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| Boschma, D.. |
| The area is mainly covered by Carboniferous sediments. Only two Devonian structures are present. The Devonian yielded sufficient fossils from Eifelian up to Famennian but in the Carboniferous fossils are scarce. Permian and Triassic cover the area unconformably in the east. In the Carboniferous several formations of the Ruesga Group and the Yuso Group have been mapped. The base of the Yuso is marked by its basal conglomerate and its unconformable position upon the Ruesga. The divergency of directions of contemporaneous major folds in the map area is controlled by fundamental faults. Two folding phases can be distinguished; Asturian folds with steep axial planes are superposed upon Sudetic recumbent folds. |
| Tipo: Article / Letter to the editor |
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| Ano: 1969 |
URL: http://www.repository.naturalis.nl/record/505935 |
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| Boschma, D.; Staalduinen, C.J. van. |
| Distinct general lithological features, separated by unconformities, serve to distinguish three groups of mappable formations in the Carboniferous of the area, the Ruesga Group, the Yuso Group and the Cea Group. The formations which compose the Ruesga Group can be found in the greater part of the area. In general they start with a limestone series developing upwards and laterally into greywackes. The conglomerates and molasse greywackes formations of the Yuso Group follow and are limited by two major structural zones; in the west the zone that runs over the Pardomino Ridge and the Pontón fault line and in the south the León line. West of the “Pardomino-Pontón” zone other formations have been mapped, but the information is still insufficient for a good... |
| Tipo: Article / Letter to the editor |
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| Ano: 1969 |
URL: http://www.repository.naturalis.nl/record/505621 |
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| Boschma, D.. |
| In the central part of the axial zone of the Pyrenees five distinct phases of folding have been distinguished from the study of minor structures. Traces of a very early phase have been found only in the northern and southern part of the region, which appear on the map as oblique fold structures, and are most prominent from the divergency of lineations and fold axes in these parts of the region. The present aspect of the mountain chain is primarily due to the effects of the main phase in which strong compression produced tight but non isoclinal folds with axial plane slaty cleavage. In the Garonne Dome the slaty cleavage was initially flatlying, in general parallel to the bedding, but occasional folds with crosscutting cleavage have been found. Steep slaty... |
| Tipo: Article / Letter to the editor |
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| Ano: 1963 |
URL: http://www.repository.naturalis.nl/record/505735 |
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| Savage, J.F.; Boschma, D.. |
| This compilation of stratigraphic and structural data accompanying the (re)issue of the 1:50000 sheets completes the project initiated by Prof. L.U. de Sitter in 1950. The total area mapped comprises about 400 km² in a strip more than 150 km from east to west. This part of the Hercynian tectogene is characterized by a very consistent sequence of Palaeozoic shelf sediments only interrupted by syn- to late-orogenetic flysch-molasse development. Neither of these sequences lend themselves to a simple geosynclinal model. Only the suprastructures of the orogene are exposed here; essentially decollement thrusting and folding. Fold and thrust vergences vary through 180° giving the centripetal pattern of the well-known Knee of Asturias. Very minor amounts of... |
| Tipo: Article / Letter to the editor |
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| Ano: 1980 |
URL: http://www.repository.naturalis.nl/record/505792 |
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| Sitter, L.U. de; Boschma, D.. |
| The Carboniferous Pisuerga basin developed north of the León line and as such is the most eastern one of the Asturide basins. The Carboniferous sequence is subdivided into Ruesga Group (roughly Lower Carboniferous + Namurian), Yuso Group (roughly Westphalian) and Cea Group (roughly Stephanian). Since the beginning of the Yuso Group the Pisuerga basin became subdivided into a western and eastern basin and since the beginning of the Cea Group the western basin became subdivided into two separate basins. The main folding started during the Stephanian. A remarkable interaction of epeirogenic and orogenic movements leads to the analysis of a close relation between sedimentological and structural features. Several pronounced structural lineaments can be traced... |
| Tipo: Article / Letter to the editor |
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| Ano: 1965 |
URL: http://www.repository.naturalis.nl/record/505953 |
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