The evolution of bornhardts in silicic volcanic rocks in the gawler ranges

Campbell, Elizabeth; Twidale, C. R.

doi:10.1080/08120099108727957

Cited by 62 publications

(29 citation statements)

References 30 publications

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“…It too is of ancient origin (Campbell and Twidale, 1991). Although there is no direct evidence on the point, Permian glaciers must have overridden the present area of the Gawler Ranges for the ice travelled southeast-northwest and glacial deposits of Permian age occur both to the north and to the southeast of the present upland.…”

Section: Crystalline Terrainsmentioning

confidence: 98%

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Geomorphological development of the eastern margin of the Australian Craton

Twidale

Campbell

1992

Earth Surf Processes Landf

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The denudation chronologies of five uplands of contrasting geological structure located at the eastern margin of the Australian Craton are examined. They are the Isa Highlands, MacDonnell Ranges and Flinders Ranges (fold mountains, orogenic setting); the Arcoona Plateau (dissected plateau, platform setting); and the Gawler Ranges (massif of old silicic volcanics, cratonic setting). In each, surfaces of Mesozoic age, many of them exhumed and of pre-Cretaceous age, are preserved. Each also appears to have been uplifted recurrently. Each was either overwhelmed or bordered by the Early Cretaceous (Neocomian-Aptian) sea.Tectonism associated with the break-up of Gondwana probably allowed this important marine transgression. Thereafter, thalassostatic and erosional/depositional isostatic responses have maintained the uplands as uplands and the intervening basins as negative topographic and structural units; the pattern of topography has been constant for the last 60-100 Ma.

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Section: Crystalline Terrainsmentioning

confidence: 98%

“…Whatever their origin, they had developed by the Jurassic. This may be demonstrated by a consideration of the weathering that took place beneath the Beck Surface, of Jurassic age (see below and Campbell and Twidale, 1991). The weathering was guided initially by steeply dipping members of the regional orthogonal system.…”

Section: Crystalline Terrainsmentioning

confidence: 99%

Geomorphological development of the eastern margin of the Australian Craton

Twidale

Campbell

1992

Earth Surf Processes Landf

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“…The degradation of what has been termed the Beck Surface occurred in the Jurassic and possibly the Triassic (Campbell and Twidale 1991), but it cannot be older because the region was inundated by Permian ice sheets. The disruption of the Beck Surface was caused by the upfaulting of the south- ern margin of the ignimbritic massif, possibly related to the separation of Australia from Antarctica.…”

Section: Gawler Rangesmentioning

confidence: 99%

“…Very old epigene and etch paleosurfaces are incompatible with conventional theories of landscape evolution such as those of Davis (1899), King (1942), andHack (1960). Despite published expressions of disbelief and incredulity, the notion that landforms can persist through the ages, and by implication, that long-continued weathering and erosion does not necessarily result in complete baseleveling or the eradication of all signs of earlier surfaces and forms, has gained a measure of acceptance during the past 2 decades (e.g., Twidale 1976Twidale , 1994Young 1983;Bishop 1988), giving rise to a model of landscape development that accommodates such ancient landscapes (Twidale 1991).…”

Section: Implications For Models Of Landscape Evolutionmentioning

confidence: 99%

“…It is bounded on the south by a major fault zone and characterized by a well-developed system of orthogonal or rhomboidal fractures that had been developed during the later Mesoproterozoic. Campbell and Twidale (1991) subdivided the massif into a series of ordered blocks on which bornhardts are developed. Many of these bornhardts display crestal bevels ( fig.…”

Section: Gawler Rangesmentioning

confidence: 99%

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Early Mesozoic (?Triassic) Landscapes in Australia: Evidence, Argument, and Implications

Twidale¹

2000

The Journal of Geology

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A B S T R A C TAustralia has strong claims to be known as the old continent. In addition to landscapes of later Cretaceous-early Tertiary derivation, remnants of early Mesozoic (Triassic-Jurassic) surfaces, which are part of the contemporary landscape, are also recognized. Being of etch type, they have two ages: one referring to the period of preparation by subsurface weathering and the other to their date of exposure. In many instances, exposure can be dated and the period of preparatory weathering closely inferred. Such old paleosurfaces are demonstrated on Kangaroo Island and are strongly implied in, for example, the Flinders, Gawler, and MacDonnell Ranges; in Arnhem Land and the Arcoona Plateaus; in many parts of the Eastern Uplands; and on several bornhardts in the Yilgarn and Gawler Cratons. They reinforce the suggestion that once in positive relief and shedding water, surfaces persist with little change for long periods. Such ancient features are incompatible with several well-known models of landscape evolution. The chronologies and events they imply extend our understanding of the landscape in the chronological context. They add to our knowledge of Earth's history.

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Decay of ignimbrite fairy chimneys of Arizona's Basin and Range Province, USA

Dorn

2023

Earth Surf Processes Landf

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Fairy chimneys of ignimbrite are well studied in Cappadocia in central Anatolia, Turkey. The ignimbrite landforms of Arizona's Basin and Range, USA, in contrast, remain relatively unexplored in geomorphic scholarship, despite decades of geological research on the characteristics of the ignimbrites themselves. This research focuses on the rock‐decay processes that modify Arizona's Basin and Range fair chimneys. Dissolution of glass and groundmass, measured along joints using digital image processing of back‐scattered electron microscope imagery, reveal a 3× higher porosity than inside the rock interior. This method also measured a 3‐4× increase in dissolution near the base of the chimney compared with the rock interior, leading to notch development that promotes chimney mass wasting and subsequent ballistic impacts. Epilithic organisms studied with electron microscopy both enhance rock decay and promote case hardening. These observations are consistent with prior understanding of how fairy chimneys evolve over time: columnar joints exposed on cliff faces experience enough decay to allow erosion of joint material, this erosion separates the chimney from the rock face and notch development near the chimney base promotes mass wasting. The rock‐decay processes studied here likely operate on very different timescales. Mass wasting events leading to ballistic impacts occur at observable timescales. Varnish microlamination dating, using ultrathin sections of rock varnish formed on fairy chimneys, indicates that the case hardening of the top of fairy chimneys are much more stable than the sides; the tops last experienced surface detachment during the early Holocene, as opposed to the sides that experienced flaking throughout the late Holocene. The timescale of basal notch development is not known, with the exception that the very surface of notches erode at rates too fast to accumulate rock varnish. The timescales of epilithic organisms enhancing rock decay and dissolution of columnar joints are not known.

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The evolution of bornhardts in silicic volcanic rocks in the gawler ranges

Cited by 62 publications

References 30 publications

Geomorphological development of the eastern margin of the Australian Craton

Geomorphological development of the eastern margin of the Australian Craton

Early Mesozoic (?Triassic) Landscapes in Australia: Evidence, Argument, and Implications

Decay of ignimbrite fairy chimneys of Arizona's Basin and Range Province, USA

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