Saturday, January 26, 2013

Flow direction?

Update comment (1/30/2013)

Thanks to comments by MudRake and Charlotte.  My first impression at the outcrop was flow R-to-L, which they also suggest.  The outcrop main face orthogonal direction to the photos, which were taken in a weathered fracture opening.  In this orthogonal direction are seen a jumble of onlap/offlap relationships that suggested a carbonate transport channel with flow perpendicular to the face.  The deeply weathered fracture opening allowed a rare opportunity to confirm this hypothesis,  road cut would not.  A cautionary tale about relying solely on new road cuts.  My team is in the process of reconnaissance mapping of every significant Mississippian outcrop location over a 4000 sq mi area.  This is at the heart of the MArkUP proposal that will be the subject of a later post.  Here is a teaser....



Original post (1/26/2013)

The outcrop photo below was photographed on 1/21/2013 in Madison County, Arkansas.  The shown section is in the uppermost Mississippian limestone.  The crinoidal beds display laminations typical of transported sediment.  Can anyone say (and justify) if the flow was right-to-left or left-to-right?  Put your reply as a comment.




2 comments:

MudRake said...

Based on the orientation of the crinoid stem debris, I would hazard a guess that flow was from the right to left.

Charlotte said...

The middle photo has stratification that would suggest transport from right to left. However these may be more accretionary beds. The bedding is very irregular; consider how much more organized these beds would look if they were deposited in a tidally influenced setting. When you look at the beds in 3D, do you get a sense of compensatory bedding, of material being shed rather than uniformly transported?