Mikrofauna osadów dolnego dewonu z otworu wiertniczego Krowie Bagno IG I

Abstract

MICROFAUNA OF THE LOWER DEVONIAN DEPOSITS PIERCED BY BORE HOLE KROWIE BAGNO IG I

Summary

Microfossils that are discussed in the present article come from the marine deposits of the lowermost Lower Devonian pierced by bore hole Krowie Bagno, south-eastern area of Poland. Siltstone-clay deposits of the lowermost Lower Devonian are overlain with a series of sandstones (Upper Siegenian - Emsian) that represent the Lower Devonian of Old-Red type. The siltstones include a rich assemblage of fossils (pelecypods, brachiopods, trilobites, tentaculites, ostracods, conodonts), very approximate to the faunistic assemblages found to occur in the type Gedinnian and Lower Siegenian deposits of West Europe, and of Volhynia and Podolia. The bore hole Krowie Bagno has demonstrated that at a depth of 1730-1832 m ostracods occur in masses, are well preserved, and, as a rule, make banks that accompany both pelecypods and brachiopods. A lot of species are identical with those occurring in the Czortków and Ivanievo Beds in the areas of Podolia and Volhynia. On the other hand, the species described from the Borshtshov Beds of Podolia are only slightly represented. At the same time the Krowie Bagno area discloses species known from the Gedinnian of the Ardennes (Primitia jonesi) and from the Lower Devonian of North America, and so far unknown from the area of Podolia. At depth of 1744-1778,3 m conodonts characteristic of the stage steinhornensis have been encountered. However, the lack of I. woschmidti Ziegler makes it impossible to determine the horizon distinguished in this stage. The specimens determined by the present author as S. steinhornensis sensu lato occur in small quantities and do not allow any species to be determined precisely. The analysis based on the research of ostracods allowed the author to make stratigraphical correlations. Deposits that occur at a depth of 1730-1830,2 m correspond to the Czortków Beds and Ivanievo Beds distinguished in the Gedinnian of Podolia, as well as to the Gedinnian deposits in the Ardennes. The boundary between the possible equivalents of the Czortk6w and the Ivanievo Beds at Krowie Bagno runs at a depth of 1804-1811 m, or even somewhat lower. A more detailed description of this boundary seems to be impossible, since the author did not have at her disposal any samples from the depth of 1780,2-1804,0 m. As far as the occucrence of the equivalents of the Ivanievo Beds in the area of Krowie Bagno is concerned, conclusions have been drawn on the basis of the mass occurrence of Carinokloedenia alata and C. carinae, as well as Poloniella alexanderi and Poloniella oleskoiensis, i.e the guide species of the Ivanievo Beds of Podolia.

Palaeontological description

Hindeodella longidentata sp. nov.

Twig-like form. Anterior and posterior branches make an obtuse angle (about 160°). Teeth of the anterior branch, initially needle-shaped, are slightly inclined backwards. When nearing the main tooth they grow larger. Among the three larger teeth there is found one thin tooth too. The two teeth situated in the neighbourhood of the main tooth are not separated by a thin tooth. The posterior branch reveals,between 4 large teeth that occur behind the main tooth, three needle-shaped, and very fine teeth. The structure of the end portion of the posterior branch of this conodont is particularly characteristic. Here are found three very high, slim, pointed and strongly backwards inclined teeth. Two of them are markedly higher than the main tooth; the third situated between them, corresponds, with its height, to the height of the main tooth. Behind these three teeth there occurs another small tooth, with a height equal to that of the posterior branch. This tooth is strongly deviated from the other ones. The posterior branch is only slightly longer than the anterior branch. The species here considered occurs in the Lower Devonian deposits pierced by bore hole Krowie Bagno IG I.

Volyniella abushikae sp. nov.

Test oval, with a straight dorsal edge; anterior and posterior edges slightly bent archwise. Posterior and anterior edges pass mildly into the ventral one. The dorsal edge makes with the anterior and the posterior edges an obtuse angle. Both valves reveal two cylindrical ribs, which are removed from the anterior and posterior edges, but they run almost parallel to them. At the dorsal edge they are high, but in the vicinity of the ventral edge their height decreases. Near the ventral branch these ribs flatten little by little out, to pass into the marginal areas of the valves. The surface of the test within the ribs is completely smooth. The test is bilaterally convex. No t e. Lack of the central nodule, which usually occurs within the marginal areas of the valves, is here the principal feature that distinguished this species from the species Volyniella silurica K r a n d. et G u r e v i c h. Volyniella abushikae sp. novo appears in the Gedinnian deposits pierced by bore hole Krowie Bagno IG I.