Revision of the Biostratigraphic Scheme in the Cambrian Series 2 and 3 Boundary Interval of the Holy Cross Mountains (Poland)

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Revision of the biostratigraphic scheme in the Cambrian Series 2 and 3 boundary interval of the Holy Cross Mountains (Poland)

Conference Paper · September 2017

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Jakub Nowicki Anna Żylińska Faculty of Geology, University of Warsaw 8 PUBLICATIONS 30 CITATIONS 38 PUBLICATIONS 776 CITATIONS SEE PROFILE SEE PROFILE

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Revision of the biostratigraphic scheme in the Cambrian Series 2 and 3 boundary interval of the Holy Cross Mountains (Poland)

Jakub Nowicki and Anna Żylińska Faculty of Geology, University of Warsaw, Żwirki i Wigury 93, PL-02-089 Warszawa, Poland; [email protected]; [email protected]

As it is typical for Cambrian strata, the most important fossils for the biostratigraphy in the Holy Cross Mountains (HCM) are trilobites. In the middle part of the section, specimens representing members of several trilobite families can be found, largely of the Ellipsocephalidae, and Paradoxididae, accompanied by the Solenopleuridae, Dorypygidae, Palaeolenidae and trilobites from the informal Conomicmacca/Myopsolenites clade. Paradoxidids were applied previously in the biostratigraphic subdivision in the studied interval, which, due to the alleged occurrence of Scandinavian taxa, was commonly correlated with the scheme as known from Scandinavia. Previous authors (e.g., Orłowski 1992) subdivided the middle part of the Cambrian in the Holy Cross Mountains into three biozones: the Paradoxides insularis Zone, a probable correlative of the Eccaparadoxides insularis Superzone from Scandinavia; the Paradoxides pinus Zone, an analogue of the modern Pentagnostus praecurrens – Acadoparadoxides pinus Zone; and the Paradoxides polonicus Zone, which was considered the equivalent of the Paradoxides paradoxissimus Superzone. A modern revision of ellipsocephalid trilobites from the HCM has pointed out that they resemble fauna from Gondwana and Avalonia (e.g., Żylińska 2013). Moreover, species representing the Palaeolenidae and the Conomicmacca/ Myopsolenites clade have allowed for the correlation of the lower part of the Paradoxides insularis zone with the Morocconus notabilis Zone of Morocco (Żylińska and Masiak 2007). The most recent taxonomic revision of the Paradoxididae from the HCM has provided new data that resulted also in the revision of the biostratigraphic scheme. None of the alleged Scandinavian paradoxidid species is in fact present in the HCM. The revised group contains four species (not eleven, as previously determined), all of which are endemic. The new biostratigraphic scheme (Fig. 1) is again based on paradoxidids and contains two assemblage zones: the lower Acadoparadoxides samsonowiczi − Acadoparadoxides kozlowskii Zone, which incorporates part of the section previously described as the Paradoxides insularis and the Paradoxides pinus zones, and the upper Acadoparadoxides slowiecensis – Hydrocephalus polonicus Zone, which incorporates the former Paradoxides polonicus Zone. The paradoxidids from the HCM strongly resemble the taxa from Morocco described by Geyer and Vincent (2014) and, despite endemism of the fauna, allow for the correlation of the entire lower zone with the Morocconus notabilis Zone of Morocco. This interpretation is also supported by other trilobite groups. Likewise, Acadoparadoxides slowiecensis from the upper zone may be related with fauna from the Morocconus notabilis Zone, but it also resembles stratigraphically younger acadoparadoxidids (although still older than Scandinavian paradoxidid taxa). On the other hand, Hydrocephalus polonicus may be related to Hydrocephalus vikensis from the Pentagnostus praecurrens – Acadoparadoxides pinus Zone (Scandinavia). The precise distribution of Acadoparadoxides slowiecensis and Hydrocephalus polonicus in the succession remains unknown due to poor exposure, therefore it is also possible that they do not co-occur with one another and the upper zone may have a much longer range, extending up to the level of the Pentagnostus praecurrens – Acadoparadoxides pinus Zone or even to the Paradoxides paradoxissimus Superzone. Despite the significant change in the biostratigraphic scheme, the correlation of the middle partof the Cambrian in the Holy Cross Mountains still needs refining. Solenopleurids and a single member of the Dorypygidae family still await a modern taxonomic revision, which may provide additional data for correlation. Moreover, the problem of recognising zonal boundaries remains an open case.

Geyer, G. and Landing, E. (Eds.) 2006. Ediacaran–Cambrian depositional environments and stratigraphy of the western Atlas regions, UCL Maghreb Petroleum Research Group, Infracambrian/Early Palaeozic Field Guide Series 1 and Beringeria Special Issue, pp. 120.

62 10th Baltic Stratigraphic Conference, Chęciny 12-14 September 2017 – Abstracts of oral and poster presentations

Geyer, G. and Vincent, T. 2014. The Paradoxides puzzle resolved: the appearance of the oldest paradoxidines and its bearing on the Cambrian Series 3 lower boundary. Paläontologische Zeitschrift, 89, 335–398. Orłowski, S. 1992. Cambrian stratigraphy and stage subdivision in the Holy Cross Mountains, Poland. Geological Magazine, 129, 471–474. Weidner, T.R., Rushton, A.W.A. and Ebbestad, J.O.R. 2014. A paradoxidid–agnostoid fauna from the mid-Cambrian (Stage 5) of the Caledonian Lower Allochthon on Tåsjöberget, Ångermanland, Sweden. GFF, 136, 513−530. Żylińska, A. 2013. Evolution of trilobite assemblages from the Cambrian Series 2 and 3 of the Holy Cross Mountains and their biogeographic significance. Przegląd Geologiczny, 61, 30–39. [in Polish] Żylińska, A. and Masiak, M. 2007. Cambrian trilobites from Brzechów, Holy Cross Mountains (Poland) and their significance in stratigraphic correlation and biogeographic reconstructions. Geological Magazine, 144, 661–686.

Fig. 1. Biostratigraphic scheme for the Cambrian Series 2 and 3 boundary interval in the Holy Cross Mountains correlated with the schemes for Scandinavia and Morocco.

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