arktos (2018) 4:25 https://doi.org/10.1007/s41063-018-0059-6 ORIGINAL ARTICLE Pre-mid-Frasnian angular unconformity on Kotel’ny Island (New Siberian Islands archipelago): evidence of mid-Paleozoic deformation in the Russian High Arctic Andrei V. Prokopiev1,2 · Victoria B. Ershova2 · Andrei K. Khudoley2 · Dmitry A. Vasiliev1 · Valery V. Baranov1 · Mikhail A. Kalinin2 Received: 15 November 2017 / Accepted: 13 August 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract We present detailed structural studies which reveal for the first time the existence of an angular unconformity at the base of the Middle Frasnian deposits across the western part of Kotel’ny Island (New Siberian Islands, Russian High Arctic). Pre-Mesozoic convergent structures are characterized by sublatitudinal folds and south-verging thrusts. Based on the age of the rock units above and below the unconformity, the age of the deformation event can be described as post-Givetian but pre-mid-Frasnian. Based on the vergence direction of thrusts deforming pre-Frasnian deposits on Kotel’ny Island, shortening occurred from north to south (in the present day coordinates). The small scale of the structures suggests that this part of the New Siberian Islands formed a distal part of an orogenic belt in the Middle Paleozoic. The angular unconformity described on Kotel’ny Island can be tentatively correlated with the Ellesmerian Orogeny. However, due to a paucity of detailed geo- logical data from the neighboring broad Arctic continental shelves, a precise correlation with known tectonic events of the circum-Arctic cannot be achieved. The subsequent Mesozoic tectonic structures with NW-trending folds and faults were superimposed on pre-existing Paleozoic and older structures. Thus, the data presented here provide additional constraints on the Paleozoic geodynamic affinity of the New Siberian Islands and provide a regional link to other Arctic regions, aiding future tectonic reconstructions of the circum-Arctic. Keywords Arctic · New Siberian Islands · Kotel’ny Island · Late Devonian deformation · Angular unconformity · Structural geology Introduction is ambiguous. It is believed that they either formed part of the Siberian [4, 25] or Arctida paleocontinents [47], have The New Siberian Islands (NSI) archipelago is located at an affinity with Arctic Alaska [7], were a discrete geologi- the boundary between the Laptev and East Siberian seas cal terrane [30, 31], or share an affinity with Laurentia or and comprises several islands varying in size and geologi- Baltica [5, 11–15]. At the present time, the NSI are mainly cal structure. The Paleozoic geodynamic affinity of the NSI considered as part of the New Siberian–Chukotka, New Siberian–Chukotka–North Alaska, Chukotka-Alaska, or Arctic Alaska–Chukotka microcontinents (superterranes, This article was selected from the third Circum-Arctic Structural microplates), or the Arctida and Bennett-Barovia terranes Event workshop which was held in Hannover (Germany) in March [e.g., 16, 28, 32–34, 43, 45 and references therein]. 2017. Kotel’ny Island is located in the western part of the archi- * Andrei V. Prokopiev pelago and is the largest island within the NSI. It is mainly [email protected] composed of deformed Paleozoic deposits (Fig. 1a–c), whereas Mesozoic and Cenozoic rocks are only locally 1 Diamond and Precious Metal Geology Institute, Siberian Branch, Russian Academy of Sciences, Lenin Prospect 39, preserved within synclines and around the periphery of Yakutsk 677980, Russia the island [20–22]. Previous studies suggest that the Paleo- 2 Institute of Earth Science, St. Petersburg State University, zoic–Mesozoic rocks of Kotel’ny Island were only deformed Universitetskaya nab. 7/9, St. Petersburg 199034, Russia into NW-striking folds in the Late Mesozoic, associated with Vol.:(0123456789)1 3 25 80° 137 139 100° ° ° a B Anisiy Cape Quaternary 2of8 Page 6 b 0° D Canada 120 r ° a Neogene-Quaternary S g o D t se N n Paleogene-Neogene A na L Fig. 2 y a S In Lower Cretaceous 40° I le 1 76° t 40 ° Lower Jurassic Baffin Bay 7 7 0 0 U ° N N ? O Triassic Brooks Rang J Canadian ? Middle Carboniferous - N Arctic Islands Alask A Permian Alaska Lower - Middle 20 Kotel'nyi Is. 160 an North Sl ° e Carboniferous Greenland Amerasia ° 8 8 0 0 Upper Devonian - ° Basin N N Lower Carboniferous Alfa-Mendeleev Ridg o Upper Devonian pe Chukchi ? ? Borderland t Middle Devonian Chukchi i 3 Sea a Lomonosov Ridg r Silurian - 180° t 0° Wrangel Lower Devonian e Island S Ordovician Svalbard Chukotka a 2 e East Siberian y Eurasian Thrust r Sea Basin a Franz Josef De Long Z Land Islands Strike-slip fault Fig. 1b Bel'kovsky Is. Severnaya New Siberian 160° Axis of anticline 20 Barents Islands 1 ° Scandinavia Zemlya E Sea L Axis of syncline lya A m Laptev Sea a Ze P vay Structural contour No R- Reshetnikov T Verkhoyansk-Kolyma Kara Sea anticlinorium A Taimyr E Angular unconformity B- Balyktakh 40° ° V 140 synclinorium Dike of Mesozoic dolerite C- Chokur anticlinorium Dike of Middle - 75° ls ra East Siberia S Late Paleozoic dolerite e U Th E 60 West Siberia 76° ° 120° R A 80° 100° B mid-Paleozoic tectonic events reported C 75° 025 136° 140° 144° km Medvezhiy Cape A c B km 1 1 km arktos (2018)4:25 arktos 0 0 -1 -1 -2 -2 Strike-slip fault 10 km Fig. 1 a Map showing areas affected by mid-Paleozoic deformations across the Arctic realm (modified from [42]). b Structural map of the western Kotel’ny Island with location of study area. Faults: 1—Mikhailov thrust, 2—Upper-Balyktakh dextral strike-slip, 3—Tuor-Yurekh dextral strike-slip fault. Shown in the lower left corner is a tectonic zonation sketch map (modified from [36]). R—Reshetnikov anticlinorium, B—Balyktakh synclinorium, C—Chokur anticlinorium. c Geological section A–B across the western part of Kotel’ny Island (modified from [20]) 1 3 arktos (2018) 4:25 Page 3 of 8 25 reverse faults and SW and NE directed thrusts [e.g., 36]. Stratigraphy of the northwestern Kotel’ny Several angular unconformities have been identified across Island the island, with well-studied angular unconformities at the base of the Aptian in the central part of the island and at On the northwestern coast of Kotel’ny Island (Fig. 2a), the base of the Paleogene [20]. The latter unconformity is the oldest exposed Paleozoic rocks are Lower Devonian related to extension associated with opening of the Eurasian in age. The Lochkovian deposits consist of alternating Basin. By contrast, the Paleozoic history of deformation on marls, dolomites and limy shales (Pshenitsyn Fm., [3, 23]) Kotel’ny Island is poorly understood. An angular uncon- (Fig. 2b). The contact with overlying rocks is not exposed. formity at the base of the Lower Carboniferous strata has Pragian–Lower Emsian deposits comprise massive bitumi- been identified in the southeast of Kotel’ny Island, where nous limestones with numerous corals (Basykh-Karga Fm., Lower Carboniferous rocks rest on Ordovician, Silurian and 165–300 m). Uppermost Lower Emsian–Upper Emsian Devonian strata, but has been poorly studied to date [20]. strata are represented by gray to black limestones with rare Here, we present the results of a study with the aim of better thin interbeds of limy shales (Shlyupka Fm., 300 m). The understanding the pre-Mesozoic deformation and tectonic Middle Devonian (Eifelian–Givetian) strata unconformably history of Kotel’ny Island, aiding correlations to the circum- overlie Lower Devonian and Silurian deposits in the north- Arctic and providing new constraints on the Paleozoic geo- ern part of the island, but are conformable in its southern dynamic affinity of the NSI. part [20]. Across northwestern Kotel’ny Island, these strata We carried out a detailed study of coastal exposures in are mostly represented by sedimentary carbonate breccias. the northwestern part of the island with the aim to elucidate Layered micritic limestones with thickness reaching a few relationships between the exposed stratigraphic units. Here tens of meters locally occur within succession (Sokolov Fm., we present new data on the structural relationship between 500–600 m). The facies transition between breccias and lay- Lower–Middle and Upper Devonian strata across the north ered limestones can be observed in a few exposures. western part of Kotel’ny Island. The Frasnian deposits (Nerpalakh Fm.) across northwest- ern Kotel’ny Island overlie Middle Devonian carbonates with evidence for significant erosion at the base [20]. The Nerpalakh Formation comprises 52 m of alternating vari- colored green and red clays and siltstones, with subordinate beds of marls, bioclastic limestones and sandstones with rare 137°30’ a b 70 Fig. 3a Lithology Cape Series Stage 75 System Domashnii Formation Thickness, m 25 40 15 40 Station Lagoon 1 17 Laptev sea 40 T3 20 Dsk 25 βMZ r 2 e Ds1 l Q 45 440 Ds1 l T3 Upp 15 c Clay T1-2 20 P 25 Carnian-Norian Dp1 s 50 le Ladinian 77 Siltstone Dn3 r iassiTr Anisian 100 30 Db1 k Midd 20 - Ds2 k e n Sandstone n 20 Dsl e l 1 Q a 160 i O k 30 0 5 ower Db1 k km Fig. 3b L Dp1 s Induan 35 Pebbles 75°57’ 35 40 Dsk Sokolov R. 2 180 Coal 40 Dnr 3 Permian 10 Thrust 40 Bedding attitude Angular Dsk ??? 10 2 unconformity 10 Strike-slip fault 80 Cleavage attitude Upper Fras- Nerpa- 55 Fig. 4 nian lakh Limestone Angular unconformity Axis of anticline Clayey Ds1 l limestone 5 v Mafic dykes Axis of syncline n e n l a i a Marl t d i 500 25 l e Q d i Ds1 l e v -600 Dps Pshenitsyn Fm.