Deformation of salt layers and interbedded salt impurities: Insights from scaled experimental models (Preliminary Results)

In many salt-rich basins (e.g., offshore Brazil, onshore Netherlands), rock salt is interbedded with other evaporites, carbonates, shales, or igneous rocks. These impurities can influence salt behavior and produce complex intrasalt structures. In this study, we used scaled experimental models to better determine factors that influence the development of intrasalt structures.

In the models, alternating layers of silicone putty and wet clay represented interbedded salt and salt impurities, respectively. To trigger deformation, we placed a narrow wedge of wet clay above the layers to simulate depositional loading in nature. In response, a minibasin formed, causing the putty to move laterally away from the depositional load. Beneath the subsiding minibasin, the internal clay layer stretched, producing boudins. Simultaneously, a broad region of shortening developed adjacent to the minibasin. The layers of silicone putty thickened, whereas the internal clay layer underwent shortening with buckle folding and thickness changes. Our modeling results and strain analysis suggest that the thickness and distribution of the clay layer affected the deformation patterns. Tight and overturned folds developed in models with a thin or deep clay layer, whereas broad folds with long wavelengths formed in models with a thick or shallow clay layer. The deformation in our experiments resembles the deformation associated with the interbedded Argo salt of the Orpheus rift basin. In this basin, buckle folds and thrust faults developed adjacent to a minibasin near the rift-basin border-fault zone. Thus, these models suggest that, although postrift basin inversion may have affected the Orpheus rift basin, the formation of minibasins in response to focused sediment loading was sufficient to produce the observed compressional structures during the late stages of rifting.