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PRESENT GEOLOGICAL SETTING AND THE DEVELOPMENT OF THE DRAGANOWA ANTICLINE, OBTAINED BY MEANS OF FORWARD TECTONIC MODELLING

Piotr Hadro

Abstract

Classic models of fault related folding frequently fails to describe complicated geological structures. The combination of tectonic modelling techniques can be used to reproduce observed geometry of folds. Indirect information contained in geophysical data can provide a good quality check for proposed tectonic models. The Draganowa Anticline is the westernmost part of the Draganowa-Iwonicz Fold. This structure is characterized by existence of very steeply dipping limbs in shallow zone which turns into gentle anticline at greater depths. My interpretation suggests that this anticline is related to the underlying thrust fault. Another structure with positive relief can be observed under the southern limb of the anticline. Interpretation of the present geological setting in the area of investigation was achieved by analysis of seismic profiles, resistivity cross-sections and well data. The shallow zone has been described by surface data: intersections and dips. Before the interpretation begins two versions of seismic processing (PreStack Time migration and PreStack Depth migration) were compared and tied to wells and surface geology. Different development scenarios has been proposed to describe the tectonic setting of the Draganowa Anticline, but without much success. Finally, the model which assumes multiple faulting in the back limb and in the hinge zone provided a good fit to the interpretation. Multiple internal faulting is confirmed by the well observations. Additionally there is a drop of seismic velocities in the center part of the anticline which may correspond with intensive faulting in this compartment. The growth of the dip with increasing depth can be explained by the concept of passive fault. The passive fault provides a barrier between strata which are actively deformed and layers which are passively dragged on the roof of the growing structure. The paper shows that even complicated geological structures may be described by means of tectonic modelling when good quality subsurface data are available. The presented approach may be used to explain the development of other similar structures in the Polish Carpathians, as well as other fold-thrust belt regions.

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DOI resolver: doi.org/10.5593/sgem2017h/15/s06.052

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