Pre-Tertiary basement structure of the central Murray Basin, and its effect on groundwater flow patterns

Abstract

The Murray Basin has an area of 320 000 km2 and is one of the most important sedimentary basins in Australia in terms of agricultural and cultural development. It is essentially a closed groundwater basin which consists of a thin cover (200?600 m) of sediments containing 4600 million megalitres of water varying in salinity from 500 mg/L to over 35 000 mg/L total dissolved salts. This study of the central Murray Basin covers an area of 200 ´ 300 km, and is based on 1700 km of seismic refraction, over 300 vertical electrical soundings and the analysis of several thousand bore logs. The pre-Tertiary basement surface was found to have highly variable relief of up to 300 m. A rectilinear system of crustal fractures has been responsible for the formation of a basement ridge complex, identified as the Ivanhoe Block. A three dimensional (3D) representation of the basement has been developed to highlight dominant trends. Occlusion of aquifers across the Ivanhoe Block is a controlling factor affecting the regional groundwater flow, and is a contributing cause of the outflow of saline groundwater to the land surface and the river system.