Imaging Granite–Metamorphic Unconformities and Structural Variability Using PSDM Seismic and Borehole Data: Implications from the Tromm Area, Germany

An initial geological model for the Tromm area is constructed through the integration of wireline log data from the GeoLaB-01 and GeoLaB-02 wells with two orthogonally oriented 2D seismic profiles (E–W and N–S), acquired in 2024, and processed and imaged in both time and depth domains . The interpretation of the pre-stack depth-migrated (PSDM) seismic data, constrained by borehole information, enables delineation of the principal lithological framework and key bounding surfaces. A major regional unconformity separating upper granitic from lower metamorphic units is consistently imaged on both seismic profiles as a laterally continuous, high-amplitude reflector associated with a strong acoustic impedance contrast. This surface correlates closely with wireline log responses from both wells, characterized by an abrupt increase in gamma-ray values and P-wave velocity, and is independently confirmed by core descriptions from the GeoLaB-01 well, validating the granite–metamorphic contact.
In addition to this well-constrained boundary, the seismic data indicate possibly a second, deeper interface at the base of the metamorphic unit separating well imaged and relatively coherent reflector bundles on top from less coherent and partly isolated seismic reflectors below. ... mehrAs this boundary was not intersected by the existing wells, it needs to be considered as unconfirmed and introduces additional uncertainty to the deeper geological model (>750 m). Seismic interpretation further indicates lateral variations in the apparent thickness of the metamorphic unit, with relatively lower thickness in the northern part of the study area that increases towards south.
Structural interpretation highlights localized seismic responses on the E–W profile suggestive of faults or ductile shear zones within the metamorphic unit, expressed by subtle reflector offsets and west dipping reflectors. The W-dipping reflector is apparently limited to the metamorphic rocks and unlikely to continue into the granites and hence unlikely to be mapped at the surface. The absence of comparable small-scale fault responses on the N–S profile suggests a predominant N–S fault strike, rendering these structures more readily detectable on the E–W-oriented seismic line while remaining poorly resolved or invisible on the N–S section. Together, these results define an initial geological model that integrates seismic, wireline, and core data, while clearly identifying both confirmed features and key uncertainties requiring further investigation.