The complex fault zone within poorly indurated strata in the Orava Basin (Western Carpathians, Poland)

• Autorzy: Fheed A.
• Konferencja: XVth International Conference of Young Geologists Her'lany 2014 : Międzybrodzie Żywieckie, Poland, May, 8th-10th 2014
• Języki publikacji: EN

Abstrakty

EN

The purpose of this paper is to identify and characterize a fault zone located within poorly indurated Pliocene clastic strata occurring in the southern part of the Orava Basin on the boundary of Outer and Central Western Carpathians, close to the Pieniny Klippen Belt. The Orava Basin is a part of the Orava - Nowy Targ intramontane basin. The fault zones within poorly indurated sediments are usually very complex. If the rocks are well indurated, a fault zone is divided into two parts - the fault gouge and the damage zone (Fossen 2010). The fault gouge is characterized by the slip plane and strong deformations such as fractures or clasts' reorientation. Not all the researchers, however, agree with a general fault zone model described by Fossen (2010). This model is indeed appropriate for strongly lithified rocks. In case of poorly lithified sediments, Rawling & Goodwin (2006) and later Gudmundsson (2011) and Loveless et al. (2011) suggested adding the third, additional zone - the mixed zone. It separates the fault gouge and the damage zone and the presence of the deformation bands and clasts' reorientation are its main features. The mixed zone records the initial deformations of the sediment and stays active for some time even after the lithification (Rawling & Goodwin 2006). Although no displacement of strata can be noticed in the studied exposure, the occurrence of numerous fractured clasts and exposure-scale fissures can be used in the interpretation of a potential fault zone. In order to describe the considered fault's anatomy, the presented research has been concentrated on the identification of three main fault parts occurring within poorly indurated strata: the fault gouge, the mixed zone and the damage zone. The analyzed exposure, whose length and height exceeds 70 and 15 meters, respectively, is located within a natural scarp in the Cichy Stream Valley. The scarp is mostly NNE-SSW to NE-SW oriented. It is dominated by poorly indurated Pliocene muddy to sand-supported paraconglomerates, mainly comprised of mudstone and sandstone clasts and up to 40% of matrix. The thickness of the rocks observed within the exposure reaches about 15 meters. Besides that, in few places, lense-shaped bodies of sandstone were observed. Their thickness is lower than 1 meter. They appear in the lower part of exposure, close to its easternmost side. From the neotectonic point of view, three groups of structures were recognized: clast-scale fractures, deformation bands and exposure-scale fissures. The paraconglomerates are dominated by the fractured clasts. The clasts are cut either by one or two sets of fractures. The planes of these fractures mainly strike NE-SW to NNE-SW. In the western part of the exposure, the measurements were the most consistent, while the eastern part shows a greater dispersion of the data. In both western and easternmost parts of the exposure, some clasts are reoriented. Inclination reaches even 90°. Fractured clasts' investigation have yielded information about the intensity of the deformation within the paraconglomerate. The counts have shown that the prevailing amount of the fractured clasts occurs in the western part of the exposure - even 126 counts per square meter. The average amount of fractures observed in the middle of the scarp is 57 per square meter, whereas in the eastern part approximately 30 fractures per square meterwere be counted. The deformation bands have been observed within the lenses of sandstones, located in the center of the eastern part of the exposure. Moreover, the whole exposure is cut by numerous fissures that either cut across or bypass the clasts. Some of them are open and wide, while other are narrow. The fissures differ between themselves in terms of size. Therefore they were subdivided into three groups: (1) cutting the whole exposure, (2) disappearing towards the top of the exposure, (3) inferior (the smallest) ones. Except for one fissure placed on the west, the first group appears mainly in the center of the eastern part of the scarp. Second group is located in the center of the exposure. The third group, in turn, can be observed mainly in the eastern part of the paraconglomerate. Besides the inferior fissures (3), they mostly strike NNE-SSW, similarly to the fractures in clasts. The fractured clasts' abundance, fissures' presence and clasts' reorientation can be interpreted as the indicators of a potential fault zone. The large amount of fractures in clasts in the westernmost part of the scarp, in combination with first group fissure presence and clasts's reorientation, leads to the conclusion that it may represent the location of the fault gouge. Whether the gouge is relatively narrow, the observed reorientation might belong to the adjacent mixed zone. The mixed zone seems to occur in few places within the scarp. Its presence can be inferred from deformation bands' location and clasts' reorientation. Quite high background of fractures at the level of approximately 50 per square meter and tension fissures' presence within the whole scarp may indicate of the damage zone location. In this case, the damage zone would cover the largest part of the exposure, leaving the rest of it for a fault gouge and the mixed zone. The model of the dominant damage zone also matches another theory, associated with a shear zone. In this case, the fissures observed within the scarp could be interpreted as the Riedel fractures related to left-lateral strike-slip fault occurring in the vicinity of the scarp.

Słowa kluczowe

EN

Pliocene; Nowy Targ; Pieniny Klippen Belt

• Wydawca: Wydawnictwa AGH
• Czasopismo: Geology, Geophysics and Environment
• Rocznik: 2014
• Tom: Vol. 40, no. 1
• Strony: 82--83
• Opis fizyczny: Bibliogr. 4 poz.

Twórcy

autor

Fheed A.

• AGH University of Science and Technology, Faculty of Geology, Geophysics and Environmental Protection; al. Mickiewicza 30, 30-962 Krakow, Poland

Bibliografia

• 1. Fossen H., 2010. Faults. [in:] Fossen H., Structural Geology, Cambridge University Press, 151-188.
• 2. Gudmundsson A., 2011. Rock Fractures in Geological Processes. Cambridge University Press, Cambridge.
• 3. Loveless S., Bense V. & Turner J., 2011. Fault architecture and deformation processes within poorly lithified rift sediments, Central Greece. Journal of Structural Geology, 33, 11, 1554-1568.
• 4. Rawling G.C. & Goodwin L.B., 2006. Structural record of the mechanical evolution of mixed zones in faulted poorly lithified sediments, Rio Grande rift, New Mexico, USA. Journal of Structural Geology, 28, 1623-1639.