Comment on “10Be and 26Al Evidence for Exceptionally Low Rates of Australian Bedrock Erosion and the Likely Existence of Pre- Pleistocene Landscapes” (Bierman and Turner, 1995)
Comment on “10Be and 26Al Evidence for Exceptionally Low Rates of Australian Bedrock Erosion and the Likely Existence of Pre- Pleistocene Landscapes” (Bierman and Turner, 1995)
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对“10Be 和 26Al 证据证明澳大利亚基岩侵蚀率极低以及可能存在前更新世景观”的评论（Bierman 和 Turner，1995）
DOI：
10.1006/qres.1997.1934
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发表时间：
1997
影响因子：
2.3
通讯作者：
C. Twidale
中科院分区：
文献类型：
--
作者：
C. Twidale
The paper published in Quaternary Research by Bierman For example, though Ayers Rock (Uluru) can be argued to be of Maastrichtian age (70 myr), and the prominent and Turner (1995) is marred by inadequate attention to the literature, both systematic and regional, concerning inselsummit bevel is the etch equivalent of the original, it is equally certain that the flanks of the residual have been bergs, bornhardts, and Eyre Peninsula. The authors’ speculations are not only at odds with the field evidence and general steepened by successive alternations of scarp-foot weathering and erosion, so that the overall morphology and theory but also internally inconsistent. Such inconsistencies, and especially the conflicting claims concerning dating on relief amplitude of the inselberg have changed through time (Twidale, 1978; Harris and Twidale, 1991). Simithe basis of cosmogenic nuclide accumulations on the one hand and the denial of the possibility of dating on that basis, larly, there are persuasive arguments that many of the inselbergs of northern Eyre Peninsula have increased in are confusing. These perceived shortcomings are considered here under three headings, but as the thrust of the paper relief amplitude as a result of repeated lowerings of the surrounding plains (Twidale and Bourne, 1975a; Twidale, under discussion concerns the antiquity of some elements of 1982a). But these processes have not eliminated the conthe landscape of Eyre Peninsula, South Australia, it is prutemporary features, which closely mimic the original dent first to consider what geologists, geomorphologists, and (Hills, 1975, p. 300). The present form is a direct descendphysicists mean by the ‘‘age’’ of a land surface. ent of the original feature which is of at least late CretaIn geological terms, the age of a stratum, or surface, refers ceous age. to its date of origin. A Neocomian sandstone bed originated in early Cretaceous times, about 130–140 myr ago. Its age is not measured by a calendar or hourglass, but its relative DO COSMOGENIC NUCLIDE ACCUMULATIONS age is deduced from its relationship to adjacent strata, and PERMIT DATING OF LAND SURFACES? its stratigraphic age from its fossil content or from its position vis-à-vis strata or other rocks of known age. Since depoBierman and Turner evidently employ the terms ‘‘age’’ sition, it has not remained in its pristine state, but it persists or ‘‘date’’ in this geological or stratigraphic sense. In the as a contemporary feature; yet it is referred to as Neocomtitle of the paper they refer to the likely existence of preian—its age of origin. Pleistocene landscapes. In columns 11 and 12 of their Table Similarly, and concerning destructional or erosional land1, they list minimum ages of samples, and presumably the scapes, an inselberg or a massif may be deduced to have surfaces from which they were taken, according to abunformed in early Cretaceous times. Its age is not measured dance of different isotopes. In an earlier contribution (Bierin the sense that a rate of erosion may be measured by man and Caffee, 1994) it was stated that isotope abundances direct comparisons over time, or to some fixed datum, but imply that the surfaces sampled ‘‘are not remnants of a is inferred, perhaps by reference to associated deposits laid Mesozoic landscape.’’ Again (p. 382), they extrapolate their down in an adjacent basin (e.g., Campbell and Twidale, maximum limiting erosion rates and conclude, though in 1991). There are exceptions, but like most strata, the majority apparent denial of the previously quoted comment, that ‘‘the of landforms are not formed instantly, but over a period of form of some Australian inselbergs originated in the Tertiary time, and are best accorded an age range rather than an age or earlier . . . .’’ These statements clearly imply a capacity (Twidale, 1956; King, 1962). This requirement is, however, to recognize antiquity and to evaluate dates and ages. Yet usually met by the latitude implied in a stratigraphic age, in reference to the inselbergs of Eyre Peninsula, Bierman for to label a feature or a stratum Neocomian, for instance, and Turner (p. 382) also state that cosmogenic nuclide abunis to imply an absolute age within a range of rather more dances ‘‘cannot be used to assign an ‘age’ to these bedrock than 10 myr. landforms.’’ They assign age limits to surfaces, and claim Commonly, the morphology of the inselberg is manithem to be very old, but how old is old? An analogy may be drawn with exhumed surfaces like that exposed on the festly altered by weathering and erosion after initiation.
