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Fault geometry and evidence of depocentre migration within a transtensional intra-basinal high : a case study from the Łączna Anticline (Intrasudetic Synclinorium, SW Poland)

Kowalski A.

Geological Quarterly

2017

Vol. 61, No. 4

779--794

The paper presents the results of geological mapping and a detailed structural analysis carried out in the Łączna Anticline. This elevated region coincides with the Zawory (Cz. Závora) mountain range in the Central Sudetes (SW Poland). The Łączna Anticline separates two minor geological units (depressions) within the northwestern part of the Intrasudetic Synclinorium – the Krzeszów and the Police brachysynclines. In numerous exposures of Triassic and Upper Cretaceous sedimentary rocks, several brittle and a few soft-sediment deformation structures have been recognized. Their orientation and spatial distribution suggest that the Łączna Anticline is a horst-like, intra-basinal high, formed due to permanent extension, dextral strike-slip movements within fault zones, and negative flower structures. The studies did not confirm the occurrence of continuous deformations such as anticlinal bends and flexures. The results show that the preservation of some lithological varieties of sedimentary rocks within modern morphological and structural elevations reflects the migration of centres of maximum subsidence within a pull-apart basin system. A new structural and geodynamic interpretation for the Łączna Anticline area is proposed.

Hydrothermal fluids influence on the thermal evolution of the Stephanian sequence, the Sabero Coalfield (NW Spain)

Botor D.

Geology, Geophysics and Environment

2012

Vol. 38, no. 4

369--393

In the present study, the thermal history of the Late Carboniferous (Stephanian) coal-bearing sediments of the Sabero Coalfield has been reconstructed in order to elucidate coal rank. The Sabero Coalfield is located in a small intramontane coal-bearing basin along the Sabero-Gordón fault zone, one of the major E-W trending strike-slip fault systems of the southern part of the Cantabrian Zone (NW Spain). The total thickness of the Stephanian succession is in excess of 2,000 m, and is composed of siliclastic rocks and intercalated coal seams with tonsteins. Mean vitrinite reflectance values in the Stephanian rocks in the Sabero Coalfield are in the range from 0.61 to 3.14% Rr, but most values are in the range from 0.8 to 1.5% Rr (based on 84 samples). Average vitrinite reflectance gradient is high (0.73% Rr/km), which suggests high value of average paleogeothermal gradient (52°C/km). The maximum paleotemperatures calculated from vitrinite reflectance values for the Stephanian rocks range between 89°C (top of the Stephanian) and 195°C (bottom of the Stephanian). Coalification of the organic matter in the Stephanian rocks was achieved in the Early Permian, and was most likely related to several almost simultaneous related to magmatic and hydrothermal activity during high subsidence period in the pull-apart basin. The primary, burial-related maturity pattern, was probably slightly overprinted by fluid migration event, which is supposed to have occurred in Early Permian time.