Wyniki wyszukiwania - BazTech

1

Trylobity w eratykach wapieni beyrichiowych znalezionych u podnóża klifu orłowskiego w Gdyni (północna Polska)

Kowalewska Agata

Przegląd Geologiczny

|

2023

|

Vol. 71, nr 6

332--339

EN

On the beach at the foot of the Orłowo Cliff (northern Poland), numerous erratics that were transported there by ice sheets from Scandinavia andsome Baltic regions can be found. Sedimentary rocks, important to palaeontological studies, contain numerous fossils and, among others, arthropods. One of the most common rock types here is beyrichian limestone. Its fossil content allows us to recognize many varieties, such as Calymene lime-stone, Nucula limestone, Elevatus limestone and others. The present study concentrated main lyon trilobites found in these rocks and belonging to two genera: Calymene and Acaste.

2

Silurian rugose coral Schlotheimophyllum Smith, 1945 from the Upper Visby Beds of Gotland, Sweden

Wrzołek Tomasz, Zatoń Michał

Annales Societatis Geologorum Poloniae

|

2023

|

Vol. 93, No. 3

251--267

EN

A rich (about 60 specimens) collection of Schlotheimophyllum, large rugose corals from the Silurian of Gotland, Sweden, was studied. Although the material is mostly fragmentary (beach pebbles), the presence of growth lines, clearly seen in thin sections, provides reliable numerical data. Analyzed were corallum shape, septal numbers, and aspects of coloniality. Uniformity of variability spectra of these parameters indicates that all of the material studied belongs to a single, variable species, which is Schlotheimophyllum patellatum (Schlotheim, 1820).

3

Coexistence of algae and a graptolite-like problematicum: a case study from the late Silurian of Podolia (Ukraine)

Skompski Stanisław, Kozłowski Wojciech, Łuczyński Piotr, Kozłowska Anna

Acta Geologica Polonica

|

2023

|

Vol. 73, no. 2

115--133

EN

This contribution presents the record of an abundant assemblage of well-preserved, thallophytic noncalcified algae and of an epibiotic form that has been recognised as a putative graptolite from the upper Silurian (Ludlow, Gorstian–Ludfordian) of Podolia (western part of Ukraine). The sediments represent a shallow peritidal zone of the shelf. A new genus and species, Voronocladus dryganti, belonging to the Dasycladales Pascher, 1931, is established. Most of the specimens representing the algal thallus are overgrown by problematical epibiotic graptolites, described as Podoliagraptus algaeoides gen. et sp. nov. This phenomenon is explained as an epiphytic mode of life of the putative graptolite on algae, and is herein compared to recently known coexistences of algae with other organisms. The excellent state of preservation, and the abundance of studied Dasycladales algae and epibiotic problematics indicate that the investigated mudstone layer can be treated as a ‘Konservat Lagerstätte’ sensu Seilacher (1970).

4

Marine snow and epipelagic suspensoids in the Reda carbonates and a pronounced mid-Ludfordian (Silurian) CIE in the axis of the Baltic Basin (Poland)

Kozłowski Wojciech

Acta Geologica Polonica

|

2020

|

Vol. 70, no. 4

529--567

EN

The mid-Ludfordian pronounced, positive carbon isotope excursion (CIE), coincident with the Lau/kozlowskii extinction event, has been widely studied so far in shallow-water, carbonate successions, whereas its deep-water record remains insufficiently known. The aim of this research is to reconstruct the sedimentary environments and the palaeoredox conditions in the axial part of the Baltic-Podolian Basin during the event. For these purposes, the Pasłęk IG-1 core section has been examined using microfacies analysis, framboid pyrite diameter and carbon isotope measurements. The prelude to the event records an increased influx of detrital dolomite interpreted as eolian dust, coupled with a pronounced decrease in the diameter of the pyrite framboids, indicating persistent euxinic conditions across the event. The event climax is recorded as the Reda Member and consists of calcisiltites, composed of calcite microcrystals (‘sparoids’), which are interpreted as suspensoids induced by phytoplankton blooms in the hipersaturation conditions present in the epipelagic layer of the basin. Both the prelude and climax facies show lamination, interpreted as having resulted from periodical settling of marine snow, combined with hydraulic sorting within a ‘benthic flocculent layer’, which additionally may be responsible for a low organic matter preservation rate due to methanogenic decomposition. Contrary to the observed basinward CIE decline in the benthic carbonates in the basin, the Reda Member records an extremely positive CIE (up to 8.25‰). Given the pelagic origin of the sparoids, the CIE seems to record surface-water carbon isotope ratios. This points to a large carbon isotope gradient and kinetic fractionation between surface and bottom waters during the mid-Ludfordian event in a strongly stratified basin. The Reda facies-isotope anomaly is regarded as undoubtedly globally triggered, but amplified by the stratified and euxinic conditions in the partly isolated, Baltic-Podolian basin. Hence, the common interpretation of the basin record as representative for the global ocean needs to be treated with great caution.

5

Petrologiczne rozpoznanie materii organicznej rozproszonej w sylurskich łupkach Gór Bardzkich (Sudety)

Nowak Grzegorz J.

Przegląd Geologiczny

|

2019

|

Vol. 67, nr 3

183--185

EN

The present paper is focused on the petrological characteristics of dispersed organic matter of the Silurian part of the Graptolite Shales from the Bardo Mts. (Sudetes). The most abundant organic component is secondarily altered organic matter represented by solid bitumen. Based on the results obtained by optical microscopy, it was possible to distinguish several types of solid bitumen. They were determined as granular, porous, coke-like, mosaic andfluidal types. All bitumen types are optically isotropic. Bitumen reflectance varies between 1.37 and 1.62%. Based on the % reflectance values, the solid bitumen identified in the studied samples are classified as pyrobitumen.

6

Graptolite biostratigraphy and dating of the Ordovician–Silurian shale succession of the SW slope of the East European Cratond

Podhalańska Teresa

Annales Societatis Geologorum Poloniae

|

2019

|

Vol. 89, No. 4

429--452

EN

This paper deals with the graptolite biostratigraphy and age determination of the Ordovician and Silurian lithological successions of the Baltic, Podlasie and Lublin basins that existed during the early Palaeozoic on the SW slope of the East European Craton. The biostratigraphic research described was conducted on core material coming from old boreholes and cores from several new wells. Graptolite zones were identified and the chronostratigraphic succession was constrained, with the depths to the stratigraphic units, especially those considered prospective for petroleum, being determined in the individual borehole sections. Old local stratigraphic schemes of the Silurian used for many years in the Polish geological literature are correlated with the standard schemes. The most complete succession of graptolite zones, both in the Ordovician and the Silurian, is observed in the Baltic region. The number of stratigraphic gaps increases towards the east and southeast of the regions. The stratigraphic range of the Sasino Shale Formation decreases in this direction; in the Podlasie and Lublin regions, it comprises only the Katian Stage. The stratigraphic range of the Jantar Formation in the western part of the area spans not only the Rhuddanian but also part or the whole of the Aeronian. In the Podlasie and especially the Lublin regions, sedimentation of the Jantar Formation began in the latest Rhuddanian–Aeronian. A large stratigraphic gap, spanning part or the whole of the Llandovery and increasing eastwards, was documented in the Podlasie-Lublin region. The biostratigraphic research allowed a more precise constraint on the temporal and spatial extent of erosion of Pridoli deposits and the beginning of coarse-grained, siliciclastic sedimentation (Kociewie Formation) in the Baltic Basin.

7

A review of Silurian fishes from north-western Hunan, China and related biostratigraphy

Zhao W. -J., Zhu M., Gai Z. -K., Pan Z. -H., Cui X. -D., Cai J. -C.

Acta Geologica Polonica

|

2018

|

Vol. 68, no. 3

475--486

EN

The Silurian fishes from north-western Hunan, China are characterised by the earliest known galeaspids Dayongaspis Pan and Zeng, 1985 and Konoceraspis Pan, 1992, and the earliest known antiarch Shimenolepis Wang J.-Q., 1991, as well as rich sinacanth fin spines. Shimenolepis from Lixian County in north-western Hunan, which was dated as the Telychian (late Llandovery), has long been regarded as the oldest representative of the placoderms in the world. As such, in addition to eastern Yunnan and the Lower Yangtze Region, north-western Hunan represents another important area in South China that yields important fossil material for the research of early vertebrates and related stratigraphy. Here we summarise the Silurian fishes known in north-western Hunan so far, and classify them into three vertebrate assemblages (i.e., the Wentang, Maoshan, and Yangtze assemblages). Based on the updated Silurian vertebrate and stratigraphic databases, the Silurian fish-bearing strata in north-western Hunan can be subdivided into the Rongxi, Huixingshao, and Xiaoxi formations in ascending chronological order, which can be correlated with the Lower Red Beds, the Upper Red Beds, and the Ludlow Red Beds in South China, respectively. A new look at the Silurian strata in Lixian suggests that the age of Shimenolepis is late Ludlow rather than late Llandovery as previously suggested. The research on Silurian fishes and biostratigraphy in north-western Hunan not only provides morphological data of early vertebrates, but also offers new palaeoichthyological evidence for the subdivision, correlation, and age assignment of the Silurian marine red beds in South China. The establishment of a related high-precision Silurian stratigraphic framework in north-western Hunan will help to elucidate the temporal and spatial distribution of Silurian fossil fishes, deepen the understanding of the evolution of early vertebrates, and unravel the coevolution between Silurian vertebrates and the palaeoenvironment.

8

Upper Homerian (Silurian) high-resolution correlation using cyclostratigraphy: an example from western Lithuania

Radzevičius S., Tumakovaitė B., Spiridonov A.

Acta Geologica Polonica

|

2017

|

Vol. 67, no. 2

307--322

EN

The Gėluva regional stage stratigraphically corresponds to the late Wenlock. This time interval witnessed significant graptolite extinctions and turnovers of conodont faunas, as well as a large positive Mulde carbon isotopic excursion. Thus, the development of a detailed stratigraphy is a necessary step in understanding the complex patterns of regional and global variations in the sediments accumulating during the time interval studied. Therefore, in this contribution we present a cyclostratigraphic analysis of gamma ray (GR) logs from four wells, which are located in the deep water facies belt of the Lithuanian part of the Silurian Baltic Basin of the Gėluva regional stage. The analysis was performed using REDFIT spectral estimation, continuous wavelet transform and signal filtering techniques. As a result two 4th order and five 5th order cycles were distinguished and named in all sections. The correlation of cycles between sections was calibrated with the graptolite biozones. The comparative analysis revealed that intra-basinal cyclostratigraphic correlation could achieve resolution of the order of several tens of thousands of years.

9

The use of X-ray computed microtomography for graptolite detection in rock based on core internal structure visualization

Kaczmarek Ł., Kozłowska A., Maksimczuk M., Wejrzanowski T.

Acta Geologica Polonica

|

2017

|

Vol. 67, no. 2

299--306

EN

This paper presents for the first time X-ray computed microtomography (μCT) analysis as a technique for Silurian graptolite detection in rocks. The samples come from the Jantar Bituminous Claystones Member of the Opalino core, Baltic Basin, northern Poland. Images were obtained with spatial resolution of 25 μm, which enabled the authors to create a 3-D visualization and to calculate the ratio of fissure and graptolite volume to the total sample volume. A set of μCT slices was used to create a 3-D reconstruction of graptolite geometry. These μCT slices were processed to obtain a clearly visible image and the volume ratio. A copper X-ray source filter was used during exposure to reduce radiograph artifacts. Visualization of graptolite tubaria (rhabdosomes) enabled Demirastrites simulans to be identified. Numerical models of graptolites reveal promising applications for paleontological research and thus for the recognition and characterization of reservoir rocks.

10

Silurian stratigraphy of Central Iran - an update

Hairapetian V., Ghobadi Pour M., Popov L. E., Männik P., Miller C. G.

Acta Geologica Polonica

|

2017

|

Vol. 67, no. 2

201--233

EN

The Silurian biostratigraphy, lithostratigraphy, and facies of Central Iran including the Kashmar (Boghu Mountains), Tabas (Derenjal Mountains, Ozbak-Kuh), Anarak (Pol-e Khavand) and Kerman regions is reviewed and updated. The current state of knowledge of the Silurian in the Zagros Basin, Alborz, Kopet-Dagh and Talysh regions, as well as in a few areas scattered across the Sabzevar Zone, and the Sanandaj-Sirjan terranes is also reviewed. Silurian volcanism in various parts of Iran is briefly discussed. The end of the Ordovician coincided with a widespread regression across Iran synchronous with the Hirnantian glaciation, and only in the Zagros Basin is there a continuous Ordovician–Silurian transition represented by graptolitic black shales of the Sarchahan Formation. In the Central-East Iranian Platform marine sedimentation re-commenced in the early to mid Aeronian. By the Sheinwoodian, carbonate platform depositional environments were established along its north-eastern margin. In other parts of Iran (e.g., Kopet-Dagh and the Sabzevar Zone), siliciclastic sedimentation continued probably into the late Silurian. The Silurian conodont and brachiopod biostratigraphy of Central Iran is significantly updated facilitating a precise correlation with the Standard Global Chronostratigraphic Scale, as well as with key Silurian sections in other parts of Iran. The Silurian lithostratigraphy is considerably revised and two new lithostratigraphical units, namely the Boghu and Dahaneh-Kalut formations, are introduced.

11

Litofacje formacji perspektywicznych dla gazu i ropy w łupkach w utworach ordowiku i syluru na obszarze bałtyckim i podlasko-lubelskim

Feldman-Olszewska A., Roszkowska-Remin J.

Przegląd Geologiczny

|

2016

|

Vol. 64, nr 12

968--975

EN

The paper presents a sedimentological analysis of Ordovician (Sandbian–Hirnantian = Caradoc–Ashgill) and Silurian (Landovery–Wenlock, lower Ludlow) claystones and mudstones from the north-eastern (Baltic Basin) and south-eastern (Podlasie-Lublin Basin) parts of the East European Craton. In both basins, formations prospective for shale gas/oil were analyzed: the Sasino Fm., Pasłęk Fm. (including the Jantar Mb.), Pelplin Fm., Udal Fm., Wrotnów Fm. and Terespol Fm. Based on lithological and sedimentological criteria, 34 lithofacies and 11 lithofacies associations have been distinguished. The most promising lithofacies arerepresentedbytheL-1,L-3andL-4associationswhicharecharacterizedbydarkgreycolour, a very low degree or lack of bioturbation, rare sedimentary structures, and common content of small pyrite concretions. They dominate in the Sasino Fm., Pas³êk Fm. (in the Jantar Mb. only) and Pelplin Fm., but are much less common in the Udal Fm., Terespol Fm. and Pas³êk Fm. (excluding the Jantar Mb.).

12

Early Silurian (Llandovery) graptolite assemblages of Saudi Arabia: biozonation, palaeoenvironmental significance and biogeography

Williams M., Zalasiewicz J., Boukhamsin H., Cesari C.

Geological Quarterly

|

2016

|

Vol. 60, No. 1

3--25

EN

Analysis of Silurian graptolite assemblages from 1017 sample horizons in 132 cores (from 65 boreholes) through the Qusaiba Member, Qalibah Formation of Saudi Arabia, provides a refined graptolite biostratigraphy for the Arabian Peninsula comparable in its resolution to that from the British Isles and the Czech Republic. Over 150 graptolite species characterize 11 biozones from the lowermost Rhuddanian lubricus Biozone to the lower Telychian guerichi Biozone, with sub-zonal resolution for several intervals. Graptolite biozonal boundaries and the Rhuddanian-Aeronian and Aeronian-Telychian stage boundaries can be placed with high precision. Detailed analysis of graptolite spatial distribution suggests persistent depth-stratified marine assemblages across the Silurian palaeo-Arabian Plate. Near-surface-dwelling assemblages probably occupied the mixed-layer of Silurian oceans, enabling colonization of shallow shelf environments. They are low-diversity (1-2 species) assemblages characterized by Neodiplograptus, Coronograptus, Neolagarograptus and Stimulograptus species and often are preserved in strata with extensive shelly faunas. Deeper marine assemblages are of higher diversity (up to 15 species per horizon), and are characterized by dorsally curved or helically coiled species of Spirograptus, Demirastrites, Lituigraptus, Rastrites and Torquigraptus. Recognition of depth-stratified graptolite assemblages provides an important tool for establishing palaeo-basin topography and water depth at the time of sedimentary deposition. At the species level, the graptolite assemblages of Saudi Arabia are remarkably similar to contemporaneous faunas from peri-Gondwanan Europe and, from the middle Rhuddanian onwards, also to the Avalonian and Laurentian Llandovery graptolites of the UK.

13

Lithologic-petrographic characterization of Silurian rocks in the Niestachów profile (Holy Cross Mountains)

Malec J., Kuleta M., Migaszewski Z. M.

Annales Societatis Geologorum Poloniae

|

2016

|

Vol. 86, No. 1

85--110

EN

The Niestachów profile is located in the southwestern part of the Holy Cross Mountains and exposes lower Ludlovian greywacke sediments of the Niewachlów Beds that occur above graptolitic claystones of the Prągowiec Beds. Within the sequence of lithologically diversified Niewachlów Beds, more than 400 m thick, 11 characteristic lithologic complexes were identified. The lower and upper parts of the Niewachlów Beds comprise fine- and medium-grained greywacke sandstones with mudstone interbeds, whereas the middle part contains coarse-grained greywacke sandstones and conglomerates. The sediments were transported by “turbiditic currents” from the southwest. Petrographic examination of the upper part of the Prągowiec Beds and the Niewachlów Beds indicates that the greywacke conglomerates and sandstones of the Niewachlów Beds are composed primarily of volcanic and sedimentary lithoclasts, with subordinate metamorphic and scarce plutonic lithoclasts. The sandstones and conglomerates were derived from an orogen containing sandstones and mudstones as well as from the magmatic rocks of a continental volcanic arc, characterized by acidic-intermediate volcanism.

14

Wykorzystanie wysokorozdzielczej mikrotomografii komputerowej oraz analizy ultradźwiękowej w charakterystyce struktury paleozoicznych gazonośnych łupków z basenu bałtyckiego

Kaczmarek Ł., Maksimczuk M., Wejrzanowski T., Łukasiak D.

Nafta-Gaz

|

2015

|

R. 71, nr 12

1017--1023

PL

W artykule przedstawiono metodykę badań próbek z horyzontów perspektywicznych dla eksploatacji łupków gazonośnych z polskiej części basenu bałtyckiego. Do badań wykorzystano wysokorozdzielczą mikrotomografię komputerową (µCT) oraz pomiar czasu przejścia fal ultradźwiękowych przez próbki. Uzyskany rozmiar piksela obrazu µCT dla próbek o większych rozmiarach wynosił 25 µm, natomiast dla niewielkich fragmentów próbek było to 5 µm. W badaniach ultradźwiękowych czynnikiem o dominującym wpływie na uzyskiwane wyniki okazała się szczelinowatość, która oddziaływała tłumiąco na propagację fal. Na podstawie analizy µCT określono procentowy udział szczelin w próbkach (średnia 0,82%) oraz przekroje przedstawiające strukturę wewnętrzną próbek z morfologią szczelin. Na podstawie prędkości propagacji fal ultradźwiękowych przez próbki obliczono dynamiczne parametry modułu Younga (zakres wyników 22÷57 GPa) oraz współczynnika Poissona (0,21÷0,40). Otrzymane wyniki wskazują na wysoką przydatność stosowania analiz ultradźwiękowych oraz wysokorozdzielczej tomografii komputerowej jako badań uzupełniających się.

EN

The article presents the methodology of characterization research of samples from prospective horizons for the exploitation of shale gas from Polish part of the Baltic Basin. High-resolution computed microtomography (μCT) and ultrasonic technique were used for the analysis. The resulting pixel size of μCT image for larger samples were 25 microns, while for small fragments of samples pixel size were 5 microns. In ultrasonic tests, fissures had a dominant impact on acoustic waves propagation. Extensive fissures surface resulted in attenuation of ultrasonic waves. Based on the μCT analysis, percentage content of fissures in the samples (average 0.82%) were determined. Furthermore a cross-section of specimens revealed the internal structure and morphology of fissures. Dynamic parameters of Young’s modulus (range 22÷57 GPa) and Poisson’s ratio (0.21÷0.40) were calculated, by converting the process of propagation velocity of ultrasonic waves through the samples. Results indicate the suitability of the use of ultrasonic analysis and μCT as complementary tests.

15

The use of cluster analysis for the segmentation of the physicochemical properties of shale gas deposits

Filar B., Kwilosz T., Miziołek M., Piesik-Buś W., Zamojcin J.

Nafta-Gaz

|

2015

|

R. 71, nr 11

898--909

EN

Cluster analysis methods have been adapted for the segmentation of data describing the generative and reservoir properties of shale gas-type formations. Tests were carried out for the segmentation of data describing the geochemical properties of core samples collected from eight wells within the stratigraphic unit of Llandovery (Silurian). The study was conducted in two stages. During the first stage, data segmentation was performed for three wells described by the largest number of measurements. The second stage of data segmentation involved a set of samples originating from all wells.

PL

Zaadaptowano metody analizy skupień do segmentacji danych opisujących właściwości generacyjne i zbiornikowe formacji typu shale gas. Przeprowadzono próby segmentacji danych opisujących parametry geochemiczne próbek rdzeniowych pobranych z ośmiu odwiertów w obrębie piętra landoweru. Badania przeprowadzono w dwóch etapach. W pierwszym etapie dokonano segmentacji danych w obrębie trzech odwiertów opisanych największą liczbą pomiarów. W drugim etapie dokonano segmentacji danych na zbiorze próbek pochodzących z wszystkich odwiertów.

16

Parametry sprężyste łupków zawierających materię organiczną określone na podstawie teoretycznych relacji Biota–Gassmana i Kustera–Toksöza

Bała M.

Nafta-Gaz

|

2015

|

R. 71, nr 12

1005--1016

PL

Wykonano próby obliczania parametrów sprężystych dla łupków ilastych, będących potencjalnymi skałami macierzystymi dla węglowodorów. Wykorzystano w tym celu znane modele teoretyczne Biota–Gassmana i Kustera–Toksöza oraz autorski program Estymacja-TP. Przeprowadzono wstępną analizę wartości parametrów szkieletowych niezbędnych do obliczeń. Analiza została oparta na danych literaturowych oraz na pracach autorki. Zmiany parametrów sprężystych skał macierzystych, jak również ich wzajemne relacje dostarczają ważnych informacji o wielkościach generowanych węglowodorów i charakterystykach geomechanicznych skał, określanych na podstawie profilowań akustycznych i pomiarów sejsmicznych. Modele syntetyczne skał ilastych zawierają uśrednione wielkości charakterystyczne dla łupków gazonośnych Barnett Shale w Teksasie, łupków Green River w Colorado oraz łupków syluru i ordowiku z basenu bałtyckiego.

EN

Tests were carried out for calculating the elastic parameters for shales, which are potential hydrocarbons source rocks. For this purpose the Biot–Gassmann and Kuster–Tosköz theoretical models and original program ESTYMACJA TP were used. A preliminary analysis of the values of the matrix of the rocks were made, which are necessary for the calculations. The analysis were based on literature data and recent works by the author. Changes in elastic parameters of source rock and their relationships provide important information about the volumes of the generated hydrocarbons and geotechnical characteristics of rocks, determined on the basis of acoustic logs and seismic measurements. The developed synthetic shale rock models contain averaged values characteristic for the organic-rich Barnett Shale in Texas, Green River shale in Colorado and Silurian, and Ordovician shales of the Baltic Basin.

17

The Silurian of southwestern margin of the East European Platform (Ukraine, Moldova and Romania) : lithofacies and palaeoenvironments

Radkovets N.

Geological Quarterly

|

2015

|

Vol. 59, No. 1

105--118

EN

Silurian strata, stretching along the western margin of the East European Platform from the Baltic to the Black Sea, represent a potential target for both conventional and unconventional hydrocarbon exploration. Distribution of the black shale facies, prospective for shale gas, and the reef facies, prospective for oil, has been studied in respect of palaeoenvironments. The Silurian sequence has been investigated in the territory of Ukraine (Volyn-Podillyan Plate, Dobrogean Foredeep) and correlated with the data on Moldova and Romania (Moldovian Platform). The occurrence of Silurian strata, their thickness, and petrographic and lithological characteristics allowed reconstructing the distribution of open-shelf, reef and lagoonal facies. The reef facies migrated during the Wenlock–Middle Pridoli, shifting towards the open sea and back towards the shore, and therefore has been termed a migrating reef facies. Correspondingly, the boundary between the open-shelf and reef facies was shifting. The facies distribution was controlled by the transgressive-regressive cycles, which caused the fluctuations of the shelf water depth in different time intervals of the Silurian. The shelf water depth of about 100 m, where the top of the oxygen-minimum layer impinged on the sea bottom, was the boundary between the open-shelf facies, represented by organic-rich sediments, and the reef buildups.

18

Pozycja stratygraficzna formacji łupków z Widełek w synklinie bardziańskiej (Góry Świętokrzyskie)

Malec J.

Przegląd Geologiczny

|

2014

|

Vol. 62, nr 11

748--754

EN

Results of the geological studies carried out in the western part of the Bardo Syncline have revealed the wrong stratigraphic position of the Silurian Widełki Formation, established by Stupnicka et al. (1991) in the Widełki area. This lithostratigraphic unit does not represent the youngest Silurian deposits overlying the greywackes of the Niewachlów Beds in the Kielce region of the Holy Cross Mts. In fact, the claystones with graptolites of theWidełki Formation underlie the greywackes of the Niewachlów Beds and belong to the upper part of the Prągowiec Beds.

19

Palaeo-earthquake events during the late Early Palaeozoic in the central Tarim Basin (NW China): evidence from deep drilling cores

He B., Qiao X., Jiao C., Xu Z., Cai Z., Guo X., Zhang Y.

Geologos

|

2014

|

Vol. 20, No. 2

105--123

EN

Various millimetre-, centimetre- and metre-scale soft-sediment deformation structures (SSDS) have been identified in the Upper Ordovician and Lower-Middle Silurian from deep drilling cores in the Tarim Basin (NW China). These structures include liquefied-sand veins, liquefaction-induced breccias, boudinage-like structures, load and diapir- or flame-like structures, dish and mixed-layer structures, hydroplastic convolutions and seismic unconformities. The deformed layers are intercalated by undeformed layers of varying thicknesses that are petrologically and sedimentologically similar to the deformed layers. The SSDS developed in a shelf environment during the early Late Ordovician and formed initially under shear tensile stress conditions, as indicated by boudinage-like structures; during the latest Ordovician, SSDS formed under a compressional regime. The SSDS in the Lower-Middle Silurian consist mainly of mixed layers and sand veins; they formed in shoreline and tidal-flat settings with liquefaction features indicating an origin under a compressional stress regime. By Silurian times, the centre of tectonic activity had shifted to the south-eastern part of the basin. The SSDS occur at different depths in wells that are close to the syn-sedimentary Tazhong 1 Fault (TZ1F) and associated reversed-thrust secondary faults. Based on their characteristics, the inferred formation mechanism and the spatial association with faults, the SSDS are interpreted as seismites. The Tazhong 1 fault was a seismogenic fault during the later Ordovician, whereas the reversed-direction secondary faults became active in the Early-Middle Silurian. Multiple palaeo-earthquake records reflect pulses and cyclicity, which supports secondary tectonic activity within the main tectonic movement. The range of SSDS structures reflects different developments of tectonic activity with time for the various tectonic units of the centralbasin. The effects of the strong palaeo-earthquake activity coincide with uplift, fault activity and syn-tectonic sedimentation in the study area during the Late Ordovician to Middle Silurian.

20

Do the available data permit clarification of the possible dependence of Palaeozoic brachiopod generic diversity dynamics on global sea-level changes? A viewpoint

Ruban D. A.

Geologos

|

2014

|

Vol. 20, No. 3

215--221

EN

At a glance, progress in palaeontology and eustatic reconstructions in the past decade permits to prove or to disprove the possible dependence of Palaeozoic brachiopod generic diversity dynamics on global sea-level changes. However, the available diversity curve is of much lower resolution than the eustatic curve. This problem can be resolved by decreasing the resolution of the latter. The other restriction linked to the chronostratigraphical incompatibility of the available data allows to focus on the Middle Palaeozoic only. A series of mass extinctions and other biotic crises in the Silurian-Devonian does not allow to interpret correctly the results of direct comparison of the brachiopod generic diversity dynamics with global sea-level changes. With the available data, it is only possible to hypothesize that the eustatic control was not playing a major part in diversity dynamics of Middle Palaeozoic brachiopods. The resolution of the stratigraphic ranges of Palaeozoic brachiopods should be increased significantly, and these ranges should be plotted against the most up-to-date geologic time scale. Until this task will be achieved, it is impossible to judge about the existence of any dependence (either full or partial) of the Palaeozoic brachiopod diversity dynamics on global sea-level changes.