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 deepwater---revisiting the delivery mechanisms

AAPG

Lugar: Estados Unidos; Año: 2009;

In the Miocene beds of Cabo Viamonte, deep-marine hyperpycnal channel-leveecomplexes occur at the toe of the depositional slope in sigmoidal clinoforms. Thehyperpycnal channel fill is composed of thick packages of transitional and recurrent(vertical and lateral) sedimentary structures without rheological boundaries, withvariable textural ranges, recurrence of inverse-normal grading, multiple internalreactivation surfaces, and abundant organic content. This complex internal arrangementallows recognition of three facies associations (FA) in the hyperpycnal channel fill. TheFA1 comprises the coarsest clastic fractions, composed of intraformational boulders,matrix- and/or clast-supported conglomerate, and gravelly sandstone, which resultsfrom the combination of inertial flows and turbidity currents generated during thecirculation of hyperpycnal flows. The FA2 comprises conglomerate, gravelly sandstone,and coarse- to fine-grained sandstone that results from rapid aggradation from ahyperpycnal turbidity current capable of transporting gravel as bed-load and up tocoarse sand in turbulent suspension. The FA3 comprises heterolithic deposits that resultfrom progressive accumulation by traction and suspension processes of low-densityhyperpycnal turbidity currents. The coarse-grained lower channel-fill is interpreted as asingle sedimentation event. This is suggested by multiple internal erosion surfaceswithout lateral continuity, the lack of lithological contrasts between sediment below andabove the reactivation surfaces, and the absence of biogenic structures. On the contrary,the fine-grained upper channel-fill, deposited mainly during the waning stages of thehyperpycnal flow, may involve more than one sedimentation event. This interpretationis supported by the presence of isolated beds with low-diversity trace fossils, within theassociated mudstones.