Scale of relief growth in the forearc of the Andes of Northern Chile (Arica latitude, 18°S)

The stream profiles of rivers of northern Chile reveal two graded segments separated by 20‐km‐long knickzones. Their formation was initiated in the Late Miocene in response to surface uplift of the western flank of the Altiplano. This phase of uplift that was coeval with the shift of deformation from the Altiplano to the sub‐Andean zone caused relief to grow at the scale of the whole drainage basin. Above and beneath these knickzones, the presence of braided channels and the absence of erosion on adjacent pediplains suggest no substantial modification in the local relief. The knickzones, however, show bedrock channels, and fluvial dissection rates have exceeded erosion rates on adjacent pediplains by two orders of magnitudes. Hence, the data imply that the only geomorphic recorders of relief growth are the knickzones that currently transpose the effects of the Late Miocene phase of surface uplift from the coast to the Altiplano.     

57Fe− and 119Sn− Mössbauer study on stannite (Cu2FeSnS4)-kesterite (Cu2ZnSnS4) solid solution

A combined ⁵⁷Fe and ¹¹⁹Sn Mössbauer study is performed on the whole solid solution stannite-kesterite consisting of natural and synthetic samples. No discontinuous change of the Mössbauer parameters of ⁵⁷Fe as well as of ¹¹⁹Sn as function of the composition is observed, thus confirming the existence of a complete solid solution between both compounds.     

Grußwort

Ohne Zusammenfassung     

Druckspannungsindizien in den Sedimenttafeln des Rheinischen Schildes

Zusammenfassung Die Horizontalstylolithen im Deckgebirge des Rheinischen Schildes zeigen eine N-S-gerichtete Verkürzung der Schichttafel an. Dabei schwenkt die Hauptspannungsrichtung linksrheinisch nach NNW, rechtsrheinisch nach NNE und NE um. Die Verkürzung der Schichttafel liegt in der Größenordnung von 0,3 bis 0,7%. Die Querplattung des Unteren Muschelkalks wird als eine materialbedingt andersartige Reaktionsvariante desselben Spannungsplanes gedeutet. Sie sollte treffender als Längsplattung bezeichnet werden.

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Horizontal stylolites in the mesozoic sedimentary plateaus on either side of the Rhein-Graben indicate a shortening in N-S-direction. The direction of main stress turns to NNW on the left, and to NNE-NE on the right side of the graben. The shortening of the plateau amounts to the order of 0,3–07%. Querplattung (dip slab jointing), typical of the lower Muschelkalk, is conditional to the material interpreted as another reaction belonging to the same stress system, and should be defined as Längsplattung (longitudinal slab jointing).

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Résumé Les stylolites horizontaux du plateau mésozoique des deux côtes du Fossée Rhénan indiquent un resserrement en direction N-S. La direction de la pression principale de la rive gauche du Rhin se tourne vers NNW, de la rive droite vers NNE et NE. Le resserrement du plateau range dans l'ordre de grandeur de 0,3–0,7%. Les diaclases plaquetées croisées (Querplattung) du Muschelkalk inférieur sont interprétées comme une autre variante de réaction du même plan, occasionée par la différence du materiel. On devrait les definir plus exactement comme diaclases plaquetées longitudinales (Längsplattung).

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N-S . NNW NNE NE. 0,3%–0,7%.

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Herrn Professor Dr.Roland Brinkmann zum 70. Geburtstag gewidmet.     

Assessment of soil erosion in a small watershed covered by loess

Loose sediments like loess are easily erodable especially on hillslopes used for agriculture. Erosion contributes to the sedimentation and pollution of lakes such threatening quasi-natural ecosystems. On the other hand soil erosion damages fertile soils.The aim of the present paper is the assessment of soil and nutrient loss in a tributary catchment of Lake Balaton, including geoecological aspects of the lake ecosystem and of the slopes mantled by loess.The USLE is applied for small topological units, for the so called erotops. Rainfall simulation experiments were applied for the determination of the erodibility of soils. The calculation is based on a new, GIS aided method. Control measurements have been going on for four years at a gauging station to check how much sediment and water actually leaves the catchment.Results of sediment yield measurements were compared with the results obtained by the application of USLE for the whole catchment. According to this comparison only 2% leaves the catchment so that redeposition processes within the catchment are very important whereas the contribution of soil erosion to the eutrophication of the lake is not very significant in the small tributaries in the northern part of Lake Balaton catchment.     

Tectono‐sedimentary evolution of the northern Iranian Plateau: insights from middle–late Miocene foreland‐basin deposits

Sedimentary basins in the interior of orogenic plateaus can provide unique insights into the early history of plateau evolution and related geodynamic processes. The northern sectors of the Iranian Plateau of the Arabia–Eurasia collision zone offer the unique possibility to study middle–late Miocene terrestrial clastic and volcaniclastic sediments that allow assessing the nascent stages of collisional plateau formation. In particular, these sedimentary archives allow investigating several debated and poorly understood issues associated with the long‐term evolution of the Iranian Plateau, including the regional spatio‐temporal characteristics of sedimentation and deformation and the mechanisms of plateau growth. We document that middle–late Miocene crustal shortening and thickening processes led to the growth of a basement‐cored range (Takab Range Complex) in the interior of the plateau. This triggered the development of a foreland‐basin (Great Pari Basin) to the east between 16.5 and 10.7 Ma. By 10.7 Ma, a fast progradation of conglomerates over the foreland strata occurred, most likely during a decrease in flexural subsidence triggered by rock uplift along an intraforeland basement‐cored range (Mahneshan Range Complex). This was in turn followed by the final incorporation of the foreland deposits into the orogenic system and ensuing compartmentalization of the formerly contiguous foreland into several intermontane basins. Overall, our data suggest that shortening and thickening processes led to the outward and vertical growth of the northern sectors of the Iranian Plateau starting from the middle Miocene. This implies that mantle‐flow processes may have had a limited contribution toward building the Iranian Plateau in NW Iran.     

Natural arsenic in Triassic rocks: A source of drinking-water contamination in Bavaria, Germany

 The aquifer system of the Upper Triassic Keuper Sandstone, an important source of drinking water in northern Bavaria, is affected by elevated arsenic concentrations. Within the study area of 8000 km², no evidence exists for any artificial source of arsenic. Data from about 500 deep water wells show that in approximately 160 wells arsenic concentrations are 10–150 μg/L. The regional distribution of arsenic in the groundwater shows that elevated arsenic concentrations are probably related to specific lithofacies of the aquifers that contain more sediments of terrestrial origin. Geochemical measurements on samples from four selected well cores show that arsenic has accumulated in the rocks. This indigenous arsenic is the source of arsenic in the groundwater of certain facies of the middle unit of the Keuper Sandstone. Received, June 1998 / Revised, January 1999, May 1999 / Accepted, June 1999