Archive for April 21st, 2014

Where sedimentology meets structural geology

April 21st, 2014

A seismite? 042114MITZPE RAMON, ISRAEL–”Like a hot dog in a bun.” Late this afternoon, while exploring the Eocene (Lutetian) Horsha Formation near the Nabatean/Roman/Byzantine city of Avdat, Yoav Avni and I ran across these odd features in a limestone layer within the chalks (near N 30.79119°, E 34.75494°). They consist of an elongate core of coarse, bioclastic sediment (the hot dog) in chalky sediments folded around them (the bun). They are all oriented in the same direction.

Another seismite type 042114Some are as big as canoes; others like gravy boats. We suspect that these are seismites — sedimentary sturctures formed by seismic shaking. The chalky, water-saturated sediment would have responded plastically as the slightly denser bioclastic sediments above collected in troughs and then began to descend down into the chalk. This is just an idea. If someone else has seen structures like these, please let us know!

Byzantine Cistern 042114Just below these funny structures is this nice Byzantine cistern filled with water. It is on the edge of a wadi, with about a half-meter step above the wadi base. It has this narrow doorway that leads into an interior cavern, all hand-carved. During a flood, the water reaches a level in the wadi where it begins to decant into the cistern, reducing the amount of sediment that would otherwise fill the cavity quickly. A couple of years ago Yoav organized a team to excavate centuries of silt from this cistern. Now it is full from the winter rains, providing a water hole for the local Bedouin children. It also shows that the Byzantine water storage and conservation techniques of 1500 years ago still work fine today.