Major episodes of geologic history of Isidis Planitia on Mars

We have mapped the area of Isidis Planitia (1–27°N, 75–103°E) in order to assess the geologic history of this region using modern data sets such as MOLA topography and the high-resolution images provided by the HRSC, CTX, and HiRISE cameras. Results of our mapping show that the geologic history of Isidis Planitia consists of three principal episodes. (1) Impact dominated episode (Noachian, until ～3.8 Ga): During this time, the oldest materials in the study area were formed mostly by impact reworking and mass-wasting. Other processes (e.g., volcanism and fluvial/glacial activity) likely operated at this time but played a subordinate role. (2) An episode related to volcanic and fluvial/glacial activities (late Noachian–early Amazonian, ～3.8–2.8 Ga): Volcanism appears as the most important process at the beginning of this episode (～3.8–3.5 Ga) and was responsible for the formation of a large circum-Isidis volcanic province by the early Hesperian epoch. Volcanic materials covered large portions of the Isidis rim, almost completely buried the previous crater record on the floor of the Isidis basin, and probably were the major contributors to the filling of the basin. Fluvial/glacial processes prevailed closer to the end of the episode (early Hesperian–early Amazonian, ～3.5–2.8 Ga) and were responsible for widespread resurfacing in the Isidis Planitia region, mostly at ～3.1–3.4 Ga. Glaciers and/or ice sheets probably resulted in a massive glaciation of the rim and the floor of the Isidis basin. The total volume of material eroded from the Isidis rim by glacial and fluvial activity is estimated to be about 35,000–50,000 km³, which is equivalent to a composite layer about 40–60 m thick on entire floor of the basin. More important, however, is that the eroded materials were likely saturated with ice/water and could form wet deposits on the floor. (3) Wind-dominated episode (since early Amazonian, ～2.8 Ga): Wind activity dominated the later geologic history of Isidis Planitia but resulted only in minor modification of the surface.     

Coronal Mass Ejections and the Index of Effective Solar Multipole

The paper considers the relationship between the cyclic variations in the velocity of coronal mass ejections (CME) and the large-scale magnetic field structure (LSMF) in cycles 21??C?23. To characterize a typical size of the LSMF structure, we have used the index of the effective solar multipole (ESMI). The cyclic behavior of the CME occurrence rate and velocity proved to be similar to that of ESMI. The hysteresis observed in variations of the CME maximum velocity is interpreted as a manifestation of different contributions from the two field structures (local and global magnetic fields) in different phases of the 11-year activity cycle. It is suggested that cyclic variations in the maximum velocity of coronal mass ejections are due to different conditions for the formation of the complexes of active regions connected by coronal arch systems, which are the main source of high-velocity CMEs.     

Carbonate–Alkaline Metasomatites of the Peschanoe Uranium Occur (Western Baikal Region): Mineral-Geochemical and Isotope-Geochemical Characteristics

Geology of Ore Deposits - Abstract—Metasomatic alterations in cataclased granites of the Primorsky Complex PR1 in the Southern Siberian Craton are represented by albitization and...     

Vertical Mixing in the Active Layer of the Black Sea

The averaged parameters of vertical turbulent mixing in the active layer of the Black Sea are discussed according to small-scale synchronous measurements of the profiles of current velocity and conditional density.     

A Tidal Semidiurnal Harmonic in the Black Sea Dynamics according to Numerical Modeling Results

The parameters of barotropic and baroclinic oscillations in the subinertial range have been obtained by numerical simulations of the Black Sea circulation using a model developed at the Marchuk Institute of Numerical Mathematics, Russian Academy of Sciences. The structures and periods of barotropic and baroclinic seiches are in good agreement with the known theoretical predictions and results of numerical modeling of seiches obtained for the Black Sea subbasins.     

High-Pressure Tectonites of Yenisei Ridge as a Result of Ductile Shear Fault Deformations in the Suture Zone

The occurrences of high-pressure tectonites localized in the tectonic suture zone of the Cis-Yenisei regional shear zone (CYRSZ) separated the cratonic and oceanic island-arc terranes were distinguished for the first time at the western margin of the Siberian Craton. Tectonites are characterized by high pressures (up to 15 kbar), which exceed significantly the background P–T parameters of regional metamorphism. The generation of tectonic overpressure is induced by rapid deformations along ductile shear zones, which is consistent with the numerical simulation results and thermodynamic calculations. These data confirm the important role of tectonic stress as an effective thermodynamic factor of metamorphic transformations in suture zones of the lithospheric crust.

     

Numerical Analysis of Surge Phenomena,Currents, and Pollution Transport in the Sea of Azov

Doklady Earth Sciences - Dynamic processes and features of transformation of pollution in the Sea of Azov, caused by the action of a real wind and atmospheric pressure in the presence of stationary...     

First solar-terrestrial storms in cycle 24 of solar activity

The dynamics of the occurrence frequency and intensity of solar-terrestrial storms at the current solar cycle (cycle 24) onset (2007–2011) is considered. The storms were identified based on the moving semidiurnal average planetary index of activity, beginning from Ap* ≥ 30. It has been established that 12, 11, and 2 only moderate storms (Ap* = 30–49), which were randomly distributed during the year, were successively observed in the first three years. After a prolonged period without storms (August 2009–March 2010), a series of storms with mixed or only moderate activity, which were regularly distributed over the seasons (ecliptic longitudes) from April to August, started appearing beginning from the storm of April 1–6, 2010. This period followed the tendency toward the transformation of the slowly rotating four-sector structure (Large-Scale Open Solar Magnetic Field, LOSMF) from the two-sector structure (March 2010). The first storm in the new cycle (April 2010) was very powerful and originated owing to the successive destabilization of the complex of two magnetic filamentary ropes. It is interesting that the origination of a new LOSMF sector was associated with a 27-day interval, during which thermal neutrons appeared at Kamchatka and volcanoes erupted in Iceland, and a strong earthquake occurred in March 2011 in Japan when the Earth was located precisely in this sector.     

Transformation of particulate organic matter at the water-bottom boundary in the Russian Arctic seas: Evidence from isotope and radioisotope data

Complex biogeochemical studies including the determination of isotopic composition of C_org in both suspended particulate matter and surface horizon (0–1 cm) of sediments (more than 260 determinations of δ¹³C-C_org) were carried out for five Arctic shelf seas: White, Barents, Kara, East Siberian, and Chukchi. The aim of this study is to elucidate causes that change the isotopic composition of particulate organic carbon at the water-sediment boundary. It is shown that the isotopic composition of C_org in sediments from seas with a high river runoff (White, Kara, and East Siberian) does not inherit the isotopic composition of C_org in particles precipitating from the water column, but is enriched in heavy ¹³C. Seas with a low river runoff (Barents and Chukchi) show insignificant difference between the value of δ¹³C-C_org in both suspended load and sediment because of a low content of the isotopically light allochthonous organic matter (OM) in particulates. Complex biogeochemical studies with radioisotope tracers (¹⁴CO₂, ³⁵S, and ¹⁴CH₄) revealed the existence of specific microbial filter formed from heterotrophic and autotrophic organisms at the water-sediment boundary. This filter prevents the mass influx of products of OM decomposition into water column, as well as reduces the influx of a part of OM contained in the suspended particulate matter from water into sediment.