Salt canopies, formed by the coalescence of salt sheets, are an integral part of the slope and deep-water areas of many passive margin salt basins. A suture separates the two coalesced salt sheets (allosuture) or two lobes from a single salt sheet (autosuture), including any trapped sediments.
Autosutures can form in two ways. An overriding autosuture is produced when part of a salt sheet overrides its neighbor in the direction of salt movement. The overridden roof subsides into the salt sheet, and these trapped sediments appear as intrasalt reflections on seismic data. An encircling autosuture forms when two lobes of a salt sheet separate to bypass an obstacle and then rejoin on the downstream side of the obstacle. Encircling autosutures tend to be short and parallel to the dominant salt-flow direction.
Allosutures separate sheets sourced from two different feeders. If neither salt sheet overrides the other, the resulting suture is symmetric, forming an upright zone of roof sediments trapped between the two sheets. More typically, one salt sheet is more vigorous (generally the larger sheet or the one whose feeder is farther updip) and overrides the other. Sediments trapped in an asymmetric allosuture are mostly from the roof of the overridden sheet. The overriding sheet shears and extends the roof of the overridden sheet, detaching it from the base of the canopy and obscuring its origin.
We present diagnostic criteria to distinguish between suture types and provide physical-model examples of each. This distinction between suture types is important because autosutures and allosutures have very different implications for canopy dynamics and evolution.