*3.2. Triassic Pod Basins*

It is known from literature that salt movement in this area started already in Early Triassic and the large salt-structures were clearly defined before deposition of the interpreted Cretaceous and younger horizons, see e.g., References [3,19,20].

Our interpretation and analysis of the Triassic sequences also revealed that the major salt structures were established already in the Early Triassic time (Figure 4). Their position is closely related to faults in the pre-salt sequence. Late Permian to Early Triassic tension, possibly related to movement along the Tornquist Zone [20,21], leads to extensional faulting. The faulting created a surface relief on the

salt, which focused the deposition into depressions that gradually developed into deep basins. As a surface relief was created, and the sediment load was enough to apply a stress above the yield stress, the lower part of the salt deformed plastically and started to move. Once the areas of deposition and areas of salt growth were fixed, the structures were exaggerated by repeating this salt flow pattern for each deposited sedimentary sequence in a self-supporting system. During Triassic time, the deposition concentrated in circular sag-basins or pods between more or less evenly spaced salt diapirs and ridges. This is seen especially in the North of the Ula Fault (Figures 5 and 6) on the Cod Terrace and Sørvestlandet High. Between the sag basins, relatively lower "salt-saddles" acted as salt-feeders into the main salt structures that develop where salt walls and saddles join up in the corners of a polygon pattern. The modeled profile in this study crosses several pod-basins and salt saddles north of the Ula –Gyda Fault Zone (Figures 2 and 5), close to the top of the salt structures 7/9-1 and Oda.

**Figure 3.** Stratigraphic column from the Central Trough area, modified from Norwegian Petroleum Directorate (www.npd.no).

**Figure 4.** General section across the Central Graben showing the sequential evolution of salt structures. The study area is situated on the Jæren High to the right on this figure. The inset map shows the position of the regional transect in red. The Figure is modified from Reference [3]. The modeled structures of this study are based on typical structures from Eastern Central Graben (Model 1) and Jæren High (Model 2) whose position is shown as a blue line.

**Figure 5.** Top Zechstein salt map showing typical Triassic pod basins (in blue colours) surrounded by a polygonal pattern of salt walls and highs (in green-yellow colour). The red line shows the position of the Northern part of Model 2.
