greenspun.com : LUSENET : Introductory Geology, Oswego State : One Thread

What exactly is the difference between an angular unconformity and a regular unconformity?

-- Ellen Hanley (ehanley11@yahoo.com), April 09, 2001


an unconformity is a surface in a rock that shows a period of erosion or non-deposition however, in an angular unconformity it appears that there was a period of erosion or non-deposition followed by the deposition of a new and different substance on top of the original rock causing the rock to now have two different orientations.

-- Toni-Ann Phelps (slickchick81@aol.com), April 09, 2001.

An angular unconformity is a discordant surface between two episodes of deposition. It is referred to as angular because between the two episodes of sedimentation the older and underlying strata have undergone folding, uplift and erosion prior to deposition of the younger sediments on top, which will give an angular discordance between the deformed rocks beneath the unconformity and the flat lying ones above it. In a regular unconformity there may have only been a hiatus or cessation in deposition or erosion but no tilting of the older beds before deposition of the younger ones, and the contact could, superficially, appear concordant.

-- Nick Lee (nick_lee@anadarko.com), April 11, 2001.

An unconformity takes place on the surface of a rock. Deposition has stopped and erosion has taken place. Erosion will have removed some rocks and sediments. Then, depostion has resumed. With an angular unconformity, the same general process takes place, yet there is more to it. Angular unconformities have separate layers that are not parallel to one another. This can be caused by deposition, then folding and uplift (which causes the unparallel layers), then erosion and more deposition (just like in regular unconformities). A good explanation and diagram of this can be found at http://met.univnorthco.edu/student/urdi1175/uncon.htm

-- Erin Varley (varley@oswego.edu), April 11, 2001.

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