Vertical variation in porosity of nāri (calcrete) on chalk, Galilee, Israel: A new interpretation as a tribute to Dan H. Yaalon

Abstract

Nāri-calcrete is a calcareous formation common in the semiarid Mediterranean region of the Levant. The profile studied in Nazareth (Galilee) is 2.75m thick and divided into the four conventional layers, i.e. a chalky bedrock, a powdery lower nāri, an indurated and platy upper nāri, and a laminar crust capping the profile. In this study, mercury intrusion porosimetry (MIP) is used to assess the genetic processes at work in the formation of nāri-calcrete. Based on the former work by Yaalon and Singer (1974) and MIP results, various parameters are proposed to describe the different layers: total porosity (NP), trapped porosity (NT), permeability (K), and strength (σc). These parameters are compared to each other for each layer, as well as with their respective calcium carbonate contents. An unexpected relationship shows that the more CaCO3 is present, the more porous the layer of the nāri. Consequently, the lower nāri is interpreted as a weathering layer of the parent chalk, whereas the upper nāri, which is the most porous and the richest in CaCO3, results from in situ recrystallization. The upper nāri permeability precludes it from playing the role of a “plugged horizon” to explain the formation of the laminar crust. In conclusion, the nāri-calcrete in Nazareth questions the conventional model of calcrete genesis as its cementation is due to in situ redistribution of CaCO3 rather than its translocation. These results strengthen Yaalon and Singer (1974)'s conclusions.