GATHODOLUMINESCENCE INVESTIGATIONS AND TRACE-EI . EMENTANALYSIS OF OUARTZ BY MICRO . PIXE : tMPLtCAilONS FOR DTAFENETTC AND PROVENANCE STUDIES lN SANDSTONE
Hot-cathodoluminescence (CL) microscopy and high-resolution trace-element analyses by Particle lnduced X-ray Emission (micro-PIXE) using the proton microprobe have been applied to samples of quartz arenite in order to obtain information about their diagenetic environment and the provenance of quartz detritus. The occurrence of an intensely zoned orange-brown cemenl generation within quartz overgrowths in quartzitic lenses from the Fontainebleau Sand (Oligocene, Paris Basin) coincides with increased Fe concentrations of up to 192 ppm. ln contrast, the Fe content of a nonluminescing generation within the same overgrowths is significantly lower. This finding suggests that the CL is either activated by the Fe itself or caused by defects induced by the incorporation of Fe into the structure. Detrital grains of quaflz from sandstone samples of different ages and locations (Wiehengebirgsquarzit, Upper Jurassic, northwestem Germany; Fontainebleau Sand, Oligocene, Paris Basin) yield a good correlation between CL color and Fe and Ti concentrations, with Fe (up to 455 ppm) being more abundant in red-browniuminescing grains and Ti (up to 298 ppm) confined to grains with blue-violet luminescence. Ti is universally present in quartz from plutonic and extrusive igneous rocks, but rarely observed in quartz from metamorphic rocks. This supports the general contention that the blue-violefluminescing quartz was formed under higher temperatures than the quartz with brown luminescence, an observation important for studies of sandstone provenance. Conceming the mechanisms of CL activation, these results do not unequivocally prove that the observed colors are activated by the elements sought. Despite the advantages of the microanalytical technique, the observed trace-element contents may still reflect submicroscopic inclusions rather than element incolporation into the structure.
Zur Stratigraphie der grobklastischen Fazies im Oxfordium des Wiehengebirges
ZusammenfassungDer Fund vonPeltoceratoides instabiliformis n. sp. in Steinbrüchen am Gehn nordwestlich von Osnabrück (Abb. 3) liefert weitere Kriterien, daß der Wiehengebirgssandstein, dessen stratigraphische Stellung wegen Mangel charakteristischer Fossilien unsicher ist, ins höhere Oxfordium zu stellen ist. Diese grobklastische Fazies vertritt im Wiehengebirge im wesentlichen die für das Wesergebirge typische kalkige Fazies des Korallenooliths. Anschließend wird zu einer neueren paläogeographischen Mitteilung über den Korallenoolith Nordwestdeutschlands kurz Stellung genommen.AbstractIn quarries at the Gehn NW of Osnabrück, several specimens ofPeltoceratoides instabiliformis n. sp. have been found. This gives further indications to the stratigraphic position of the „Wiehengebirgs sandstone“ — which is uncertain, due to the lack of characteristic fossils — to be of Upper Oxfordian age. In the Wiehengebirge though, this coarse clastic facies substitutes to a large extent the calcareous facies of the „Korallenoolith“ typical for the Wesergebirge.A recent paleogeographic report on the „Korallenoolith“ of NW-Germany is then briefly discussed.RésuméLesPeltoceratoides instabiliformis n. sp. découverts dans des carrières du Gehn au nord-ouest d'Osnabrück fournissent d'autres indices affirmant que „le grès du Wiehengebirge“ dont la position stratigraphique est incertaine faute de fossiles caractéristiques doit être attribué à l'Oxfordien supérieur. Dans le Wiehengebirge, ce faciès clastique à grain grossier remplace dans l'essentiel le faciès calcaire du „Korallenoolith“ typique pour le Wesergebirge.Il suit une brève critique d'une communication paléogéographique récemment parue sur le „Korallenoolith“ du Nord-Ouest de l'Allemagne.Краткое содержаниеО стратиграфии крупн окластической фации оксфордского яруса в Вихенгебирге. На основании находок Peltoceratoides instabiliformis n. sp. в каменоломнях окрестностей г. Оснаб рюка песчаник Вихенг ебирге отнесен к верхним отл ожениям оксфордского яруса. В Вихенгебирге крупнокластическая фация замещает главным обр азом известковую фац ию кораллового оолита, доминирующую в Везер гебирге. Дискутируют ся новейшие палеогеографически е данные о коралловых о олитах северо-западн ой Германии.
Mississippian Barnett Shale: Lithofacies and depositional setting of a deep-water shale-gas succession in the Fort Worth Basin, Texas
The Mississippian Barnett Formation of the Fort Worth Basin is a classic shale-gas system in which the rock is the source, reservoir, and seal. Barnett strata were deposited in a deeper water foreland basin that had poor circulation with the open ocean. For most of the basin's history, bottom waters were euxinic, preserving organic matter and, thus, creating a rich source rock, along with abundant framboidal pyrite. The Barnett interval comprises a variety of facies but is dominated by fine-grained (clay- to silt-size) particles. Three general lithofacies are recognized on the basis of mineralogy, fabric, biota, and texture: (1) laminated siliceous mudstone; (2) laminated argillaceous lime mudstone (marl); and (3) skeletal, argillaceous lime packstone. Each facies contains abundant pyrite and phosphate (apatite), which are especially common at hardgrounds. Carbonate concretions, a product of early diagenesis, are also common. The entire Barnett biota is composed of debris transported to the basin from the shelf or upper oxygenated slope by hemipelagic mud plumes, dilute turbidites, and debris flows. Biogenic sediment was also sourced from the shallower, better oxygenated water column. Barnett deposition is estimated to have occurred over a 25-m.y. period, and despite the variations in sublithofacies, sedimentation style remained remarkably similar throughout this span of time.