Abstract
Abstract. Bolboforma is a microfossil of uncertain origin with affinities to protophytic algae. It generally occurs at high latitudes and/or in cool and temperate waters and has a high stratigraphic potential especially for the Miocene. Calcareous cysts of dinoflagellates represent the ‘benthic cyst stage’ of unicellular organisms belonging to the marine phytoplankton.The occurrence of Bolboforma, Bachmayerella is documented here and, for the first time, some calcareous cysts of dinoflagellates tentatively attributed to Alasphaera and Pithonella from Badenian (Langhian–Middle Miocene) sediments in Austrian and Moravian localities. Alasphaera and Pithonella were previously described from Cretaceous and Danian sediments only, therefore, their range has been extended into the Paratethyan Middle Miocene.Correlation of Bolboforma bioevents with standard geological time-scales allows confirmation, and in some cases refinement, of age assignments based on other microfossil groups, such as foraminifera and calcareous nannofossils, in Paratethyan areas. In particular, this paper presents a case study of the biostratigraphy of the Grund Formation outcropping at its type locality in Lower Austria. Age attribution of the Grund Formation has been uncertain for some time. The recovery of Praeorbulina glomerosa circularis and Uvigerina macrocarinata, associated with Bolboforma reticulata, allows the correlation of the Grund Formation with the Early Badenian (Middle Miocene). As planktonic foraminifera are generally very rare or absent in shelf deposits of many other Austrian and Moravian Middle Miocene sedimentary sequences, Bolboforma, and in particular B. reticulata, remains an important biomarker to identify lower Badenian sediments.Additionally, the new species Bolboforma gneixendorfensis Spezzaferri & Rögl is described. It is generally double-chambered with a weakly reticulate wall texture and is associated with Bolboforma reticulata, B. bireticulata and/or B. moravica.
Highlights
Bolboforma comprises a group of marine calcareous microfossils of uncertain origin with affinities to protophytic algae
The aims of this study are: (1) to document the occurrence of Bolboforma in Middle Miocene inner shelf to upper bathyal facies from Austrian and Moravian sequences; (2) to refine and confirm an age attribution of the sediments using the distribution of Bolboforma; (3) to document for the first time the presence of calcareous cysts of dinoflagellates in these areas
The biostratigraphy of the Grund Formation has been investigated in eight profiles excavated at the type locality
Summary
Bolboforma comprises a group of marine calcareous microfossils of uncertain origin with affinities to protophytic algae. Bolboforma specimens are monocrystalline, calcitic hollowshaped and consist of a spheroidal or subspheroidal single chamber. In some cases the wall may be built of at least three layers (Poag & Karowe, 1987). They may encapsulate a smaller chamber and produce cysts. Cysts are smooth or weakly ornamented and their function is still unknown (Spiegler, 1987; Spiegler & Daniels, 1991). Rare double-chambered Bolboforma specimens/species display a septum separating a large chamber from a smaller terminal aperture-bearing chamber (Daniels et al, 1981). The wall texture is smooth or strongly ornamented with a short neck or collar generally bordering the aperture. Specimens range in size from 50–250 μm, but their diameter is usually less than 150 μm
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