SEA-LEVEL AND TECTONIC CONTROLS ON LATE QUATERNARY SEDIMENTATION IN SAN DIEGO TROUGH, OFFSHORE CALIFORNIA

High-resolution deep-tow boomer seismic-reflection data are used to characterize late Quaternary (< 50 Ka) deposition in San Diego Trough, a structurally active basin located in the California Continental Borderland. Four modern submarine canyon-channel systems feed sediment into San Diego Trough: Newport, Oceanside, Carlsbad, and La Jolla, from north to south. Newport Canyon, which is more than 50 km north of San Diego Trough, contributes sediment longitudinally, whereas the other three systems are lateral sources. Contrary to typical depositional models in which coarse clastic supply dominates submarine fan deposition during marine lowstand, our examination of deposition in San Diego Trough during Holocene transgression reveals that two of the four canyons remain active. As sea level rose, Oceanside and Carlsbad Canyons were stranded on the outer shelf, deprived of littoral sediment. At present only Newport and La Jolla Canyons have their heads on the inner shelf and continue to feed sediment to their submarine turbidite channel extensions. Within San Diego Trough, all channels extending from these canyons have low relief levees. The juxtaposition of Newport and La Jolla Canyon sediment persisted throughout the latest Quaternary. Displacements along strike-slip faults and related pull-apart depressions and uplifted ridges considerably affected the sediment dispersal of the Newport and Carlsbad canyon-channel systems contributing sediment to San Diego Trough. Deformation approximately 40 km south of Newport Canyon ultimately led to the deflection of Newport channel 20 km to the west. This deflection resulted in Newport channel feeding northern San Diego Trough. Along the eastern side of San Diego Trough, anticlinal folding along a strand of the Coronado Bank fault resulted in blocking progradation of Carlsbad submarine fan and redirecting its sediment to the mid La Jolla Fan area. Late Quaternary deposition in San Diego Trough reveals a complex interplay of river- and littoral drift-fed canyon-channel systems prograding into an elongate structurally active deepwater basin.