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

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

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

Distintos orígenes para las formas graníticas menores

[Abstract] The many minor forms developed on granitic terrains, on bornhardts and other residual hilis, on boulders, on sheet structures and on platforms, vary in origino Different modes of initiation and subsequent development are discussed and it is concluded that several forms typical of granite are convergent

Playas of inland Australia

[Abstract] Playas, mostly in the form of salinas, are characteristic of the Australian arid zone. Many are associated with lunettes in sebkha complexes or assemblages and can be attributed to the deflation of bare alluvial flats. Many playas are structurally controlled. Lake Eyre, for example, occupies a downfaulted segment of the crust, and many other playas large and small are associated with faults. Lakes Frome, Callabonna, Blanche, and Gregory each displays a linear shoreline, but also and arguably, all are located on a regional structural arc. Lake Gairdner occupies a valley probably blocked by faulting. Others may be caused by preferential weathering along fracture zones, some linear but others arcuate. Many salinas are developed in dismembered rivers channels, the position and pattern of which are structurally determined. But many owe their existence to the interaction of several of these factors. The various salts precipitated in playas constitute a significant resource, regional and local, past, present and future