Mark Wilson March 16th, 2012
MITZPE RAMON, ISRAEL–Melissa and I finished our work in the Jurassic of Makhtesh Gadol yesterday, so today we went out with Yoav to explore the Upper Cretaceous and Eocene exposures just a few kilometers north of Mitzpe Ramon. This is what we do near the end of each expedition so that we have more ideas for the next. It was cold and very windy on the barren hillsides this morning, but we still saw and learned a great deal.
We examined outcrops of four units: The Ora Formation (Upper Cretaceous) is primarily shales and claystones and below the stratigraphic column shown above. It has an interesting limestone unit composed mostly of rudistid bivalves and their shelly debris shown later below. The Gerofit Formation, also Upper Cretaceous, is a mix of limestones and marls unconformably above the Ora Formation. The Mishash Formation (Upper Cretaceous again) is a chert-rich unit unconformably above the Gerofit here. Andrew Retzler and Micah Risacher, who worked in the region two years ago, will immediately ask, where are the Zichor and Menuhah Formations that are supposed to be between the Gerofit and Mishash? They are absent due to a deep unconformity. On top of the Mishash, above another significant unconformity, are nummulitic limestones of the Avedat Group (Eocene). These three unconformities are all structurally and paleoenvironmentally significant — and they no doubt will be future projects for Wooster Geologists.
Some items of interest in this long section. Just below the Vroman Bank in the Ora Formation is the above cemented horizon with well-distinguished Thalassinoides burrows. These were produced by crustaceans burrowing into stiff mud in shallow waters. This unit is usually not very well exposed, but Yoav and I dropped down into an ancient cistern to see this outcrop.
This is a polished surface at the top of the Vroman Bank in the Ora Formation. Erosion in a small wadi over the centuries smoothed it off. We can see here borings known as Gastrochaenolites, some with outlines of bivalve shells still inside them. This is thus a carbonate hardground.
Some of the units in the Gerofit Formation are lithographic limestones, meaning they are very fine-grained and of uniform composition. You can see in the above photo that the stress pattern around my hammer blow is preserved as a nearly perfect sphere. This rock has been the premier building stone in Israel for millenia. It is known as “Jerusalem Stone” because so many buildings in that city are made of it and its equivalents.
Melissa is standing in what appears to be an ancient quarry for the lithographic limestone. There is a small Iron Age fort made of the stone nearby. Note how bundled up Melissa is. Not the usual image of Israel in this blog!
Finally, all our localities today were on ground that has been part of an IDF training base for decades. There is much discarded military gear around. I thought I would add this old British tin-hat to our blog’s collection of shot-up helmets! (We have German examples already, and somewhere in there is a Russian set.) I neglected to take a photo of a well-worn Egyptian helmet we found this morning.