Bottom Currents, Deep Sea Furrows, Erosion Rates, and Dating Slope Failure- Induced Debris Flows along the Sigsbee Escarpment in the Deep Gulf of Mexico

Abstract

fax 01-972-952-9435. AbstractObservations from high resolution bathymetry surveys, sidescan images and direct observations from submersibles and ROVs have shown that there are an impressive set of nearly parallel troughs (or furrows) running in a band several kilometers wide along the base of the Sigsbee Escarpment. In the area of the Atlantis and Mad Dog prospects individual furrows are 20 to 30 m wide and 3 m to 8 m deep. We have both measured and directly observed strong bottom currents flowing parallel to these furrows.Neither the reason for the strong currents nor their association with the zone of furrowed seafloor is fully understood at this time.However, the high-resolution geophysical data collected from an AUV as part of the Atlantis area survey show that the pattern of furrows is interrupted in various places along the base of the escarpment. In several places the interruption corresponds to location of a debris flow deposit. Sub-bottom profiles across these debris flows show that they have armored the underlying sediments and protected them from erosion. This indicates that the strong bottom currents are presently eroding the furrowed area. It also suggest that, at an earlier time the currents were not strong and in this time the now-missing sediment (up to 10 m) had been deposited. These observations, when combined with detailed knowledge of the shallow stratigraphy of the area, data concerning the erodibility of the bottom sediments, and time-series measurements of currents provides a method for evaluating the age of the debris flows. This analysis has been carried out for a number of individual debris flow deposits along the base of the escarpment. It is shown that, although there has been considerable activity of these mass gravity flows over the past 20,000 years, the activity has decreased significantly over the last few millennia. These techniques have also proved useful as a screening tool to evaluate the relative ages of various features across the area so the ancient and more recent features can be differentiated.

Submarine Mass Movements and their Consequences

“…In the landward segment of the escarpment, the location and geometry of sedimentary pathways are controlled by underlying extensional grabens associated with deflated salt walls and minibasins (Fig. The furrowed seafloor extends for~2 km off the toe of the escarpment in a basinward direction and has been mapped for several kilometers along the escarpment (Bryant and Bean 2000;Niedoroda et al 2003). Debris flows and furrows characterize the front and toe of the escarpment.…”

Is Scour Important for Pile Foundation Design in Deepwater?

“…Presence of strong bottom currents is evidenced by development of mega-furrows, flukes and ripples on the seabed (Niedoroda et al 2003, Clukey et al 2007. Presence of strong bottom currents is evidenced by development of mega-furrows, flukes and ripples on the seabed (Niedoroda et al 2003, Clukey et al 2007.…”

“…For a seabed scour study where the speed and duration of the bottom current matters most, a more specific example was provided by Niedoroda et al (2003) where a synthetic 100-year long record was developed based on current meter measurement 10m (32.8 ft) above the seabed in a furrowed areas approximately one kilometer south of the Sigsbee Escarpment. The data shows that the accumulated duration of current over 1.64 ft/s in a 100-year event is more than 12 days and the peak speed can reach over 4.27 ft/s.…”

“…General scour has been studied by Niedoroda et al (2003) when investigating the age of a major debris flow in the Atlantis project area in the Gulf of Mexico. General scour has been studied by Niedoroda et al (2003) when investigating the age of a major debris flow in the Atlantis project area in the Gulf of Mexico.…”

The economic importance of contourites

“…The impingement of the strong NE-flowing bottom currents against the east-west slope escarpment reworked the shelfderived sediments at the escarpment base and started development of ENE-migrating barchan sand dunes above the terrace, as seen in the seismic amplitude map of Figure 8. Extensive fields of (Bryant et al 2000;Kenyon et al 2002;Niedoroda et al 2003;Bryant & Slowey 2004). Similar strong bottom currents probably caused the formation of the barchan dunes identified in the uppermost Palaeocene-lower Eocene section of the Santos Basin, indicating bottom-current activity in a period when coarse-grained sediments were delivered to the basin to form potential reservoirs.…”