Morphometry and spatio-temporal evolution of salt karren

Abstract

Morphometric data on karren developed in evaporite rocks, and especially salt, are almost lacking. Additionally, the models proposed to explain the evolution of some karren such as solution flutes (rillenkarren) and solution bevels are not based on real examples but on physical experiments or conceptual models poorly supported with data. Rocksalt, thanks to its high solubility and transport-controlled dissolution kinetics, offers the opportunity to investigate the morphological evolution of karren in short periods of time. This work uses high-resolution, multi-temporal 3D surface models generated by Structure from Motion (SfM) photogrammetry of a salt exposure in the Cardona salt diapir, NE Spain, to address the following issues: (1) morphometric characterisation of salt karren, (2) comparison with data from other lithologies and (3) morphological evolution of salt karren. Solution pits and solution flutes in salt tend to have significantly larger width and much larger depth than in carbonate rocks and gypsum. Solution flutes and solution bevels show complex evolutionary patterns that do not align with the commonly advocated parallel retreat and morphological persistence model. Instead, flutes can experience substantial morphological changes involving coalescence by the destruction of slim ridges and splitting caused by incision in the resulting broad flutes. The rillenkarren-bevel junction experiences a general downward and backward displacement, but locally can propagate forward by the development of intra-bevel flutes that merge with the rillenkarren slopes. Pedestals can grow vertically at rates as high as 5 cm/year.