Review article Unique vs. non-unique stratal geometries: Relevance to sequence stratigraphy Octavian Catuneanu a, * , Massimo Zecchin b a Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, Alberta, T6G 2E3, Canada b Istituto Nazionale di Oceanografia e di Geofisica Sperimentale - OGS, Sgonico, TS, 34010 Italy article info Article history: Received 26 June 2016 Received in revised form 18 September 2016 Accepted 20 September 2016 Available online 21 September 2016 Keywords: Sequence stratigraphy Unique stratal geometries Non-unique stratal geometries Sequence stratigraphic methodology abstract The sequence stratigraphic architecture includes a complex array of stratal geometries with different degrees of stratigraphic significance. The ‘non-unique’ variability of the sequence stratigraphic frame- work (i.e., stratal geometries which are not diagnostic for the definition of systems tracts and bounding surfaces) is irrelevant to the workflow of sequence stratigraphy. What is relevant is the observation of the ‘unique’ stratal geometries that are diagnostic for the definition of units and surfaces of sequence stra- tigraphy. In downstream-controlled settings, these unique stratal stacking patterns relate to the forced regressive, normal regressive, and transgressive shoreline trajectories. Multiple controls interact during the formation of each type of stacking pattern, including accommodation, sediment supply, and the energy of the sediment-transport agents. This interplay explains the non-unique variability, but does not change the unique criteria that afford a consistent application of sequence stratigraphy. The distinction between unique and non-unique stratal geometries is critical to the sequence stratigraphic methodology. Failure to rationalize the non-unique variability within the context of unique stratal geometries is counterproductive, and obscures the simple workflow of sequence stratigraphy. This is the case with uncalibrated numerical modeling, which may overemphasize non-unique or even unrealistic strati- graphic scenarios. While useful to test the possible controls on stratigraphic architecture, modeling re- quires validation with real data, and plays no role in the sequence stratigraphic methodology. © 2016 Elsevier Ltd. All rights reserved. Contents 1. Introduction ...................................................................................................................... 185 1.1. Rationale .............................................................. ..................................................... 185 1.2. Methodology vs. modeling in sequence stratigraphy .............................................................................. 185 2. Unique vs. non-unique stratal geometries ............................................................................................ 186 3. Controls on sequence development .................................................................................................. 188 4. Discussion ........................................................................................................................ 190 4.1. Forced regression vs. fluvial topsets ............................................................................................ 190 4.2. Examples of unique and non-unique stratal geometries ....................................... .................................. 190 4.3. Sequence stratigraphic methodology vs. modeling ............................................................................... 191 5. Conclusions ...................................................................................................................... 193 Acknowledgments ............................................................ .................................................... 194 References ........................................................................................................................ 194 * Corresponding author. E-mail address: octavian@ualberta.ca (O. Catuneanu). Contents lists available at ScienceDirect Marine and Petroleum Geology journal homepage: www.elsevier.com/locate/marpetgeo http://dx.doi.org/10.1016/j.marpetgeo.2016.09.019 0264-8172/© 2016 Elsevier Ltd. All rights reserved. Marine and Petroleum Geology 78 (2016) 184e195