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Permian strata of northern Siberia contain a rich record of the late Paleozoic history of Siberia and surrounding fold and thrust belts (FTB). More than 850 uranium-lead (U-Pb) detrital zircon ages collected from the Permian strata provide vital information about sediment source areas and history of the sedimentary basins. The detrital zircon populations obtained from the Permian clastics of northern Siberia are characterized by large percentages of late Paleozoic and early Paleozoic zircons, whose ages can be correlated with magmatic events known from the Ural-Mongolian Orogen. Our data suggest that Permian clastics of northern Siberia were mainly sourced from orogens developed along the western and southwestern margins of the Siberian Craton (in present-day coordinates), with an additional sediment contribution from the reworked sedimentary cover and basement of Siberia. The contribution from Siberian sources is distinguished in the Precambrian part of the detrital zircon populations by wide distribution of ca. 1700-2000 Ma and 2500-2750 Ma zircons with an almost total lack of zircons ranging in age from 800 to 1700 Ma. We propose that a major fluvial system, which we here term the "Paleo-Khatanga", was the main sediment transport pathway along the western and northern margins of Siberia during the Permian. From a regional overview of detrital zircon populations in Permian deposits across the Arctic realm, we propose that the New Siberian Islands, Alexander and Farewell terranes were sourced from the western framework of the Ural-Mongolian Orogen and were located along the northern margin of Baltica during the late Paleozoic. The Arctic-Alaska-Chukotka Terrane on the other hand does not have Uralian signatures in the detrital zircon populations of the Permian sediments, and can be reconstructed adjacent to the northern margin of Laurentia. Our new data presented here help to better define the enigma of Arctic paleogeography during the Paleozoic.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb detrital zircon isotope data from Mesoproterozoic to Lower Cambrian strata of the St Petersburg region are used to characterize the paleogeographic and tectonic evolution of the Baltica continent. We dated fifteen samples and divided them into three groups based on their distribution of detrital zircons. The first group (comprising Lower Mesoproterozoic rocks) is dominated by Early Mesoproterozoic and Late Paleoproterozoic zircons, mostly derived from weathering of proximal source region including rapakivi granites exposed across the neighboring Baltic Shield. The second group includes Upper Ediacaran samples (Redkino and Kotlin Regional Stages), with major zircon populations ranging in age between 1970-1850 and 1600-1550 Ma, respectively, correlating with magmatic and metamorphic events within the Svecofennian Orogeny and rapakivi granite igneous activity in the interior of Fennoscandia. The third group of samples, collected from both the uppermost Ediacaran and lowermost Cambrian deposits (Kotlin, Lontova and Dominopol Regional Stages), contains older Paleo-Mesoproterozoic zircons as well as Late Neoproterozoic-earliest Cambrian zircons, indicating a Timanian source area and exhibiting a age spectra similar to spectra for coeval rocks of the Scandinavian Caledonides. Therefore, we conclude that reworking and transport of continental detritus from the Timanian Orogen began during Late Ediacaran, earlier than previously supposed, with transport of Timanian detritus not only to the marginal part of Baltica (known from the Scandinavian Caledonides), but also to the distal interior of Baltica.

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Microbially mediated clay mud mounds are widely developed in the Lower Ordovician succession east of St. Petersburg (Russia) and are associated with a diverse and abundant fauna of brachiopods, ostracodes, echinoderms, bryozoans and conodonts. The lithology of one such mud mound in Putilovo Quarry has previously been studied, but the faunas associated with the mounds have not been investigated to date. Clay lenses in the Putilovo mud mound yield conodont assemblages belonging to the Baltoniodus triangularis and lowermost part of the Paroistodus originalis zones and these stratigraphical intervals are much thicker in the mud mound than in the coeval Lower Ordovician succession lateral to the mound. The compositions of the conodont and brachiopod assemblages are generally the same in the mud mound as in contemporaneous beds. The occurrence of relatively fewer conodont elements in the mud mound than in the surrounding successions probably indicates the higher rate of accumulation of the mud mound clays. Juvenile brachiopods are more numerous in the clays of the mud mound than outside the build-up, supporting the hypothesis that the mounds included ecologically stressed environments.