David, ALL oil deposits [and gas] are above subduction zones or old subduction zones. Don't forget the subduction process doesn't stop at the edge of the plate riding over the top. It continues on down, down, down, down at a shallow or steep angle depending on the conditions. Steep by the Andes, shallower under NZ. But those angles have probably changed over the eons. Changed so much that ophiolites can get flicked up onto the TOP of the plate.
The sediment is thick. Oh wow, cyberspace is amazing. One click with Google and bingo, a map of the world showing the thickness. It almost takes my breath away [not kidding]http://www.ngdc.noaa.gov/mgg/image/sedthick.jpg
source: ngdc.noaa.gov
A kilometre of sediment is a LOT of sediment. I wonder how much of it is made of fishy stuff. I dare say some is. Radiolarian ooze is the name of the mid ocean muck and that's little fishy guys who ran out of steam.
Sure enough, there's some information and even photos. Here's a pornographic one for Jay to start with: ngdc.noaa.gov
More: ngdc.noaa.gov note little fishy guys.
When a kilometre of sediment [or more] is subducted, we can imagine that the light stuff would rise through the cracked, bent, shaken, crushed, heated, leaky matrix of mayhem going on in the process of being buried umpty kilometres back down into the mantle.
That's where volcanoes get their bang.
Not all the juice goes up the volcanoes. The stuff that doesn't has to go somewhere and my theory is that it ends up stuck under impermeable sedimentary layers. What else can it do? It can't just sit forever in one place with more and more being pushed into the subduction zone and looking for a way out, or it would come busting through, which it does in volcanoes. Taupo will do it again one of these days, with great loss of life [70,000 people], because that's a gaseous volcano which goes bang, not squirt.
I think the oil and gas fields must be filled from below.
The extremely high pressures and hot conditions, presence of zeolites and other stuff would cause polymerisation, cracking, and a wide variety of chemicals would result, which is what we have in crude oils.
Take a look at Java for example. The oil fields are all nicely arrayed in just the right place to have been filled from sediment subducted from the plate going under the south of Java. The Ural mountains got their the same way the Rockies got there. Banging and bumping and subduction. There's the oil, right alongside the Urals.
Actually, it's a couple of decades since I really checked this theory out, so maybe it's time for me to see if anything has changed.
There is obviously more than one way to skin the dragon because coal is in situ fossil deposits of trees and swamp goo. No subduction there! Heavy deposits like the Orinoco and Athabasca are maybe from in situ fish funerals, but there is a heck of a lot of it. Is there anywhere where we can see geosynclinal marine deposits happening right now in sufficient quantity to form such vast quantities of oil?
I'm not completely sure what happens in subduction zones but there certainly is a heck of a lot of action involving a LOT of fish funerals, volcanoes, mountains, sediment, heat, sound and fury, perhaps signifying nothing.
Meanwhile, I think I'll design a marine vacuum cleaner to do something about that porno picture.
Mqurice |
