shaped, the marginal rim being raised above the level of the spokes.  The central area is more strongly raised, producing a central, conical hub.

 

The diameter of Kornicker and Imbrie's specimens ranged from 0.17 - 0.27 mm., the average being 0.23 mm.  This specimen is thus somewhat larger than any of theirs.

 

Kornicker, Louis S., and John Imbrie, 1958, "Holothurian Sclerites from the Florena Shale (Permian) of Kansas," Micropaleontology, vol. 4, no. 1, pp. 93-96, pl. 1.

Rumi

In this entry I would like to show two of the commonest Foraminifera from my sample of the Florena Shale.  The most common forams by far are the fusulinids, but as these are not identifiable without thin sections, they will have to wait until I'm equipped to deal with them.  Excepting the fusulinids, the commonest foram is Globivalvulina bulloides (Brady, 1876):

 

G_bulloides.jpg

 

This taxon has an enrolled biserial structure, and in spiral view it typically exhibits one large and two smaller chambers, the sutures between them forming a rough T-shape.  In the umbilical view the triangular projection into the umbilical area is characteristic.  The many specimens show several different growth stages, but all are easily identifiable.

 

The second most common non-fusulinid is Tetrataxis corona Cushman and Waters, 1928:

 

T_corona.jpg

 

This taxon is looks much like a Chinese straw hat: a very low cone, with a concave umbilical area.  Chambers are added marginally, typically four per whorl, hence the generic name.  Specimens vary greatly in size, representing various growth stages.  The larger ones very frequently exhibit chipped or broken edges, probably due to postmortem damage.

 

Rumi

In this second entry I would like to show well-preserved specimens of two ostracodes: the very long-ranging taxon Amphissites centronotus (Ulrich and Bassler, 1906), and the Permian taxon Cornigella parva Kellett, 1933.  The former belongs in the family Amphissitidae, while the latter is placed in the family Drepanellidae.

 

A_centronotus.jpg

 

This specimen is a relatively late instar, but not fully mature, as final instar specimens average about 50% larger.  The species is very easy to recognize, the very large and prominent central node being quite distinctive.  Additionally, there are two strong ventral flanges, the inner flange curving upward to the anterior cardinal angle.  There is a fairly strong dorsal ridge, the ends curving abruptly downward to form anterior and posterior ridges, the former being the longer of the two.  The flanges and ridges are considerably weaker on early instars, but the prominent central node is still unmistakable.  So far as I am aware, this taxon occurs throughout the Pennsylvanian (and perhaps earlier), and disappears by mid-Permian time, a range in excess of 100 Ma.  It has been assumed that this species was a free-swimming benthic form, as the prominent flanges would not be well-suited to an infaunal mode of life.

 

C_parva.jpg

 

Betty Kellett described two species of the genus Cornigella from the Fort Riley Limestone of the Chase Group, higher in the Permian section of Kansas: Cornigella parva Kellett 1933, and Cornigella binoda Kellett 1933.  They differed in the number of lateral nodes, the former species having a larger number of nodes, while in the latter species only the two prominent dorsal nodes were present.  However, Kellett noted that her specimens showed considerable variation, which she attributed to poor preservation and diagenetic crushing.  She went so far as to suggest that the two described taxa might actually be the same.  Looking at Florena specimens, which are well-preserved complete carapaces, I would agree with her suggestion.  The lateral nodes exhibit varying degrees of development; although the two dorsal nodes are always strongly developed, the ventral and anterior nodes may be considerably weaker.  The specimen shown here is very well-preserved, and the full (?) complement of lateral nodes is clearly represented.  (Note that, since we are looking at a complete carapace, the posterior dorsal node of the right valve is also obvious, as is a hint of the anterior dorsal node.)  This specimen is also of interest, in that it shows a lot of the surface sculpturing, not too obvious on other specimens.  I have chosen the name C. parva for this taxon, as Kellett's description appears first on the page, and should thus have priority.

 

I have not seen the description or illustrations of the generotype Cornigella minuta Warthin, 1930, which was described as having eight "prominent spines", one projecting well above the hinge line.  Type specimens were from the Pennsylvanian Wetumka Formation of Oklahoma.  I would follow Kellett's judgement in deciding that the Permian taxon was not conspecific with that of Warthin.

 

I had hoped to illustrate a perfect carapace of Ectodemites pinguis (Ulrich and Bassler, 1906) from the Florena, which I had temporarily stored in a small black plastic tray (the lid of a micromount box) on my desktop.  Unfortunately, when I went to retrieve it for photography, it had simply disappeared -- even though I thought it to be well covered!  Now it's fodder for the vacuum cleaner, one of the hazards of microfossil collecting................!

Rumi

I recently received some samples of washed residues from various shales and marls noted for their microfossil content.  One of the best of these is from southern Kansas, of Permian (Wolfcampian) age, from the Council Grove Group, Beattie Limestone Formation, Florena Shale Member.  The sample is amazingly rich, and I have recovered numerous species of Foraminifera and Ostracoda, as well as many nice bryozoan fragments.  In this blog entry I would like to show one of the more interesting microfossils that the Florena Shale is particularly noted for: the oogonia of charophytes, members of the algal family Characeae, commonly known as Stoneworts.  These large green algae live in relatively shallow, fresh to brackish waters -- although the tiny oogonia can easily wash down streams to the sea, where they will settle to the bottom in quiet, shallow areas.  (An excellent example is provided by The Fleet, a brackish lagoon on the southern coast of Dorset, England, where charophyte oogonia are abundant in bottom samples.)  Charophytes have been around for a long time, the earliest known oogonia coming from Devonian shales.

 

C_moreyi.jpg

 

This is a relatively large specimen from the Florena Shale, very typical in appearance.  The plants are called Stoneworts because they slowly secrete calcium carbonate, which eventually coats the leaves and stems, and particularly the reproductive products, the oogonia.  These are quite small, roughly egg-shaped, with a prominent spiral structure due to the shape of strip-like cells which grow to encase the delicate reproductive cells.  These strip-like cells vary in number, a valuable taxonomic trait.  This taxon, Catillochara moreyi (Peck, 1934), like all late Paleozoic forms, has five spirals.  (To count them, one needs to look at the specimen in end view, where the strip-like cells converge to a point, or small pit -- depending on which end one looks at.  On this specimen the point is to the right.)  Whole specimens like this one are typically white, because we are looking at a relatively thick outer coating of calcium carbonate.  Interestingly, the spiral-forming strips are coal black, and are usually well-preserved inside the outer coating.

 

C_moreyi2.jpg

 

This smaller specimen is broken, and the black spiral "egg case" beneath is readily apparent.  Holocene specimens from The Fleet look exactly the same when broken, or when the outer coating has yet to develop.

 

In further entries to this blog I will show off a few of the more interesting ostracodes and forams.

 

Rumi

About a month or so ago I received a sample of "microfossil dirt" from the Gene Autry Shale Member of the Golf Course Formation, which crops out in Johnston County, Oklahoma, in the Ardmore Basin. The Golf Course Formation is of Lower Pennsylvanian (Morrowan) age. The sample contains abundant foraminifera, although it is not rich in numbers of species. There are also some good ostracodes. Preservation is quite variable: a few specimens are essentially perfect, but most show varying degrees of crushing or recrystallization.

blogentry-4190-032043600 1291485537.jpg

The commonest foram in the sample is Ammodiscus semiconstrictus Waters, 1927. Most specimens are almost perfectly circular, like the one on the left, while others show deformation to a more-or-less oval shape, like the one on the right. Size of these specimens shows much variation: the larger specimen in this image is 1.0 mm in greatest width, and a few are a bit larger. Some tiny specimens are only 0.2 mm in width. The test is finely arenaceous, and seems to be composed mainly of tiny bits of carbonate mud. This wall composition is typical of all but one of the foraminifera specimens I have found in this sample thus far.

blogentry-4190-089832100 1291485520.jpg

Another common species in the sample is Hyperammina bulbosa Cushman & Waters, 1927. These are never found intact. The test shows only two chambers, a sac-like proloculus followed by a long, straight tubular chamber. In this image we see three proloculi, with the straight tubular chamber broken off at some distance away. (The specimen on the left is 1.8 mm long.) Fragments of the tubular chambers are very abundant, more so than the proloculi. (Each individual has only one proloculus, but the tubular chamber can easily be broken into 5-10 pieces, making such fragments more abundant.) A fairly long fragment of this sort is shown at the bottom of the image. These tubes may be slightly irregular, and occasionally show fine, transverse growth lines. The tubular chambers do not contain septa, however.

blogentry-4190-031143000 1291485403.jpg blogentry-4190-036173000 1291485427.jpg

Less common is Nodosinella glennensis Harlton, 1927. This is a robust, uniserial species with a round, terminal aperture. The subglobular chambers are typically crushed at right angles to the growth axis, as seen in the image on the left. (Length of this specimen is 2.2 mm.) The image on the right shows a terminal chamber, broken off from the remainder of the test, with the terminal aperture clearly indicated. This final chamber was only partially crushed.

blogentry-4190-048849100 1291485447.jpg

More rarely, one finds a specimen that has been crushed parallel to the axis of growth. This produces a form that looks like a stack of coins. In this image, the early chambers are on top, and the test is resting on its terminal face. (If you turn it over, the aperture is present in the center of the terminal face.)

blogentry-4190-029436700 1291485472.jpg

I suspect that this last image shows a specimen of the same species that has not been crushed. Chambers have been broken off of both ends, but the size and uniserial construction are correct. It looks very much like Harlton's original illustrations of the species, which was described from relatively undeformed specimens.

blogentry-4190-014155700 1291485553.jpg

Finally, we see Endothyra whitesidei Galloway & Ryniker, 1930, a specimen that is 1.1 mm in greatest width. This specimen was unique in the sample, and looks rather different from the others. It is amber in color, and slightly shiny. The Treatise on Invertebrate Paleontology describes all members of the superfamily Endothyracea as being calcareous imperforate, with some arenaceous material in the more "primitive" forms. I see no trace of arenaceous structure in this specimen, but it is certainly imperforate.

I continue to struggle with the whole question of wall composition. If you see sand grains or sponge spicules in the wall, then the specimen is clearly agglutinated. Calcareous, hyaline walls, with their (usually) obvious perforations are also easy to recognize. What is not clear to me is the distinction between the secreted calcareous (but imperforate) type of wall, and the agglutinated wall composed of fine calcareous particles in a secreted, calcareous cement. How would they look different?

Rumi

In picking out my sample of microfossils from the Middle Pliocene Coralline Crag Formation, Suffolk, England, I noted a few fragments of what appeared to be a species of the ostracode genus Pterygocythereis, a particularly spiny-looking genus of the family Trachyleberididae. I assumed it to be Pterygocythereis jonesi (Baird, 1850), the common species of the North Sea. As luck would have it, while finishing the picking of the last bit of the sample, up popped a complete valve, in almost perfect condition.

blogentry-4190-059842100 1291063720.jpg

To my surprise, it turned out not to be the common North Sea species; rather, it is Pterygocythereis siveteri Athersuch, 1972. The image does not do it justice, as even with image stacking software, the great length of the alae and the 3-D spininess are not very apparent. (Published dorsal views of the complete carapace are quite impressive!) Further cleaning of the specimen should greatly improve its appearance.

In the standard book on the recent Ostracoda of Great Britain, we find the following: "British records of P. siveteri are sub-Recent, and there are, as yet, no live records outside the Mediterranean." (Athersuch, Horne and Whittaker 1989: 146) Presence of this species thus provides further evidence that the Middle Pliocene sea around southern Great Britain was warmer than it is now, and that the ostracode fauna was essentially Lusitanian, characteristic of the modern Mediterranean Sea and of the Atlantic Ocean off the northwest coast of Africa.

The genus Pterygocythereis today is commonly encountered in the sublittoral zone, down to a depth of about 200 meters. Faunal studies of the Coralline Crag have suggested that it was deposited in a high energy environment with a maximum depth of about 20 meters, which seems to fit. However, this species is rather rare in the Coralline Crag, suggesting that it may not have been a member of the original, local biocoenosis.

Athersuch, J., D. J. Horne, and J. E. Whittaker, 1989, Marine and Brackish Water Ostracods, The Linnaean Society of London.

Rumi

I have always enjoyed looking at ostracodes of the family Trachyleberididae, for their varied and complex structures, and interesting ornamentation. The family seemingly first appeared in the Middle Jurassic, became abundant during the Cretaceous, and remains abundant in the seas of today.

About a month ago, in an exchange of microfossil material with an Italian friend, I received a sample of material from the Coralline Crag of southeastern England, a well-known and extensively studied Middle Pliocene (Zanclean) marine deposit of cross-bedded sands. The deposit averages about 12 meters in thickness, varies from weakly to more strongly consolidated, and is highly fossiliferous. The name comes from an abundance of bryozoans, which early scholars mistakenly thought were corals. Ostracodes and foraminifera are both abundant. Faunal studies have suggested that the sea was a bit warmer when this formation was laid down, perhaps more closely resembling the Mediterranean Sea, or the Atlantic Ocean off the northwest coast of Africa. Hence the Coralline Crag contains many species that do not much resemble those found in the marine littoral deposits of modern-day England.

I have recovered quite a few species of both forams and ostracodes from my sample, and am just beginning the identification process. The species I want to show off in this entry is the first I have identified, chosen to be investigated first because it is both common and showy. The taxon is correctly known as Cletocythereis jonesi Wood et al., although it was previously known by various other names through misidentification. It is a typical trachyleberidid, although with much coarser surface sculpture than most. The valves are subquadrate and rather thick, with an amphidont hinge.

blogentry-4190-087368100 1289508717.jpg

The surface is coarsely reticulate, with a strong sub-central tubercle, and dorsal and ventral ridges. The anterior margin is also reticulate, divided into elongate, transverse cells. The ventral ridge terminates posteriorly in a complex loop. The eye tubercle, just below the anterior dorsal margin, is large and shiny.

blogentry-4190-008130200 1289508742.jpg

Here is an interior view of the same right valve, unfortunately obscured by residual matrix. The ventral margin exhibits a strong concavity; the posterior dorsal corner is not broken, contrary to appearances, and is a close match to images of the type specimens.

blogentry-4190-074003500 1289515228.jpg

The hinge of the right valve has a strong, round anterior tooth. The posterior tooth is weaker, and the middle element is of the smooth groove-and-bar type; the right valve has the grooved element, and there is a corresponding thin bar in the left valve.

blogentry-4190-065177400 1289508762.jpg

This dorsal view shows the thickened central part of the carapace, due to the dorsal and ventral ridges, and the relatively flat anterior and posterior margins.

Personally, I think this is a really handsome microfossil -- considering that its largest dimension is only about 1 millimeter in length!

In future entries in this blog I hope to illustrate a few other ostracodes and forams from this interesting formation, if I am able to make more identifications. Fortunately, I have access to a good research library!

Two interesting references are:

Wilkinson, I. P., 1980, "Coralline Crag Ostracoda and their environmental and stratigraphical significance," Proceedings of the Geologists' Association 91:291-306.

Wood, A. M., R. C. Whatley, C. A. Maybury, and I. P. Wilkinson, 1992, "Three new species of cytheracean Ostracoda from the Coralline Crag at Orford, Suffolk," Journal of Micropaleontology 11:211-220.

Rumi

Finally, I Can Stop Whining!

In a number of recent posts to the Forum I have complained incessantly about my inability to locate microfossils here in my home state of Arizona. Well, no more! A sample that I processed over the weekend produced a few nice ostracodes, and I am optimistic about finding more. The locality is the well-known Kohl Ranch site, just northeast of Payson, Arizona, reputed to be the best spot for collecting invertebrate fossils in the state. The material comes from the "beta" member of the Naco Formation, a purplish, siliciclastic mudstone of Middle Pennsylvanian (Desmoinesian) age. The megafossils of this locality were listed by Brew and Beus (1976), and thirteen species of ostracodes were listed by Lundin and Sumrall (1999). (Several other publications deal with more specialized aspects of the fauna.) The reported fauna is representative of an offshore, shallow, marine environment, probably less than 20 meters in depth. (Brew and Beus 1976: 889)

blogentry-4190-010321200 1289235922.jpg blogentry-4190-050154800 1289235941.jpg

Two of the better specimens are shown in the attached photos. Both are complete single valves, and are partially pyritized. The male valve is a bit better preserved than the female, but both are adequate to show the basic features of the species -- which is the commonest one found in this particular sample. The ventral frill (velum) of the male is smaller, with a smaller posterior spine. The frill of the female is larger and incurved, presumably to form a brood pouch. This type of velum is characteristic of the family Hollinidae, although the various genera exhibit it in different degrees of development.

The remaining matrix on these specimens certainly detracts from their appearance, and I am going to try further cleaning with kerosene. Thus far the sample has simply been boiled with some sodium bicarbonate.

It is interesting that no other microfossils have been found in this formation. Although fusilinids are reported, I have seen no other forams at all, nor have I seen any conodonts.

A future entry in this blog will present some photos of the locality.

Brew, Douglas C. and Stanley S. Beus, 1976, "A Middle Pennsylvanian Fauna from the Naco Formation near Kohl Ranch, Central Arizona," Journal of Paleontology 50:888-906.

Lundin, Robert F. and Colin D. Sumrall, 1999, "Ostracodes from the Naco Formation (Upper Carboniferous) at the Kohl Ranch Locality, Central Arizona," Journal of Paleontology 73:454-460.

×