The basal Unit 1a mostly consists of compact, massive beds of silt, clay and some sand, suggesting relatively continuous deposition in a near-shore lacustrine environment. The abundance of small (~250 mm) selenite crystals corroborates this scenario as they
form under relatively stable lacustrine conditions (Magee, 1991). Occasional discontinuous beds of sand, granules and pebbles in this unit point to some degree of variations in lake level and/or a source of coarse sediment in relatively close proximity.