Triassic Buntsandstein Research Articles

Lead isotope systematics of epigenetic lead-zinc mineralization in the western part of the Rheinisches Schiefergebirge, Germany

In the western part of the Rheinisches Schiefergebirge three different types of epigenetic lead-zinc vein mineralization in Paleozoic rocks can be distinguished: 1. Syntectonic Variscan veins, 2. post-Variscan (Saxonian) veins mainly in Paleozoic siliceous clastic rocks, 3. post-Variscan carbonate-hosted mineralization in the Aachen-Stolberg area. Ore impregnations occur in the Triassic Buntsandstein (Bunter sandstone) and Muschelkalk of the Maubach-Mechernich triangular depression covering the Paleozoic rocks. Data points define two distinct populations in both lead isotope diagrams and thus indicate two major Variscan and post-Variscan mineralization events. The lead isotope pattern of the Paleozoic sedimentary rocks bears good evidence that this thick rock sequence may be the main source of metals for the mineralization. The metals were mobilized at deeper levels by saline fluids at different times. There are no direct indications for remobilization of the older Variscan vein ore deposits. The sandstone- and carbonate-hosted ore impregnations of Maubach-Mechernich have a similar lead isotope pattern to the post-Variscan mineralization in the Paleozoic sedimentary basement.

Inversion of Reservoir Quality: An Example from the Triassic Buntsandstein, Offshore Netherlands

Sandstones from the Triassic Main Buntsandstein form a major gas reservoir in the Netherlands offshore. The sequence is dominated by siliciclastics deposited in an arid continental setting, and include dune, interdune, sheetsand, and fluvial sandstones. Reduction in reservoir quality is caused primarily by dolomite, halite, and anhydrite cementation, with minor authigenic illite and chlorite. Integration of petrographic and isotopic data has allowed the origins and relative timing of the different cements to be constrained. The carbon and oxygen isotopic composition of dolomite ([delta][sup 13]C = -3.76 to -9.3%, [delta][sup 18]O = -3 to +2.9% PDB) combined with strontium isotopic data (0.7091 to 0.7109 [sup 86]Sr/[sup 87]Sr) suggest that is precipitated from meteoric groundwater. Halite and anhydrite formed from a mixture of meteoric water and saline fluids expelled from underlying evaporites and claystones. Sulfur isotopic data (+4.2 to +12.1 CDT) support6 this interpretation for the origin of the anhydrite. Precipitation of the major authigenic minerals occurred during early diagenesis, prior to burial depths of 500 m. Cementation and groundwater flow followed the zones of highest permeability and caused an inversion of reservoir quality. Sandstones with the highest depositional porosity and permeability (i.e., dune sandstones) are the most cemented, and have poorermore » reservoir quality compared to the fluvial and interdune sandstones, which originally had lower depositional porosity/permeability. Formation of authigenic illite and chlorite occurred during burial and has significantly reduced permeability. Information on the depositional settings and paleogeography, combined with expected groundwater flow, has helped define potential exploration areas of reduced reservoir quality as a result of extensive early cementation.« less

Development of the Permian-Triassic Sequence in the Basin Fringe Area, Southern Netherlands

Geological studies in the fringe area of the southern Permian basin led to new insights in the distribution and development of the Permian-Triassic sequence. During the Permian, the fringe area formed a platform, attached to the London-Brabant Massif, while during the Triassic it is characterized by strongly subsiding half grabens. In the southern Netherlands, Rotliegende sandstones and conglomerates have a much wider distribution than previously recognized. The Rotliegende deposits are capped by claystones and carbonates of the Upper Permian Zechstein. In the offshore, an important feeder system of clastics from the London-Brabant Massif was active during deposition of the Rotliegende and the Zechstein. In course of time, the location of major sandstone deposition shifted westward. Deposition of the Triassic Buntsandstein was controlled by the development of a large feeder system, which transported clastics from the Vosges northward, through the Roer Valley Graben and West netherlands Basin into the Off Holland Low. This system was responsible for the deposition of the economically important sheet sandstones of the Volpriehausen, Detfurth, Hardegsen, and Solling formations. A regional unconformity occurs below the Solling Formation. The sandstones are capped by claystones, evaporites, and sandstones of the Rot Formation. During deposition of the Muschelkalk, the differencesmore » in subsidence decreased and shallow marine sediments are interbedded with evaporites. Several unconformities occur within the Keuper. In the previous half grabens in the southern Netherlands, the Keuper is incomplete, which may be indicative for a possible reversal of the tectonic movements during this period.« less

The role of mixing-zone dolomitization in sandstone cementation: evidence from the Triassic Buntsandstein, the Iberian Range, Spain

Petrographic and geochemical data suggest that dolomite cement in shallow-marine sandstones of the Triassic Buntsandstein in the Ateca horst of the Iberian Range, Spain, has precipitated in the zone of mixing between phreatic meteoric and marine waters. Dolomite or rhombohedric crystals consisting of concentric bands of alternating syntaxial dolomite and calcite have filled isolated voids (350 μ–12 mm in diameter). Subsequently, limpid dolomite followed by sparry calcite precipitated in void center as the latest cements. The carbonates have low δ 13 C PDB (−9.5 to −6.0%) and δ 18 O PDB (−8.1 to −3.2%.) values and are enriched in radiogenic strontium ( 87 Sr/ 86 Sr = 0.710112 to 0.720293) indicating a dominantly meteoric component in the porewaters. The overall sequence of carbonate cementation suggests precipitation from porewaters that evolved in the mixing zone with successively increased meteoric influence, and finally to fully meteoric probably due to a major sea-level fall.

Diagenetic K‐feldspar pseudomorphs in the Triassic Buntsandstein sandstones of the Iberian Range, Spain

ABSTRACTEarly diagenetic K‐feldspar in the Triassic Buntsandstein of the Iberian Range (Spain) occurs as pseudomorphs after detrital K‐feldspar (Or<93) and plagioclase (Ab<96). These pseudomorphs are chemically pure (Or>99), untwinned, commonly heavily clouded by vacuoles and tiny inclusions, dark‐luminescing and are composed of numerous fine euhedral crystals of K‐feldspar. The latter property suggests that the pseudomorphs form via dissolution of detrital K‐feldspar and plagioclase and precipitation of authigenic K‐feldspar. X‐ray diffraction analysis shows that the authigenic K‐feldspar is intermediate microcline.

Palaeomagnetic evidence for rotations and deformation in the Nogueras Zone, Central Southern Pyrenees, Spain

A multicomponent palaeomagnetic remanence from the Lower Triassic Buntsandstein redbeds of the Central Southern Pyrenees has been interpreted as being composed of three components; a low blocking temperature recent viscous magnetization (L), an intermediate blocking temperature Eocene remagnetization (I), and a high blocking temperature Lower Triassic remanence (H). These palaeomagnetic results can be used in conjunction with structural evidence to identify poles of rotation during the development of the Nogueras Zone antiformal stack. Poles from individual sites reflect local deformation and folding, including vertical rotation due to shearing between adjacent thrust sheets. The I component was sometimes acquired syn-tectonically during thrust motion, and can be used to define intermediate stages of structural development. Results from sites located on a single thrust sheet (‘No. 7’) indicate that it rotated by 45° clockwise during emplacement. This is reflected in an easterly increase in displacement estimated from the construction of balanced cross-sections. Thrust sheets appear to have been pinned close to the present day location of Pont de Suert during the later stages of structural development. The arcuate path of thrust sheet motions, and the potential movements in and out of cross-section, can lead to over- and under-estimates of minimum displacement when using line-length cross-section balancing techniques.

Die Schwermineralführung des Buntsandsteins in Tiefbohrungen Frankens und benachbarter Bundesländer (1953--1960). Stratigraphische und paläogeographische Aspekte

Die Schwermineralführung des Buntsandsteins in Tiefbohrungen Frankens und benachbarter Bundesländer (1953--1960). Stratigraphische und paläogeographische Aspekte

Schrägschichtungsanalyse am Beispiel des Buntsandstein in Nordbayern

Schrägschichtungsanalyse am Beispiel des Buntsandstein in Nordbayern

Quelques directions de courants dans le Buntsandstein de la Sarre et de la Lorraine septentrionale

Abstract Study of the oblique and intersecting stratification planes of the lower Triassic Buntsandstein sandstone of the Saar and northern Lorraine region shows provenance was from south and west. Major current direction was W-E, but the SW-NE direction was important.