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The Nullarbor plain, in southern Australia, presents very interesting and well-developed karstic phenomena. The present day activity is apparently non-existent, due to arid conditions and to the paucity of vegetation. Thus, it is probable that very different conditions prevailed in the past, particularly during the last glacial periods. Atmospheric as well as oceanic circulations were quite different from those of today. Furthermore, a large underground drainage system developed in the limestone platform and reached a depth of at least 100 m; practically the local sea-level. To produce such large dimensions at or below the base level, a lowering of the sea level is necessary, which was the case during the glacial periods. On the other hand, ’’mixing corrosion’’ took (and takes) place at the interface between waters with different mineralization, i.e. fresh water from inland and salt water from the ocean. GOEDE et al. (1990) give an age greater than 400.000 years for speleothems from the region, which is also the limit for the U/Th datation method. From a paleomagnetic study on a black calcite stalagmite fi om the Koomooloobooka cave, we show that it has a reversed direction of remanent magnetisation. It was therefore formed during a period when the geomagnetic field was reversed, and so the stalagmitic floor is at least older than 780.000 years (Brunhes-Matuyama limit).