Anoxic Sediments In Slope Basins and Open Slope of the Western Side of the Gulf of California
Enrique H. Nava-Sanchez and Donn S. Gorsline
Several small slope basins have been formed along the eastern side of the Baja California peninsula by lateral faults associated with the main rifting systems of the central Gulf. These small basins have floors in the depth range of from 250 to 500 m, within the upper part of the oxygen minimum in the Gulf waters. Gravity cores and box cores obtained in three of these basins (El Coyote, La Giganta and Santa Rosalia) show that the sediments are being deposited in near anoxic conditions which eliminates bioturbation, preserving the primary seasonal (?) laminations. Gravity cores with maximum penetration of 2.7 m are laminated throughout their length indicating that these conditions have been present for at least several centuries. The laminae couplets (light-dark laminae pa rs) appear to be annual much like those of the well known Santa Barbara Basin in the California Borderland.
The nonbioturbated sediments are also seen in box and gravity cores taken on the open slope in the area of the Santiago submarine canyon at the southerneastern end of the peninsula. These cores lie in the depth range from 200 to 600 m in the zone where the oxygen minimum intersects the open slope.
These newly discovered anoxic areas plus a small shelf basin on the Pacific side at about the same latitude give us an opportunity to extend studies of high resolution paleoclimatic/oceanographic records down to 23° W latitude and into the Gulf.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California