Playa Esqueleto and Other Outcrops - Braided, Conglomeratic Submarine Channels: Upper Cretaceous Rosario Fm., Baja California, Mexico.
School of Earth Sciences, University of Leeds, Leeds, United Kingdom. [email protected]
In the area of Canyon San Vicente there is excellent 3-D exposure of a submarine canyon, canyon-fill including mass transport and channel-levee systems, with a submarine channel-levee system eventually aggrading out of canyon confinement. Channel style varies stratigraphically from thick vertically amalgamated channels to thin laterally accreting channels vertically segregated by inter-channel/overbank facies. Here we document the latter style and report facies architectures from several channels of varying size. Channels are generally incised into structureless sandstone, which may represent frontal splays or channel mouth lobes, cutting down and ‘soling out’ at a level associated with older overbank deposits. Channel bases are flat and marked by deposition of a thin sheet-like conglomerate. Channel migration is marked by lateral accretion packages (LAPs) stacking towards the cut bank. The final stages of channel fill are often by the deposits of sandy turbidity flows and debris flows; overlying those and the LAPs is usually another thin sheet-like conglomerate representing a final burst of the system. After the final stages of channel fill and sheet conglomerate deposition there is commonly deposition of laterally extensive debrites possibly reflecting a lack of confinement. Thin bedded heterolithics are found interbedded and are eventually succeeded by another conglomeratic channel. All the evidence suggests active migration of channels within a wider channel belt with flows (especially when unconfined) interacting with topography related to the channel-belt margin (slumps and slides) generating debris flows. We present a detailed facies analysis and suggest methods for reservoir prediction.
AAPG Search and Discovery Article #90070 © 2007 AAPG Foundation Grants in Aid