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Marine and Petroleum Geology 19 (2002) 901–919 www.elsevier.com/locate/marpetgeo

Middle to Eopleistocene Sequences on the : an approach to interpret offshore seismic

M.K. Kos’ko*, G.V. Trufanov

VN1Okeangeologia, 1 Angliisky Avenue, 190121 St Petersburg, Russian Federation

Received 6 June 2000; received in revised form 10 June 2002; accepted 26 June 2002

Abstract The New Siberian Islands divide the Laptev from the . The comprises three island groups: , Anjou Islands, and Lyakhov Islands. The regional structural ensemble comprises De Long, Kotel’nyi, Faddeya and Lyakhov tectonic Domains. Aptian–Albian, Late Cretaceous, Palaeocene–, Oligocene–Miocene, and –Eopleistocene tectono-stratigraphic and igneous sequences have been identified on the Islands. The succession of these sequences and their structural and compositional characters provide to distinguish specific stages in the tectonic history of the showing alteration of regional tectonic environment through the middle Cretaceous and the Tertiary correlative to major -East , , and Global events. LS1, LS2, and LS3 major regional unconformities have been identified offshore by German geoscientists based on MCS data in the New Siberian Islands area. It is hypothesized in this paper that three offshore sedimentary cover units bounded by the unconformities correlate to the onshore sequences the following way: Unit I comprises Aptian–Albian and late Cretaceous Sequences, Unit II, Palaeocene–Eocene and Oligocene– Miocene Sequences, and Unit III comprises Pliocene–Eopleistocene Sequence and overlying . q 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Pliocene–Eopleistocene Sequence; Offshore seismic survey; Regional unconformities

1. Introduction basis of general global scale seismostratigraphic approaches, and extrapolations from neighboring onshore. The tectonic evolution of the New Siberian Islands in the There are no deep wells in the region to support the late and in the Tertiary has not been widely and interpretation. This paper is intended to contribute to the adequately discussed. The authors did geological mapping dating of seismostratigraphic units and deep reflectors on the New Siberian Islands in 1972–1977 as a part of the recorded by offshore seismic surveys within the New Ministry of Geology of the USSR regional geoscience Siberian Islands area on the assumption that the sequences research program. The resultant comprehensive geological established onshore extend offshore. The boundaries descriptions and were presented as regular publi- between the sequences are expected to form regional cations of the Ministry of Geology of the USSR (Kos’ko, disconformities mapable by seismic surveys within the Bondarenko, & Nepomiluev, 1985; Trufanov, Belousov, & sedimentary cover on the shelf. Three seismostratigraphic Neplmiluev, 1986). units are reliably distinguishable offshore based on the BGR A large amount of offshore seismic profiling has been MCS data (Franke & Hinz, 1999; Hinz et al., 1997). performed in the region recently (Drachev, Savostin, & TheseareUnitIborderedbyLS1andLS2regional Bruni, 1995a; Drachev, Savostin, Elistratov, & Bruni, unconformities, Unit II between unconformities LS2 and 1995b; Drachev, Savostin, Groshev, & Bruni, 1998; Franke LS3, and Unit III from LS3 up to sea bottom. Regional & Hinz, 1999; Hinz et al., 1997, 1998, Sekretov, 1998). The north-east , circum Arctic, and global scale interpretation of the seismic data can be performed on the structural characters and tectonic events are reviewed in detail as an approach to dating the offshore * Corresponding author. seismostratigraphic units.

0264-8172/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0264-8172(02)00057-0 902 M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919

Fig. 1. Location .

2. Previous work and data Palaeozoic and Mesozoic strata and igneous rocks and on the structural pattern of the Islands collected in 1895–1902 The discovery and the geologic research in the New served the basic information on the geology of the New Siberian Islands have a long history discussed in many Siberian Islands till the middle fifties. publications (Gramberg & Pogrebitsky, 1984; Kos’lo et al., Regular geological mapping at 1:1 000 000 scale was 1985; Krasny & Putintsev, 1984; Samusin & Belousov, performed on the New Siberian Islands in 1955–1956 1985; Toll, 1899, 1904; Trufanov et al., 1986; Vitenburg, (Sorokov, Vol’nov, & Voitzekhovsky, 1961), and 1960; Vol’nov, Voitsekhovsky, Ivanov, Sorokov, & Yashin, 1:200 000 scale mapping was performed in 1972–1977. 1970). Major geoscientific information was obtained as a The maps and accompanying explanatory notes were result of a few projects. The first was the 1895–1896 published and are available (Kos’lo et al., 1985; Samusin expedition headed by Bunge (1887). A participant of the & Belousov, 1985; Trufanov et al., 1986). The 1:200 000 project,Toll investigated ice and Quaternary strata on mapping was accompanied by drilling aimed to penetrate Bol’shoi Lyakhov Island and studied a section of loose sediments. The depth of the majority of the drill holes bearing deposits of Utes Derevyannykh Gor on was up to 200 m. The 1:200 000 mapping was also Novaya Sibir’ Island. The next project was a multi- supported by specific biostratigraphic, paleontological and disciplinary research performed by a team of the Russian lithological research. Cassiterite placers were discovered Polar Expedition on the yacht ‘’ in 1900–1902 headed and explored on Bol’shoi Lyakhov Island. The prospecting by Toll. Coal bearing deposits on were and exploration involved a large amount of drilling discovered by Toll and were first mentioned in his brief including reference drilling. The cores were documented posthumous report of (1904). Toll and his three companions in detail and much analytical lithological, mineralogical, perished on their way from Bennett Island to the Anjou and paleontological research was performed. The results Islands. The report along with sample collection including were summarized in a monograph by Dorofeev, Blago- early was found by a rescue party veschensky, Smirnov, and Ushakov (1999). The present day headed by Kolchak in 1903 (Kolchak, 1904; 1906). knowledge of the geology of the archipelago is, therefore, Scientific results of the Russian Polar Expedition were based on the results of a series of regional and industrial published by Vollosovich (1902, 1905).Dataonthe projects, and some minor specific scientific projects. M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 903

Fig. 2. Geological map of the New Siberian Islands. From the Geological Map of (Sokolov, 1990/1992) amended and simplified.

3. Regional geologic background gently dipping thrust sheets through undisturbed horizontal layering. The New Siberian Islands are located between The De Long Islands area is believed by many Russian 135825.50 –158824.60 east and 73811.20 –77807.40 north geoscientists to be a fragment of a former Hyperborean (Fig. 1). The Islands separate the from the Platform (Khain, Koronovsky, & Yasamanov, 1997; East Siberian Sea. The archipelago comprises three Shatsky, 1935) with early Palaeozoic basement (Eghia- island groups. Starting from the north these are the De zarov, 1977). The Anjou Islands and Lyakhov Islands are Long Islands, the Anjou Islands, and the Lyakhov located within a late Mesozoic fold belt, extending here Islands. from and Chukotka. The last orogeny in the fold belt The bedrock geology exposed on the islands is variable took place in the early Cretaceous. It was manifested by in composition, age, and structural style (Fig. 2). Strata from folding, faulting, and thrusting, emplacement of , the through Recent are known here. and the formation of foredeep and intermontane basins. types include clastics, pelites, and carbonates deposited Some of those features are well known on the islands. The under nonmarine, shallow marine and deep marine environ- Anjou Islands represent an outer, moderately deformed zone ments. Magmatic rocks are mafics, ultramafics, granites and of the fold belt. Intense thrusting, tectonic piling, and intermediate and alkaline types from early Palaeozoic to fragments of an ophiolitic sequence have been documented Recent in age. Structural styles range from tectonic piling of on the Lyakhov Islands. It allows projection of the former 904 M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919

sedimentary cover with locally outcropping Cretaceous sediments and siliciclastics penetrated by shallow drill holes. It is hypothesized that the sedimentary cover overlies a composite basement comprising blocks of deepseated carbonates (Avetisov, 1982) stitched by inten- sely deformed siliciclastics and intruded by igneous bodies. Jurassic strata have been deformed. Cretaceous and Tertiary layers locally display complex folding and faulting on the general background of undisturbed layering. Stratigraphic and facies variability in the Cretaceous–Tertiary sedimen- tary cover within the Domain is shown in Fig. 4. The Lyakhov Domain is variable in structural style, age of exposed bedrock and in manifestation of the igneous activity. The south-eastern part of the Bol’shoi Lyakhov Island is a north-western extremity of the Lyakhov–South Anyui suture (Eghiazarov, 1977; Krasnyi & Putintsev, 1984; Natal’in, 1984; Zhamoida, Krasny, & Strel’nikov, 1989). A set of tectonic sheets each consisting of its own rock type: early Palaeozoic (?) orthoamphibolite, serpenti- nized and melanged ultramafics, pillow , and Per- mian– turbidites was observed on south-eastern Bol’shoi Lyakhov Island (Savostin & Drachev, 1993). The pile of the tectonic sheets has been gently folded. Magnetic survey data suggest that mafic and ultramafic bodies dip Fig. 3. Tectonic Domains scheme. south-east and that they extend offshore. The rest of the Lyakhov Domain is underlain by Jurassic—earliest Cretac- South Anyui from the Chukotka Mainland (Zonen- eous turbidites known from mapping in the west and in the shain, Kuz’min, & Natapov, 1990). The De Long, the north of Bol’shoi Lyakhov Island, on Malyi Lyakhov Island, Kotel’nyi, the Faddeya, and the Lyakhov Domains have and on Stolbovoi Island. The deformation is intense on been distinguished in the area (Fig. 3). Bol’shoi Lyakhov Island and less intense on Malyi Lyakhov The De Long Domain has the oldest basement. Island and Stolbovoi Island where moderately compressed Moderately tilted Cambrian to siliciclastics open folds have been observed. outcrop on Bennett Island (Kos’ko et al., 1985; Vol’nov & Early Cretaceous plutons are abundant on the Sorokov, 1961). Deformed early Palaeozoic basic lavas, Bol’hoi Lyakhov Island. The radiometric ages are: volcanoclastics, and siliciclastics with dikes and sills of Uranium–Lead isochrone zircon 118.69 ^ 0.42 and andesite–basalt, basalt, and dolerite are known from 120 ^ 1.7 Ma; Argon–Potassium biotite from 118 ^ 6to . Late Mesozoic, Tertiary, and Quaternary 122 ^ 7 Ma; Argon–Potassium microcline 112 ^ 5 and lavas and tuffs are widely distributed on the islands and 114 ^ 6(Dorofeev et al., 1999). The plutons crosscut the offshore. fold and thrust structure. Similar granite bodies are believed The Kotel’nyi Domain is remarkable for a continuous to be present in the adjacent offshore from the interpretation sedimentary sequence dominated by carbonates from the of the gravity and magnetic surveys. Basic and acidic dikes Ordovician to the middle , by carbonates and have also been reported on the Island. Fragments of Tertiary siliciclastics from the Upper Devonian to the , and sedimentary basins have been discovered on Bol’shoi pelitic to sandy sediments from the Mesozoic to the Lyakhov Island. Cenozoic (Kos’ko et al., 1985). Igneous rocks are sparse. The major tectonic events, which preceded and enabled They are basic dikes and small intrusive bodies of probable the establishment of a wide spread continuous sedimentary middle Palaeozoic age, lower Triassic volcanics and tuffs, cover were the uplift and subsequent erosion of a late and Cretaceous felsic volcanics. The pre-Cenozoic struc- Mesozoic fold belt extending to the southern portion of the tural style is a combination of extensional blocks and study area. This event had dramatic manifestation within the moderately compressed map scale folds as can be observed Lyakhov Domain, a less intense effect on the Kotel’nyi and on the regional geologic maps (Lopatin, 1999). The Tertiary the Faddeya Domains, and has not been found on the De strata have been faulted and gently folded in some places. Long Domain. The structure of the south-eastern part of the There is some difference in the Cretaceous and the Tertiary Bol’shoi Lyakhov Island is believed to be detached stratigraphy between the western (Kotel’nyi Island) and the fragments of ophiolitic sequences of variable ages showing eastern (Zemlya Bunge) parts of the Domain (Fig. 4). more than one episode of compression. The oldest unit here The Faddeya Domain is an area of an extensive Cenozoic is composed of amphibolite and schist, some of which can M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 905

Fig. 4. Correlation of sequences chart. be definitely attributed to primarily igneous rocks of Ordovician was hypothesized. The final stage of com- ophiolitic character. The metamorphic grade of the unit is pression started probably in the Jurassic and terminated by epidote-amphibolite. The K–Ar whole rock age of the or during the Aptian in accordance with the ages of granite amphibolite is: 473 ^ 14; 215 ^ 8; and 166 ^ 7Ma intrusions sealing the thin-sheeted assemblage. The granites (Drachev & Savostin, 1993). On the assumption that those are of S type, indicative of a collisional geodynamic figures date a series of thermal events the existence of an environment. ophiolitic sequence in the Faddeya Domain in the The emplacement of granite plutons was accompanied 906 M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 and succeeded by volcanic eruptions as evidenced by acidic One sample of coal from the lower sedimentary unit and lava layers and the presence of a pyroclastic admixture in one sample of tuffaceous argillite from the volcanic unit the sediments. produced spores characteristic of the late early Cretaceous. The identification was made by V.D. Korotkevich (Kos’ko et al., 1985; Lopatin, 1999; Vol’nov & Sorokov, 1961). It is 4. The onshore middle Cretaceous to Eopleistocene assumed here that the late early Cretaceous whole rock K/Ar Sequences age of 119–112 ^ 5 Ma is related to the from this unit (Drachev, 1989). The above sedimentary and volcanic The late Mesozoic–Quaternary sedimentary cover is units on the basis of spore identifications and radiometric widely spread in the region. It comprises Aptian–Albian, dating are attributed to the Aptian–Albian Sequence. Late Cretaceous, Palaeocene–Eocene, Oligocene–Mio- cene, Pliocene–Eopleistocene, and to Recent 4.1.2. Pliocene–Eopleistocene Sequence Sequences. The stratigraphy was constructed by correlation The Cretaceous lava unit is overlain by a Pliocene to of fragments of sections observed in outcrops and drill hole Recent lava unit about 300 m thick. It comprises a series of cores. The distances between reference drill holes and five basalt flows 40–100 m thick each. The basalts are outcrops can exceed many tens of kilometers. So only the practically unaltered, greenish black in color. There are general characters of the sequences were established slightly altered reddish basalts at the top of the flood sheets. reliably. The relationships between separate sedimentary The basalts are composed of , andesine-labrador, cover units are known as well from mapping based on the augite, olivine, ore minerals, apatite, and brown chloritized observations on talus and eluvium. The contacts between volcanic glass. Plagioclase was cericitized, chloritized, and the units were observed in outcrops in a few cases in albitized in places. Olivine was substituted by iddingsite, complex structural settings. Nevertheless the conclusions on chlorite, and serpentine. There are opal, carbonate, ana- the disconformities and unconformities between the units lcime, chlorite, and ceolite in the interstices. are reliable as they were supported by paleontological age Some researchers think that this unit is Cretaceous in age determinations and lithological distinctions between the (Lopatin, 1999; Vol’nov & Sorokov, 1961). But the basalts units. The Pleistocene to Recent strata are not discussed in in this unit are less altered than the underlying basalts. This the paper. suggests that they are younger, and coeval with late Tertiary to Recent lavas known on Zhokhov and Vil’kitski Islands 4.1. De Long Domain (Gramberg & Pogrebitsky, 1984; Kos’ko et al., 1985). Volcanic cones and flows on the top of the volcanic Early Cretaceous and late Tertiary–Quaternary plateau on Bennett Island in the opinion of Masurenkov and Sequences are known on the De Long Islands (Fig. 4). Flerov (1989) are Quaternary. The chemistry and mineral composition allowed these researchers to conclude, that the 4.1.1. Aptian–Albian Sequence basalts from the base of the section on one hand, and those Early Cretaceous strata were mapped on Bennett Island. from the top on the other, originated from different melt They are widely distributed through the Island and comprise sources (Masurenkov & Flerov, 1989), which supports the basaltic lava, basaltic , argillite, , and coal. The different age sequences in the volcanic section on the Island. base of the section consists of a coal-bearing unit 20 m Zokhov Island completely rests on an eroded stratovol- thick. The unit is composed of black fissile argillite, cano. Coastal cliffs are built of alternating flows of massive like sandstone, brick red argillite and coal layers. and blistered lava, agglomerate and tuff. Massive columnar Basalt lava and tuff with lenses of tuffaceous argillite basalts of crater facies outcrop on the top of the overly the coal-bearing unit. The thickness of the volcanic stratovolcano. The slopes are covered with volcanic ash unit is 60 m. This unit extends beyond the limits of the lower with large volcanic bombs. The major volume of extrusive coal-bearing strata overlying an uneven eroded surface of products is composed of porphyric olivine, olivine– Cambrian and Ordovician strata. Separate lava sheets are 2– pyroxene, and olivine–plagioclase basalt of the picrite– 15 m thick. Two varieties of basalt were reported. One is olivine group. Limburgites, described earlier as nepheline almost black and massive, the other one is fissured basalts, completely compose Vil’kitsky Island but are less amygdaloidal and blistered brown, green and violet in abundant on (Silant’ev, Bogdanovsky, color. Relics of olivine and pyroxene as well as labrador and Savostin, & Kononkova, 1991; Vol’nov et al., 1970). andesine-labrador and altered volcanic glass were estab- Fragments of mantle spinel lherzolite, quartzite, carbona- lished in thin sections. The tuffs are variegated in color, tized aphyric volcanic rocks are present in the volcanic sand- and grit-size with volcanic bombs up to 2 m in breccia. Blocks of silicified Carboniferous and of diameter. The clasts consist of basalt and volcanic glass. a dolerite collected from the loose debris are believed to be The cement is carbonaceous. The lavas have been clasts of the volcanic breccia (Makeev, Davydov, & chemically classified as alkaline oceanic type, or as island Ustritsky, 1991). The dolerite differs from volcanic rocks spreading center type (Lopatin, 1999). composing both islands in mineral composition, in the M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 907

Fig. 5. Simplified Geological map of Kotel’nyi Island (Kos’ko, 1994). metamorphic alteration, and in the chemical characteristics. (Drachev, 1989), 0.53–6.1 Ma (Bogdanovskii et al., 1992), So the volcano rests on the basement built of late Palaeozoic 1.06 ^ 0.05, 1.20 ^ 0.04, 1.28 ^ 0.02 Ma (Layer, Parfe- marine strata and basic volcanics. nov, Surnin, & Timofeev, 1993). Limburgite of Zhokhov K–Ar whole rock age determination of basalts on Island by the same methods gave 1.88–4.21 Ma, and on Zhokhov Island gave values of 3–10 Ma (Vinogradov, Vil’kitskiy Island 0.4–0.89 Ma (Bogdanovskii et al., 1992). Gaponenko, Gramberg, & Shimaraev, 1976), 1.5–9.0 Ma Paleomagnetic properties of volcanics on Zhokhov Island 908 M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 indicate 10–20 Ma (Vinogradov et al., 1976). A single to light gray and brownish-gray. Pebbles and gravel are 40Ar– 39Ar dating of Zhokhov alkaline basalt is mostly rhyolite and . Sandstone and mafic volcanic 1.2 ^ 0.19 Ma (Layer et al., 1993). The above values are rocks are rare. The thickness of the sequence is about 100– mostly Pliocene and Quaternary, but it is not excluded that 150 m. Its Cenomanian–Turonian age is based on fossil the volcanism began in the Miocene. plant and spore identifications.

4.2. Kotel’nyi Domain 4.2.3. Palaeocene–Eocene Sequence Palaeocene strata were penetrated by a drill hole close to Aptian–Albian, Late Cretaceous, Palaeocene–Eocene, the south coast of Zemlya Bunge. They are clay, clayish and Oligocene–Miocene, and Pliocene Sequences are distrib- sandy silt, clayish and silty sand with pebble and gravel sand uted within Kotel’nyi Domain (Fig. 4). interbeds. There are brown coal layers up to 7 m thick. Coaly plant fragments are common. Sulfide nodules were 4.2.1. Aptian–Albian Sequence reported. Clays are kaolinite, chlorite, and hydromica in Aptian–Albian strata known as the Balyktakh formation composition. High content of kaolinite shows that the on Kotel’nyi Island form three isolated synclines affected by source rocks were weathered. The thickness in the drill hole faults (Fig. 5). They are spread as well in the east of the is 90 m. A Palaeocene age was determined by microfossil Kotel’nyi Domain on Zemlya Bunge, where they are poorly assemblage identification (Lopatin, 1999). exposed. The composition, sedimentary structure and fossil plants The Balyktakh formation consists of pelite, silt, siltstone, show a lacustrine/alluvial depositional environment sand and sandstone with layers and lenses of conglomerate, (Lopatin, 1999). acidic tuff, tuffaceous sandstone and layers of coal up to Eocene strata of marine origin were discovered by 25 m thick. The observed section is topped by a sheet of Ivanenko on the west coast of Kotel’nyi Island (Lopatin, rhyolite. Siderite and pelitic-calcarous concretions are usual 1999). They are monotonous light gray sand with ripple in the sediments. The strata are gray and brownish-gray in marks and clay seams 6 m thick. The strata overly color. The base of the unit is erosional and unconformable. weathered Palaeozoic rocks. The sand yielded a rich Silty pelite at the base of the formation contains clasts, assemblage, foraminifers, and marine dia- pebbles, and boulders of Palaeozoic and Mesozoic rocks toms. The age is early Eocene on the basis of micro- with diagnostic shells and microfossils. paleontological identifications. Rhyolite is a porphyric rock with quartz, feldspar, and Fine-grained pelitic sands and sandy clays with horizon- plagioclase as phenocrysts. The fabric is glassy, micro- tal and wave type bedding and pebble and gravel sand at the felsitic, spherulitic, micropoikilitic, fluidal. base outcrop on the south-west coast of Kotel’nyi Island. The thickness of the Aptian–Albian Sequence on the They are late Eocene in age from palynology and alluvial in Kotel’nyi Island in a composite section is 500 m. origin from compositional and sedimentary structure The Aptian–Albian age was established on the basis of characters (Lopatin, 1999). the identification of abundant fossil plants and spores Nonmarine Eocene strata are known on the north-east of (Kos’ko et al., 1985; Lopatin, 1999). the Kotel’nyi Domain. They comprise interbedded fine- and Specific sections of each syncline slightly vary in the medium-grained gray sand with pelite and brown coal thickness, composition, and age. Correlation of individual interbeds; variegated silty pelite with interbeds of sand and constituent packages between the synclines is problematic. gravel, with pelitic–siderite concretions; greenish-gray and A nonmarine sedimentary environment under rather brownish-gray clayish silt, and variegated silty pelite with energetic tectonic setting was inferred for the Aptian– scattered lignitized plant fragments, with a layer of coarse Albian basin on the above characters. sand on the top. The section is 65 m thick. A nonmarine depositional environment was inferred from compositional 4.2.2. Late Cretaceous Sequence and structural features and the absence of marine The sequence was discovered in drill holes on the east of (Trufanov et al., 1986). the Kotel’nyi Domain close to its boundary with the Faddeya Domain. It is composed of indurate and plastic 4.2.4. Oligocene–Miocene Sequence clay and silt with seams and layers of sand, sandstone, The Oligocene–Miocene Sequence is known in many gravel, pebble, and brown coal. Clay and silt layers and localities on Kotel’nyi Domain. It is well exposed on the packages are 2.5–16 m thick. There are layers of clay west coast of Kotel’nyi Island and on the east coast of composed mostly of montmorillonite. Some clay beds, Bel’kov Island (Kos’ko et al., 1985). Here the strata is separating coal layers, contain coalified plant roots. Sand mostly silty and pelitic sand with silt and clay layers up to and pebble layers are 0.2–7 m thick. Tuffaceous sand and 5 m thick, with pebble lenses and layers up to 2.5 m thick, were reported. Brown coal layers are up to 7 m brown coal lenses and beds usually 0.1–0.4 m thick, and thick. Fossil plants, including tree trunks, prints of leaves sometimes up to 3.5 m thick. Coalfied plant debris is and debris, are often present. The sediments are usually dark abundant. In the west of Zemlya Bunge the strata is mostly ..Ksk,GV rfnv/Mrn n erlu elg 9(02 901–919 (2002) 19 Geology Petroleum and Marine / Trufanov G.V. Kos’ko, M.K.

Fig. 6. Geological map and cross-section of Cape Derevyannykh Gor area, Novaya Sibir’ Island. 909 910 M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 clay with interlayers of silt and lignitized wood up to 1.2 m exposed in coastal cliffs in the south-west and extends from thick. here to the south-west of the Island beneath the Tertiary Sand is fine-grained, white, gray and brown in color, cover. It is definitely absent on the north-west of the Island, quartz and quartz–feldspar in composition. Clay minerals in which is evidenced by drilling. There is no data to show pelitic and silty pelitic sediments are predominantly whether the Late Cretaceous Sequence spreads beneath hydromica, chlorite, kaolinite and montmorillonite. younger sediments to the north Faddeya and east Novaya The sequence overlaps disconformably Palaeocene– Sibir’ Islands. Eocene strata and unconformably late Devonian and The general features of the sequence on Faddeya Domain Carboniferous rocks which were weathered before the are the same as those on the Kotel’nyi Domain. But the deposition of Oligocene strata. scope of information is different. The thickness of the sequence on the Kotel’nyi Domain On Faddeya Island, as in the east of the Kotel’nyi varies from 35 to 9 m. Domain, the lower unit of the sequence is present, while on The age of the sequence was determined based on Novaya Sibir’ only the uppermost portion of the lower unit Miocene fossil plants and Oligocene and Miocene spore was recorded, and the rest of the sequence is regarded as its assemblage identifications (Kos’ko et al., 1985). upper unit. Comparisons between sections of the lower unit in the west of Faddeya Domain and in the east of Kotel’nyi 4.2.5. Pliocene–Eopleistocene Sequence Domain show that amount of coal decreases southward The Pliocene–Eopleistocene Sequence was observed in along with the increase of pelitic matter. outcrops on the periphery of Kotel’nyi Island, on east The base of the sequence was discovered by a drill hole Bel’kov Island, on west Zemlya Bunge. It was penetrated by in the middle of Faddeya Island. Late Cretaceous strata lie a drill hole on south Zemlya Bunge. It consists of sand, silt, horizontally on early Cretaceous rhyolite weathered and pebble, grit, and clay; separate pebbles and boulders as well disintegrated to loose grit, rock debris, and clay material. as angular clasts are scattered through all types of The section here from the bottom is as follows: sediments. Coalified plant fragments are common. Sand is mostly clayish and silty, immature compositionally, fine- † poorly sorted sand with weathered rhyolite debris and and medium-grained. Pelites are sandy and silty. Clay pelitic admixture. There is a 0.7 m thick layer of brown minerals are hydromica, chlorite, and montmorillonite. coal at the base with rounded and angular clasts of Marine bivalves and assemblage of marine and fresh weathered rhyolite. Thickness 7.0 m; water were reported from the sediments. The † indurate greenish-gray clay with sand seal. A 0.25 m local bedrock underlying the sequence is widespread in the thick brown coal in the lower portion of the package with lower portion of the section. fossil plants. Thickness 10 m; The base of the sequence was observed on Bel’kov Island † thin interbeds of gray and greenish-gray silt and poorly and on Zemlya Bunge. In both cases it overlies the eroded sorted greenish-gray tuffaceous sand. Fragments of surface of the Oligocene–Miocene Sequence. coalified plants and brown coal in the silt. Thickness 9 m; The age of the sequence within Kotel’nyi Domain is late † gray and greenish-gray clay with rhyolite pebbles, Pliocene according to paleontological and palynological debris, and sand, with brown coal seals. Thickness identifications. 7m. The observed thickness is 5–15 m. The upper portion of the sequence on Novaya Sibir’ 4.3. Faddeya Domain Island contains more and thicker beds of silt and sand and brown coal. Silt and sand are often tuffaceous with particles All the above sequences are present on the Faddeya of volcanic glass. They grade to silt and sandstones in some Domain (Fig. 4). places. The strata in the drill hole are inclined by 208. They are 4.3.1. Aptian–Albian Sequence involved in a complex fold and thrust structure in the near This sequence is known in three small localities on the coast strap on the south-west Novaya Sibir’ Island (Fig. 6). surface and is believed to be widely spread in the subsurface The total thickness of the sequence is about 300 m. The of Faddeya Island. They seem similar to better known strata estimate was made by correlation and addition of the on Kotel’nyi Island. No Aptian–Albian sediments were thickness in the observed fragments of sections. found on Novaya Sibir’ Island. The fossil plants and spore assemblages indicate Cenomanian, Turonian, and, may be Coniacian ages. 4.3.2. Late Cretaceous Sequence The Late Cretaceous Sequence is present on Faddeya and 4.3.3. Palaeocene–Eocene Sequence Novaya Sibir’ Islands. On Faddeya Island it was discovered The sequence was mapped within Faddeya Domain as in drill holes in the center and offshore close to the south the Anjou Formation of Eocene age. It is widely coast of the Island. On Novaya Sibir’ Island the sequence is discontinuously spread in the subsurface and is observed M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 911 on the surface in a few small localities. It overlies mud and clay are subordinate constituent parts. Discontinu- disconformably the Aptian–Albian and the late Cretaceous ous thin beds of pebble, gravel and grit are present. Pebble Sequences. The contacts with earlier strata were not layers sometimes grade to conglomerate with iron hydrox- observed. There is no Palaeocene strata within the Faddeya ide cement. Fragments of brown coal, wood, coalfied plants, Domain. scattered pebbles and boulders are typical. There are a few The sequence is composed of pelite, silt, and subordinate thin coal beds in the lowermost portion of the sequence. A sand in packages up to 12–17 m thick. There are rare brown layer of pebble and coarse grained sand with scattered coal layers and thin discontinuous beds of pebble. The pebbles and boulders rests at the base of the sequence. sediments are variable in color and sedimentary structures. The sand varies in grain size and contents of silt and clay Coal layers contain fragments of tree trunks and bark. Tree admixture. Variable types of thin bedding were observed. roots were found in the beds underlying the coal layers. Packages of inclined thin bedding can be 3–5 m thick. Pebble shapes vary from subangular to well rounded. Similarly complicated thin bedding is characteristic of the Pebbles consist of quartz, rhyolite, basalt, and sandstone. silt and clay layers. Pebbles and boulders are well and Pelite–siderite concretions were met in all types of poorly rounded. They are built of rhyolite, basalt, dolomite, sediments. limestone, siltstone, sandstone, quartz, and chert. Brown Variations in the proportion of different types of coal pebbles are usual. The presence of carbonate clasts, sediments and their characters show a facies zonation which were not reported from the Palaeocene–Eocene traceable from the north-east of Kotel’nyi Domain to the Sequence, evidences the appearance a new provenance area west of Faddeya Domain including west of Novaya Sibir’ built of bedrocks similar to those exposed on Kotel’nyi Island. In the north of Zemlya Bunge (NE Kotel’nyi Island. Domain) and in the middle and south-west of Faddeya Fossils include plant, lagoonal, swamp and lacustrine Island grit pebble beds and scattered pebbles, boulders, and diatoms, fresh water ostracodes, marine molluscs, estuarine angular clasts are usual. Autochthonous coal beds were microfossils. These assemblages along with composition, reported from here. Sands constitute a subordinate portion sedimentary structure, lithofacies relationships indicate of the sequence. On the north of Faddeya Island sand depositional environments, which were near shore marine, constitutes about half of section, neither pebbles, nor coal lagoonal, alluvial and lacustrine. Alluvial environments are beds were observed. On north-west Novaya Sibir’ Island a more typical of the Miocene portion of the sequence. In section of clay with shell fragments of marine bivalves, well general terms the Oligocene–early Miocene depositional sorted sand with scattered pebbles, and silt was measured. A setting was a near shore lacustrine–alluvial plain, beach, north-west trending facies and paleogeographic zonation and tidal zone (Lopatin, 1999; Trufanov et al., 1986). and north-east transition from onshore to near shore marine The thickness of the sequence from 13 to 190 m, transition can thus be inferred. increasing northward and eastward (Lopatin, 1999; Trufa- The Eocene age of the sequence is evidenced by fossil nov et al., 1986). plants and spore identifications. Maximum thickness of the sequence within the Faddeya 4.3.5. Pliocene–Eopleistocene Sequence Domain is 90 m. The Pliocene–Eopleistocene Sequence covers all the underlying strata disconformably and unconformably. 4.3.4. Oligocene–Miocene Sequence There is an erosional hiatus at the contact between the The Oligocene–Miocene Sequence forms an almost Pliocene–Eopleistocene Sequence and the overlying Pleis- continuous cover over the earlier strata on Faddeya and tocene sediments. Pliocene strata of the sequence are known Novaya Sibbir’ Islands. It is interrupted in a few localities, in coastal outcrops on Faddeya and Novaya Sibir’ Islands. where the older sediments penetrate to the surface or to the On the south-west coast of Novaya Sibir’ Island, Pliocene base of the Quaternary or Pliocene strata. The sequence is sediments overly late Cretaceous strata with angular observed in outcrops and in drill holes and comprises the unconformity (Lopatin, 1999). The unconformity disagrees Nerpichin Formation of Oligocene–early Miocene age with the Pliocene age of the uppermost unit involved in the (Lopatin, 1999; Trufanov et al., 1986) and some locally fold structure, which is indicated on maps of the south-west distinguishable Miocene map units. The base of the Novaya Sibir’ Island (Lopatin, 1999; Trufanov et al., 1986), sequence is discomformable. An erosional surface was and attributed to the Oligocene–Miocene Sequence. The observed in outcrops between Nerpichin Formation and the Pliocene age of the unit was initially doubtful because it had Anjou Formation of the Palaeocene–Eocene Sequence and not enough reliable support in dating of recovered fossils was mapped between the Nerpichin Formation and Cretac- and pollen and spore assemblages, and there is close eous Sequences. An erosional contact was observed similarity in lithology to the Oligocene–Miocene strata between early Miocene strata of the sequence and the late (Trufanov et al., 1986). Cretaceous Sequence. Erosional contacts were reported Pliocene strata consists of interlayered mud, silt, and between separate portions of the sequence. sand with lenses of and rare grit and pebble size clasts. The major sediment type of the sequence is sand. Silt, Variable fauna and flora collections along with sedimentary 912 M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 features show alluvial, alluvial–lacustrine, lacustrine, and 4.4.3. Pliocene–Eopleistocene Sequence near shore marine environments. The thickness of the Pliocene and Eopleistocene sediments are proluvial and Pliocene strata does not exceed 10 m (Lopatin, 1999). alluvial poorly sorted debris in a clay–silt sand matrix on The Eopleistocene strata are the major portion of the the slopes of topographic highs changing seaward to near sequence which is spread all over the Domain as an shore marine silt, sand and clay with pebble and gravel undisturbed flat sheet. It differs from the Early Pliocene layers. Sand and pebble dominate at the lower portion of a portion in higher content of pelitic component and in near shore marine sections. Near shore sediments contain predominance of mostly brackish and near shore marine fragments of thin shells of molluscs and abundant lignitized environments. The thickness of the Eopleistocene portion wood (Dorofeev et al., 1999). The age was established by on Faddeya Island is up to 50 m, and up to 75 m on Novaya fossil identifications (Lopatin, 1999). The maximum thick- Sibir’ Island (Trufanov et al., 1986). ness 52 m in drill holes on Bol’shoi Lyakhov Island was reported by Samusin and Belousov (1985). 4.4. Lyakhov Domain

There are Eocene–Eocene, Oligocene–Miocene, and 5. Discussion Pliocene–Eopleistocene Sequences within Lyakhov Domain (Fig. 4). 5.1. Depositional and tectonic settings In the late early Cretaceous the Lyakhov Domain was an area of extensive granitic plutonism, and in the late The late Mesozoic–Tertiary Sequences represent sedi- Cretaceous it was subjected to denudation and weathering mentary cycles controlled by tectonics and eustasy. The (Dorofeev et al., 1999). erosional events at the start of the late early Cretaceous and It is possible to trace the variations in the characters of at the Oligocene–Miocene and Pliocene–Eopleistocene the Tertiary Sequences depending on their position with Sequence boundary were accompanied by structural events. respect to present day and buried relief thanks to observations made in the course of prospecting and detailed 5.1.1. The late early Cretaceous mapping performed on Bol’shoi Lyakhov Island. Those The unconformity at the base of the Aptian–Albian results were summarized in a recently published monograph Sequence documents gentle structuring between the late (Dorofeev et al., 1999). Jurassic on Kotel’nyi Domain and most likely a series of unspecified erosional and structural events on De Long 4.4.1. Paleocene–Eocene Sequence Domain. On Bennett Island, the mid-Palaeozoic till mid- The lower unit of the sequence consists of disintegrated Cretaceous break in the stratigraphic record can be rock debris and clay up to 30 m thick, which are chemically constrained to the Pennsylvanian till the mid-Cretaceous if reworked eluvia. The upper unit was mapped in a buried a block of silicified limestone with Carboniferous fossils on river valley. It is proluvial sandy clay with abundant rock Zhokhov Island is a xenolith of underlying strata (Makeev debris, alluvial pebble and gravel with lenses of sand and et al., 1991). clay, changing to interbedded clay, silt and sand down The southern portion of the study area in the middle valley. A transition to deltaic and lagoonal facies was Cretaceous was an evolving orogen as evidenced by S-type identified from specific thin bedding and the presence of granite plutons close to 120 Ma in age (Dorofeev et al., brown coal seams. The sediments’ provenance was the 1999; Kos’ko, Lopatin, & Ganelin, 1990). weathering products of the lower unit (Dorofeev et al., The Anjou Islands area belonged to a vast denuded, 1999). The thickness of the unit is up to 30 m (Lopatin, peneplained area. There are no marine fossil records from 1999). here while fossil plants, compositional and sedimentary structure features are quite typical of nonmarine environ- 4.4.2. Oligocene–Miocene Sequence ments. Gently dissected topography was inferred from the Down cutting of valleys started in the early Oligocene as presence of underlying bedrock clasts through the sections. a response to regional regression (Dorofeev et al., 1999). The topography, along with manifestations of acidic Sedimentation started in the late Oligocene and continued volcanism and discontinuity of individual packages in the through the Miocene. The sediments are sandy clay with sections, evidence moderate scale tectonic activity. The grit, pebble, fine-grained sand and pebble beds and lenses. present day isolated patches of mid-Cretaceous strata are Near shore marine, deltaic, alluvial, proluvial, and lacus- believed to be remnants of a much wider sedimentary basin, trine settings were identified. The following succession of dismembered later by tectonics and erosion. The presence of sediment types was discovered in paleovalleys up section: coal in the strata in contrast to lignite and brown coal in the alluvial–deltaic–lagoonal–deltaic–alluvial, showing a upper units of the sedimentary cover can be a result either of transgression–regression trend. Total thickness of the deep subsidence followed by uplift and inversion of the Sequence is up to 100 m (Dorofeev et al., 1999). basin before the late Cretaceous, or of high PT values in the M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 913

Fig. 7. Examples of folding in Late Cretaceous sequence. Novaya Sibir’ Island, Utes Derevynnykh Gor. Sketch drawings of outcrops. neighborhood of an active compressional orogen to the Those environments persisted on the Lyakhov Domain since south. the late Cretaceous (Dororfeev et al., 1999). Sedimentation The De Long Domain was a subaerial basalt plateau. Its of reworked weathering products commenced near the huge dimensions can be seen on anomalous magnetic field early/late Paleocene boundary on Bol’shoi Lyakhov and on maps. A subaerial setting is inferred from the association Zemlya Bunge, and in the early Eocene on Kotel’nyi Island with coal bearing sediments, presence of volcanic bombs and within the Faddeya Domain. On Bol’shoi Lyakhov it and minor fragments of lava produced by volcanic was described in terms of a river valley incision. Nonmarine eruptions, manifestations of weathering. sediments dominate in the Eocene–Paleocene sequence. Marine sediments are known in the upper part of the 5.1.2. The late Cretaceous sequence within the Faddeya and Kotel’nyi Domains. Late Cretaceous strata are present on the Anjou Islands Absence of the upper portion of the Paleocene–Eocene on east Kotel’nyi and west Faddeya Domains. They lie on Sequence on Zemlya Bunge and within the Faddeya weathered lavas of the late early Cretaceous sequence with Domain indicates that the pre-Oligocene syn- or post- erosional contact. The late Cretaceous sequence lies within depositional uplift was more intense here than on Kotel’nyi the contour of the late early Cretaceous Sequence. The late Island and in the Lyakhov Domain. Cretaceous Sequence contains less clastic and more pelitic Tectonic differentiation of a regional peneplain was a material than the late early Cretaceous. There are no clasts general tendency in the geologic evolution in the Palaeo- of Palaeozoic bedrock while rhyolite pebbles similar to the cene–Eocene. Gentle elevation was characteristic of the early Cretaceous lava are abundant. These features evidence Lyakhov Domain. The peneplain was gently inclined to the much more gentle topography, and consequently weaker north-west and north-east which resulted in the appearance geodynamics. There is a minor acidic volcanoclastic of near shore marine sediments in the west Kotel’nyi and component in late Cretaceous strata, which was brought north Novaya Sibir’. The differentiation thus took place presumably from far distant volcanic areas. The late along with a wide regional transgression. Cretaceous sedimentary basin inherited the early Cretaceous Basin. It was isolated from the open sea (no marine fauna). 5.1.4. The Oligocene–Miocene The subsidence rate and scale were low as shown by low An erosional event in the beginning of the Oligocene thickness and low grade of coalification. preceded the deposition of Oligocene–Miocene strata. The The Lyakhov Domain was a low denudative peneplain event is manifested by the disconformity at the base of the subjected to extensive weathering and accumulation of the Sequence and intense down cutting in paleo river valleys on weathering products in situ (Dorofeev et al., 1999). Bol’shoi Lyakhov Island. The erosion and down cutting were caused by the tectonic uplift and/or regression. The 5.1.3. The Paleocene–Eocene deposition continued later in the Oligocene and continued The Cretaceous–Tertiary boundary is marked by a through the Miocene mostly under near shore marine moderately elevated peneplain and by extensive weathering. conditions changing up section to alluvial environments on 914 M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919

Fig. 8. Geological map of Cape Vysoki, Novaya Sibir’ Island. the Anjou Islands and predominantly nonmarine environ- distributed middle and late Miocene. Oligocene sediments ments on the Lyakhov Island. In both areas transgression– are mostly marine, while nonmarine environments are more regression is well documented by alteration in environments typical of the Miocene. The patchy distribution and the through time. The distribution of environments and facies predominance of nonmarine environments is interpreted through the Islands show that the Lyakhov Domain here as an evidence of unstable depositional and tectonic remained tectonically and topographically higher than the settings through the middle-late Miocene due to a Kotel’nyi and the Faddeya Domains. deformation event. The major constituent of the Oligocene–Miocene Folded and thrusted late Cretaceous and Miocene strata Sequence is the wide spread Nerpichin Formation of were mapped on the south-west Novaya Sibir’ (Figs. 6 and 7). Oligocene–early Miocene age. It comprises also patchy Conjugate folds and faults are well observed in outcrops in

Fig. 9. Folded Paleocene–Eocene sequence. Novaya Sibir’ Island, Cape Vysoki. Sketch drawings of outcrops. M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 915

Kotel’nyi Island (Kos’ko et al., 1985; Kos’ko et al., 1990). Faults are distinctly recognizable in the topography as straight valleys and linear saddles. They affect Oligocene– Miocene strata, which fill N–S fault controlled grabens. It is plausible that central type alkaline basalt eruptions on the De Long are at least partly contemporary to the formation of the Oligocene–Miocene sequence southward. The only data in support is the higher content of pyroxene and amphibole, which can be volcanic, among heavy minerals in Oligocene–Miocene sediments than in earlier sediments.

5.1.5. The Pliocene and Eopleistocene The deposition in the Pliocene was preceded by erosion and deformation. The deformation was confined to separate zones whose boundaries were not reliably defined being covered under Quaternary sediment. Pliocene and Eopleistocene sediments are proluvial and Fig. 10. Major structural features of the East Arctic continental margin. alluvial on the slopes of and close to topographic highs changing seaward to coastal plain, brackish, and near shore the south-west of the island in the Utes Derevyannykh Gor marine types. Nonmarine slope sediments are abundant on area. Cretaceous and the uppermost Pliocene strata form the Lyakhov Domain, less abundant on the Kotel’nyi fold and thrust structures in a 2-km wide strip trending along Domain circling the topographic highs with exposed the coast in a WNW direction. Reverse faults and thrusts bedrock, probably absent on the Faddeya Domain. The dipping, to the north–north-east at 40–708, have a spacing variation of different depositional type sediments up section of 50–600 m here. Folds are parallel to faults and the and aerially shows transgression that started in the Pliocene structure as a whole is SSW vergent. Northern limbs of and reached its maximum in the Eopleistocene. The anticlines dip at 30–558, southern limbs are vertical or transgression was interrupted by a sharp regression at the overturned and are thrusted in many cases. Recumbent folds Eopleistocenethe/Pleistocene boundary. have been observed. The length of big folds exceeds 4 km, Eopleistocene sediments were elevated up to 90 m above the width is from 100 to 250 m. The length of small folds sea level. No other evidence of tectonic activity was does not exceed few hundred meters, the wavelength being reported. from few meters up to few tens of meters. Height of folds is Alkaline basalt stratovolcanoes evolved through the from few meters up to 40–70 m. Pliocene and Quaternary on the De Long Domain. A zone of less intense folding and faulting extends from north-west Kotelnyi Domain eastward through the north 5.2. Regional and global correlations Faddeya Domain. Gentle folds of Paleocene and Miocene strata were mapped on Strelka Anjou and on north Faddeya The discussion in this section is aimed to show the Island. The array of NW striking folds with dip angles on the validity of and constraints to the extrapolation offshore of limbs up to 408 displays an en echelon pattern. Complicated the sequences and their relationships established on the New outcrop scale folds and faults in Paleogene and Neogene Siberian Islands. strata in the north of Faddeya Island (Strelka Anjou) and in The late Kimmerian tectonism embraced the north-east the north of Novaya Sibir’ Island (Capes Vysoki and Eurasia in the early Cretaceous. The tectonism extended to Goristi) have been described by Trufanov and co-workers Alaska and the Northern . Major events of the (Figs. 8 and 9). These features document a compressional tectonism were ‘the closure of the South Anyui Ocean’— setting and horizontal motions within the zone. present day South Anyui suture, emplacement of granites, There is more evidence for horizontal motions in post accumulation of molasses in foredeep and intermontane early Miocene time. An array of nearly to N–S faults was basins (Egiazarov et al., 1977; Khain et al., 1997; Krasny & mapped on Anjou Islands. On Kotel’nyi Island they extend Putintsev, 1984). The Aptian–Albian Sequence within the 90–110 km (Fig. 5). Being conjugated with north-west Kotel’nyi and the Faddeya Domains is a late Kimmerian striking faults they form wedge shaped structural blocks. molasse. It is hypothesized that a huge foredeep or a series Fault dips are close to vertical. Major faults consist of of smaller separate foredeeps was formed in the Novosibirsk separate subordinate faults, which join at low angles or trough between the De Long Domain in the north and overlap each other. Fault zones vary in width from a few Kotel’nyi and Faddeya Domains in the south and extended meters to 4 km. Vertical and right hand lateral displacement from here to the east along the Vil’kitsky basin and the south along the faults can be seen on the geological map of Hanna trough (Grantz, Holmes, & Kososki, 1975; Grantz, 916 M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919

May, & Hart, 1990; Thurston & Theiss, 1987) to the The intense geodynamic activity was characteristic of the Colville basin on Alaska (Fig. 10). The hypothesis is Oligocene–Miocene time (Khain et al., 1997). Slow supported by the age and structure of the Vil’kitsky Basin elevation of the North-East Eurasia characteristic of the (Grantz et al., 1990) and by a discovery of a platform type end of the Eocene changed to more energetic uplift in the Domain on the North Wind Ridge north of the Vil’kitsky Oligocene. The peak in the geodynamic energy and the scale Basin (Grantz, Clark, Phillips, & Srivastava, 1998). Early of elevation in the Arctic was in the Miocene (Gramberg & Cretaceous strata in the Vil’kitsky Basin parallel the south Pogrebitsky, 1984; Musatov, 1996). The elevation flank of the basin being driven to the fold and thrust front of destroyed the Palaeocene–Eocene peneplain and resulted the late Kimmerian fold belt and thinning northward to the in a mountainous relief similar to that of the present day in axis of the basin. The thickness of later sequences is North-East Eurasia (Krasny & Putintsev, 1984). maximum along the axis of the basin and thins towards the The base of the Oligocene–Miocene Sequence is Kimmerian fold belt in the south. This pattern allows correlated here to middle Oligocene eustatic lows (Haq attribution of the formation of the early Cretaceous et al., 1987) and to an erosional interval within the sequence to the orogeny in the late Kimmerian fold belt. Sagavanirktok Formation on the Northern Alaska (Moore The late early Cretaceous volcanism on the De Long et al., 1994). Domain correlates with similar events in many circum The erosional disconformity at the base of the Pliocene Arctic (Gramberg & Pogrebitsky, 1984; Korago & strata on the New Siberian Islands marks the start of a new Stolbov, 2000; Stolbov, 1997; Verba, Kim, & Volk, 1998). transgression whose was in the Eopleistocene. The base of the Aptian–Albian Sequence correlates with The transgression of the Arctic continental margins the Lower Cretaceous Unconformity on Northern Alaska expanded from the Arctic Basin (Gramberg & Pogrebitsky, and offshore (Moore et al., 1994; Thurston & 1984). The disconformity is correlative to a series of eustatic Theiss, 1987). lows (Haq et al., 1987). A hiatus and an erosional interval The late Cretaceous was a time of slowing down of the close to 2 Ma in the Upper Brookian Sequence is known in geodynamic activity within the late Mesozoic fold belt in Northern Alaska (Moore et al., 1994). the North-West Eurasia (Khain et al., 1997; Krasny & The events and geodynamic regimes documented by the Putintsev, 1984). Wide transgressions took place on the disconformities and structural and depositional characters of west of the Eurasian and in the . the Cretaceous to Tertiary Sequences on the New Siberian The accumulation of a thin nonmarine late Cretaceous Islands reflect east Arctic wide and global evolution trends sequence on the New Siberian Islands is a weak response to and events. Consequently, they are manifested in the this global trend. The depocentres migrated northward close sedimentary cover of the North-East Arctic continental to the early/late Cretaceous boundary in the Vil’kitsky margin. The pre-Aptian unconformity related to the Basin, in Hanna trough, and in the Northern Alaska (Grantz culmination of the orogeny in the North-East Eurasia and et al., 1990; Moore et al., 1994; Thurston & Theiss, 1987). in the North-West America is the first order structural The base of the late Cretaceous Sequence correlates with feature. It is the base of the Cretaceous Quaternary structural the deposition of coarse-grain nonmarine clastics and a stage of the sedimentary cover in the East Arctic. The late depositional unconformity close to the early/late Cretaceous Cretaceous/Tertiary unconformity is coincident with Arctic boundary in North Alaska (Moore et al., 1994; Thurston & and global wide change in the geodynamic trend: slowing Theiss, 1987) and to a series of short term eustatic lows down in the tectonic activity through the late Cretaceous and (Haq, Hardenbal, & Vail, 1987). the increasing activity in the Palaeogene. The late The Palaeocene–Eocene time was a period of tectonic Miocene–pre-Pliocene unconformity manifests the estab- quiescence between the global scale Laramide and Pyrenean lishment of a very active geodynamic regime which is orogenies (Khain et al., 1997). North-East Eurasia was an practically the same as today. The pre-late Cretaceous and accumulative–denudative peneplain (Krasny & Putintsev, the pre-Oligocene erosional events manifests subordinate 1984). A worldwide transgression evolved through the time stages of this general trend of the geodynamic evolution. starting in the late Palaeocene. It is believed that change in the tectonic and paleogeographic environments in the Arctic 5.3. Seismostratigraphic comments close to the Cretaceous/Tertiary boundary was a result of destruction and subsidence of a provenance area which There is a variety of models of the structure and occupied the central part of the present day stratigraphy of the sedimentary cover on the shelf adjacent trough the Mesozoic till the Palaeogene (Gramberg & to the New Siberian Islands. They differ in the dating and Pogrebitsky, 1984). the number of the constituent seismostratigraphic units. Karl The base of the Palaeocene–Eocene Sequence correlates Hinz and his colleagues distinguished LS1, LS2, and LS3 with the word-wide regression (Khain et al., 1997) and with regional seismic reference horizons, which are, respect- deposition of nonmarine coarse clastics (Sagavanirktok ively, the boundaries of three seismostratigraphic units Formation) on the Northern Alaska (Moore et al., 1994; (Hinz et al., 1997; Franke & Hinz, 1999). The units are Thurston & Theiss, 1987). indicated in this paper as Unit I, II, and III up section. Other M.K. Kos’ko, G.V. Trufanov / Marine and Petroleum Geology 19 (2002) 901–919 917 researchers distinguished many more units (Drachev et al., Only three regional seismostratigraphic units have been 1998; Gramberg & Pogrebitsky, 1984; Kim & Yashin, identified offshore up to date. Those are Unit I bounded by 1999; Lazurkin, 2000). The involvement of one of the LSI and LS2 regional reflectors, Unit II bounded by LS2 and authors in current compilations and completed projects on LS3 reflectors, and Unit III between reflector LS3 and the the geology and the tectonics of the Russian Arctic shelf sea bottom. (Hinz et al., 1997; GRASS, 1996) familiarized him with Unit I is mostly late early Cretaceous and comprises most of seismic data in the New Siberian Island region. It is upper Cretaceous strata as well, Unit II is Paleogene to evident, that the identification more than three regional Miocene, and Unit III is Pliocene–Quaternary in age. seismostrtigraphic sequences at present is not adequately The above dating is as hypothetical as the earlier controlled by the existing seismic records, although it is published versions, but in the opinion of the authors it valid as a hypothesis or preliminary framework. better fits with the major regional and global events and The estimates of the age of the base of the sedimentary trends of the tectonic evolution of the Arctic continental cover vary from the Riphean (Kim & Yashin, 1999; margin of the North-East Eurasia. Lazurkin, 2000) till the Tertiary (Cruise Report, 1977;), and the latest Cretaceous (Drachev et al., 1998). Franke and Hinz (1999) put the base of the sedimentary cover—LS1— Acknowledgments close to the Cretaceous/Tertiary boundary admitting that the deposition could start in the latest Cretaceous. Roeser and The paper was prepared within a VNIIOkeangeolo- co-authors in an earlier publication ascribed a Cretaceous gia/BGR agreement for cooperative geoscientific research age to the lowermost thick unit of the sedimentary cover in the Laptev Sea (Laptev Sea Joint Project, LSP). The (Roeser, Block, Hinz, & Reichert, 1995). A new argument authors thank Karl Hinz and Martin Block for the that the base of the sedimentary cover in the west Laptev opportunity to see seismic records and preliminary Sea is not older than early Cretaceous was presented interpretations which helped to focus on the features critical recently (Vinogradov & Drachev, 2000). to decipher offshore geology, and for productive discus- The discussion in the previous sections leads to the sions. The authors’ thanks are to be extended to Franz hypothesis that Unit I of the sedimentary cover is Tessensohn and to Norbert W. Roland for their reviewing Cretaceous, mostly late early Cretaceous in age, Unit II is and comments to the first version of the paper, and to the Tertiary pre-Pliocene in age, and Unit III comprises anonymous reviewer whose detailed and benevolent com- Pliocene to Recent sediments. This dating is as hypothetical ments served a basis to drastic reworking of the paper. as the age estimates made by other researchers, but it is A large portion of the paper was written during Mikhail more compatible with the scale of correlative regional and Kos’ko stay in BGR in early 1997. It gives us pleasure to global events and trends of geodynamic evolution. present our thanks to BGR staff for their kind and efficient It is obvious that Units I, II, and III are not universally support. spread in the New Siberian Island area. 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