Layla Lakes, Saudi Arabia: The World-Wide Largest Lacustrine Gypsum Tufas

Abstract

Throughout the center of Saudi Arabia the anhydrite upper Jurassic Heethformation can be followed N to S. Locally it is punctured by hypogene karst sinkholes. The most prominent are the former Layla Lakes at 22.17°N 46.70°E. The lakes (17 originally) have been drained in the late 1980’s, revealing 19 sinkholes, some of them composites of several subsidence centers. The largest is 1.1 km long, 0.4 km wide and about 40 m deep. Others are less than 10 m across and rather recent. The bottom of the former lakes and the flats around them are composed of thick layers of fine-grained lake chalks. The most striking feature of these sinkholes is the several meters thick tufa covering the vertical walls of the sinkholes. It formed sub-aqueous and is entirely composed of gypsum. Morphologically the tufa displays thick bulbous forms at the bottom changing to conical forms at middle depthto gour-, gutter-, or shovel-like forms near to the former lake surface. The mineralogy and morphology of this tufa appear to be singular world-wide.