Description:
In a basalt quarry at Deer Park, near Melbourne, Australia, an upper basalt flow (late Tertiary/Pleistocene) is separated from the lower basalt flow by a layer of red, baked, clayey material about 300 mm thick. The upper 100-150 mm portion of the baked layer is strongly columnar, rich in quartz and contains Mg-poor montmorillonitic clay. The lower portion of the baked layer is blocky when dry and also rich in quartz but contains much more Mg in the montmorillonitic clay as well as in soft, white nodules of saponite. Small amounts of mica and feldspar, and probably a trace of kaolinite are also present in the baked layer. Amorphous materials such as allophane are absent. It has been concluded that the baked layer formed from the weathering of the lower basalt as well as quartz-rich materials transported by wind and/or water, and was indurated by the heat of the subsequent basalt flow.