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Nd and Sr isotopic evidence for provenance of clastic material of the Upper Triassic rocks of Silesia, Poland

Konieczna N., Belka Z., Dopieralska J.

Annales Societatis Geologorum Poloniae

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2015

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Vol. 85, No. 4

675--684

EN

Nd and Sr isotope data were used to characterize the sources of the Upper Triassic (Keuper) siliciclastic rocks of Silesia in southern Poland. This continental succession, consisting predominantly of fine-grained mud- stones and siltstones, yields a remarkably uniform Nd isotopic composition. Nd model ages T2DM vary from 1.56 to 1.69 Ga and εNd values are in the range from –8.9 to –11.2, documenting old crust contribution in the provenance. In contrast, the Sr isotopic composition (87Sr/86Sr) of the clastics exhibits a relatively large variation from 0.710 to 0.723. The isotopic compositions indicate that the southern part of the Germanic Basin in Silesia was supplied with clastic material from the Bohemian Massif. The axis of the drainage area must have crossed from SW to NE the Saxothuringian units of the East Sudetes and most probably also the area of the Tepla–Barrandian Unit. There is no indication of any sediment transport from the Moravo-Silesian Belt and the Fore-Sudetic Block. It seems, that the Palaeozoic rocks of the latter domain must have been buried completely during Late Triassic times.

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Devonian conodont and ammonoid succession of the eastern Tafilalt (Ouidane Chebbi section), Anti-Atlas, Morocco

Belka Z.

Acta Geologica Polonica

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1999

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Vol. 49, no. 1

1-23

EN

Devonian conodonts and ammonoids occurring in association in the Ouidane Chebbi section of the eastern Tafilalt (Anti-Atlas, Morocco) are described and analysed in terms of stratigraphy. The excellently exposed sequence spans the entire Devonian; it includes open-marine carbonates and shales deposited outside the tropical realm. Except for its Middle Devonian part, the Ouidance Chebbi section is not condensed. Although the sequence was only sampled in a preliminary fashion, most of it lithological units have been dated with some precision. The study is an attempt to enhance the precision in the correlation between the Devonian conodont and ammonoid sequences. Graphic correlation method was used for estimating the precise position of the zonal and stage boundaries for the Middle and Upper Devonian intervals. The stratigraphy of the Lower Devonian at Ouidane Chebbi is still poorly defined. The Eifelian/Givetian boundary is well constrained, especially by both conodonts and ammonoids. It occurs within the uppermost part of the Kacak Event-Level, a characteristic shale horizon that beginsin the ensensis Zone and ranges into the hemiansatus Zone. Biostratigraphic indications from conodonts show that the top of the Pharciceras limestone unit is located within the norrisi Zone and the Givetian/Frasnian boundary should be placed within the characteristic black styliolinites level of the Frasne Event. The onset of the Kellwasser facies falls within the Zone 12 (winchelli Zone) of the Frasnian and it extends into the rhomboidea Zone. The combined evidence from ammonoid and trilobite data suggests that the marine deposition persisted at Ouidane Chebbi at least up to the time of the Upper praesulcata Zone.

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Late Visean/early Namurian conodont succession from the Esla area of the Cantabrian Mountains, Spain

Belka Z., Lehmann J.

Acta Geologica Polonica

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1998

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Vol. 48, no. 1

31-41

EN

Conodont fauna recovered from pelagic nodular limestone sequence exposed near Santa Olaja de la Varga precisely dates the upper part of the Alba Formation in the Esla area of the Cantabrian Mountains. In terms of goniatite stratigraphy, the formation ranges into the early Namurian E2 interval which has been identified by the occurrence of the conodont Gnathodus bollandensis. The investigated conodont fauna includes exclusively deep-water forms and is dominated by species of Gnathodus and Lochriea. The former genus is represented primarily by the bilineatus lineage, in which a new species Gnathodus cantabricus sp. nov. has been recognized and is described herein. Representatives of the another gnathodontid girtyi lineage,generally present in the late Visean/early Namurian deep-water faunas, are extremely rare. The vertical succession of Lohriea species is closely comparable to those recognized in Northern England, Poland andUkraine. The Visean/Namurian boundary is thus placed at the first occurrence of Lochriea cruciformis, 4.7 m below the top of the Alba Formation.