--> Abstract: Architecture of a Modern Transient Slope Fan (Villafranca Fan, Gioia Basin - Southeastern Tyrrhenian Sea), by Fabiano Gamberi and Marzia Rovere; #90124 (2011)

Datapages, Inc.Print this page

AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Architecture of a Modern Transient Slope Fan (Villafranca Fan, Gioia Basin - Southeastern Tyrrhenian Sea)

Fabiano Gamberi1; Marzia Rovere1

(1) ISMAR-CNR Bologna, Bologna, Italy.

The high resolution of geophysical data applied to the study of the modern seafloor provides excellent details on the architecture of deep-water fans. Multibeam bathymetry and CHIRP profiles covering have been used in this study of the Villafranca transient slope fan located in the northeastern Sicilian margin. Hanging above the 300-m high erosional flank of the Stromboli axial valley, perpendicular to the fan elongation, it represents a particular kind of transient fan. The fan is composed of a leveed channel followed downslope by a depositional lobe. The relief of the eastern levee above the channel axis changes due to longitudinal variations in the rate of sediment overbanking; albeit the low sinuosity of the channel, an increased rate of overbank is observed in the outside of the channel bends. Downslope from a knickpoint, an increase in levee relief is due to the entrenchment of the central tract of the channel. The erosional channel deepening followed a landslide that lowered the distal slope portion, also causing a step along the channel course. The landslide is characterized by an extensional headwall domain and by a slightly deformed main body that has suffered very restricted downslope movement. It was caused by the gliding of the levee wedge as a consequence of its undermining due to the excavation of the Stromboli valley in the distal slope. Retrogressive sediment failures are widespread in the eastern levee; they form high mobility mass transport deposits such as a debris flow that spread in the eastern portion of the depositional lobe. The Villafranca depositional lobe has an internal architecture that largely differs from that of classic fan models. Straight, around 500-m-wide and 10 m deep channels and longitudinal bars are in fact the main elements that compose the Villafranca channel-mouth depositional lobe. The channels narrow and deepen downslope, pointing to a progressive establishment of lateral flow non-uniformity in approaching the step at the edge of the depositional lobe. Thick transparent layers or thin well layered deposits, sometimes arranged in smaller scale bedforms, accumulate on the bars. On the contrary, prevailing erosional or bypass processes are responsible for reduced sedimentation in the channels. The architecture of the Villafranca fan lobe has the potential to be applied as analogue for seismics or outcrop-based studies of fans developed in topographically complex slope and connected to a deeper base level.