Seismic stratigraphy of sedimentary cover in the Podvodnikov Basin and North Chukchi trough

The multichannel seismic reflection data (MCS data) obtained in the Arktika-2014 expedition revealed the essential fact that must be taken into account by the tectonic model of the Central Arctic region. The Brookian, Lower Cretaceous, and Upper Jurassic unconformities are continuously traced from the North Chukchi offshore trough into the Podvodnikov Basin, indicating that the depocenter in the latter accumulated both Cretaceous sedimentary sequences and Early–Middle Mesozoic ones.     

Thermotomographic model and oil-and-gas forecasting for the sedimentary cover of the Laptev Sea shelf

2D and 3D geotemperature models of the sedimentary cover within the Laptev Sea shelf have been calculated. The presence of several “thermal domes” (zones of uplifted isotherms) has been found. Based on analogous sedimentary basins with domes, which correlate to the location of hydrocarbon deposits, the forecasting has been made that the Ust-Lena graben and Omoloi trough are the most promising areas for oil-and-gas prospecting.     

Sedimentogenesis in the Amundsen Basin from geophysical data and drilling results on the Lomonosov Ridge

Studies in the Amundsen Basin have revealed six seismostratigraphic complexes (SSCs) in this region. The horizons bounding these complexes were dated by identifying the linear magnetic anomalies. The recognized SSCs are correlated with the seismostratigraphic and lithostratigraphic units of the Lomonosov Ridge. Based on these correlations, the lithological composition of SSCs in the Amundsen Basin is suggested. The formation of SSC2 is supposed to be due to the diagenetic processes associated with the transition of opal-A to opal-CT. It is found that, generally, the rate of sedimentation in the Amundsen Basin has consistently decreased since the beginning of its formation. However, in the Chattian time, the global regression resulted in a sharp increase in the rate of sedimentation in the basin. Arguments in favor of the duration of the Middle Cenozoic sedimentary hiatus on the Lomonosov Ridge reduced to 16.3 Ma are presented. It is supposed that the decrease in the intensity of oceanic crustal accretion in the Eurasian Basin, which is identified by the slowdown in the rate of its opening in the interval from 46 to 20–23 Ma might have resulted in a gradual sea level falling in the Arctic Ocean isolated from the World Ocean. This fact probably accounts for the Lomonosov Ridge having remained in subaerial conditions over the period from 36.7 to 20.4 Ma.     

Gas-Geochemical Anomalies of Hydrocarbon Gases in the Bottom Sediments of the Lomonosov Ridge and Podvodnikov Basin of the Arctic Ocean

Doklady Earth Sciences - This paper reports new data on the composition of hydrocarbon gases in bottom sediments of the Laptev–East Siberian marginal shelf transition zone, the continental...     

鄂尔多斯盆地基底结构及早期沉积盖层演化

鄂尔多斯盆地基底主要形成于太古宙—古元古代,岩石组成极为复杂,大多经历了较强的区域变质作用,变质程度一般达到了(高)角闪岩相—麻粒岩相,属变质程度较深的区域变质岩系,主要是各种片岩、片麻岩及变粒岩、石英岩、大理石及花岗片麻岩等;基底结构具有较为明显的分区特征,可划分为北部、西北部及中南部三个大区,走向总体以北东向为主;从演化过程来看,鄂尔多斯盆地基底是华北克拉通形成过程中的太古宙微陆块之一,古元古代末可能是其与华北拼合为一体的关键时期。早期沉积盖层主要经历了长城纪陆内裂陷、蓟县纪边部沉降、青白口纪—南华纪整体隆升和震旦纪边缘拗陷4个演化阶段,沉积环境总体以海相为主,晚期局部具陆相特征,不同时期的沉积物特征有较大差异,可能主要受构造、气候环境的共同制约;早期沉积盖层整体上受基底结构和构造控制明显,越早期影响越大;盆地西南边缘一直是最活跃的构造沉降区,基底构造所处位置特殊可能是其最主要的原因。     

The deep-seated crustal structure in the western part of the Black Sea and adjacent areas: Seismic reflection measurement

In recent years the northwestern Black Sea has been investigated by a great number of geophysical methods. Charts of the M discontinuity and (isopachous) charts of the “granitic”, the “basaltic”, the Paleozoic, the Jurassic-Triassic, the Upper and Lower Cretaceous and the Eocene layers were plotted based on the results of the combined data of these investigations together with associated drilling data. The data for different velocity levels confirms the concept of layered-block structure of the crust, where large blocks are divided by deep faults penetrating to the upper mantle. Sedimentation within each block is continuous while reverse fault zones, dividing the East European Platform with a crustal thickness of more than 40 km and the Scythian Platform with a crust of about 30 km thick, and the latter from the Black Sea depression with crust of about 20 km, are discontinuous. Therefore, one can speak of a continuous-discontinuous nature of the sedimentation.

An inverse relationship in thicknesses of the “granitic” and sedimentary layers has been established. In places of intensive sedimentation the thickness of the “granitic” layer is less than that within the stable unsagging blocks. On the whole the greater the thickness of “basaltic” layer, the greater is the crustal thickness.

The relationship between the main geological structures of the area should be sought in the nature of structure of these “granitic” and “basaltic” layers.     

Sedimentary cover of the Lomonosov Ridge: Stratigraphy,structure, deposition history,and ages of seismic facies units

Seismic and geological information on the Lomonosov Ridge is considered with reference to drilling data obtained during the ACEX-302 expedition. A new zonation proposed for the composite section of the ridge sedimentary cover and based on marine microfossils (silicoflagellates and dinocysts) from several boreholes is correlated with biostratigraphic zones of Paleogene sections in northern West Siberia. Principal stages of the Arctic basin development in the Aptian-Cenozoic are defined in onshore and Lomonosov Ridge sections. Synchronous formation of sedimentary sequences in the ridge, an element of the Arctic basin, shelves, and epicontinental seas is established for the period under consideration.     

Structural elements of the sedimentary cover in the Deryugin Basin of the Sea of Okhotsk

A map of the tectonic zoning of the sedimentary cover in the Deryugin Basin area was constructed based on the structural data. For this purpose, a structural-tectonic map of the sedimentary cover was compiled using CDP seismic reflection and gravimetry data. Depending on the size, spatial position, and orientation, the structural elements of different orders were grouped into tectonic systems. The latters were subdivided into structural zones consisting of higher order structural elements in the form of relative rises and troughs. The corresponding maps and schemes are also presented in this paper.     

Geological structure of the sedimentary cover and evaluation of the oil and gas potential of the Deryugin Basin (Sea of Okhotsk)

Results of interpretation of the seismic refraction survey in the southern part of the Deryugin Basin are presented. A geological-geophysical model was developed, and a scheme of the sedimentary cover evolution of the basin (Late Cretaceous-Pleistocene) is suggested. The data obtained indicate a high hydrocarbon potential comparable with that of the adjacent oil and gas-bearing shelf of northeastern Sakhalin.     

Dating and correlation of reference seismic horizons in the Laptev Sea Basin

Four seismic horizons (L1, L2, L3, and L4) were recognized in the Laptev Sea Basin. The seismic complexes that lie between the horizons were found and dated (125-55.8, 55.8-33.9, 33.9-5.3, and 5.3-0Ma). A Paleozoic carbonate plate exists in the southwestern Laptev Sea Basin below the L1 horizon. Rifting in the Laptev Sea Basin began shortly after the Verkhoyansk orogeny ended at about 125 Ma BP. The evolution of the Laptev Sea Basin is correlated with that of the Eurasian Basin and the climatic history of the region.     

Seismic crustal structure between the Transylvanian Basin and the Black Sea, Romania

In order to study the lithospheric structure in Romania a 450 km long WNW–ESE trending seismic refraction project was carried out in August/September 2001. It runs from the Transylvanian Basin across the East Carpathian Orogen and the Vrancea seismic region to the foreland areas with the very deep Neogene Focsani Basin and the North Dobrogea Orogen on the Black Sea. A total of ten shots with charge sizes 300–1500 kg were recorded by over 700 geophones. The data quality of the experiment was variable, depending primarily on charge size but also on local geological conditions. The data interpretation indicates a multi-layered structure with variable thicknesses and velocities. The sedimentary stack comprises up to 7 layers with seismic velocities of 2.0–5.9 km/s. It reaches a maximum thickness of about 22 km within the Focsani Basin area. The sedimentary succession is composed of (1) the Carpathian nappe pile, (2) the post-collisional Neogene Transylvanian Basin, which covers the local Late Cretaceous to Paleogene Tarnava Basin, (3) the Neogene Focsani Basin in the foredeep area, which covers autochthonous Mesozoic and Palaeozoic sedimentary rocks as well as a probably Permo-Triassic graben structure of the Moesian Platform, and (4) the Palaeozoic and Mesozoic rocks of the North Dobrogea Orogen. The underlying crystalline crust shows considerable thickness variations in total as well as in its individual subdivisions, which correlate well with the Tisza-Dacia, Moesian and North Dobrogea crustal blocks. The lateral velocity structure of these blocks along the seismic line remains constant with about 6.0 km/s along the basement top and 7.0 km/s above the Moho. The Tisza-Dacia block is about 33 to 37 km thick and shows low velocity zones in its uppermost 15 km, which are presumably due to basement thrusts imbricated with sedimentary successions related to the Carpathian Orogen. The crystalline crust of Moesia does not exceed 25 km and is covered by up to 22 km of sedimentary rocks. The North Dobrogea crust reaches a thickness of about 44 km and is probably composed of thick Eastern European crust overthrusted by a thin 1–2 km thick wedge of the North Dobrogea Orogen.     

Tectono-Geodynamic Settings in the Conjugation Zone of the Lomonosov Ridge,Eurasian Basin,and Eurasian Continental Margin

Geotectonics - Interpretational analysis of new seismic data allowed us to reconstruct the geodynamic settings that led to the formation of an ensemble of tectonic structural elements in the...     

Gas-Geochemical Parameters of Bottom Sediments in the Northern Part of the East Siberian Sea and Podvodnikov Basin of the Arctic Ocean

Doklady Earth Sciences - New data on the gas and chemical composition of bottom sediments of the marginal-shelf part of the East Siberian Sea, continental slope, and Podvodnikov Basin of the Arctic...     

Basin infilling in the southern-central part of the Sergipano Belt (NE Brazil) and implications for the evolution of Pan-African/Brasiliano cratons and Neoproterozoic sedimentary cover

The Neoproterozoic sedimentary cover deposited across the interface of several Pan-African/Brasiliano fold-thrust belts with their respective cratons is strongly similar and has been widely correlated throughout Gondwana. In particular, the upper part of the cratonic cover of the São Francisco Craton has been interpreted as a ring of foreland basin sediments. However, detailed studies carried out around the southern-central part of the Sergipano Belt (NE Brazil) and its interface with the northern margin of the São Francisco Craton demonstrate that: (1) sedimentation records the evolution of a passive continental margin and is divided into two cycles (I and II), each one comprising a basal siliciclastic megasequence overlain by a carbonate megasequence; (2) the cratonic cover comprises cycle I and part of the basal megasequence of cycle II; (3) all of these rocks spread continuously across the craton margin into the Sergipano Belt, where they occur around basement domes and are overlain by a metadiamictite formation and a metacarbonate formation that complete cycle II; and (4) basement and cover underwent the same Brasiliano (670–600 Ma) compressive deformation under sub-greenschist metamorphic conditions. These data deny the foreland basin model for the cratonic sediments to the south of the Sergipano Belt and, coupled with recent data on the evolution of other margins of the craton, indicate that the Neoproterozoic sedimentary cover derives from highs existing close to the centre of the ancient São Francisco Plate. This sedimentary cover was also influenced by highs of an Andean-type margin that evolved ca 900–640 Ma along the western side of the plate. Such evolution also applies to the Neoproterozoic cover of other cratons of the Pan-African/Brasiliano orogeny.     

Sedimentary cover and late Cenozoic history of the Okushiri Ridge (Sea of Japan)

A complex (petrographic, micropaleontological, and X-ray diffraction) investigation of the sedimentary cover on the northwestern slope of the Okushiri Ridge in the Sea of Japan revealed that its basal layers are of Oligocene age and composed of terrigenous silty-clayey sediments, which were deposited in coastalmarine environments with calm hydrodynamics and low sedimentation rates. The relative sea-level rise combined with regional tectonic processes at the early-middle Miocene transition resulted in widening and deepening of sea basins and accumulation of a thick diatomaceous-clayey sequence of middle-upper Miocene sediments. Tectonic activation in the Pliocene was responsible for development of the ridge and exhumation of rocks formerly occurring at depth of 500–1000 m.