Summations Only

Re: ""life (as fossils) were growing where they were found"". I have no idea of why I put that "(as fossils)" in there - It indeed makes no sense. Maybe it was a bit of relict text that should have been eliminated in the editing.The main point intended, is that something like that crinoid was too fragile to not be broken up, while alive or after death, by any sort of strong current. It didn't get washed in from some distant place. The pictured specimen is remarkable in its preservation, somehow having escaped destruction by predators and scavengers. As I said before, even if the fossil origin is not obvious, the bulk of limestones are made up of the destroyed calcium carbonate shells etc of critters (disclaimer - Not a carbonate petrologist of a paleontology expert).Surprising to me, was to find that modern stalked crinoids do have a little self-mobility. Not going to outrun much anything though.Corrections to any misstatement I may have made are welcome.MooseEdited by Minnemooseus, : Touch up subtitle.

Younger sediments deposited on top of older tilted sediments is the definition of an angular unconformity. "Volcanics" can substitute for "sediments", younger and/or older. Still an angular unconformity.MooseEdited by Minnemooseus, : Change subtitle.

All that is required is a covering of later material, sediments or volcanics. The covering material need not be rock, be flat, or be a "slab" (whatever that is).In northern Minnesota, glacial sediments are on top of the Ely Greenstone and sedimentary rocks (dated 2.7 billion years old) that are at some locations now vertical. The glacial deposits are not lithified, but that early preCambrian/Pleistocene contact is an angular unconformity. And in absolutely no way is that contact a fault.Moose

My "bolding". I think Edge didn't state that real well. I think he meant "An angular unconformity occurs when the sedimentary layering in the two layers are of different attitudes", or something like that. Better stated as "An angular unconformity occurs when the later sedimentary layer has a different attitude (strike and dip) than the earlier layer. Your much loved Steno Principle of Original Horizontality. Which is to say that the dipping lower rock strata was NOT originally deposited dipping like that.Later deformation might cause the later layers to also no longer be horizontal. There is even the possibility that the later deformation might have caused the lower layers to rotate back to horizontal. Here is a photo of an angular unconformity that shows a history of two deformations. The older rocks are near vertical while the later rocks dip at about 45 degrees. See the source page for a little more information on how this happened. I recall once having seen a photo of a similar situation, only that there was a third more or less horizontal sedimentary unit on top. Two angular unconformities in the same photo. Alas, I haven't been able to track down that photo.Moose

Posted by the non-admin mode, to show that such can be done. Admins are exempt from summation mode restrictions, but inadvertently such is also extended to the non-admin linked ID.Anyway, despite appearances that the summation mode had started after AdminPhat message 2873, it actually didn't kick in until 5 messages later, which is after Percy had posted his 2 replies to Faith (messages 2877 and 2878).Adminnemooseus (pretending to be Minnemooseus)