Morphological investigations of Miliolidae (Foraminifera) from the Upper Permian of the Southern Alps, based on thin sections and stereoscopic X-ray microradiographs

Abstract

Shallow marine deposits of the Upper Permian and lowermost Triassic in the Southern Alps between Val Adige (Southern Tyrol, northern Italy) in the west and the Karawanken Mountains (northern Yugoslavia) in the east contain abundant miliolid foraminifera of the genus Hemigordius Schubert, 1908. These two-chambered Miliolacea show a great diversity of morphotypes due to numerous combinations in the mode of coiling, the shape of the umbonal thickening, the degree of involution, and the dimensions of the test. The spectrum of internal structures of Hemigordius observed in thin-sections is schematized and illustrated in a diagram. Of special interest are irregularly coiled specimens whose complicated mode of coiling is analysed with help of stereomicroradiographs. According to the number of spiral planes, their angles in between and the number of volutions a streptospiral and a glomospiroid type are distinguished. While the streptospiral mode is characterized by a ± regular coiling plan, the glomospiroid type does not show any rules in the succession of the spiral planes and angles. p [Three-dimensional illustrations eludicate the streptospiral and glomospiroid coiling plan of the genus Hemigordius. The new developed X-ray microradiographic technique used in our investigation is described in some details. © 1990 E. Schweizerbart'sche Verlagsbuchhandlung.