Tertiary evolution of the coastal lowlands and the Clyde River palaeovalley in southeast New South Wales

• Published in: Australian journal of earth sciences Vol. 46; no. 2; pp. 173 - 180
• Main Authors: Spry, M. J., Gibson, D. L., Eggleton, R. A.
• Format: Journal Article
• Language: English
• Published: Melbourne, Australia Taylor & Francis Group 01.04.1999; Blackwell Science Pty
• Subjects: basalt; Bergalia Formation; Clyde River; drainage (geomorphology); Oligocene; sediments
• ISSN: 0812-0099; 1440-0952
• DOI: 10.1046/j.1440-0952.1999.00702.x

Fluvial sediments, here assigned to the Bergalia Formation, adjacent to the middle reaches of the Clyde River near Batemans Bay on the New South Wales south coast were deposited prior to a basalt valley flow with K-Ar ages averaging 27.7 ± 0.3 Ma. Similar Bergalia Formation sediments are preserved near Mogo, south of Batemans Bay, and suggest that the Clyde River flowed south through the Mogo area prior to diversion to the east. The diversion resulted from local-scale neotectonic movements or sea-level changes after the mid-Oligocene. The previously undescribed deposits at these two locations provide evidence that relief comparable to or greater than the present existed in the Clyde River valley by this time. The basalt and sediments in the Clyde River valley indicate that the coastal lowlands in southeast New South Wales were developed prior to the mid-Tertiary period.