Fossils of the Carpathian Region by István Főzy & István Szente

Author:István Főzy & István Szente
Language: eng
Format: epub
Publisher: Indiana University Press
Published: 2014-05-14T16:00:00+00:00

Alveolina

Eocene beds in the Transdanubian Range overlie much older formations, especially Triassic rocks that are extremely thick and cover large areas. Accumulation of these sediments mainly commenced in continental fluvial and lacustrine environments. At first, transgression resulted in the development of lagoons and inlets, in which miliolinids proliferated in large numbers (just as they do today); this group is able to tolerate salinity conditions different from those found in seawater and comprises the spindle- or cigar-like elongated alveolinids, which are another group of larger foraminifera.

Alveolina is found frequently and in large quantities in the lower part of Eocene successions. The internal structure of the tests of these foraminifera—which occasionally reach a few centimeters in size—is also characteristic: chambers that form coils and are arranged parallel to the axis are subdivided by secondary septa. As well as observing microscopic thin-section images from the often-mentioned Alveolina limestone under transmitted light, it is also possible to recognize that, due to their microcrystalline structure, the dark material of the shell predominates—contrary to the inner space of the chambers, which can be seen as rows of small light spots. At one time—due to nomenclatural considerations—forms now known as Alveolina were mentioned under the name Fasciolites; however, the former name is still considered valid. Alveolina remains from Hungary were described in a monograph by Mária JámborKness, who worked on the Eocene larger foraminifera for decades.

Alveolina belongs to the group of so-called porcelaineous foraminifera. Even in these successions they are found alongside hyaline foraminifera, which later became the dominant forms—with the most common being Nummulites.

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