Ancient landscapes: Their nature and significance for the question of inheritance

It is widely believed that much of the world's scenery is youthful. Thornbury's assertion that little of the world's scenery is older than Tertiary and that most of it is no older than Pleistocene dies hard. Yet there is ample evidence, long recognized, that very ancient forms and surfaces (here the term surface is used in the sense of a planation surface, surface d'aplanissement or Einebnungsflache) are an integral part of the contemporary landscape, and that such features are not restricted to the low latitude regions, though they are well preserved there. Many of them were formed in environments very different from that in which they now occur and are thus inherited. Paleosurfaces of many age ranges have been recognized. They can conveniently be considered as of three types: exhumed, epigene and etch

Landscape inheritance: Report of Working Group Number 2

The conventional wisdom is, or until recently has been, that the earth's scenery is essentially youthful, much of it being of pleistocene age. The validity of this assertion was questioned, surfaces and forms of much greater antiquity being cited from several cratonic regions, and also from the older orogens. Exhumed forms, some of them of great age (one inselberg landscape of Archaean age was noted), are more common and extensive than has previously been supposed. Epigene forms of Mesozoic ate are increasingly being demonstrated from the world's cratons and orogens. Etch features also are more widely eveloped than has been realized. It was recommended that studies of denudation chronology be undertaken, possible in relation to contrasted cratonic regions. The nature and age range of surfaces that make up the shields ought to be analysed, the processes responsible for shaping the surfaces, and, in the case of the ancien epigene forms, the reasons for their survival

Early Mesozoic (?Triassic) landscapes in Australia: evidence, argument, and implications

© 2000 by The University of Chicago. All rights reserved.Australia 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

Bornhardts, Bloques e Inselbergs

[Abstract] Bornhardts are steep-sided domical hills. The profiles are associated with sheet fractures, and their plan form with steeply dipping fractures of orthogonal or rhomboidal systems. They are well developed in massive rocks, especially, but not only, in granite, and they occur in various climatic settings. They are found in multicyclic landscapes. They occur in massifs as well as in isolation, as inselbergs; in either setting they meet the adjacent plain or valley floor in a piedmont angle or nick. They may be the basic form from which are derived nubbins and castle koppies. Bornhardts are upstanding for various reasons. For example, sorne are tectonic forms, while others are exposed stocks. Such causations have only local validity. Two competing hypótheses find favour as general explanations. Sorne workers conclude that bornhardts are remnants of circumdenudation, monadnocks de position or Fernlinge, residuals shaped by and remaining after scarp retreat. Others consider that bornhardts are structural forms, Hartlinge, or monadnocks de dureté, which have evolved in two stages and are etch forms. The rock compartments on which they are based resisted subsurface weathering either because of their composition or because of their low fracture density. They are comparable to corestone boulders, with the important difference that whereas corestones are detached, bornhardts remain in physical continuity with the main mass of country rock

Los modelos de evolución del paisaje y la supervivencia de paleoformas

[Abstract] Qne ofthe factots rnitigating against the recognition and acceptance ofvery old palaeosurfaces was, and in sorne rneasure rernains, the tacit acceptance ofsorne ofthe better known rnodels oflandscape evolution. Thus both the steady state and peneplanation rnodels irnply virtual conternporaneity of surface, and though scarp retreat allows for a greater age, the rnaxirnurn is deterrnined by the duration of a cycle, probably of the order of 33 Ma; rnuch younger than rnany fitrnly dated epigene surfaces. Basically landforrn and landscape persistence involves the stability, or only slow rate ofchange, ofsurfaces (divides) ofbounding scarps, or both. Such slow rates ofchange are induced by such factors as resistant bedrock: hence the preservation of rnany palaeoforrns on quartzites, etc. In addition, several rnechanisrns, such as uplift, through drainage, and consequent local «aridity>,; incision and unequal activity; and reinforcernent or positive feedback rnechanisrns, enhance the persistence of surfaces

Reflexiones sobre el destino de algunas ideas geomorfológicas

[Abstract] In geomorphology, as in other sciences, investigation is concerned with the collection and characterisation of data, and the generation and testing of working hypotheses. Considering the analysis of landforms and landscapes, the reasons some explanations have been accepted, others rejected, and yet others refuted but later approved, are examined. In particular, why hypotheses which were considered plausible but were shown to be flawed still received general acclaim, whereas others of obvious merit were ignored, are discussed. The roles of chance and the human factor are also broached

Origen, edad y conservación de una "plataforma elevada", Yarwondutta Rock, Noroeste de la Península de Eyre, Australia Meridional

[Abstract] Yarwondutta Rock is a dimpled platform that was shaped at ground level by soil moisture but subsequently elevated, not because of local tectonism, but by the erosional lowering of the surrounding pedimented plains. Concave or flared slopes fashioned in the erstwhile piedmont were revealed during this erosional phase which took place in the earlier Pleistocene. The elevated platform is now buttressed against dissection by the calcreted surrounding pediments. It is concluded that in technical terms, Yarwondutta Rock appropriately can be referred to as an ‘elevated platform’. ‘Criticism and testing are the essence of our work.’ Remark by Herman Bondi on the occasion of Karl Popper’s 90th birthday anniversary (But with a reminder that a ‘criticism’ is an assessment or evaluation, and is neither implicitly, nor of necessity, adverse. C.R.T.).[Resumen] Yarwondutta Rock es una plataforma pellizcada que fue modelada a nivel del suelo por la humedad del mismo, pero que posteriormente se elevó, no a causa de la tectónica local, sino por el descenso erosivo de las llanuras pedimentadas circundantes. Las laderas cóncavas o acampanadas formadas en el antiguo piedemonte quedaron al descubierto durante esta fase erosiva que tuvo lugar en el Pleistoceno más temprano. La plataforma elevada está ahora reforzada contra la erosión por los pedimentos circundantes de calcreta

Convergencia litológica y climática en la morfología granítica

[Abstract] The major and minor forms eommon to granite (and related erystalline lithologies) and to daeite, sandstone and limestone are listed and briefly deseribed. Faetors eondueive to lithologie eonvergenee (the development ofthe same form in different materials) are identified. The importanee of elimatie faetors in the development of granite landforms, is diseussed, and examples of elimatie eonvergenee (1andforms due to similar meehanisms but driven by different elimatieally eontrolled proeesses) are given. Sorne eonelusions on the importanee ofgranite landform evolution in general geomorphologieal theory are suggested