Tuesday, July 31, 2007
Twisted Polystrate Plants
At Joggins, Ian was taking photographs of the numerous polystrate fossil plants there (a polystrate plant is one that cuts through multiple geological strata). He then noticed something he hadn't before -- they were almost always twisted. So he decides to start examining the twists more closely. Not only are they all twisted, they are all twisted in a clockwise ascending spiral (80% of those studying were spiraled in this fashion; 17% showed no spiralling, and the remaining showed counterclockwise spiralling).
So what causes the spiralling? Do they grow like this? No. And the plants were all bent the same way on the same bedding plane. Underwater tornadoes? No, they would have had to stay centered on the plant while burying it at the same time. Changing flow directions? No.
What is really unusual is that many are bent past the failure point (i.e. they should have broken), but are not broken, indicating that they were being supported while being twisted and buried.
Ian's solution was Coriolis forces due to rapidly shifting continents. He cited an interesting paper which may be showing similar forces in play in the mid-Oceanic ridge.
I don't know a lot about physics, so I can't really comment on Ian's proposed mechanism, but the pattern of twisted polystrate fossils is certainly an interesting one!