Oceanic basins in prehistory of the evolution of the Arctic Ocean

During geodynamic reconstruction of the Late Mezozoic-Cenozoic evolution of the Arctic Ocean, a problem arises: did this ocean originate as a legacy structure of ancient basins, or did it evolve independently? Solution of this problem requires finding indicators of older oceanic basins within the limits of the Arctic Region. The Arctic Region has structural-material complexes of several ancient oceans, namely, Mesoproterozoic, Late Neoproterozoic, Paleozoic (Caledonian and Hercynian), Middle Paleozoic-Late Jurassic, and those of the Arctic Ocean, including the Late Jurassic-Early Cretaceous Canadian, the Late Cretaceous-Paleocene Podvodnikov-Makarov, and the Cenozoic Eurasian basins. The appearances of all these oceans were determined by a complex of global geodynamical factors, which were principally changed in time, and, as a result of this, location and configuration of newly opened oceans, as well as ones of adjacent continents, which varied from stage to stage. By the end of the Paleozoic, fragments of the crust corresponding to Precambrian and Caledonian oceans were transported during plate-tectonic motions from southern and near equatorial latitudes to moderately high and arctic ones, and, finally, became parts of the Pangea II supercontinent. The Arctic Ocean that appeared after the Pangea II breakup (being a part of the Atlantic Ocean) has no direct either genetic or spatial relation with more ancient oceans.     

Quantitative analysis of Phanerozoic sedimentation

This paper is the conclusion of many years of study of Phanerozoic sedimentation over the area of the present continents (without Antarctica). The compilation of the schematic lithological-paleogeographical maps for each section of the Phanerozoic systems (except the Quaternary) is taken as a basis for these studies; Ronov calculated areas of distribution and volumes of different groups of sedimentary and volcanogenic rocks within platforms and geosynclines, as well as changes in a mean rate of accumulation and intensity of volcanic activity.The volume of geosynclinal sediments of the whole of the Phanerozoic is 457 · 10⁶ km³. The volume of platformal sediments is 182 · 10⁶ km³.Our data confirm a periodic character in changes in the area, volume and rate of accumulation of sedimentary and volcanic deposits, concurrent with tectonic periodicity; the Hercynian and Alpine cycles being the most pronounced, the Caledonian weaker and the Salairian (Sardian) and Kimmerian cycles weaker still. The high rates of sedimentation and the high general intensity of volcanism are characteristic of the initial parts of tectonic cycles. The major transgressions and the peaks of carbonate accumulation fall in their middle parts. The high rates of sedimentation and the increase of clastic sediments corresponds to their final parts.Side by side with this cyclic character, our data reveal a certain time trend in the Phanerozoic changes under review. This is a general reduction of sea-covered area within the present continents and an increase of volume of sediments and of mean rates of subsidence. Since the changes within platforms and geosynclines have the same trend, they are obviously controlled by global processes. The global rhythm exists in spite of obviously uncoordinated movements of separate major blocks of the lithosphere, in particular of continental platforms. This is indicative of a global tendency predominating over regional ones.     

A model of a homogeneous isotropic turbulent flow and its application for the simulation of cloud drop tracks

Abstract

A model of a homogeneous isotropic turbulent flow is presented. The model provides different realizations of the random velocity field component with given correlation latitudinal and lateral functions and a spatial structure which obeys the Kolmogorov theory of homogeneous and isotropic turbulence. For the generation of the turbulent flow the structural function of the flow in the form suggested by Batchelor (Monin and Yaglom, 1975) was used. This function describes the spectrum of turbulence both in the viscous and inertial ranges. The isotropy and homogeneity of the velocity field of the model are demonstrated.

The model is aimed at simulating the ‘‘fine'’ features of drop's (aerosol particles') motion, such as the deviations of drops’ velocity from the velocity of the flow, detailed structures of drops’ tracks, related to drops’ (particles') inertia. The model is intended also for the purpose of studying cloud drops’ and aerosol particles’ motion and their diffusional spreading utilizing the Monte Carlo methods.

Some examples of drop tracks for drops of different size are presented. Drops’ tracks are very sophisticated, so that the relative position of drops falling initially from the same point can vary drastically. In some cases drops’ tracks diverge very quickly, in other cases all drops move within a turbulent eddy along nearly the same closed tracks, but with different speed. The concentration of drop tracks along isolated paths is found in spite of the existence of a large number of velocity harmonics. It is shown that drops (aerosol particles) tend to leave some areas of the turbulent flow apparently due to their inertia. These effects can possibly contribute to inhomogeneity of drops’ concentration in clouds at different spatial scales.     

Carbonaceous metalliferous sediments and oceanic anoxic events in the Earth’s Phanerozoic history

The oceanic anoxic events (OAE) intermittently occurring in the Earth’s Phanerozoic history left fingerprints in the geological record in the form of carbonaceous metalliferous sediments. The analysis of the available data on the S, Mo, Sr, Os, and Nd isotope compositions reveals that the role the volcanic factor was multiply higher during the accumulation of these sediments. The sediments maximally enriched in planktonogenic organic matter (up to 5% on average and up to 30% in separate layers) are widespread on continental margins and in adjacent onshore areas. On active margins, they are largely confined to the back parts of marginal seas, where they are characterized by lower organic matter concentrations (averaging approximately 2.5% and up to 10% in separated beds). The deposition of carbonaceous metalliferous sediments in the Phanerozoic associates with 16 oceanic anoxic events, which happened in different geodynamic settings with intensified ophiolitic, island-arc, and trappe volcanism. The underwater lava eruptions and hydrothermal solution discharges served as a triggering mechanism for the chemical, biological, sedimentological, and climatic processes that stimulated the development of anoxic environments in the ocean and the deposition of carbonaceous metalliferous sediments.     

Structural units of the central arctic and their relations to the mesozoic arctic plume

The integration of information obtained from onshore and offshore geological and geophysical research undertaken in the context of the International Polar Year has led to the following results. The continental crust is widespread in the Arctic not only beneath the shelves of polar seas in the framework of the Amerasia Basin but also in the Chukchi-Northwind, Lomonosov, and Mendeleev ridges; a combination of continental and oceanic crusts is inferred in the Alpha Ridge. The Amerasia Basin is not an indivisible element of the Arctic Ocean either in genetic or structural terms but consists of variously oriented basins different in age. The first, Mesozoic “minor ocean” of the Arctic Ocean—the Canada Basin—arose as a result of impact of the Arctic plume on the high-latitude region of Pangea. This inference is supported by the vast Central Arctic igneous province that comprises the Jurassic-Mid-Cretaceous within-plate and ocean-island basaltic and associated rocks. The rotational mechanism of opening of this basin is explained by the slant path of the plume head motion, which resulted in breaking-off and displacement of a fragment of Pangea. The effect of the Arctic plume was expressed during all stages of the opening of the Canada Basin and exerted effects on the adjacent part of the Eurasian continent during the formation of the Verkhoyansk-Chukotka tectonic domain. The Canada Basin was an element of the segmented system of Atlantic spreading ridges, while the Arctic plume that initiated its evolution was genetically related to the episodically acting African-Atlantic superplume. In comparison with the Pacific superplume, the low productivity of African-Atlantic lower mantle upwelling became the cause of slow and ultraslow spreading in the Atlantic and Arctic oceans and determined the passive character of their margins, including the Canada Basin.     

大地构造学和地球动力学现代问题——从板块构造学到全球动力学

６０年代板块构造概念的出现标志着地球科学革命性的进步。３０年来，我们获得的经验表明，现代板块构造在岩石圈和软流圈物性、三种板块运动形式、扩张和俯冲的均衡以及板块运动原因等都与经典板块构造有很大不同。同时，它仍有一些问题和缺陷。世纪交替之时，随着象地震层析成像等新技术的发展，有可能建立新的全球理论来取代板块构造。新理论应该包括整个固体地球，岩石圈是分层的，而且地球内部的对流准自动地进行。同时，地球层圈之间具有相互作用。还应该承认，构造圈（岩石圈＋软流圈，深至４００ｋｍ）中以板块构造为主，而在软流圈之下地幔柱构造起控制作用。在所有的上部层圈能够探测到抬升或下降过程中热—物质流之间的补偿。整个地球历史中，地球和其层圈的内生过程，包括板块构造和地幔柱构造相互作用的变化，具有旋回性和方向性。由此，地球体积呈脉动性变化是必然的。此外，还必须考虑宇宙因素对地球动力学的影响     

Development of the Verkhoyansk-Kolyma orogenic system as a result of interaction of adjacent continental and oceanic plates

The Mid-Cretaceous Verkhoyansk-Chukchi Tectonic Domain is characterized by fanlike diverging systems of tectonic sheets and imbricate thrusts verging to the two framing continents. The Verkhoyansk and New Siberian-Chukchi-Brooks Fold-Thrust systems of the deformed margins of the Siberian and Hyperborean-North American continents, respectively, adjoin the inner Verkhoyansk-Kolyma Collision System. The above fold-thrust systems include the Verkhoyansk and Colville foredeeps coeval with thrusting. The Verkhoyansk-Kolyma Fold-Nappe System is composed of Cambrian to Upper Jurassic oceanic, marginal-sea, and island-arc complexes and bounded by a collision suture consisting of the Kolyma Loop abutted on the South Anyui segment along a left-lateral strike-slip fault. The inner root zone and the outer zone of nappes overthrusting the adjacent continents are distinguished in the suture. Several levels of structural unconformities, olistostrome-molasse sequences, and zones of amphibolite-greenschist metamorphism coeval with thrusting correspond to particular stages in the evolution of the Verkhoyansk-Kolyma System. The Neoproterozoic and Early Paleozoic oceans closed during the Baikalian and Caledonian orogenies. The Alazeya-South Anyui-Angayucham ocean that evolved from the Devonian to the Late Jurassic was subject to gradual closure against the background of trilateral compression during convergence of the Siberian and Hyperborean-North American cratons and accretion and collision along the Pacific margin. The fold-nappe structure of the Verkhoyansk-Kolyma Orogen and the boundary collision suture were disturbed by left-lateral strike-slip faults during Mid-Cretaceous compression, and the South Anyui segment of the suture was displaced to the northwest along the strike-slip fault. The Mid-Cretaceous Orogeny at the Pacific margin gave rise to meridional compression of its back zone and latitudinal squashing of the Verkhoyansk-Kolyma Orogen with formation of the Kolyma and Kobuk looplike limitations.