Between 29 and 27 million years ago, the extrusion of Ethiopia’s flood basalts was interrupted and deposition of continental sediments occurred.

[1] The formation, also called silicified limestone and interbedded lacustrine deposits was first extensively characterised in the 1930s by Merla and Minucci.

Between the towns of Hagere Selam and Inda Maryam Qorar (Dogu’a Tembien), roadcuts show around 45 metres thick sedimentary deposits.

The loose to massive sediments of the uppermost part of the formation show well-developed bedding; they are black in colour.

The parts that were originally filled with sediment are preserved as quartzite; in the air-filled cavities translucent quartz has crystallised, sometimes with well-formed crystals.

Depending on mineral inclusions, the colours of the quartzite range from black to pale white over yellowish and pink.

[1] In the Ethiopian flood basalts, rock-hewn churches are absent because the rock is too hard to excavate and vulnerable to underground water flow.