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Horse stable in northern NJ with small outcrop of Decker Ferry Formation, snails identified by Weller as "Loxonema ? sp." and ostracodes. G
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These are 2 photomicrographs (XPL and PPL) . Can somebody tell me if it is an Ostracod or no ? I found so much of this structre in different shape. Continental Limestone , Tunisia Thank you in advance !
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Another Interesting Ostracode From The Coralline Crag Formation
Rumi posted a blog entry in Microfossil Mania!
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. 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.- 10 comments
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An Interesting Ostracode From The Pliocene Of England
Rumi posted a blog entry in Microfossil Mania!
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. 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. 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. 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. 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.- 2 comments
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