Mark Wilson April 19th, 2014
MITZPE RAMON, ISRAEL–Usually on Saturdays Yoav Avni and I do something “touristic”, like visit an archaeological site or museum. Since it is the Passover holiday, though, and we are both averse to crowds, we decided to do a little stratigraphy outside Mitzpe Ramon instead. Our challenge from Amihai Sneh was to sort out the lower boundary of the En Yorqe’am Formation (Upper Cretaceous, Cenomanian), so we added another section to our argument.
The above image is taken from N 30.62947°, E 34.82085°, about three kilometers northeast of town along the rim of Makhtesh Ramon. (Check those coordinates out on Google Maps. Very cool, especially if you tilt the Earth image to show the cliff edge.) The three critical formations are labelled above with our new concept. The top boundary of the En Yorqe’am with the Zafit Formation is not controversial; it’s the base of the En Yorqe’am that is at issue. Presently it is defined as the top of the cemented carbonates shown just above the “Y” of En Yorqe’am. With this definition the unit is about 20 meters thick — less than half its thickness elsewhere. This has led to some tectonic arguments about uplifts, erosion and unconformities that are not supported by the record in the rocks, other than this anomalously thin section. From our studies of the boundary to the south, we believe we have good evidence to put it here between the massive and bedded limestones as shown. The fossils support this (especially oysters) and the thickness of the En Yorqe’am goes back to an expected 50 meters or so. That’s the argument we’re going to make to Amihai, at least. I will see more of this unit with Amihai further north next week.