Weathering mechanism of arenite sandstone with sparse calcite cement content

Abstract

We conducted a multifaceted analysis of the weathering zones of arenite, containing a minute amount of calcite cement, based on mineralogical, chemical, and physical properties. The survey targeted sandstone with mudstone interbeds belonging to the Cretaceous Izumi Group. The survey revealed that the weathering mechanism is a chain reaction; the most important process is the pore opening between the grains caused by the dissolution of calcite cement in the initial stage of weathering. Subsequently, the pores between the grains connect and widen, separating the sand grains within the sandstone. This primary weathering action may be a major difference from wacke. During calcite dissolution in the initial stage, sulfuric acid generated by pyrite oxidation in sandstone plays an important role. Chlorite breaks down as calcite dissolves; however, iron resulting from the breakdown disappears only after the pore water has been replaced by acidic water.Sandstones with advanced diagenesis are dense and hard, and it was previously assumed that thick weathering zones could not develop because they were less susceptible to weathering. However, we discovered that weathering caused arenite with a minute amount of calcite cement to disintegrate into grains down to a depth of 30 m. The surface layer of the weathered arenite lost fine particle fraction and crept to form a fragile soil layer susceptible to landslides.