Diagenetic stages of oil-saturated sandstones of the pashyisky horizon at the Romashkinskoye oil field

It was identified three stages of reservoir rock formation of the Pashyisky horizon of the Frasnian stage of the Upper Devonian at the Romashkinskoye field, based on optical microscopic studies. The first stage, associated with clastic deposits sedimentation and marked by clastic grains dense structural packing formation, close to cubic. The second diagenetic stage of quartz sandstones is associated with the subsidence stage of sediments into the burial zone. During this period were actively proceeding the processes of grains mechanical deformation, blastesis of quartz clasts, the formation of siderite fragments, and fibrous chalcedony, partially metasomatic replacing clay layers in sandstones. The third diagenetic stage in quartz sandstones is associated with the migration of underground gas-water solutions. Analysis of the transformation degree of the Pashyisky horizon quartz sandstones at different areas of the Romashkinskoye field revealed the relationship between the intensity of secondary diagenetic processes and the degree of rocks oil saturation. Keywords: pashyisky horizon; oil; sandstone; reservoir; diagenesis.

IDENTIFICATION OF INHOMOGENEOUS LAYERS AND RESERVOIR LENSES IN TERRIGENOUS DEPOSITS

The possibilities of localizing residual oil reserves in depleted deposits of Tatarstan oilfield analyze in the article. The object of the study is the Pashian deposits of the Frasnian stage, Upper Devonian of the Almetyevskaya area, Romashkino oilfield. Possibilities of bypassed oil searching are considered. Sedimentation and heterogeneity of strata in the terrigenous Devonian sediments within the study area are analyzed in the paper. The analysis was carried out on the basis of well logging data. A detailed correlation of strata has been carried out, and members have been identified according to the rhythm of the layers’ occurrence in the Pashian horizon. The distribution of reservoirs and seals was studied based on the results of the detailed correlation. The analysis is based on a systematic analysis of the research object, which made it possible to consider the problem from different sides. The analysis of structural surfaces, maps of total and oil-saturated thicknesses, porosity, oil saturation, net-to-gross content and dissection along the upper and lower Pashian deposits was carried out. The influence of the structural factor on the reservoir properties of the formations is analyzed. The analysis made it possible to assess the heterogeneity of reservoirs in area and section and to predict the bypassed oil reserves localization.

Upper Devonian (Frasnian stage) of the north-western part of the Russian Platform: paleomagnetic data

Paleomagnetic determinations for the Devonian strata of the Main Devonian Field, available in the international paleomagnetic data base, do not make it possible to construct both detailed magnetostratigraphic scales and reliable trajectories of the apparent polar wander path of the paleomagnetic pole. This is primarily due to the insufficient amount of data that determine modern reliability criteria. Obtaining more complete series of reliable paleomagnetic determinations is one of the important tasks of paleomagnetic studies. The paper presents new paleomagnetic determinations from a collection of rocks of the Frasnian stage of the Upper Devonian (Ilmen and Bureg Beds of the Semiluky Formation), sampled on the southern shore of Lake Ilmen, east of the village. Korostyn in 2009. Magnetomineralogical studies were carried out to determine the magnetic minerals of carriers of natural remanent magnetization. Three characteristic components of natural remanent magnetization have been identified. Two components correspond to the Late Paleozoic magnetization reversal (in the Carboniferous and Permian times). The third, bipolar component of the Frasnian age passes the reverse polarity test of the geomagnetic field.. The obtained position of the paleomagnetic pole by the bipolar component of the natural remanent magnetization is consistent with the available data on the section of the Late Upper Devonian of the Main Devonian Field.

Definition of Foraminiferal Zones in the Famennian Stage (upper Devonian) of Tajikistan

Seven foraminiferal zones [Parathurammina dagmarae–Saltovskajina scitula–Neoarchaesphaera, Septaglomospiranella primaeva, Quasiendothyra (Eoquasiendothyra) bella, Q. (Eoendothyra) communis, Q. (E.) regularis, Q. (Q.) kobeitusana–Endoglomospiranella imminuta, and Q. (Q.) konensis–End. Nigra] have been identified from Famennian Stage carbonate sections in Tajikistan and compared to foraminiferal sequences from the Franco-Belgian Basin, the Russian part of the Eastern European Platform, the Ural Mountains (Russia), and Kyrgyzstan. The lower Famennian boundary is marked by the rapid extinction of all Frasnian Stage multicameral forms, which are replaced by a complex of single-chambered foraminifers of the P. dagmarae–S. scitula–Neoarchaesphaera Zone. This boundary practically coincides with the base of the middle Palmatolepis triangularis conodont zone. The upper Famennian boundary is recognized by the sharp change from endothyroid foraminifers of the Quasiendothyra konensis–Endoglomospiranella nigra Zone to a complex of simple mono- and bilocular forms of the Carboniferous Bisphaera malevkensis–Earlandia minima Zone. This boundary in the most intensely studied section at Shishkat is located 16 cm below the boundary of the Siphonodella praesulcata and S. sulcata conodont zones.

Comparison of the Domanic outcrops in Volga-Ural and Timan-Pechora basins

Domanic (and domanicoid) deposits are in a great interest of researchers and oil companies, since they possess authigenic oil and gas content. The article presents the results of study outcrops in the Volga-Ural and Timan-Pechora basins. The stratigraphic interval included sediments from the Middle Frasnian stage of the Upper Devonian to the Turnasian stage of the Lower Carboniferous. The main types of rocks were characterized by microscopic examination of thin sections and geochemical parameters of organic matter. It is shown that the domanic deposits of the Timan-Pechora basin are similar in structure and lithological composition to the deposits of the Volga-Ural Basin. The upper part of the domanic section is distinguished by the predominance of the carbonate-siliceous type of rocks over the kerogen mixed varieties. According to the geochemical parameters, the organic matter in the rocks of the sheltered deposits of the Volga-Ural and Timan-Pechora basins belongs to type II, but on the outcrops of the Volga-Ural region, the organic matter of the high-carbon sequence is more mature than on the outcrops of Timan-Pechora basin.

C isotopic variations in the lower–middle Frasnian (lower Upper Devonian) of the Rudny Altai

We conducted isotope–geochemical studies of the Upper Devonian of the Rudny Altai. Whole-rock carbon isotope analyses of the studied section represented by carbonate fore-reef facies reveal a negative excursion at the base of punctata Zone. When compared to conodont biofacies turnovers and the Upper Devonian events chart, the new data have demonstrated a synchronism between the negative excursion and the coeval decline in conodont biodiversity corresponding to the Middlesex anoxic event of the Frasnian Stage of the Upper Devonian.

Revision of the hydroid Plumalina Hall, 1858 in the Silurian and Devonian of New York

The feather-shaped Plumalina Hall, 1858 is revised on the basis of new and reexamined specimens from New York. Previously described from Givetian through Famennian deposits, a single compression of P. tenera n. sp. from the Rochester Shale extends the range into the Wenlock, and provides new information regarding Plumalina's biology. We assess the utility of morphologic characters in diagnoses of taxa, and present the first quantitative analysis of fossil hydroids to distinguish P. brevis n. sp. (Frasnian) from other Devonian species.Plumalina has been compared to plants, graptolites, and octocorals. Some interpretations have proposed affinities among hydrozoans based on colony form and the presence of putative polyp bases. Our analysis shows that, like extant thecate hydrozoans, Plumalina had a delicate, chitinous hydrocaulus with weakly articulated hydrocladia. An assemblage of in situ specimens, steeply inclined relative to the bedding plane in an Ithaca Formation (Frasnian Stage) turbidite, indicates that Devonian species produced sessile, erect colonies attached to a hard substrate, comparable to extant hydroids that feed in currents. Morphometric comparisons between putative Plumalina polyp bases and polyp bases of modern analogues reveal similarities to hydroids in the superfamily Plumularioidea McCrady, 1859. Plumalina is the most abundant fossil hydroid so far reported, and is pertinent to interpretations of the hydrozoan record.

Extent and duration of marine anoxia during the Frasnian–Famennian (Late Devonian) mass extinction in Poland, Germany, Austria and France

The intensity and extent of anoxia during the two Kellwasser anoxic events has been investigated in a range of European localities using a multidisciplinary approach (pyrite framboid assay, gamma-ray spectrometry and sediment fabric analysis). The results reveal that the development of the Lower Kellwasser Horizon in the early Late rhenana Zone (Frasnian Stage) in German type sections does not always coincide with anoxic events elsewhere in Europe and, in some locations, seafloor oxygenation improves during this interval. Thus, this anoxic event is not universally developed. In contrast, the Upper Kellwasser Horizon, developed in the Late linguiformis Zone (Frasnian Stage) in Germany correlates with a European-wide anoxic event that is manifest as an intensification of anoxia in basinal locations to the point that stable euxinic conditions were developed (for example, in the basins of the Holy Cross Mountains, Poland). The interval also saw the spread of dysoxic waters into very shallow water (for instance, reefal) locations, and it seems reasonable to link the contemporaneous demise of many marine taxa to this phase of intense and widespread anoxia. In basinal locations, euxinic conditions persisted into the earliest Famennian with little change of depositional conditions. Only in the continental margin location of Austria was anoxia not developed at any time in the Late Devonian. Consequently it appears that the Upper Kellwasser anoxic event was an epicontinental seaway phenomenon, caused by the upward expansion of anoxia from deep basinal locales rather than an ‘oceanic’ anoxic event that has spilled laterally into epicontinental settings.

Shape Analysis of Frasnian Species of the Late Devonian Conodont Genus Palmatolepis

Multielement taxonomy and shape analysis have led to substantial revisions in the taxonomic concepts of 13 Frasnian species of Palmatolepis, which previously have been based largely on visual discrimination of the Pa elements. Septimembrate apparatuses have been recognized in three species and diagnostic Pb elements are associated with the Pa elements of eight others. The multielement reconstructions thus derived provide the a priori classification that is tested by the canonical variate analysis of the outlines of the Pa elements. The outlines are digitized from a TV image and quantified by calculating mean tangent angles within a specified number of intervals between landmarks. The mean tangent angles for each interval are the variables used in the canonical variate analysis. In a series of comparisons limited to three species each, all 13 species separate into isolated clusters that are completely congruent with the a priori groups based, with two exceptions, on multielement taxonomy. Thus, shape analysis provides a rigorous separation of closely similar species that have been difficult to distinguish by visual discrimination of the Pa elements. Shape analysis is treated herein as an integral part of the systematic descriptions. Newly described species are P. bohemica, P. boogaardi, P. luscarensis, and P. muelleri. The new taxonomic concepts lead to significant revisions in the biostratigraphic ranges of a number of species of Palmatolepis involved in the zonation and graphic correlation of the Frasnian Stage.