Submarine Ramp Facies Model for Delta-Fed, Sand-Rich Turbidite Systems

Abstract

Some sandy turbidite successions contain facies that differ in significant ways from those predicted by the canyon-fed submarine fan depositional model. The key differences are the absence of a master slope channel or canyon through which sediment is transported to the basin, and the lack of facies segregation into distinct channel and overbank or interchannel facies associations within the turbidite sequence. These types of sequences can be better described using a delta-fed submarine ramp depositional model. The primary components of this model are: (1) a sandy deltaic system that has prograded to the shelf-slope break; (2) an abbreviated section of mud-rich slope deposits traversed by multiple shallow channels that transport sand from the delta front to the deeper basi ; (3) very sandy proximal ramp deposits composed dominantly of laterally continuous sheets of Facies B turbidites; and (4) less sandy distal ramp deposits characterized by an increase in the abundance of Facies C and D turbidites. Ramp turbidites characteristically display statistically random patterns of bed thickness. Submarine ramp development requires rapid sediment accumulation (> 800 ft or 250 m/m.y.) in turbidite basins of shallow to moderate depth where deltaic progradation is rapid enough to mask the structural relief along basin margins. The delta-fed submarine ramp facies model may be useful in describing short-lived sandy depositional episodes in some rapidly aggrading and prograding basinal sequences. As such, they represent one member in a spectrum of submarine fan depositional styles.