letter
Bornhardts - an alternative view
Twidale, C. R.; Bourne, Jennifer A.
Zeitschrift für Geomorphologie Volume 21 Issue 3 (1977), p. 363 - 365
17 references
published: Sep 27, 1977
ArtNo. ESP022002103010, Price: 29.00 €
Abstract
We are confident that Lester King will be neither disappointed nor deterred to learn that we still do not agree with his views on the origin of bornhardts, most recently set out with his customary skill and enthusiasm in the "Zeitschrift für Geomorphologie” (King 1975). First, consider Professor King’s several objections to the hypothesis which endeavours to explain bornhardts (and other, lesser, granitic residuals) by subterranean weathering — the two stage hypothesis of some workers. First as he did in an earlier paper (King 1966), he raises the matter of the discrepancy between depth of weathering and the much greater elevation of the bornhardts above the plains. We have looked at this matter and asked ourselves whether the inselbergs could not have emerged in phases each accompanied by a period of weathering which would allow for a considerable disproportion to develop between inselberg height and depth of weathering. We argued that if such episodic exposure had occurred there should be evidence of former piedmont zones, or hill-plain junctions, perched high on the slopes of the residuals. We looked for flared slopes, platforms and associated minor forms that have been initiated in the subsurface, at the weathering front on the granite residuals of Eyre Peninsula (Twidale & Bourne 1975 a and b). We found many and moreover were able to correlate them, albeit tentatively in some instances, with palaeosurface remnants (Twidale & Bourne 1975 a; Twidale, Bourne & Smith 1976). There is evidence of a similar phased exposure of Ayers Rock (see Twidale 1977).
Keywords
bornhardts • weathering • slopes • platforms • inselberg • hill-plain junctions • piedmont zones