La herencia de Pangea

[Abstract] Very old palaeosurfaces have been identified and dated in several parts of the former Gondwana and Laurasia. In Australia the separation from Antarctica was complete by the end of the Eocene so that any surface of earliest Tertiary and certainly of Mesozoic age can be regarded as Gondwanan. Similarly, in the Northern Hemisphere, Laurasia existed from the end ofthe Carboniferous to the Jurassic so that any landscape elements older than]urassic can be regarded as Laurasian.The ages of these ancient surfaces have been determined in various ways and with various degrees ofconfidence, but correlative deposits associated with the widespread Early Cretaceous marine transgression , and the relationship of land surfaces to Cretaceous shorelines and Early Tertiary volcanic extrusions, or regolithic veneers have proved especially useful. Faulting of known age has also_been used though it tends to give dates that are too young ,for the dislocated surfaces. Many exhumed surfaces have been preserved by burial, but epigene-etch features like those ofthe Gawler Ranges, Hamersley Ranges and the Arnhemland Massif (Kakadu) have stood as uplands throughout the Cainozoic with little change. The same is true of the remnants of planation surfaces of the Iberian elements ofthe Hesperian Massif. Epigene-etch surfaces ofMesozoic age are also reported from southern and West Africa, from southern India and from the Guyana Craton ofSouth America. In addition, epigene-etch features, as well as exhumed features ofvarious ages, are, increasingly, being recognised from the Laurasian components of Pangaea, for instance in the Linares-Ubeda region in the south of Iberian Peninsula, so that it is possible to refer to the Pangaean inheritance. These survival can in sorne measure be explained in terms oftheir being uplands, but obviously the conventional models of landscape evolution need to be reconsidered

Desarrollo de formas multietapa en varias situaciones geomorfológicas y a diferentes escalas

[Abstract] That many landforms have their origins in the distant past is highlighted by the multistage concept, whereby the structural properties of bedrock which have been exploited by shallow groundwaters are taken fully into account. Fractures of various types are par- ticularly vulnerable to weathering and hence to erosion. Examples are discussed from various lithological and environmental settings - plutonic, volcanic and sedimentary rocks, and different climates

Geomorphic evolution of the Peninsular Hesperian massif: study of a sector situated between Lugo and Ourense provinces (Galicia, NW Spain)

[Abstract] This paper deals with the relief generation in Ourense, an interior territory of the Galicia Country, at NW Spain, after the breakdown of Pangea 200 million years ago. The rupture of supercontinent causes the main effects in the outer part of Galicia, the present coast line and the shelf, but also the inner parts of Galicia where the landscape changes dramatically mainly ruled by fluvial incision connected with uprising, (orogenic, epirogenic, or isostatic origin), or even with eustatic oscillations, that shaped the previous old mesozoic landscape. Various things complicate the correct understanding of Galician geomorphology:1) the prevalent hercynian structure, (presumably reactivated during the Alpine Orogeny), causes that the epigenic processes, (fluvial, glaciar, marine and etching), acting on Galicia from Mesozoic to present times, produce end forms identified erroneously at the previous literature as tectonic and not as etch forms profiting from lithological or structural contrasts. 2) the common morphotectonic model accepted by all previous researchers establishes for the whole of Galicia a blocky pattern, (horst and graben like), due to extensional tectonic regime. This model is proved as no longer valid because the Galician tertiary basins, even were described at the past as graben depressions never have this origin. 3) big differences exist between the north and western sides of Galicia that show contrasted tectonic regime: compressional (with forms as the so called raised platforms), at the northern coast border, and extensional (with forms so typical as the Rias), at the western side. The study area is located at the confluence of two tectonic domains where the above mentioned effects are coincidents and specially well showed through different effects: prominent assimetry of fluvial captures (west facing), pronounced river incision and different kinds of tertiary basins: either strike slipe faults (Maceda, Xinzo de Limia, etc), or overslipped by inverse faults, Quiroga, A Rúa, etc.), or even corresponding with depressions never, (or anywise passively), affected by tectonic movements, (Monforte). The paper include a detailed inventory of surfaces and terrace levels and their incision sequence which allow stablish a relative chronology of geomorphic evolution at this area of NW Spain during meso-cainozoic times

Morphological and structural evidences concerning the origin of sheet fractures

[Abstract] Sheet fractures are well and widely developed in massive rocks, i.e., rocks lacking other partings, and they have been discussed in the literature for more than a century. Yet there is no agreement as to their origino Two contrasted interpretations hold sway. Almost without exception, geologist adhere to the pressure release or erosional offloading hypothesis. Engineers and engineering geologist, on the other hand, interpret sheet partings as buckling, i.e., crumpling or bending out of plane, related to compressive stresses, particularly lateral stresses. After a review of nomenclature and a description of the characteristics of sheet fractures, a critique ofprevious explanations of their origin is presented. What are perceived to be critical Enes of structural and morphological evidence. bearing on the origin ofsheet fracture are next reviewed, and this is followed by a discusion of the possible origins of the structures

TL estimation of ages of pottery fragments recovered from granite caves in the NW coast of Spain

[Abstract] Granite caves and cavities are geomorphological environments associated with underground water flows with a strong turbulent regime linked to seasonality. Though not much studied, they have a great sedimentary and geomorphological interest but sometimes also archaeological because remains of human activity (mainly lithic industry and pottery). Pottery remains appear either exposed or buried and may be characterised mineralogically and dated by thermoluminescence (TL). Water dynamics justifies erosion and fragmentation of ceramic remains which appear broken and spread inside the cavities. This fact hinders their dating due to the small size of the fragments and the disappearance of the original sedimentary context, which does not allow the calculation of part of the received annual radiation dose. In this work, the results from the dating and the estimation of ages of different ceramic fragments of several granite caves of Galicia are presented. The obtained ages go from Medieval (1 ka BP) to Roman or pre-Roman (2 ka BP), Chalcolithic (6 ka BP) and even the beginning of the Neolithic (7 ka BP)

Morphological and mineralogical characterization of speleothems from the Chimalacatepec lava tube system, Central Mexico

Siliceous, opal-A speleothems of the Chimalacatepec lava tube system in central Mexico are characterized here for the first time. Morphologically, they can be classified into cylindrical and planar, and display a wide array of shapes, inner textures, and locations within the lava tube. All speleothems analyzed here are composed of opal-A, and their pores are filled with calcite and monohydrocalcite. Microscopic examination reveals a variety of microbial-looking, silicified filaments and cell casts embedded within the micro lamination of the structures. The abundance of biofilms in the Chimalacatepec lava tube may share similarities with other volcanic caves elsewhere. The direct presence of such bimorphs in the microstructure of the speleothems suggests the biological mediation of these structures. Potential mechanisms include nucleation and sorption of silica on extracellular polymeric substances in the biofilms that, along with the SiO2 saturation in the water film and evaporative effects, result in the formation of a speleothem. That said, the presence of microbes in these and other cave systems, or their inevitable interactions with the mineral phase of the speleothems, should not be surprising. In view of this, these structures can be most accurately described as biospeleothems. This study contributes to our understanding of the diversity of such structures in these types of cave systems and our ability to recognize the presence of microbes in these

Microrrelevo litorâneo versus pegadas fossilizadas humanas na região El Caracolero (Claromecó, Argentina)

Se discute el origen de una serie de cavidades que han sido interpretadas como huellas humanas en un lugar de la costa Atlántica pampeana conocido como el Caracolero de Claromecó (partido de Tres Arroyos, provincia de Buenos Aires, Argentina). Las mencionadas huellas se encuentran en una roca que aflora en la plataforma de abrasión litoral. Su descubrimiento y la atribución de una alta antigüedad de ca. 30.000 años 14C AP tuvieron repercusión en los medios de comunicación, donde fueron inicialmente dadas a conocer. Los resultados de los estudios litológicos realizados permitieron establecer que el sustrato rocoso está constituido por una arenita con cemento carbonático que se correlaciona con depósitos de la transgresión pleistocena de edades cercanas a los 120.000 años AP. Los rasgos morfológicos de las cavidades de la plataforma de abrasión se corresponden con aquellos producidos por disolución natural del carbonato y definidos en la literatura geológica principalmente como “pans” y “pits”. Finalmente, de acuerdo con la información disponible, se concluye que las cavidades definidas como icnitas humanas de Claromecó no poseen claro origen antrópico, y, por tanto, hasta que no se demuestre lo contrario no pueden ser consideradas en la discusión arqueológica sobre el poblamiento temprano de América.The aim of this paper is to discuss the origin of a series of cavities from an area of the Atlantic coast in the Pampean Region known as the Caracolero from Claromecó (Tres Arroyos County, Buenos Aires Province, Argentina) which, have been interpreted as human footprints. They are located on a rock that outcrops on the littoral abrasion platform. The discovery of the footprints and their ascription of a high antiquity ca. 30.000 years 14C BP was initially disclosed to the media, where they first had an impact. The lithological studies carried out allowed to establish that the features of rocky substratum consist of an arenite with carbonate cement linked to deposits from the Pleistocene transgression dating back to 120.000 years BP. The morphological features of the abrasion platform’s cavities match those produced by natural carbonate dissolution and are mainly defined as “pans” and “pits” in the geological literature. Finally, according to the available information, it is concluded that the cavities from Claromecó do not have a clear anthropic origin. Therefore, they cannot be taken into account in the archaeological debate about the early peopling of the Americas.Neste artigo, discute-se a origem de uma série de cavidades que têm sido interpretadas como pegadas humanas num lugar do litoral atlântico pampiano conhecido como o Caracolero de Claromecó (partido de Tres Arroyos, província de Buenos Aires, Argentina). As mencionadas pegadas se encontram numa rocha que aparece na plataforma de abrasão litoral. Seu descobrimento e a atribuição de uma alta antiguidade de ca. 30.000 anos 14C AP tiveram repercussão nos meios de comunicação, em que foram inicialmente dadas a conhecer. Os resultados dos estudos litológicos realizados permitiram estabelecer que o substrato rochoso está constituído por uma arenito com cimento carbonático que se correlaciona com depósitos da transgressão pleistocena de idades próximas aos 120.000 anos AP. Os traços morfológicos das cavidades da plataforma de abrasão se correspondem com aqueles produzidos por dissolução natural do carbonato e definidos na literatura geológica principalmente como “pans” e “pits”. Finalmente, de acordo com a informação disponível, conclui-se que as cavidades definidas como pegadas fossilizadas humanas de Claromecó não possuem claramente origem antrópica e, portanto, até que não seja demostrado o contrário, não podem ser consideradas na discussão arqueológica sobre o povoamento precoce da América.Fil: Bonomo, Mariano. Universidad Nacional de La Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Blasi, Adriana. Universidad Nacional de La Plata; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentin