Ball-and-pillow structures are soft-sediment deformation features that form when denser, water-saturated sediment layers sink into underlying less-dense layers, creating rounded “ball” shapes. These structures are important indicators of rapid sedimentation and seismic activity and are often found in deltaic and turbidite deposits.
Source Lowe, D. R. (1975). “Water Escape Structures in Coarse-Grained Sediments.” Sedimentology, 22(2), 157-204.