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Fractured clasts in the Mt Currie Conglomerate at Kata Tjuta (Central Australia): evidence of Early Cambrian earthquakes?

Tokarski Antek K., Strzelecki Piotr J.

Geology, Geophysics and Environment

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2020

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Vol. 46, no. 1

29--33

EN

Lower Cambrian Mt Currie conglomerate at Kata Tjuta bornhardts (Central Australia) bears numerous fractured clasts. Clast-cutting fractures are restricted to particular clasts, the matrix of the conglomerate is not fractured. The fractures are tectonic joints of two sets. The joints were formed due to either seismic or aseismic deformation. In the former case, the fractures may result from Early Paleozoic earthquakes.

2

Neotectonic activity of the Skawa River Fault Zone (Quter Carpathians, Poland)

Zuchiewicz W., Tokarski A. K., Świerczewska A., Cuong N. Q.

Annales Societatis Geologorum Poloniae

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2009

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Vol. 79, No 1

67-93

EN

The Skawa River catchment basin in the Outer Western Carpathians of Poland is situated upon morphostructures showing differentiated mobility in the Quaternary. Long profile of river channel reveals the lowest values of concavity index among the Polish Outer Carpathian rivers, pointing to low degree of river profile maturity, particularly in its middle reach coinciding with a zone of abnormally high river bed gradients. The Skawa River valley utilizes in its middle and northern reaches the Skawa River Fault Zone (SRFZ) composed of differently oriented oblique-slip faults, visible on DEM images as well-marked, rectilinear topolinea-ments. The NNW–SSE to N-S faults in the Silesian Nappe were probably reactivated in Late Pleistocene times as normal faults downthrowing their eastern sides, as shown by abnormally high position of the Weichselian Early Glacial straths on the western valley side. Such an episode of neotectonic activity (late Early Glacial times of the Last Glacial stage) has not been recognized so far in the other river valleys of the Polish segments of the Western Outer Carpathians. We conclude that some of the NNW-SSE to N–S trending faults were reactivated as strike-slip faults. This would conform to the present day stress arrangement within the Polish segment of Carpathians. Moreover, deformations of the Pleistocene straths between Osielec in the south and Wadowice-Zator areas in the north appear to indicate both pre-Weichselian and Weichselian reactivation of the Silesian and - to a lesser extent - Magura frontal thrusts. These movements continued also in the Holocene, although to a smaller extent, most probably due to moderately strong and/or strong earthquakes of magnitudes exceeding 5.5-5.7, resulting in clast fracturing within Holocene alluvium, particularly strong on the Silesian frontal thrust, and less intensive on the Carpathian marginal and Magura frontal thrusts, as well as on some faults that belong to the SRFZ. We are convinced that the record of seismically-induced clast fracturing on one of major fault zones in the Outer Carpathians should lead to revision of the hitherto-existing seismic risk assessment of this region, and particularly of the city of Kraków and other urbanized areas, as well as the planned artificial water reservoir at Świnna Poręba.

3

Fractured clasts in neotectonic reconstructions: an example from the Nowy Sącz basin, western outer Carpathians, Poland

Tokarski A.K., Świerczewska A., Zuchiewicz W.

Studia Quaternaria

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2007

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Vol. 24

47-52

EN

This paper presents the results of a detailed analysis of fractured clasts hosted within Miocene and Pleistocene paraconglomerates that are exposed close to a map-scale overthrust. Both these paraconglomerates bear numerous fractured clasts (22-50%). The architecture of fractures (joints and minor faults) is well-organized and independent of both clast orientation and the degree of clast roundness. The fractures were formed in situ, most probably due to neotectonic activity of the map-scale overthrust. The number of fractured clasts is positively correlated with the clast size, and negatively correlated with the grain-size of clasts of detrital rocks. The number of fractured clasts increases in clasts of detrital rocks, compared to those of quartzites and magmatic rocks.

4

Tarasy rzeczne Nysy Kłodzkiej oraz drobne plejstoceńskie struktury tektoniczne w strefie sudeckiego uskoku brzeżnego i przełomu bardzkiego w Janowcu

Badura J., Przybylski B., Tokarski A., Świerczewska A.

Przegląd Geologiczny

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2007

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Vol. 55, nr 3

228-228

EN

New research in the N part of the Bardo Gorge [close to the Sudetic Marginal Fault] evidenced the occurrence of two hitherto unknown Pleistocene river terraces. The terraces were interpreted basing on digital elevation model [DEM] 1;10,000 and radars sweeping of the Earth’s surfaces [DETM level 2]. Moreover, the results of petrographical analysis of deposits exposed in the 22 high river terrace show two-tier structure of the terrace. This suggest a polygenetic age of the terrace. Within the last terrace fractured clasts and small-scale faults were observed. Fractured clasts were studied in the bottom part of the 22-m-high river terrace where numerous fractured clasts occur. This part of the terrace is composed of gravels containing clasts up to 80 cm across. The matrix is sandy-clayey. The fractures are usually restricted to particular clasts. The fractures compose two sets striking NW-SE and N-S. Gravels exposed in the uppermost part of the terrace are cut by few strike-slip, N-S striking, sub-vertical faults which can be traced along a vertical distance up to 50 cm. These faults cut the gravel matrix but omit clasts. Fractures cutting the clasts do show a well organized architecture which is independent of orientation of a-b surfaces of the host clasts. These features indicate that the fractures were formed in situ within the studied gravels. Furthermore, for the majority of fractures, the angle between the fracture and the a-b surface of the host clast is less than 80, confirming the in situ origin of fractures. The fractures of one set are parallel to the strike of the Sudetic Marginal Fault. This suggests that the origin of the fractures is related to that of the fault. The fractures of the second set may represent Riedel shears associated with the activity of the Sudetic Marginal Fault. The orientations of minor faults confirm this supposition. Summing up, we believe that during the Pleistocene, the Sudetic Marginal Fault was a dextral strike-slip fault, at least in the discussed area.

5

Neofractures versus inherited fractures in structural analysis : A case study from Quaternary fluvial gravels (Outer Carpathians, Poland)

Tokarski A. K., Świerczewska A.

Annales Societatis Geologorum Poloniae

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2005

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Vol. 75, No. 1

95--104.

EN

This paper presents the results of a detailed analysis of flysch-derived clasts within Quaternary fluvial gravels exposed close to a map-scale overthrust. These clasts are commonly fractured. For a given population of clasts, the number of fractured clasts is positively correlated with the clast size and negatively correlated with the grain size of clast-forming rocks. The fractures comprise both those inherited from earlier joints cutting source strata, and those formed in situ within the gravels (neofractures). These two groups of fractures show different diagnostic features. The inherited fractures are orientated at random in relation to geographic coordinates, where as the neofractures show a well-organized architecture. The inherited fractures are mostly inclined 80–90° to the a-b planes of the host clasts, whereas the neofractures are usually inclined at 0–80° to these planes. The occurrence of neofractured clasts within the analysed gravels results from tectonic activity post-dating gravel deposition.

PL

W czwartorzędowych żwirach rzecznych odsłoniętych w pobliżu regionalnego nasunięcia w polskich Karpatach Zachodnich powszechnie występują spękane klasty skał fliszowych. W analizowanym materiale klasty skał drobnoziarnistych są częściej spękane, niż klasty skał gruboziarnistych. Obserwuje się też dodatnią korelację pomiędzy liczbą spękanych klastów a ich wielkością. Wśród spękań występują spękania odziedziczone po spękaniach ciosowych tnących skały macierzyste oraz neospękania, które powstały in situ w żwirach. Te dwie grupy spękań cechuje różna orientacja w stosunku do współrzędnych geograficznych oraz do powierzchni a-b klastów, tj. płaszczyzny zawierającej oś o maksymalnym (a) i pośrednim (b) wymiarze. Spękania odziedziczone są zorientowane chaotycznie w stosunku do współrzędnych geograficznych, podczas gdy orientacja neospękań jest uporządkowana. Spękania odziedziczone są zorientowane niemal pionowo (80-90°) względem powierzchni a-b klastów macierzystych, natomiast neospękania są zorientowane pod katami 0-80° do tych powierzchni. Pochodzenie neospękań jest wynikiem aktywności tektonicznej, która miała miejsce po osadzeniu analizowanych żwirów.