Tectonic controls on nearshore sediment accumulation and submarine canyon morphology offshore La Jolla, Southern California Nicolas Le Dantec a, ⁎, Leah J. Hogarth a , Neal W. Driscoll a , Jeffrey M. Babcock a , Walter A. Barnhardt b , William C. Schwab b a Scripps Institution of Oceanography, UCSD, 9500 Gilman Drive, La Jolla, CA 92093-0208, USA b U.S. Geological Survey, Woods Hole, MA 02543, USA abstract article info Article history: Received 11 February 2009 Received in revised form 15 October 2009 Accepted 25 October 2009 Available online 10 November 2009 Communicated by J.T. Wells Keywords: tectonic deformation submarine canyon morphology nearshore sediment accumulation CHIRP seismic and swath bathymetry data acquired offshore La Jolla, California provide an unprecedented three-dimensional view of the La Jolla and Scripps submarine canyons. Shore-parallel patterns of tectonic deformation appear to control nearshore sediment thickness and distribution around the canyons. These shore-parallel patterns allow the impact of local tectonic deformation to be separated from the influence of eustatic sea-level fluctuations. Based on stratal geometry and acoustic character, we identify a prominent angular unconformity inferred to be the transgressive surface and three sedimentary sequences: an acoustically laminated estuarine unit deposited during early transgression, an infilling or “healing-phase” unit formed during the transgression, and an upper transparent unit. Beneath the transgressive surface, steeply dipping reflectors with several dip reversals record faulting and folding along the La Jolla margin. Scripps Canyon is located at the crest of an antiform, where the rocks are fractured and more susceptible to erosion. La Jolla Canyon is located along the northern strand of the Rose Canyon Fault Zone, which separates Cretaceous lithified rocks to the south from poorly cemented Eocene sands and gravels to the north. Isopach and structure contour maps of the three sedimentary units reveal how their thicknesses and spatial distributions relate to regional tectonic deformation. For example, the estuarine unit is predominantly deposited along the edges of the canyons in paleotopographic lows that may have been inlets along barrier beaches during the Holocene sea-level rise. The distribution of the infilling unit is controlled by pre-existing relief that records tectonic deformation and erosional processes. The thickness and distribution of the upper transparent unit are controlled by long-wavelength, tectonically induced relief on the transgressive surface and hydrodynamics. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The importance of underlying structures in controlling the formation and evolution of morphological features and sediment accumulation has long been appreciated (Shepard and Emery, 1941; Emery, 1958). Several studies illustrate the influence of tectonic deformation on geomorphology, such as continental slope morphol- ogy on tectonically active margins (Pratson and Haxby, 1996) or drainage patterns and formation of fluvial terraces (Peters and van Balen, 2007). Long-term retreat of modern beaches (Honeycutt and Krantz, 2003), the preservation and evolution of barrier-island systems (Belknap and Kraft, 1985; Schwab et al., 2000; Thieler et al., 2001; Harris et al., 2005), and short-term dynamic processes such as the position and stability of sandbars in the nearshore (McNinch, 2004), are also affected by underlying structures. Here we present new geophysical and geological data that show the importance of tectonic deformation in controlling canyon location and morphology and modern sediment distribution offshore La Jolla, California. The sedimentary and morphological evolution of continental margins depends on many factors, three of which are eustasy, sediment supply, and tectonic deformation (Christie-Blick and Driscoll, 1995; Posamentier and Allen, 1999). Discerning how these parameters affect sediment accumulation is often difficult even when the factors are operating at different spatial scales (Sommerfield and Lee, 2003, 2004). On active margins tectonics plays a large role in controlling the nearshore physiography. In our study site, the shore- parallel deformation caused by transpression and transtension associated with the dextral Rose Canyon Fault (Fig. 1) can be isolated from the cross-shore oriented base-level changes imparted by regional tectonic uplift and eustatic sea-level fluctuations. Our work examines how local deformation affects the relief on the transgressive surface, which in turn, plays an important role in controlling regions of sediment bypass and accumulation. Marine Geology 268 (2010) 115–128 ⁎ Corresponding author. Tel.: +33 2 23 23 55 99; fax: +33 2 23 23 67 17. E-mail addresses: nledantec@ucsd.edu (N. Le Dantec), lhogarth@ucsd.edu (L.J. Hogarth), ndriscoll@ucsd.edu (N.W. Driscoll), jbabcock@ucsd.edu (J.M. Babcock), wbarnhardt@usgs.gov (W.A. Barnhardt), bschwab@usgs.gov (W.C. Schwab). 0025-3227/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2009.10.026 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo