One of the key objectives of the studies proposed by the Ordovician Subcommission is the improvem... more One of the key objectives of the studies proposed by the Ordovician Subcommission is the improvement of regional stratigraphy for further advancements in global correlation. The results of this work can be found in numerous updates and reviews published in the recent Geological Society, London, Special Publications 'A Global Synthesis of the Ordovician System'. Several of these papers refer to the Baltic Ordovician conodont biozones. While different schemes share many common features, their correlation with stages and biozones differ in detail. Considering the recent developments in the studies of the Sandbian stratigraphy in the Baltoscandian region, it is possible to complement the current conodont biozonation. Pygodus anserinus, Amorphognathus tvaerensis and A. superbus conodont zones are recognized in the Sandbian Stage in Baltica. The lower boundary of the stage is located within the Pygodus anserinus Zone, and the main part of the stage corresponds to the Amorphognathus tvaerensis Zone. In Scandinavia, the upper boundary of the stage correlates with a level within the A. superbus Zone or lies in a conodont-poor interval in the eastern Baltic region. The lower boundary of the A. inaequalis Subzone is tentatively correlated with the base of the Sandbian in Scandinavia but is located in the uppermost Darriwilian in the eastern Baltic region. In both areas, the A. tvaerensis Zone is subdivided into the Baltoniodus variabilis, B. gerdae and B. alobatus conodont subzones. The A. inaequalis Subzone-in some cases indicated as a zone-has been included in the regional stratigraphic charts for more than a decade. However, so far, A. inaequalis (Rhodes) has been reliably identified and also illustrated only from Avalonia, i.e. outside the palaeocontinent Baltica. A recent restudy of collections from the Fjäcka main section and the Smedsby Gård drillcore (both from Sweden), as well as from several Estonian sections, did not prove the occurrence of A. inaequalis in these areas. The A. tvaerensis Zone comprises almost the whole Sandbian, both in Scandinavia and the eastern Baltic areas. During this long age, the morphology of the P and M elements of A. tvaerensis (Bergström) gradually changed, and elements of distinct morphology appeared and were assigned to a new species, Amorphognathus viirae Paiste, Männik et Meidla, 2022, in the upper part of the range of the species. In succession, A. viirae appears in the upper part of the B. gerdae Subzone. Cur rently, A. viirae has been identified in numerous Estonian sections, as well as in the Fjäcka main section and the Smedsby Gård drillcore in Sweden. Based on published figures, it occurs evidently in the Mójcza Formation of the Holy Cross Mountains (Poland) and the Black Knob Ridge section in Oklahoma (USA), in the GSSP for the base of the Katian Stage. A. inaequalis has also been reported and an eponymous zone identified in two other sections located on the palaeocontinent Baltica, in the Bliudziai-150 drillcore (Lithuania) and the Kovel-1 drillcore (Ukraine). During the restudy of collections from these sections, no elements of A. inaequalis were found in either of them. The earliest recorded elements of the genus Amorpho gnathus have been assigned to A. tvaerensis, and the specimens from the upper range of this species reidentified as A. viirae. Analysis of the new material and revision of previous collections has revealed problems related to the Sandbian conodont biozonation of the palaeocontinent Baltica and demonstrated the need for its updating. The new proposed zonation excludes the A. inaequalis Subzone, as the occurrence of its nominal taxon on the palaeocontinent Baltica could not be proved. Additionally, a new unit, the A. viirae Zone, has been included in the zonation. It corresponds to the upper part of the former B. gerdae Subzone, which is now treated as a zone. Also, all subzones based on the succession of Baltoniodus species have been elevated to the rank of zones.
Stratigraphy and Geological Correlation, Sep 1, 2015
Much of the material of Paleozoic successions of Kotelnyi Island (New Siberian Islands) is com po... more Much of the material of Paleozoic successions of Kotelnyi Island (New Siberian Islands) is com posed of various carbonates, which accumulated in relatively shallow conditions in the Ordovician-Middle Devonian. Such deposits are widespread in synchronous sections throughout the Eastern Arctic and therefore attract attention as a potential tool for interregional correlations. In paleotectonic reconstructions, Kotelnyi Island either is included in terrain which was disconnected from the Siberian Platform in the Paleozoic or is joined to it. These different interpretations result from lack of primary evidence. This paper presents new data on stratigraphy and macro and microfauna of the Upper Ordovician and Silurian of the central regions of Kotelnyi Island. For this interval, we propose a correlation of the studied sections with those of adjacent regions. A conclusion is drawn on the basis of the similarity of lithology and fossil assemblages and also shared trends in the evolution of the sedimentary environment that the Upper Ordovician-Silurian beds of Kotelnyi Island, Taimyr, and the Siberian Platform accumulated in a single shelf basin, which apparently also extends to northeastern Chukotka.
Conodonts and chitinozoans were studied from the Neitla section, which exposes the boundary betwe... more Conodonts and chitinozoans were studied from the Neitla section, which exposes the boundary between the Porkuni and Juuru regional stages. This level, although not proved biostratigraphically, has been traditionally considered to correspond to the Ordovician-Silurian boundary. However, stable carbon isotope data indicate that the system boundary lies higher in the succession, in the lower part of the Juuru Regional Stage. Rare conodonts and chitinozoans discovered in the section do not provide any criteria for locating the boundary. Although conodonts are represented by taxa characteristic of the Silurian, all of them are known to have already appeared elsewhere in the Upper Ordovician. Materials and methods Two sections (Neitla-I and Neitla-II, see Fig. 1A) on the bottom of the gravel pit, with a distance of about 10 m between them, were described and sampled in 2009, 2010 and 2015. Both expose the uppermost Ärina Fm (Kamariku Mb) and the lowermost Varbola Fm (Koigi? Mb) underlain by reef limestone of the Tõrevere Mb.
Multiproxy correlation is used to address the boundary of the Kukruse and Haljala regional stages... more Multiproxy correlation is used to address the boundary of the Kukruse and Haljala regional stages across the Estonian part of the Baltoscandian Ordovician Palaeobasin. New biostratigraphic information on conodonts, chitinozoans and ostracods from the Peetri outcrop, northwestern Estonia, integrated with micropalaeontological data from five core sections all over Estonia, allows justification of the position of the stage boundary and correlation between conodont and chitinozoan biozones. In the Peetri outcrop a marked stratigraphic hiatus was recognized at the Kukruse-Haljala boundary-the Baltoniodus gerdae conodont Subzone and the Armoricochitina granulifera, Angochitina curvata, Lagenochitina dalbyensis and Belonechitina hirsuta chitinozoan zones are missing in the section. The lowermost part of the Tatruse Formation in central Estonia and the Adze Formation in southern Estonia are older than previously thought, and the results show a principal advantage of the multiproxy method over singlegroup studies. The lower boundary of the Haljala Regional Stage is tied to the interval with gaps that are common all over the stratotype region.
One of the key objectives of the studies proposed by the Ordovician Subcommission is the improvem... more One of the key objectives of the studies proposed by the Ordovician Subcommission is the improvement of regional stratigraphy for further advancements in global correlation. The results of this work can be found in numerous updates and reviews published in the recent Geological Society, London, Special Publications 'A Global Synthesis of the Ordovician System'. Several of these papers refer to the Baltic Ordovician conodont biozones. While different schemes share many common features, their correlation with stages and biozones differ in detail. Considering the recent developments in the studies of the Sandbian stratigraphy in the Baltoscandian region, it is possible to complement the current conodont biozonation. Pygodus anserinus, Amorphognathus tvaerensis and A. superbus conodont zones are recognized in the Sandbian Stage in Baltica. The lower boundary of the stage is located within the Pygodus anserinus Zone, and the main part of the stage corresponds to the Amorphognathus tvaerensis Zone. In Scandinavia, the upper boundary of the stage correlates with a level within the A. superbus Zone or lies in a conodont-poor interval in the eastern Baltic region. The lower boundary of the A. inaequalis Subzone is tentatively correlated with the base of the Sandbian in Scandinavia but is located in the uppermost Darriwilian in the eastern Baltic region. In both areas, the A. tvaerensis Zone is subdivided into the Baltoniodus variabilis, B. gerdae and B. alobatus conodont subzones. The A. inaequalis Subzone-in some cases indicated as a zone-has been included in the regional stratigraphic charts for more than a decade. However, so far, A. inaequalis (Rhodes) has been reliably identified and also illustrated only from Avalonia, i.e. outside the palaeocontinent Baltica. A recent restudy of collections from the Fjäcka main section and the Smedsby Gård drillcore (both from Sweden), as well as from several Estonian sections, did not prove the occurrence of A. inaequalis in these areas. The A. tvaerensis Zone comprises almost the whole Sandbian, both in Scandinavia and the eastern Baltic areas. During this long age, the morphology of the P and M elements of A. tvaerensis (Bergström) gradually changed, and elements of distinct morphology appeared and were assigned to a new species, Amorphognathus viirae Paiste, Männik et Meidla, 2022, in the upper part of the range of the species. In succession, A. viirae appears in the upper part of the B. gerdae Subzone. Cur rently, A. viirae has been identified in numerous Estonian sections, as well as in the Fjäcka main section and the Smedsby Gård drillcore in Sweden. Based on published figures, it occurs evidently in the Mójcza Formation of the Holy Cross Mountains (Poland) and the Black Knob Ridge section in Oklahoma (USA), in the GSSP for the base of the Katian Stage. A. inaequalis has also been reported and an eponymous zone identified in two other sections located on the palaeocontinent Baltica, in the Bliudziai-150 drillcore (Lithuania) and the Kovel-1 drillcore (Ukraine). During the restudy of collections from these sections, no elements of A. inaequalis were found in either of them. The earliest recorded elements of the genus Amorpho gnathus have been assigned to A. tvaerensis, and the specimens from the upper range of this species reidentified as A. viirae. Analysis of the new material and revision of previous collections has revealed problems related to the Sandbian conodont biozonation of the palaeocontinent Baltica and demonstrated the need for its updating. The new proposed zonation excludes the A. inaequalis Subzone, as the occurrence of its nominal taxon on the palaeocontinent Baltica could not be proved. Additionally, a new unit, the A. viirae Zone, has been included in the zonation. It corresponds to the upper part of the former B. gerdae Subzone, which is now treated as a zone. Also, all subzones based on the succession of Baltoniodus species have been elevated to the rank of zones.
Stratigraphy and Geological Correlation, Sep 1, 2015
Much of the material of Paleozoic successions of Kotelnyi Island (New Siberian Islands) is com po... more Much of the material of Paleozoic successions of Kotelnyi Island (New Siberian Islands) is com posed of various carbonates, which accumulated in relatively shallow conditions in the Ordovician-Middle Devonian. Such deposits are widespread in synchronous sections throughout the Eastern Arctic and therefore attract attention as a potential tool for interregional correlations. In paleotectonic reconstructions, Kotelnyi Island either is included in terrain which was disconnected from the Siberian Platform in the Paleozoic or is joined to it. These different interpretations result from lack of primary evidence. This paper presents new data on stratigraphy and macro and microfauna of the Upper Ordovician and Silurian of the central regions of Kotelnyi Island. For this interval, we propose a correlation of the studied sections with those of adjacent regions. A conclusion is drawn on the basis of the similarity of lithology and fossil assemblages and also shared trends in the evolution of the sedimentary environment that the Upper Ordovician-Silurian beds of Kotelnyi Island, Taimyr, and the Siberian Platform accumulated in a single shelf basin, which apparently also extends to northeastern Chukotka.
Conodonts and chitinozoans were studied from the Neitla section, which exposes the boundary betwe... more Conodonts and chitinozoans were studied from the Neitla section, which exposes the boundary between the Porkuni and Juuru regional stages. This level, although not proved biostratigraphically, has been traditionally considered to correspond to the Ordovician-Silurian boundary. However, stable carbon isotope data indicate that the system boundary lies higher in the succession, in the lower part of the Juuru Regional Stage. Rare conodonts and chitinozoans discovered in the section do not provide any criteria for locating the boundary. Although conodonts are represented by taxa characteristic of the Silurian, all of them are known to have already appeared elsewhere in the Upper Ordovician. Materials and methods Two sections (Neitla-I and Neitla-II, see Fig. 1A) on the bottom of the gravel pit, with a distance of about 10 m between them, were described and sampled in 2009, 2010 and 2015. Both expose the uppermost Ärina Fm (Kamariku Mb) and the lowermost Varbola Fm (Koigi? Mb) underlain by reef limestone of the Tõrevere Mb.
Multiproxy correlation is used to address the boundary of the Kukruse and Haljala regional stages... more Multiproxy correlation is used to address the boundary of the Kukruse and Haljala regional stages across the Estonian part of the Baltoscandian Ordovician Palaeobasin. New biostratigraphic information on conodonts, chitinozoans and ostracods from the Peetri outcrop, northwestern Estonia, integrated with micropalaeontological data from five core sections all over Estonia, allows justification of the position of the stage boundary and correlation between conodont and chitinozoan biozones. In the Peetri outcrop a marked stratigraphic hiatus was recognized at the Kukruse-Haljala boundary-the Baltoniodus gerdae conodont Subzone and the Armoricochitina granulifera, Angochitina curvata, Lagenochitina dalbyensis and Belonechitina hirsuta chitinozoan zones are missing in the section. The lowermost part of the Tatruse Formation in central Estonia and the Adze Formation in southern Estonia are older than previously thought, and the results show a principal advantage of the multiproxy method over singlegroup studies. The lower boundary of the Haljala Regional Stage is tied to the interval with gaps that are common all over the stratotype region.
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Papers by Peep Männik