Magnetic interpretations are largely based on the gradients produced by susceptibility boundaries. This juxtaposition of rocks with contrasting magnetic content may arise from a number of scenarios:
1. Lateral variation of magnetic content within a lithologic unit,. i.e., heavy sands in low energy stream deposits, or varying susceptibilities or thickness within a shale unit.
2. Fault movement, bringing rocks of differing susceptibilities adjacent to each other across the susceptibility boundary (fault).
3. Fluids preferentially moving along fault boundaries to either oxidize existing magnetic material, destroying the magnetic susceptibility, or deposition and chemical alteration of mineralization to more magnetic minerals.
4. Structural juxtaposition bringing two different lithologic units adjacent to each other, i.e., isoclinal folds.
5. Migration of hydrocarbons to near surface areas forming magnetic epigenetic minerals in the overlying sediments.