The quaternary evolution of Buena Vista Lagoon and the adjacent inner margin, San Diego County, California

The evolution and geomorphology of Buena Vista Lagoon and the adjacent inner margin were studied using historic aerial photography, corehole data and high resolution seismic reflection profiles. An integration of these three data sets was used to document the Late Quaternary evolution of the lagoon, and the paleochannels and submarine canyons on the inner margin of the Oceanside Carlsbad area of northern San Diego County. Buena Vista Lagoon is an estuary, which formed in a late Wisconsin (Oxygen Istope Stage 3) river valley. This valley was incised into its floodplain, creating two marine terraces. Shelf geomorphology and paleogeography are dominated by buried paleochannels, submarine canyons and a tectonic barrier formed by splays of the Rose Canyon Fault Zone (RCFZ). The width of the shelf, trend of the paleochannels and evolution of the submarine canyons are directly related to the position and activity of the RCFZ. The paleochannels trend parallel to the fault zone where the shelf narrows and the RCFZ controls shelf break. Paleochannels from Santa Margarita and San Luis Rey Rivers trend perpendicular to the shoreline on the wide northern portion of the shelf. Loma Alta, Buena Vista, Aqua Hedionda and Canyon de las Encinas Creeks incised paleochannels on the narrowest portion of the shelf. The tectonic barrier formed by transpression along a bend of the RCFZ controlled the trend of the paleochannels, which parallel the shelf break. The four creeks coalesce to form a single channel near Aqua Hedionda Lagoon and to cut the Carlsbad submarine canyon. The Late Quaternary evolution of Buena Vista Lagoon began some 25 ka to 18 ka when sea level was glacioeustatically lowered about (-)100 m. allowing Buena Vista Creek to incise a valley across its former floodplain and the newly exposed shelf. As sea level rapidly rose (17 to 7 ka), the shoreline advanced to the mouth of the valley, creating an estuary. As the rise in sea level slowed ( 4 ka to the present), south-flowing longshore currents formed a barrier spit which sealed the mouth of the estuary, forming Buena Vista Lagoon.