Shoreface tongue geometry constrains history of relative sea‐level fall: examples from Late Cretaceous strata in the Book Cliffs area, Utah

Progradational shoreface tongues preserve a near‐complete depositional record of relative sea‐level highstands, falls and lowstands. Two distinct styles of progradational shoreface tongue are examined in an extensive outcrop and subsurface dataset from Late Cretaceous strata of the Book Cliffs area, Utah, representing (i) highstand through attached lowstand progradation and (ii) highstand through detached lowstand progradation. Using this dataset, key geometrical attributes of the shoreface tongues and their internal facies architecture are identified and quantified that enable the reconstruction of relative sea‐level fall history. For example, attached, wave‐dominated lowstand shoreface deposits record a slow (0.2– 0.3 mm yr –1 ), low‐magnitude (> 14 m) relative sea‐level fall punctuated by minor rises. Detached, weakly wave‐influenced lowstand shoreface deposits record a more rapid (0.4–0.5 mm yr –1 ), high‐magnitude (> 45 m) relative sea‐level fall synchronous with a marked change in sediment delivery and depositional process regime at the shoreline.