engleski

From oriented to virtual sections of foraminiferal tests, new insights in architecture of larger benthic foraminifera

For the systematic classification of larger benthic foraminifera oriented test sections are necessary, because species are identified based on their internal structures. In this region, Kochansky Devidė (1952, 1955) introduced this approach simultaneously promoting micropaleontology as an important part of geological science. Well known are her illustrations in which different sections of the same specimen reveal different characteristics, demonstrating that identification based on random sections is difficult or impossible. How to get a proper section without destroying the test? Traditionally, manual grinding of the test to preferred orientations (axial and equatorial planes) is a way to expose key-characters of isolated specimens. When tests are embedded in rocks, within a large number of random sections a few preferred oriented sections often enable identification. Exposing internal structure by grinding has disadvantages in destroying the shells, it is time consuming and, extensive technical and professional skills are needed. The application of X-ray device and scanning electron microscopy from the 1950s and 1960s resulted in excellent observations and illustrations of foraminifera, but there are still some disadvantages (further study of the specimens due to the sample preparation is impossible, because either outer or „grindingly open” inner structures are available). Recently, nondestructive method that at the same time allows the study of internal and external characteristics of foraminifera has been introduced. The X-ray microtomography offers an accurate interpretation of internal structures, dimensions of structural elements, volumetric rendering and the analysis of ontogenetic development without test destruction. Almost 30 specimens of well preserved sphaerogypsinids were examined by X-ray microscope Xradia – ZEISS MicroXCT-400, producing detailed structural description of the tests, which do not show any equatorial (or axial) plane.

Larger Benthic Foraminifera; Thin sections; Micro-CT

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