Interplay between shoreline migration paths, architecture and pinchout distance for siliciclastic shoreline tongues: evidence from the rock record TORE M. LØSETH* 1 , RON J. STEEL  , JEFF P. CRABAUGH à and MAIJA SCHELLPEPER à *Department of Geology, University of Bergen, N-5007 Bergen, Norway (E-mail: tore.loseth@hydro.com)  Department of Geosciences, University of Texas at Austin, Austin, TX 78712, USA àDepartment of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA ABSTRACT Facies, geometry and key internal stratigraphic surfaces from eight Cretaceous and Eocene clastic shoreline tongues have been documented. The regressive parts of all the studied tongues represent storm-wave influenced strandplains, deltas or fan-deltas, and the regressive shoreline trajectories varied from descending to ascending. The transgressive parts of the tongues are dominated by either estuarine or coastal-plain deposits. The distance from the coeval, up-dip non-marine deposits to the basinward pinchout of amalgamated shoreface sandstones, measured along depositional dip, is here termed the sand pinchout distance. The study shows that the angle of regressive-to-transgressive turnaround (defined by the angle between the regressive and subsequent transgressive shoreline trajectories) and the process regime during turnaround largely control the sand-pinchout distance. The amount of transgressive erosion can also partly control the pinchout distance, but this parameter was comparable for the different examples presented here. If the type of depositional system at turnaround and the depth of transgressive erosion are constant, small angles of turnaround are associated with large pinchout distances, whereas larger angles of turnaround result in smaller pinchout distances. The model developed allows sand-pinchout distance to be predicted, using data for the landward parts of shoreline tongues. The dataset also shows that steeply rising (aggrading) shoreline trajectories tend to produce more heterolithic sandstone tongues than those formed by lower-angle trajectories. Keywords Angle of turnaround, facies architecture, pinchout distance, sequence stratigraphy, shoreline tongue, shoreline trajectory. INTRODUCTION Shallow-marine sandstone bodies forming basin- ward-extending clastic wedges or tongues in the geological record usually have a lower regressive part and an upper transgressive part (Fig. 1A). The marine sandstone segment of such tongues has a down-dip pinchout distance defined as the distance between coeval up-dip non-marine deposits and the final basinward disappearance of amalgamated shoreface sandstones into non- amalgamated sandstones, siltstones and mud- stones of shelf or deeper-water affinity (Fig. 1A). There is both academic and applied interest in pinchout distances because (i) they vary greatly and the controls on this variability need to be understood (Leckie, 1986; Anderson, 1991; Cant, 1995; Gardner, 1995; Muto & Steel, 1997, 2002, 2004; Cross & Lessenger, 1998), and (ii) there is economic advantage in being able to predict the geometry and character of potential reservoir 1 Present address: Hydro Oil & Energy, PO Box 7190, N- 5020 Bergen, Norway. Sedimentology (2006) 53, 735–767 doi: 10.1111/j.1365-3091.2006.00791.x Ó 2006 The Authors. Journal compilation Ó 2006 International Association of Sedimentologists 735