No abstract

The Laptev Shelf in the eastern Siberian Arctic represents a rare tectonic setting 12 where an active oceanic spreading centre, the Gakkel Ridge, intersects a continental margin. 13 The North America-Eurasia plate boundary follows the Gakkel Ridge and passes into a 14 continental shelf; this has resulted in the development of a wide rift system that has been 15 active since the Late Cretaceous. The new long-offset seismic profiles provide a reliable basis 16 for deciphering the structural characteristics of this rift system. We use two new seismic 17 profiles, along with one acquired in the 1990s, to examine the crustal architecture of the rift 18 system. Our approach combines seismic interpretation, time to depth conversion of seismic 19 profiles and 2D gravity forward modelling. The obtained results indicate the presence of 20 hyperextended continental crust beneath the Ust' Lena Rift Basin and exhumed continental 21 mantle at the base of the syn-rift succession along the rift axis. The upper crust was removed 22 by brittle stretching, while the lower crust experienced extreme ductile thinning. Our results 23 show that continental crust can be eliminated in the course of rifting without a considerable 24 heat input from asthenospheric mantle.

Nonstructural type traps in the sedimentary cover of the northern side of the Dnieper-Donets depression are poorly studied by seismic methods due to many factors among which are the following: complicated geological structure and not so high quality of given data of geological-geophysical studies of last years. Identification of lithologically screened gas-saturated object has been demonstrated based on the studies of elastic dynamic characteristics by the methods of AVO-analysis and elastic seismic inversion. Acoustic and elastic properties have been analyzed in the wells with cross-dipole real and synthesized acoustics. Gas-saturated intervals have been identified based on the ratios VP /VS and acoustic impedance. According to AVO-studies within the northern side of DDD in the stratum of productive horizons of the moscovian horizon a positive answer has been obtained to the question «if AVO analysis works correctly in general within the limits of the northern side of DDD deposits». Determining factors that influence on the result during the application of AVO-analysis at the most part of gas condensate field of the northern side of DDD are effective thicknesses, depths of occurrence, lithology, poro-sity and quality of given seismic data and data from geophysical surveys of wells. Taking into account minor effective thicknesses, small values of porosity, significant depths of occurrence of productive layers typical for the northern side of DDD, the majority of gas-saturated intervals are not at all identified in the wave field by dynamic characteristics of seismic signal. All the seismic anomalies analyzed had effective thicknesses from 6 to 20 m. Within the limits of deposits of the northern side of DDD, AVO-anomalies of the 2nd class are modeled. Along with positive experience of identification of dynamically cont-rasting objects in the wave field limitations to use methods of AVO-analysis and elastic seismic inversion are generalized for the northern side shown in particular and the whole Dnieper-Donets depression.

The questions of the wise use and maintenance of the ecological state of the natural monuments of the Tomsk region, which are popular for recreation, are raised. The research was carried out on the example of Peschanoуe Lake on the left-bank terrace of the Tom River near Tomsk. The data on the state of the coastal zone of this lake are given.