Holocene sedimentary environments in Lake Eyre, South Australia

Abstract

In late Pleistocene time Lake Dieri (ancestral ‘Greater Lake Eyre') was permanently filled during a wet climatic phase. Towards the close of Pleistocene time the watertable fell, Lake Dieri dried up, and its sediments deflated. Later the watertable rose, establishing ephemeral Lake Eyre in the deflated area, and Holocene sedimentation commenced. At about this time Lake Eyre tilted to the south and three sedimentary environments developed: (1) a saline playa environment without saltcrusts in the northern end of the lake, where water drains away before wholly evaporating; (2) a terminal salina environment in the south end, where evaporation of brines leaves saltcrusts overlying gypseous sediments; and (3) a saline flocculation environment between the playa and salina environments, where sediments are deposited by flocculation when muddy floodwater from the north meets highly saline water of the southern salina.

In the northern playa environment, sedimentation is limited to the top of the capillary fringe above the watertable, below which sediments remain moist and protected from aeolian erosion, but above which they dry and blow out of the lake. In the southern salina environment sedimentation has not kept pace with the Holocene rise in watertable. If and when it does reach such a level, downward leaching of salt and deflation of exposed sediments is likely to occur. In the flocculation environment new deposits of clay are added but kept permanently wet by rising groundwater. When flocculated sediment builds too high, its excess is transferrred by surface water into the salina deposits to the south.

Key words:

• Lake Eyre
• South Australia
• Holocene sedimentation
• ephemeral sedimentary controls
• terminal lake
• sedimentary environments