Syndepositional faulting. The features shown above in a cross section of a rift basin generally indicate that sedimentation (deposition) was occurring at the same time as faulting. Strata (sedimentary layers, shown in shades of blue) filling the rift basin thicken toward the fault because maximum subsidence (downdropping) occurs adjacent to the fault. Although the top surface of a sedimentary layer is originally horizontal, movement on the fault eventually rotates the layer to be inclined toward the fault. Older strata show the most rotation. The uplifted block (left) of the fault undergoes erosion, and coarse material is deposited immediately adjacent to the fault on the downdropped side.