From Submarine Canyon to Basin Floor: Architecture and Facies Distribution in a Structurally Confined Submarine Fan, Modelo Formation, California

Outcrops of the Late Miocene Modelo Formation in the Eastern Ventura basin (EVB), southern California, represent a longitudinal transect through a deepwater, clastic depositional system, from proximal submarine canyon to more distal distributary lobe deposits. The Modelo Formation was deposited in a transtensional deepwater sub-basin, the EVB, adjacent to the San Gabriel fault and south of the Ridge basin. Previous isopach mapping indicates that the Modelo Formation is thickest in the axis of the sub-basin, and thins toward syndepositionally active normal faults that form the basin margins. The EVB is presently undergoing inversion, and hence, the Modelo Formation is exposed in very young surface anticlines and synclines. Ancient turbidite systems, such as the Modelo system, deposited in structurally complex, confined basin settings are often prolific hydrocarbon reservoirs. High-resolution outcrop studies provide an improved understanding of the diversity and spatial distribution of sandbody architectures and facies within these depositional systems.

Proximal Modelo exposures, nearest to the San Gabriel fault, are in abrupt erosional contact with underlying strata and are interpreted as the infill of a submarine canyon. Strata at this location are bedded and slumped mudstones, as well as channels filled with conglomerates, coarse-grained sandstones, and linked debrite-and-turbidite-sandstone packages. These strata exhibit poor lateral and vertical connectivity, and are interpreted to reflect a high degree of sediment bypass. Medial exposures, in the vicinity of Lake Piru, comprise mudstones and thick-bedded packages of medium-coarse-grained sandstone. These amalgamated packages (several tens of meters thick) are interpreted as channel complexes and proximal lobes deposited basinward of the canyon mouth in a sand-rich fairway. Distal exposures of the upper Modelo Formation, in the Hopper Canyon area, include siliceous and organic-rich mudstones, and very-fine- to coarse-grained sandstone. The oldest upper Modelo sandstones in the Hopper Canyon area are thin-bedded, poorly-sorted, lithic-rich, and very-fine- to fine-grained. Younger upper Modelo sandstone packages in the Hopper Canyon area are thick-bedded and medium- to coarse-grained. They are often amalgamated and contain abundant cross-stratification. The succession of strata in the Hopper Canyon area is interpreted to be older lobe elements overlain by younger distributive channels and lobes.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California