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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 50 (1966)

Issue: 3. (March)

First Page: 638

Last Page: 638

Title: Aspects of Wall Ultrastructure in Some Hyaline Foraminifera: ABSTRACT

Author(s): Kenneth M. Towe, Richard Cifelli

Article Type: Meeting abstract

Abstract:

Electron-microscopic examination of interior wall structure in some of the hyaline Foraminifera discloses that a variety of microcrystalline arrangements exists. In many instances the term "radial wall" is a misnomer. Some radial forms (Ammonia beccarii) are completely lacking in fibrous or prismatic crystals, displaying instead a very finely layered array composed of many plate-like crystals. In such cases, the appearance in polarized light is caused by the statistical, preferred orientation of c-axes giving rise to a more or less uniform extinction. The "prismatic" appearance is derived from the effect produced by the superimposition of "chitinous"-lined pore canals, even within the thickness of a thin section. An indistinctly radial form (Cibicides refulgens) has an id ntical microcrystalline arrangement except that the statistical c-axis uniformity is poorer, some areas being relatively well oriented with respect to the test surface and others not. True prismatic morphologic types do occur (Lenticulina calcar) as do walls composed of uniformly oriented microrhombs. The wall of the "granular" form Nonion labradoricum is constructed of lamellae, each lamella being composed of tabular granules sutured together. Each granule is a single crystal of calcite.

The lamellar character of the walls of many of the hyaline Foraminifera is not in agreement with the models suggested for this group. Indeed, some forms are non-lamellar. The concept that each chamber overlaps all previous chambers is not supported in every case by the data.

These observations clearly support earlier suggestions that any rational classification of the Foraminifera will have to consider the detailed structure and architecture of the walls. The fact that radial wall structure (in the petrographic sense) can be represented by several different microcrystalline morphologic types is as important as the difference recognized between radial and granular forms.

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Copyright 1997 American Association of Petroleum Geologists