Analogue Modelling to Support Seismic Interpretation in the Eastern Carpathian Bend Zone, Romania

Studying the complex subsurface structures in fold-and-thrust belts, such as the Eastern Carpathian Bend Zone, remains challenging due to poor seismic data quality caused by steep and intricate structures alongside multiple detachment levels.

To address this, we have conducted eight analogue modelling experiments at the Structural Modelling Laboratory of Babes-Bolyai University with mechanical stratigraphy scaled to the area of interest. We used coloured quartz sand, glass microspheres and silicone to simulate brittle rocks, ductile shales, and salt, respectively. The materials were layered in a 120 cm long deformation box, which was shortened at a constant rate of one centimetre per hour. The experiments were monitored using timelapse photography and particle image velocimetry. The models were consolidated, serially sectioned, and photographed. MOVE software (Petroleum Experts) was used for importing the section images and interpreting the 3D structural style for the models.

The structural style of the experiments varied based on the change in parameters, such as layer thickness, materials, shortening amounts, as well as the timing of erosion and salt deposition. The following description will refer to the most common deformation features observed in the experiments but will use the equivalent formation names and ages. The most noteworthy features are the post-salt lower Miocene's decoupling from the pre-salt section, the lower Miocene upper Kliwa formation decoupling from the Oligocene lower Kliwa formation along the lower Miocene Podu Morii shales, and the distinct wavelengths for the post-salt, upper Kliwa, and pre-upper Kliwa structures.

Considering well data, outcrop data, analogue modelling observations, and the 3D model, we performed seismic interpretation. This guided seismic data interpretation revealed short-wavelength upper Kliwa disharmonic folding, Oligocene–Cretaceous thrust-related hanging-wall anticlines, and large thrust fault displacements leading to hanging-wall erosion and out-of-sequence reactivation of the thrust faults. The results of these experiments proved to be effective tools for comprehending the controlling factors of deformation in the Eastern Carpathian Bend Zone and can aid in the interpretation of subsurface data, especially in areas with poor seismic data quality.