Stable Isotopes Carbon C13 and Oxygen O18 as Indicators of Triassic Limestone Sedimentation Environment and Diagenesis

The results of researches of the stable isotopes, carbon 13C and oxygen 18O, measured in Triassic limestones of Opole Silesia in Poland were presented in this article. The study was carried out to obtain data for interpretation of the environment of these rocks formation. Moreover, it was possible to form the theory about diagenetic processes which influenced on the mineral composition of limestone and some of their carbonte phases. The results of study show a general differentiation of δ13C and δ18O contents in carbonate minerals. All δ18O values are less than 0 ‰. It indicates that the origin oxygen isotope composition could be probably reset by diagenesis. The crystallization temperatures of low-Mg calcite and high-Mg, calculated on the basis of δ18O values are greater than 25 oC. They are higher than typical for sea basin and are also not be related to the presence of hydrothermal solutions. The increased temperatures of calcites crystallization are related to diagenetic processes that took place after the deposition and burial of carbonate material. The preservation of high-Mg calcite, an ustable carbonate phase, which is usually trasformed into low-Mg calcite during diagenesis, is probably connected with the increased salinity of the sea basin in which studied limestones were formed.

VERTEBRATE TAPHONOMY OF TWO UPPER MIOCENE BONEBEDS IN WESTERN PROTO-AMAZONIA (SOLIMÕES FORMATION, BRAZIL): INSIGHTS FROM MACROVERTEBRATE AND MICROVERTEBRATE FOSSILS

ABSTRACT The Niterói and Talismã sites comprise two of the most important fossiliferous deposits of the Neogene in Brazil. After 30 years of research, these sites have revealed rich assemblages of vertebrates and provided a glimpse of the Amazonian fauna and environment during the Miocene. Despite this, detailed studies that attempt to explain the genesis of these bonebeds are still scarce and hamper more robust paleoenvironmental and paleoecological reconstructions. Here we provide the first in-depth taphonomic analysis for both locations. Sedimentological and taphonomic evidence suggest that the depositional environments of Niterói and Talismã were similarly represented by shallow and calm waters in lacustrine/swampy contexts. We propose that the accumulation of bones and teeth is the result of attritional (day-to-day) mortality of organisms of the local community in a low sedimentation environment. The thanatocoenosis was exposed to biostratinomic processes for longer periods of time, which explains the high disarticulation, disassociation, fragmentation and loss of skeletal elements. The almost absence of weathering indicates that the aquatic environment slowed down the organic degradation of bioclasts, while the rarity of abrasion shows a limited influence of hydraulic flows in transporting and remobilizing bioclasts. Thus, both sites preserve mostly autochthonous to parautochthonous bioclasts, with a moderate level of time-averaging. Our results corroborate the hypothesis that lentic environments can present remarkable preservational conditions for the formation of attritional accumulations of vertebrate remains. Moreover, we show how the different collecting methods affect the description of preservational features and taphonomic interpretations of both fossil assemblages.

Spektrometria masowa i analiza izotopowa biomarkerów frakcji nasyconej

GC-IRMS analysis extends and confirms (or not) the interpretation based on the results of GC-MS analyses. For example, it is very useful in determining the sedimentation environment of organic matter. GC-MS analysis of biomarkers and the results are reliable, but only GC-IRMS studies can confirm it. In this study, the origin of BNH (28,30-bisnorhopane from chemoautotrophic bacteria) and origin of higher carotenoids and their derivatives from Chlorobiaceae or Chromotiaceae bacteria were confirmed through isotopic analyzes. Biomarkers were analyzed using the GC-IRMS and EA-IRMS apparatus. The obtained chromatograms from the IRMS analyses were compared with the archival GC-MS analyses for the same samples in order to identify individual chemical compounds. In addition to the existing methodology of sample preparation for analyses, a non-standard method was also used, consisting in the separation of n-alkanes from branched hydrocarbons. The repeatability of the method was determined on the GC-IRMS and the values of δ13C for selected biomarkers from the saturated fraction were determined. It was found that samples with low biomarker content are not suitable for analysis. On the other hand, too high concentration of the analyte causes an increase of the chromatogram baseline and worse separation of the peaks, which is also a problem. For the crude oils the δ13C values were initially determined for the biomarkers of the saturated fraction from the hopanes group: bisnorhopane (BNH), oleanane, C29 norhopane, C30 hopane, moretane and the C31-C35 homohopane series. Relatively small differences in δ13C values were found between BNH/hopanes and BNH/crude oils, which suggests the same source of origin for all biomarkers (including BNH). Determining biomarkers in the aromatic fraction using the GC-IRMS method was not successful. In the future, a special methodology for preparing samples for carbon isotopic analyses of aromatic fraction will be required.

Paleoenvironmental analysis of wet meadow in the Deseado Massif: Implications for the Holocene occupation of Argentinian Patagonia

Paleoenvironmental data from wet-meadow environments in the arid-semiarid region of Patagonia are still incipient and the paleoenvironmental records came from pollen sequences of caves and rockshelters. The main reasons to study wetland records are their undisturbed (by humans) sedimentologic continuity, in contrast to deposits in rock shelters and caves; and their regional presentation of environmental changes that can be compared to archeological data. The aim of this paper is to evaluate the past hydrological dynamic of a wet-meadow from Deseado Massif and its relationship with the human occupation. For this purpose, we present the results of the sediment and pollen analysis of Mallín La Primavera wet-meadow that provide a sequence starting in the mid-Holocene. The results indicate a lower water table in the mallín prior to 6900 cal yr BP. Sediment analysis indicates low energy sedimentation environment with flood events and very low energy streams. Human occupational data show chronological discontinuities in mid-Holocene in several regions of Patagonia and the southern cone. In the studied region, two chronological hiatuses (7828–6434 cal yr BP and 3005–2710 cal yr BP) where recognized that appear to correlate with shrub steppes, indicating dry conditions. These conditions may explain the lack of archeological radiocarbon dates in the area during this period. The integration of sediment and pollen results from the Deseado Massif indicates dry and windy conditions for the middle Holocene. The lack of archeological radiocarbon dates would have been influenced by the loss of moisture in water sources such as springs and their associated wet meadows ( mallines).

STUDY OF GENESİS OF PRODUCTİVE SERİES SEDİMENTS BY PETROPHYSICAL PARAMETERS

It is known that over than 90% of oil produced in Azerbaijan is extracted from the South Caspian Basin. The South Caspian basin is one of the largest deeply buried basins. Sedimentation process here is characterized by high rate as 25 km for 150-170 mln. years (0.6-0.7 km/mln.years). Last year’s due to acceleration in search and exploration works and assessment of the outlook for oil and gas deposits research of the genesis of Productive Series attracts a lot of attention. İn this paper “Quantitative and qualitative models of log facies” on the basis of well logging data the analysis of lithology, facies and genesis of sedimentary rocks in Pirallahi structure have been done and results were derived. Within the framework of the study by use of Neuralog software based on LL, SP, GL, NGL and other log types the data have been transformed into the LAS format, then the, porosity, bulk clay coefficient and thickness of facies alteration models have been designed by use of Petrel software. Study of sedimentation environment constantly draws the interest of geoscientists due to the direct dependence of structure and identification of oil and gas traps on sedimentation environment. This paper deals with study of genesis of Productive Series deposits based on quantitative and qualitative analysis of logging curves. The study target is Kirmaky suite across Pirallahi field of Absheron oil-gas bearing region. Study of sedimentation environment constantly draws the interest of geoscientists due to the direct dependence of structure and identification of oil and gas traps on sedimentation environment. This paper deals with study of genesis of Productive Series deposits based on quantitative and qualitative analysis of logging curves. The study target is Kirmaky suite across Pirallahi field of Absheron oil-gas bearing region. Keywords: facies analysis, log facies, genesis, flow, bar, coastal plain.

Integrated reservoir characterization based on a comprehensive study of the geological structure using 3D seismic survey

The 3D seismic survey is the undisputed leader among tools of identifying potential exploration targets and reservoir characterization. This paper shows surveys that are crucial in the exploration and development of significant amounts of hydrocarbon resources, and enables operator companies to map complex geological structures and select better drilling locations. The purpose of the research is to have better understandings of formations and update previous studies in the oil field of Mangyshlak Basin, Western Kazakhstan. The Main results are the acoustic impedance, Vp/Vs ratio, lithological and reservoir properties data. The quality controls and analysis of results show a good match with well logs and good recovery of seismic signal in inversion, but it should be improved in some areas. The results, from a scientific point of view, expand the already known geological and geophysical studies of the reservoir and improve the quality of interpretation using seismic methods in studying the sedimentation environment.

APPLICATION OF SEISMIC METHODS FOR INTEGRATED RESERVOIR CHARACTERIZATION

3D seismic survey is the undisputed leader among tools of identifying potential exploration targets and reservoir characterization. This paper shows surveys that are crucial in the exploration and development of significant amounts of hydrocarbon resources, and can be used by operator companies to map complex geological structures and select better drilling locations. The purpose of research work is to have better understandings of formations and update previous studies in oil field of Mangyshlak Basin, Western Kazakhstan. The Main resultsare the acoustic impedance, Vp / Vs ratio, lithological and reservoir properties data. The quality *Автор для переписки. E-mail: [email protected] НЕФТЬ И ГАЗ 2020. 3–4 (117–118) 85 ГЕОФИЗИКА controls and analysis of results show good match with well logs and good recovery of seismic signal in inversion, but it should be improved in some areas. The results, from a scientific point of view, expand the already known geological and geophysical studies of the reservoir and improve the quality of interpretation using seismic methods in studying the sedimentation environment of the site.