Miocene deep-marine hyperpycnal channel levee complexes, Tierra del Fuego, Argentina: Facies associations and architectural elements

PONCE, J.J.; CARMONA, N.B.

Sediment transfer from shelf to deep water—Revisiting the delivery system

AAPG-SEPM

Año: 2011; p. 75 - 93

In the Miocene beds of Cabo Viamonte, deep-marine hyperpycnal channel levee complexes occur at the toe of the depositional slope in sigmoidal clinoforms. The hyperpycnal channel fill is composed of thick packages of transitional and recurrent (vertical and lateral) sedimentary structures without rheologic boundaries, with variable textural ranges, recurrence of inverse-tonormal grading, multiple internal reactivation surfaces, and abundant organic content. This complex internal arrangement allows recognition of three facies associations (FAs) in the hyperpycnal channel fill. The FA1 comprises the coarsest clastic fractions, composed of intraformational boulders, matrix- and/or clastsupported conglomerate, and gravelly sandstone, which results from the combination of inertial flows and turbidity currents generated during the circulation of hyperpycnal flows. The FA2 comprises conglomerate, gravelly sandstone, and coarse- to fine-grained sandstone that results from rapid aggradation from a hyperpycnal turbidity current capable of transporting gravel as bed load and particles up to the size of coarse sand in turbulent suspension. The FA3 comprises heterolithic deposits that result from progressive accumulation by traction and suspension processes of low-density hyperpycnal turbidity currents. The coarsegrained lower channel fill is interpreted as a single sedimentation event. This is suggested by multiple internal erosion surfaces without lateral continuity, the lack of lithologic contrasts between sediment below and above the reactivation surfaces, and the absence of biogenic structures. Onthe contrary, the fine-grained upper channel fill, deposited mainly during the waning stages of the hyperpycnal flow, may involve more than one sedimentation event. This interpretation is supported by the presence of isolated beds with low diversity trace fossils within the associated mudstones.