Middle paleozoic segment of the apparent polar wander path from the Siberian platform: New paleomagnetic evidence for the Silurian of the Nyuya-Berezovskii facial province

The paper presents results derived from study of the Silurian of the Nyuya-Berezovskii facial province. Variegated sedimentary rocks of the Meutian and Kurungian series (Llandoverian, Wenlockian, and lower Ludlovian) are studied. Detailed thermal demagnetizations of the collections revealed two stable magnetization components; one of them (Ds = 193.8, Is = 19.2; k = 10.7, α₉₅ = 6.1) is bipolar and is likely to have formed during or shortly after the rock formation, i.e., in the interval from the Early Silurian to the beginning of the Late Silurian. The second component is unipolar and apparently metachronous, and its formation time can be bounded by the latest Early to the Middle Devonian. Based on the paleomagnetic results of this study, paleolatitudes and kinematics of Siberia are estimated for the Middle Paleozoic. The inferred paleomagnetic poles provide additional constraints on the Middle Paleozoic segment of the apparent polar wander path from the Siberian platform.     

Refined δ<Superscript>13</Superscript>С trend of the Dal’nyaya Taiga series of the Ura uplift (Vendian,southern part of Middle Siberia)

New data were obtained on δ¹³С_carb and δ¹⁸O variations in the sequence of deposits of the Dal’nyaya Taiga series at the western and eastern flanks of the Ura anticline. The summary δ¹³С curve was plotted in view of the correlation of sequence–stratigraphic data of the basin analysis. A series of positive anomalies was found within the succession. Alternatives for global chemostratigraphic correlation of the Dal’nyaya Taiga series of the Ura uplift were considered.     

Systematics of Paleomagnetic Directions from Early–Middle Devonian Rocks of Minusa Troughs: New Data and Old Problems

Izvestiya, Physics of the Solid Earth - Paleomagnetic results from numerous Early–Middle Devonian volcanic sequences of the Minusa trough, southern Siberia, are presented. The analysis of...     

The first magnetostratigraphic data on the stratotype of the Lopata Formation,Northeastern Yenisei Ridge: Problems of its age and paleogeography of the Siberian Platform at the Proterozoic–Phanerozoic boundary

New paleomagnetic and magnetostratigraphic data are presented for the stratotype of the Upper Riphean Lopata Formation (Teya River, Yenisei Ridge). The paleomagnetic pole calculated is significantly distinct from the Phanerozoic and Riphean poles of the Siberian Platform and is similar to the Late Vendian–Early Cambrian poles of the Madagascar Group. The stratigraphic range studied is characterized by an anomalously high frequency of geomagnetic inversions (15 zones of magnetic polarity), which is comparable with the inversion frequency of the Late Vendian sections of Baltica. These data, along with previous paleontological findings, indicate an age of the Lopata Formation of 555–540 Ma.     

First U-Pb age of detrital zircons from sandstones of the Upper Emsian Takaty formation of the Western Urals with regard to the problem of primary sources of the Uralian diamond placers

Several alternative points of view currently exist on the origin of the primary sources of diamonds from the Cenozoic Western Urals placers. Some researchers suppose that their economic diamond resource potential is related to diamonds from tuffisitic facies of the mantle kimberlites-lamproites or impact structures. Other researchers suggest that diamonds originated from the eroded sandstones of the Upper Emsian Takaty Formation of the Lower Devonian, which represents ancient (fossil) placers or intermediate reservoirs. It is assumed that these reservoirs collected diamonds from worn kimberlite bodies, which were located in the Urals or on the East European platform (EEP). This paper presents the first U-Pb (LA-ICP-MS) age of detrital zircons from quartz sandstones of the Takaty Formation, which spans a range from 1857.5 ± 53.8 to 3054.0 ± 48.0 Ma. The absence of detrital zircons younger than 1.86 Ga excludes that the structural complexes of the Uralian, Fennoscandian, and Sarmatian EEP parts were the provenance areas that supplied the clastic material to the sedimentary basin, which accumulated the Takaty Formation. The similar age of our zircons and ancient crystalline complexes of the Volga-Uralian EEP part allows consideration that it was a single provenance area. If we assume that the diamond resource potential of the Western Urals is completely or partly related to the ancient diamond placers from the Takaty Formation, then the intermediate diamond reservoirs from its structure originated due to redeposition of destruction products of primary diamond-bearing rocks of the Volga-Uralia area. Thus, within the Volga-Uralian part of the EEP basement, we may expect identification of a previously unknown stage of kimberlite formation, which is significantly older than that responsible for the diamond resource potential of the Arkhangel’sk province.     

Validity of paleomagnetic poles and principles of constructing their wander paths: A case study of the East European platform

Methods of selecting paleomagnetic data for the construction of apparent polar wander paths (APWPs) are analyzed. It is shown that the existing criteria of reliability of paleomagnetic data cannot be regarded as evidence for their validity. In other words, no unambiguous dependence exists between the reliability and the closeness of paleomagnetic poles to a hypothetical region crossed by the reliable APWP. A new approach to the construction of paleomagnetic APWPs based on simple principles (principle of space and principle of time) is proposed. Using a numerical implementation of this algorithm, three stable clusters were determined (L _p = 164, F _p = 43; L _p = 144, F _p = 13; and L _p = 170, F _p = ?2); the respective maximum estimates of their ages are 248–251, 345, and 385 Ma. These clusters can be regarded as reliable paleomagnetic poles in the Paleozoic of the East European platform.     

Primary Data on U/Pb-Isotope Ages and Lu/Hf-Isotope Geochemical Systematization of Detrital Zircons from the Lopatinskii Formation (Vendian–Cambrian Transition Levels) and the Tectonic Nature of Teya–Chapa Depression (Northeastern Yenisei Ridge)

The main results are presented on U/Pb-isotope dating of 100 detrital zircons and, selectively, on the Lu/Hf-isotope system of 43 grains from sandstones of the Lopatinskii formation (the lower stratigraphic level of the Chingasan group). Ages from 896 ± 51 to 2925 ± 38 Ma were obtained with a pronounced maximum of ~1890 Ma in the curve of probability density, along with ε_Hf estimates from +8.4 to–15.1, which allow one to throw doubt upon the molasse nature of the Lopatinskii formation.     

Paleomagnetic data for Siberia and Baltica in the context of testing some geodynamic models of the formation of the Central Asian Mobile Belt

The synthesis of the paleomagnetic data for the Siberian (Siberia) and East European (Baltica) platforms shows that since the Early Paleozoic they could have experienced coherent movements as a part of consolidated continental agglomeration (a composite continent), which also includes the Arctida continent. Based on the paleomagnetic data, the relative positions of the Siberia and Baltica during the Ordovician is reconstructed, and a series of paleogeographical reconstructions describing the drift of the composite continent is suggested. The results of the lithologic–facial analysis of the sedimentation settings within the Ordovician basins of the Siberian and East European platforms and paleoclimatic markers are consistent with the suggested configuration and paleogeographical position of the composite continent. The suggested reconstructions and the ages of detrital zircons from the Early Paleozoic complexes of the platform margins and some objects of the Central Asian Mobile Belt (CAMB) reasonably well agree with the hypothesis (Sengör et al., 1993) which interprets the formation of the structure of CAMB Paleozoides as a result of the evolution of the island arc stretching along the margins of Siberia and Baltica.     

Systematics of Early Cambrian Paleomagnetic Directions from the Northern and Eastern Regions of the Siberian Platform and the Problem of an Anomalous Geomagnetic Field in the Time Vicinity of the Proterozoic–Phanerozoic Boundary

Representative paleomagnetic collections of Lower Cambrian rocks from the northern and eastern regions of the Siberian platform are studied. New evidence demonstrating the anomalous character of the paleomagnetic record in these rocks is obtained. These data confidently support the hypothesis (Pavlov et al., 2004) that in the substantial part of the Lower Cambrian section of the Siberian platform there are two stable high-temperature magnetization components having significantly different directions, each of which is eligible for being a primary component that was formed, at the latest, in the Early Cambrian. The analysis of the world’s paleomagnetic data for this interval of the geological history shows that the peculiarities observed in Siberia in the paleomagnetic record for the Precambrian–Phanerozoic boundary are global, inconsistent with the traditional notion of a paleomagnetic record as reflecting the predominant axial dipole component of the geomagnetic field, and necessitates the assumption that the geomagnetic field at the Proterozoic–Phanerozoic boundary (Ediacaran–Lower Cambrian) substantially differed from the field of most of the other geological epochs. In order to explain the observed paleomagnetic record, we propose a hypothesis suggesting that the geomagnetic field at the Precambrian–Cambrian boundary had an anomalous character. This field was characterized by the presence of two alternating quasi-stable generation regimes. According to our hypothesis, the magnetic field at the Precambrian–Cambrian boundary can be described by the alternation of long periods dominated by an axial, mainly monopolar dipole field and relatively short epochs, lasting a few hundred kA, with the prevalence of the near-equatorial or midlatitude dipole. The proposed hypothesis agrees with the data obtained from studies of the transitional fields of Paleozoic reversals (Khramov and Iosifidi, 2012) and with the results of geodynamo numerical simulations (Aubert and Wicht, 2004; Glatzmayer and Olson, 2005; Gissinger et al., 2012).