Dust flux, Vostok ice core

Dust flux, Vostok ice core
Two dimensional phase space reconstruction of dust flux from the Vostok core over the period 186-4 ka using the time derivative method. Dust flux on the x-axis, rate of change is on the y-axis. From Gipp (2001).

Thursday, May 9, 2013

Atlantis redux

This story is drawing a lot of attention to this post. (and why is that map upside-down?)

I won't say whether or not Atlantis exists. The topic isn't of great interest to me. But before you get too excited, be aware there are other means for large chunks of granite to find their way to the seafloor.

First of all, it is not clear whether the granite is embedded in the oceanic crust or is a clast (which we sometimes call a "raft"). It seems a long way offshore, but debris flows can go a long way.

Let's see where it is. According to the description, it is about 1500 km SW of Rio de Janeiro.

From the description of the location, I would place it somewhere near the red star. That sits on what does indeed seem to be a geologically interesting feature.

See all those roughly horizontal lines at the right of the image? Those are fracture zones. You can trace those all the way across the Atlantic to the find the corresponding point on the African coast where the two continents were attached prior to the opening of the Atlantic Ocean. The green on the left is part of South America. The light blue next to the green is the shallow water of the continental shelf, which we also consider to be part of the continent. The water depths of the continental shelf are generally no more than about 200 m.

The dark blue section between the continental shelf and the abyssal deeps where we see the fracture zones is  the continental slope, which is characterized by an increase in water depth from 200 m or so to about 4000 m. We normally consider this also to be part of the continent. It is covered by sediments and crap that have fallen off the continent (and is colonized by various organisms living on the seafloor).

The feature appears to be a relatively shallow area.

If we zoom in a bit, we can see what looks like a canyon running through the feature--whatever it is. Canyons on the continental slope are like the lower stretches of great river systems. They funnel flows of material from a tremendous area, all of which is higher up the slope. The flows through these canyons can be enormous, especially after earthquakes.

The Brazilian margin is tectonically similar to the site of the 1929 Grand Banks earthquake. If 180 cubic km of material got remobilized down the Brazilian slope by an earthquake sometime in the past, it would not surprise me if it contained some pretty impressive chunks of granite.

The feature looks like something that has come down the Brazilian slope. Google Earth images are insufficient for us to establish the age of the event--but that will probably come as more work is done on the feature.

No comments:

Post a Comment