Complex Depositional History of a Sinuous, Conglomeratic Submarine Slope Channel

Abstract

The infill history of a submarine channel is typically far more complex than its stratigraphic record. Multiple phases of erosion and deposition, the development of multiple generations of levees and terraces, and the nature of final fill, are suggestive of many events and a complex fill that does not necessarily record the activity of the channel during most of its history. Therefore, interpreting process of channel inception and evolution from the final fill can be, at best, challenging. The Upper Cretaceous San Fernando Channel System, part of the deep-marine phase of the Rosario Formation, Baja California, Mexico, offers a superb quasi-three-dimensional view of a channel-fill complex at outcrop. Different stages of lateral migration, first time described in outcrop, indicated by lateral accretion deposits with variable orientation, are described and interpreted to develop an inferred depositional history of the channel complex. The channel-fill is dominated by clast-supported conglomerate with common imbrication. Matrix-rich conglomerates, lenticular sandstones and debritic deposits are other common facies internal to this channel fill. Surrounding the coarse-grained deposits are the intra-channel-belt heterolithics (internal levees) with some less common overbank dune-forms. The channel-fills are dominated by lateral accretion deposits, suggesting the channels developed on a largely graded-slope. Lateral-accretion deposits are marked by couplets of conglomerate and sandstone; both imbricated and chaotic conglomerates; and amalgamated conglomerate bodies. Bedded conglomerates which define large lateral accretion deposits and sets record evidence of at least two major stages of channel shifting. The results are synthesised into a conceptual geological model for the inception and evolution of coarse-grained deep-marine slope channels dominated by lateral accretion processes.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016