The Tournaisian-Visean boundary and evolutionary trends in the Eoparastaffella interiecta group in Mokrá near Brno (Czech Republic)
| Authors | |
|---|---|
| Year of publication | 2005 |
| Type | Article in Proceedings |
| Conference | S.C.S. Mid -Congress 2005 Conference Day |
| MU Faculty or unit | |
| Citation | |
| Field | Geology and mineralogy |
| Keywords | Tournaisian; Visean; foraminifers; evolution; biostratigraphy |
| Description | In Mokrá the Tournaisian-Visean boundary falls within a sequence of alternating shales and thin-bedded calciturbidites. The tectonically complicated sequence contains a very rich fauna of foraminifers, conodonts, trilobites and brachiopods and therefore represents a key section for the calibration of the Tournaisian-Visean boundary interval. In conodont fauna all important guides of the latest Tournaisian have been encountered. The diverse trilobite association correlates well with the Erdbach Limestone of the Rheinische Schiefergebirge. The brachiopod fauna is remarkably diversified. Two discrete but subsequently mixed brachiopod associations can be tentatively differentiated. The first prevailing association is probably sub-authothonnous, of deep-water origin and comprises large smooth rhynchonellids similar to Ilopsyrhynchus, the small chonetoid Rugosochonetes sp. and a rhipidomellid Aulacella sp. These taxa are commonly complete (mostly deformed), with valves attached; a minute discinacean, Orbiculoidea sp., is much rarer but probably belongs to the same association. The second fossil association is represented by brachiopod fragments, commonly associated with coarse biodetritic and clastic material. There are two spiriferid genera, Prospira and Tylothyris, the medium-sized reticulariid Reticularia, large chonetoids referable to Rugosochonetes, a rhipidomellid, Rhipidomella sp., and two or three poorly preserved productids, of which Plicatifera is characteristic. These taxa are probably allochtonnous, and represent a shallow shelf fauna. In the foraminifers most of the guides for the latest Tournaisian are also present but the eoparastaffells microfauna is especially rich. The best represented group is Eoparastaffella interiecta and related forms which show a considerable variability but share a common body-plan. A wide variety of biometric parameters were investigated and a few were selected as useful to characterize the morphological spectrum observed in the group. Moreover reference juveniles at different stages of ontogenic development were obtained by decomposing the growth history of typical adults and included in the biometric analysis. Based on an approach combining classical descriptive analysis and biometry of juveniles and adults the diagnoses of the already known E. interiecta interiecta VDOVENKO, E. tummida tummida PRONINA and E. florigena PRONINA were emended and new taxons have been distinguished including E. elongata n. sp., E. interiecta vdovenkovi n. ssp. and E. tummida inflata n. ssp. The great variability in the morphospace occupied by the group is demonstrated by several transitional forms. The results of the biometric study in Mokrá were compared with associations of Eoparastaffella of similar age in other important sections in southern China, Iran and Ireland. The representatives of the group are most abundant in the latest Tournaisan above the Scaliognathus anchoralis conodont Zone and below the entry of Eoparastaffella simplex VDOVENKO, but are present from the upper part of the Scaliognathus anchoralis Zone up to the early Visean. The record of Eoparastaffella in Mokrá starts in the upper part of the Scaliognathus anchoralis Zone with E. rotundiformis n.sp., higher up E. interiecta vdovenkovi n.ssp.occurs together with the last Scaliognathus anchoralis europensis within the range of Darjella monilis MALACHOVA and Elevenella parvula BOZORGNIA together with Biseriella bristolensis (REICHEL) and Lysella gadukensis (BOZORGNIA). E. elongata n.sp. and E. interiecta interiecta nssp. occur higher in the Gnathodus pseudosemiglaber Horizon succeeding to the S. anchoralis Zone with the first primitive Eoparastaffella simplex VDOVENKO within the range of the Polygnathus bischoffi RHODES, AUSTIN et DRUCE. E. tummida inflata n.ssp. enters still higher, accompanied by Loeblichia fragilis LIPINA. The last entry of the sequence is typical E. simplex VDOVENKO. |
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