INTRODUCTION

According to the concept of the accretionary assemblage of terranes, developed in the 1970s–1980s [29], orogenic belts of continental margins are mosaics of terranes of various geological structure and geodynamic natures. Earlier researchers (e.g., [1, 2, 4, 10, 22, 23] and others) found that the formation of the eastern part of the Eurasian continental margin was caused by two different geodynamic processes: subduction of the oceanic plate beneath the continental one and transform sliding of the oceanic plate along the continental one. A considerable part of the eastern Eurasian margin is occupied by the Sikhote Alin orogenic belt (SAOB). It stretches from the northern coast of the Sea of Japan in the south to Sakhalin Bay (Sea of Okhotsk) in the north, and, together with the Hokkaido–Sakhalin branch, is incorporated into the larger Sikhote-Alin–North-Sakhalin orogenic belt [2].

The SAOB is formed by terranes of different ages and geodynamic histories: they are fragments of Jurassic and Early Cretaceous accretionary prisms, Early Cretaceous arc systems, and an Early Cretaceous syn-shift turbidite basin (Zhuravlevka–Amurian terrane) [2].

According to [2, p. 184], “the Early Cretaceous units of the Zhuravlevka–Amurian terrane form a complex system of densely compacted folds and are highly fragmented during their sinistral strike-slip motions (which occurred mainly in the Late Albian) along the series of newly formed NNE-trending faults. In this respect, a reliable reconstruction of the initial coordinates and configuration of the paleobasin where these sediments accumulated is not possible yet.”

The paleomagnetic method allows us to add a quantitative measure to analysis of pre-accretionary terrane history, and, therefore, it is one of the major methods in geodynamic studies [10]. In recent years, reliable paleomagnetic data have been obtained for various SAOB rocks [1, 9, 10], including the Cenomanian–Turonian (~95 Ma) volcanic units of the Utitsa Fm. [14], for which high paleolatitudes of formation, close to the modern location, were revealed. However, the problem of estimating the motion distance for the Zhuravlevka–Amurian terrane (ZH) along the transform margin in the Early Cretaceous, as well as that of inferring the coordinates of the turbidites’ formation, remains unresolved.

In the present work, we provide the results of paleomagnetic (primarily) and petrochemical studies of the Berriasian–Valanginian sandstones from the Komsomolsk Series, collected in the coastal outcrop of Sakhalin Bay; the studies were aimed at the determination of the extent of motion and the formation coordinates of the Early Cretaceous Zhuravlevka–Amurian turbidite basin.

BRIEF GEOLOGICAL CHARACTERISTICS OF THE STUDY AREA

The studied Early Cretaceous deposits are exposed along the coast of Sakhalin Bay between Cape Promezhutochnyi and Cape Mofet (Fig. 1). Initially, these units were referred by G.S. Vedernikov et al. (1956) to the Late Jurassic–Early Cretaceous Orel’ Fm. Later, organic fossils (various aucelins and inoceramids) were found and referred by A.A. Kapitsa and V.N. Vereshchagin to the Valanginian; based on this, in the 1960s, V.E. Pilatskii et al. (1968) correlated these deposits to the Komsomolsk Series.

Fig. 1.
figure 1

Geological characteristic of the study area. Arbitrary notes: (1) Paleozoic Galam terrane (GL); (2–6) terranes representing fragments of various structures: (2) Jurassic accretionary prism (Badzhal, BD), (3) Jurassic near-continental turbidite basin (Ulban, UL), (4) Cretaceous syn-shift near-continental turbidite basin (Zhuravlevka–Amurian terrane, ZH), (5) Hauterivean–Albian arc system (Kem terrane, KM), (6) Hauterivean–Albian accretionary prism (Kiselevsk–Manoma, KS); (7) Late Cretaceous–Paleogene granitoids; (8) Late Cretaceous effusive rocks; (9) Pliocene deposits with brown coal interbeds; (10) pre-Quaternary alluvial deposits; (11) rhythmically interbedding siltstones and argillites; (12) rhythmically interbedding siltstones and fine-grained sandstones (rhythm thickness is 8–12 cm); (13) interbedding fine-grained sandstones (2–10 cm), siltstone beds (0.2–1.5 m), and members (1.5–2.0 m) of rhythmically interbedding siltstones and fine-grained sandstones (rhythm thickness is 8–10 cm); (14) boundaries of members having their own numbers; (15) faults; (16) member numbers; (17, 18) bedding elements: (17) normal occurrence, (18) recumbent occurrence; (19) sampling points (sites). Tectonic scheme is after [2].

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According to the modern ideas, [3, 5, 6, 12, 21], the deposits of the Gorinskaya and Pionerskaya formations (both of the Komsomolsk Series) correspond, in terms of the faunal complex, to the Berriasian (139.8–145.0 Ma) and Valanginian (132.9–139.8 Ma) stages of the Lower Cretaceous, respectively.

Judging by the tectonic scheme of Sikhote Alin, the studied deposits are located at the northern termination of the Zhuravlevka–Amurian turbidite basin (terrane) [2, 4]. The terrane is comprised predominantly of sandstones, siltstones, argillites, and their rhythmic interleaving with total thickness of about 15 000 m [4, 23].

The detailed investigation of the Berriasian–Valanginian section of the Komsomolsk Series on the coast of Sakhalin Bay suggests that this section includes packets of 10–150 m thick composed of interleaving large-rhythmic sandy flysch and accompanying massive sandstones (2–15 m thick). These packets contain members (0.5–5.0 m thick) of finely rhythmic sandy or sandy–clayey flysch. Also, rare members (0.5–1.5 m thick) of finely bedding silty argillites are reported in packets. The interleaving packets alternate with thicker members of sandy–clayey flysch (10–50 m) and/or finely bedding silty argillites (10–30 m). The sandstones in the interleaving packets often contain lenses of sedimentation breccias varying in length from 50 cm to a few meters. In turn, the large members of sandy–clayey flysch and finely bedding silty argillites include individual beds of massive fine-grained sandstones of up to a few meters thick [13].

In the large-rhythmic sandy flysch, rhythms of up to 2.5 m thick are seen with elements of ABC and ABCD cycles as defined by A. Boume [13]. The rhythms have clear lower erosional boundaries, often with outliers of underlying rocks. The lower element of a rhythm is usually represented by sedimentation breccias or gravel sandstones. At the bases of the rhythms, molds of vortex hollows are observed. The massive sandstones in the same packets have the same sedimentation features as the large-rhythmic flysch, but represented only by elements A and AB from the sequence defined by A. Boume.

In the small-rhythmic sandy flysch, the rhythms are up to 30 cm thick, while in the members of finely rhythmic sandy–clayey flysch, their thickness ranges from 3 to 25 cm. The rhythms of the last two flysch types are represented mostly by CD and BCD elements. At the bases of the rhythms of sandy–clayey flysch, there are molds of parallel grooves and ridges, whereas polyhedral structures are formed in the pelitic part of the rhythms (their detailed description is given in [7]).

Silty argillites are represented by fine (up to few millimeters thick) interleaving of argillites and siltstones. They contain lens-shaped interbeds (0.5–1.5 cm thick) of sandstones with fine and parallel bedding. Sandstones with parallel bedding often form convolute folds as a result of processes associated with submarine landslides.

The samples for paleomagnetic and petrochemical studies were collected from the sandstones of the lower part of the mentioned section (Fig. 1), in the interval of 0.7–6.7 km to the northwest of the mouth of Gr. Vilka stream. The thickness of this section is 1140 m. According to the geological map [3, 5], these deposits refer to the Pionerskaya Fm. of the Komsomolsk Series. The sedimentary section is generally represented here by predominantly coarse interleaving of fine-grained sandstones (2–10 m) and members (1.5–4.0 m) of rhythmically alternating siltstones and fine-grained sandstones, and also siltstone beds (0.2–1.5 m) (Fig. 1). In addition, the mentioned alternation of rocks contains even thicker members of alternating siltstones and sandstones (up to 60 m), those of siltstones and argillites (up to 40 m), and siltstone beds (up to 70 m).

The sandstones are characterized by grain size ranging from 0.1 to 0.35 mm. They are composed of detrital mineral grains (40–60%), rock fragments (10–30%), and cement. The detrital mineral grains are represented by quartz (up to 60%), feldspars (up to 40%), singular grains of biotite and tourmaline, and accessory minerals. The grains are angular or semirounded, weakly corroded in shape. There is an admixture of tufogenic material (elongated grains of clearly acute shape). The rock fragments are composed of effusive units, clayey shales, siltstones, and quartzites. The cement is composed of fine-grained quartz aggregates, sericite and chlorite flakes, and rare grains of carbonate and rutile. Accessory minerals include apatite, zircon, and ore mineral.

The siltstones are dark gray and black in color, composed of mineral grains (40–60%), rock fragments (5–10%), and cement (30–55%). Quartz is predominant (up to 60%) in the mineral fraction, and the biotite content is also sometimes increased (10–15%). Accessory minerals are represented by zircon and apatite. The cement is porous, less often basal; in composition, it is clayey, often cericitized. Admixture of tufogenic material (up to 5%) is reported.

The rocks of the Pionerskaya Fm. dip to the northwest and southeast at 75°–40°.

In addition to this, to perform petrochemical characteristic of the rocks, we used the analysis results for the Gorinskaya Fm. samples collected 10 km to the northwest of Gr. Vilka stream. According to the earlier studies [34], no stable paleomagnetic signal was revealed in them.

PALEOMAGNETIC STUDIES

The reliability of the obtained petromagnetic and paleomagnetic results was provided by a thorough selection of rock specimens and application of modern measurement techniques [17, 20, 24] using highly precise instrumentation manufactured in Russia (IGP and TAF-2), the Czech Republic (JR-6A), and the United States (MF-1FA and 2G Enterprises).

The samples for paleomagnetic studies were collected at the sites (10 to 25 of independently oriented hand specimen samples at each sampling point). The hand specimens were cut using a diamond saw. One or two cubic (2 cm in size) specimens were made out of each hand specimen.

Demagnetization of the specimens was performed by two methods: thermomagnetic cleaning and cleaning using variable magnetic field. The convergence for the natural remanent magnetization (NRM) components in the rocks, measured by different cleaning methods, can be an additional criterion in substantiation of the primary character of the distinguished magnetization component. Measurement of remanent magnetization during thermomagnetic cleaning was made on a JR-6A spin-magnetometer; in the case of cleaning using variable magnetic field, a 2G Enterprises cryogenic magnetometer was used. Before transportation from a nonmagnetic oven to the measuring tools, the specimens were placed into a container of μ-metal. All specimens were usually demagnetized up to temperature of 550–600°C and alternating magnetic field of 50–100 mT. The cleaning stage depended on the behavior of the magnetization vector during the demagnetization procedure.

The NRM components were distinguished using the component analysis, employing the PMGSC software package ver. 4.2 by R. Enkin [31]. We extracted the components, calculated on two–four points of stepwise cleaning and corresponding to the rectilinear segments in the orthogonal diagrams. After this, the high-temperature and high-coercive magnetization components were analyzed.

Most of the studied specimens have a two-component composition of the NRM vector (Figs. 2a, 2c). In some specimens, predominantly in those from the site P1702, a three-component composition of the NRM is observed (Figs. 2b, 2d).

Fig. 2.
figure 2

Examples of orthogonal diagrams (in terms of the geographic coordinate system) when conducting paleomagnetic cleaning using (a) alternating magnetic field and (b–c) temperature for sandstone samples of the Komsomolsk Series.

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The low-temperature (LT) and low-coercive (LC) magnetization components are usually distinguished in the ranges of 25–300°C and 1–15 mT, respectively (Fig. 2). In our opinion, these components were produced by superposition of the secondary and modern (viscous) magnetization components and, therefore, were not further analyzed.

The middle-temperature and middle-coercive magnetization components are distinguished in the ranges of 300–400°C and 15–25 mT, respectively. Since these components were revealed only in a few specimens from the site P1702, they were not analyzed.

The high-temperature (HT) and high-coercive (HC) magnetization components have close directions. In the orthogonal diagrams constructed on the basis of thermomagnetic cleaning, the HT component is distinguished in the temperature interval from 380–430 to 540–580°C and drops down to the origin of the coordinates (Figs. 2b, 2d), representing the characteristic ChRM one. The HC magnetization component is distinguished in the orthogonal diagrams in the interval from 20–25 to 40–60 mT (Fig. 2a) and is also a characteristic one (excluding several specimens not included in the entire statistical sampling).

To exemplify, let us present the results of paleomagnetic cleaning for some specimens, where these magnetization components have been revealed.

In the specimen P170307a, cleaning using variable magnetic field established two magnetization components (Fig. 2a). The HC one is distinguished based on six points in the range from 25 to 49 mT and runs to the origin of the coordinates.

As is shown by the results of thermomagnetic cleaning, the magnetization of specimen P170402 is also characterized by two components. The HT component is distinguished based on seven points in the temperature range from 380 to 575°C and then drops to the origin of the coordinates (Fig. 2c).

In specimens P170201 and P170206, three magnetization components were revealed (Figs. 2b, 2d). The HT one runs to the origin of the coordinates, and in the mentioned specimens it is distinguished in the ranges of 390–550 and 500–565°C, respectively.

The results of paleomagnetic studies of the Early Cretaceous sandstones from the Pionerskaya Fm. (Zhuravlevka–Amurian terrane) are presented in Table 1.

Table 1.   Results of paleomagnetic studies
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Fold Test

The ChRM component was detected in 35 of 51 specimens from the studied Pionerskaya Fm. sample. This component demonstrates increased clustering in terms of the stratigraphic coordinate system: by a factor of six based on specimens (Ks/Kg = 6.2) and by a factor of more than 100 based on sites (Ks/Kg = 134.7) (Table 1). The maximum clustering is observed after the introduction of a 97% correction to the rock occurrence, indicating a “prefolding” age close to the time of rock formation (Fig. 3).

Fig. 3.
figure 3

Projections of the directions of the characteristic magnetization component (ChRM) in the Pionerskaya Fm. sandstones in terms of the (a) geographic and (b) stratigraphic coordinate systems; (c) panel represents the fold test results. The gray-filled star denotes the mean ChRM direction and the gray circle around it corresponds to the 95% confidence interval.

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Despite considerable advances in petromagnetic and paleomagnetic studies, there are certain issues, including those related to the method of carrying out these studies; in particular, one of these issues is that of underestimating the inclination of the magnetization vector in sedimentary rocks. This phenomenon was discovered experimentally. In 1948, E. Johnson found in laboratory conditions that the declination (Dec) of NRM in redeposited clays fits well to that of the terrestrial magnetic field, while the inclination (Inc) of NRM appeared to be smaller than that of the terrestrial field at the redeposition moment [24]. The value of Inc underestimation (or inclination error) can be from 1 to 10–30°. As is usual, the inclination error is considerably smaller in sandy rocks than in silty ones, and its value is often within the limits of the measurement error (≈5°).

In order to measure the probable underestimation of inclination in the Pionerskaya Fm. sandstones, we studied the correlation between the ratio of the minimum and maximum semiaxes of the anisotropy ellipsoid of initial magnetic susceptibility (K3/K1), on the one hand, and the tangent of the angle inclination ChRM, on the other hand [28]. The obtained correlation factor was 0.21, suggesting an absence of any mutual dependence of the calculated parameters. This indicates, most likely, that the inclination values were underestimated insignificantly and, since the obtained results do not allow us to estimate its value, it was not taken into account in the following calculations.

Based on the mean ChRM direction calculated from the specimens, we found the paleomagnetic pole coordinates and the paleolatitude of formation of the studied rocks. The calculation results are presented in Table 1.

PETROCHEMICAL STUDIES

All analytical studies were conducted at the Center for Collective Use (Kosygin Institute of Tectonics and Geophysics, Far East Branch of the Russian Academy of Sciences, Khabarovsk). The contents of the main rock-forming oxides were determined using the X-ray fluorescence analysis on an S4 tool (manufactured by Brucker company, Germany). The specimens were made by compaction with lithium metaborate; the standards used were CO LDI-3 (gabbro); WMF-1a (mineralized gabbro); and standard specimens made of the rocks collected in the Russian Far East, namely, DVB (basalt), DVA (andesite), and DVD (dacite). The measurement error was no more than 10%. L.M. Il’in was the analyst.

For petrochemical characteristic of the Berriasian–Valanginian sandstones of the Komsomolsk Series from the coastal outcrops of Sakhalin Bay, we used the data of silicate analysis of 20 rock samples from the Gorinaskaya (8 samples) and Pionerskaya (12 samples) formations (Table 2).

Table 2.   Contents of rock-forming oxides (in %) in sandstones of the Komsomolsk Series
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The bulk chemical compositions of the sandstones from the Gorinaskaya and Pionerskaya formations differ insignificantly. According to the M. Herron diagram [32], the sandstones are represented by sublitharenites, subarkoses, and quartz arenites (Fig. 4a). Notably, the points of the Pionerskaya Fm. compositions tend to the sublitharenite domain, whereas the samples from the Gorinaskaya Fm. are closer to the subarkoses and quartz arenites.

Fig. 4.
figure 4

Figurative points of compositions for sandstones of the Komsomolsk Series in the diagrams by (a) M. Herron, (b) M. Bhatia, (c) B. Roser and R. Korsch, and (d) J. Maynard et al.

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To determine the geodynamic setting under which the studied rocks formed, we used the discrimination diagrams by M. Bhatia, J. Maynard, B. Roser, and R. Korsch [16, 25, 26, 33, 35] (Figs. 4b–d).

In the Bhatia discrimination diagram [27], the figurative points of the sandstones fall within the domain of active continental margins and within the one of continental volcanic arcs (Fig. 4b).

The SiO2–K2O/Na2O discrimination diagram developed later by B. Roser and R. Korsch [35] includes the domain of oceanic island arcs, and those of passive and active continental margins. In it, almost all figurative points of the analyzed rock samples fall within the domain of active continental margins, excluding three points located between the domains of oceanic island arcs and active continental margins (Fig. 4c). In the discrimination diagram by J. Maynard [33], all figurative points of the studied rock samples fall within the domain of active continental margins (Fig. 4d).

DISCUSSION

The figurative points of the compositions of the studied rocks in the Bhatia and Roser–Korsch discrimination diagrams (Figs. 2b–d) fall within the domains corresponding to various geodynamic settings: continental volcanic arcs, active continental margins, and oceanic island arcs. Such a distribution suggests, in our opinion, probable variations in the provenance areas of the terrigenous material. The provided petrochemical data agree with the earlier results [2, 4, 15, 22, 23] on the formation of the studied rocks under the geodynamic setting of a syn-shift turbidite basin at the transform boundary of a continent–ocean type, where mixing of rocks of close but not identical genesis is possible. Analogous conclusions have been made based on the petrochemical studies of the sedimentary rocks from the southern Zhuravlevka–Amurian terrane; according to [15], mixing of figurative points of genetically different sources of terrigenous material, demonstrated in the discrimination diagrams, “is likely the main characteristic feature of sedimentation under the setting of a transform margin of the Californian type” [15, p. 422].

As we have found, the studied rocks acquired the prefolding magnetization component at a time close to that of the formation of the rocks proper in the near-equatorial zone (Table 1, Fig. 5), but this does not agree with the available biostratigraphic data (boreal fauna findings [21]) for the rocks of the Komsomolsk Series. However, in addition to the new paleomagnetic data indicating the formation of rocks at low latitudes, there is also biostratigraphic evidence: the Lower Cretaceous sedimentary rocks within the limits of the Sikhote Alin contain a specific complex of Tethyan Late Pliensbachian ammonoides, among which the Mediterranean taxa (Arieticeras and Protogrammoceras) dominate [8]. Moreover, findings of Tethyan fauna (Pseudosubplanites ammonite of the Berriasian age [21]) are reported in deposits of the Komsomolsk Series of the Zhuravlevka–Amurian terrane. Proceeding from this, we can conclude that presently there is an ambiguity in the available paloebiogeographic determinations for the studied Early Cretaceous rocks.

Fig. 5.
figure 5

Geodynamic reconstruction of the eastern continental margin of Eurasia for 133–140 Ma ago, after [4] with additions. Arbitrary notes: (1) pre-Jurassic continent; (2) Jurassic terranes (fragments of Jurassic accretionary prisms); (3) fragments of the pre-Mesozoic continent in accretionary prisms; (4) fragment of the Early Cretaceous turbidite basin; (5) strike-slip faults; (6) subduction zone.

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The obtained paleomagnetic data allow us to quantitatively estimate the paleolatitudes at which the studied rocks of the ZH formed: given the measurement error, they can be determined at 10°–18° N (Fig. 5, Table 1). This means that after their formation, the rocks of the Pionerskaya Fm. drifted northwards by more than 4000 km (3900–4800 km) along the continental maleomargin. Taking the available paleomagnetic data on the Cenomanian–Turonian volcanic rocks (Utitsa Fm., ≈95 Ma in age [14]) into consideration, we can conclude that the mean drift rate of the ZH in the time interval of 133–95 Ma ago was 10–13 cm/yr. The polarity, or, more precisely, the hemisphere for the obtained paleomagnetic pole was chosen to be the northern one due to the following reasons: (1) if we choose the southern hemisphere, the drift rate of the ZH would appear to be about 40 cm/yr, which is double the calculated motion rate for the Izanagi Plate (about 20 cm/yr); (2) with the northern hemisphere being chosen, the drift rate of the studied blocks of the ZH fit the motion rate for the Izanagi Plate along the eastern continental margin of Eurasia.

Nevertheless, another interpretation is also possible for the onset time of the northward drift of the studied rocks. It is supposed that a convergent regime at the eastern continental margin of Eurasia changed to a transform one ca. 135 Ma ago (see, for example, [2, 4] and others) and correlates in time to the change in the rate and direction of the Izanagi Plate drift [30]. The drift rate of the Izanagi Plate, calculated to the coordinates of Honshu Island being 40° N and 140° E [30], abruptly increased ca. 135 Ma ago from 5 to 30 cm/yr, while the drift direction changed from northwestern to submeridional (Fig. 6). According to the later kinematic calculations and geodynamic constructions [36] and to the results shown in [11], the change of a subduction geodynamic regime to a transform one at the eastern active margin of the Eurasian paleocontinent in the Cretaceous time could have occurred considerably later, namely, in the second half of the Aptian. In addition to the rate and direction of the Izanagi Plate drift after the model from [30], Fig. 6 shows the analogous data for the same point (Honshu Island) after the model from [36] for the entire Cretaceous. According to the latter, since the beginning of the Cretaceous and approximately until 120 Ma B.P. (second half of the Aptian), the plate moved to the southwest and west at 11–13 cm/yr. About 120–115 Ma ago, the rate and direction of the Izanagi Plate drift abruptly changed and it began to move to the NNW at 17–18 cm/yr, increasing to more than 20 cm/yr in the second half of the Late Cretaceous. We can suppose that this was the time when the subduction regime changed to a transform one. Again, emphasize that it is one of the possible scenarios, inferred mainly from the calculated kinematics of oceanic plate motions in the Pacific. The direct geological data on the structural–lithologic parageneses, stratigraphy, and compositions of the ZH rocks (see [2, 4] and others) indicate an earlier (135 Ma ago) change of the mentioned regime at the eastern continental margin of Eurasia. The direct calculations of the motion rates for the studied ZH blocks (see above) agree with the calculated motion rates for the Izanagi Plate along the Eurasian continental margin in the second half of the Early Cretaceous and in the Late Cretaceous.

Fig. 6.
figure 6

Comparison between kinematic parameters of the Izanagi Plate in the Cretaceous based on different models. Arbitrary notes: (1) model from [30]; (2) model from [36]. Kinematic parameters are calculated for the Honshu Island coordinates (40° N, 140° E).

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We think that the time of change in the geodynamic regime and the motion rates of particular blocks at the eastern continental margin of Eurasia in the Cretaceous need to be specified more precisely. This can be done through (1) exact dating of the key objects, whose geodynamic nature is reliably determined, and (2) improvement in determination of the directions of the ancient magnetization components in these objects.

The results obtained in the present work agree with the earlier published data on the existence of large-amplitude sinistral strike-slips at the eastern margin of Eurasia in the Cretaceous (e.g., [2, 4, 18, 19, 22, 23] and others). In particular, according to [2, 4], the fragments of the Zhuravlevka–Amurian terrane formed and were accreted to the continent under the setting of sinistral strike-slip dislocations related to the sliding of the Izanagi oceanic plate along the transform continental boundary.

It is worth noting that the calculated paleolatitudes (10°–18° N) of formation of the studied Valanginian rocks (Komsomolsk Series) are comparable to the paleolatitudes (4° S to 11° N), at which the Berriasian–Valanginian basalts of the Rozhdestvenskaya Fm. [26] formed (these basalts are part of the Hokkaido–Sakhalin branch of the Sikhote Alin–North Sakhalin orogenic belt).

CONCLUSIONS

The results of petrochemical studies of sedimentary rocks from two formations (Gorinskaya and Pionerskaya) of the Komsomolsk Series, collected in the northernmost part of the Zhuravlevka–Amurian terrane, are consistent with the data obtained earlier [2, 4, 22, 23] and indicate that the studied rocks formed under the setting of a syn-shift turbidite basin at the transform boundary of the continent–ocean type, where rock fragments of close (but not identical) composition mixed.

Resulting from our paleomagnetic studies, the ancient “prefolding” characteristic magnetization component has been revealed in the sandstones of the Pionerskaya Fm., Komsomolsk Series; based on this component, the coordinates of the paleomagnetic pole and the paleolatitudes at which the studied rocks formed have been calculated. The Valanginian sandstones of the Pionerskaya Fm., which are the part of the Zhuravlevka–Amurian syn-shift turbidite basin, formed at near-equatorial latitudes (10°–18° N) near the continent–ocean boundary. In the time interval of 133–95 Ma ago, the block hosting the studied rocks underwent northward drift (translation along the continental margin) by more than 4000 km. Notably, the mean motion rate could have been either 10–13 cm/yr in the case of the earlier (135 Ma ago) change of a subduction geodynamic setting to a transform one, or up to 20 cm/yr in the case of a later change (120–115 Ma ago).