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aboard the R/V K. Piri Reis, which is operated by Dokuz Eylül University (Izmir, Turkey) (Fig. 1A). MCS data were acquired on a 450 m streamer in 2008, and on a 700 m or 1500 m streamer in 2010. The common midpoint (CMP) spacing was 3.125 m, streamer depth was 3-4 m, and ABSTRACT"Wave" fi elds have long been recognized in marine sediments on the fl anks of basins and oceans in both tectonically active and inactive environments. The origin of "waves" (hereafter called undulations) is controversial; competing models ascribe them to depositional processes, gravity-driven downslope creep or collapse, and/or tectonic shortening. Here we analyze pervasive undulation fi elds identifi ed in swath bathymetry and new high-resolution multichannel seismic (MCS) refl ection data from the Sea of Marmara, Turkey. Although they exhibit some of the classical features of sediment waves, the following distinctive characteristics exclude a purely depositional origin: (1) parallelism between the crests of the undulations and bathymetric contours over a wide range of orientations, (2) steep fl anks of the undulations (up to ~40°), and (3) increases in undulations amplitude with depth. We argue that the undulations are folds formed by gravity-driven downslope creep that have been augmented by depositional processes. These creep folds develop over long time periods (≥0.5 m.y.) and stand in contrast to geologically instantaneous collapse. Stratigraphic growth on the upslope limbs indicates that deposition contributes to the formation and upslope migration of the folds. The temporal and spatial evolution of the creep folds is clearly related to rapid tilting in this tectonically active transform basin.on June 2, 2015 geology.gsapubs.org Downloaded from (TUBITAK)-BİDEB supported a six-month research visit for Kurt to LDEO and the University of Missouri. We thank the captains and crew of the R/V K. Piri Reis, who made the acquisition of these data possible despite challenging conditions. We thank Hydroscience Technologies Inc. for supporting the seismic systems of R/V K. Piri Reis, Landmark for ProMAX software, and Seismic

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