Characteristic Bed Thickness Variation in Submarine Levee Deposits: Rosario Formation, Baja California, Mexico
Ian Kane1, Ben Kneller2, Mason Dykstra3, Ahmed Kassem2, and Bill McCaffrey1
1 University of Leeds, Leeds, United Kingdom
2 University of Aberdeen, Aberdeen, United Kingdom
3 University of California, Santa Barbara, CA
Submarine levees are prospective in areas such as the Nile Fan, the Gulf of Mexico and elsewhere. Despite this, facies models of such deposits are not advanced, due to their poor preservation potential in the continental rock record, and the consequent paucity of outcrop studies. The Upper Cretaceous Rosario Formation of Baja California, Mexico, offers, however, excellent 3-D exposure of a deep-marine channel-levee complex. Around Arroyo San Fernando, levee facies consist of thinly interbedded non-amalgamated, sharp based sandstones and siltstones, often highly bioturbated, with variable palaeocurrents and often containing slide blocks and slumps. Tractional structures in proximal levee facies consist of climbing and subcritical ripples, with lesser parallel lamination and massive bedding; in the most proximal of logs overturned ripples are found. In distal levee outcrops starved ripples are abundant. Moving away from the channel axis, sandstone bed thickness obeys a power-law decay, with standard deviation decreasing linearly. The levee crest is identified based upon moving averages of bed thickness, which show thinning upwards of inner- and thickening upwards of outer-levee deposits. Palaeocurrents converge with the channel-axis on the inner-levee, and diverge from it on the outer-levee; distal outcrops are characterised by significantly more palaeocurrent scatter. The relationship of palaeocurrent direction and bed-thickness to overbank flow character and the implications for levee growth are investigated. Additionally, Cruziana ichnofacies, created by creatures transported in turbidity currents, are only abundant in channel-proximal outcrops, and thus are diagnostic of levee position in this system.