Time filter

Source Type

Sankt Stefan ob Leoben, Austria

Upper Paleocene (Thanetian) carbonate arenites are for the first time described from the Weitenau area in the central Salzburg Calcareous Alps. Their occurrence north of the Lammer Basin fill sheds new light on the tectonic evolution of the Northern Calcareous Alps in Palaeogene to Neogene times. According to our findings, northward thrusting of the Lammer unit seems to be related to the Eocene orogenic phase of the Northern Calcareous Alps. It can be separated from northeastward thrusting during the Miocene lateral extrusion stage. An Early Cretaceous age of thrusting must be refused. Resedimented bioclastic material of the Kambühel Formation is rarely preserved in the Northern Calcareous Alps. Thus the newly-discovered is of great relevance. Exact biostratigraphic dating alongside component analysis of these resediments allow a better palaeogeographic-tectonic reconstruction of the investigated area.

Gusterhuber J.,Peter Tunner Strasse | Dunkl I.,University of Gottingen | Hinsch R.,Rohol Aufsuchungs | Linzer H.-G.,Rohol Aufsuchungs | Sachsenhofer R.F.,Peter Tunner Strasse
Geologica Carpathica | Year: 2012

In the present paper we apply a multi-technique approach (shale compaction data, seismic stratigraphy, isopach maps, moisture content of lignite, fission track data) to assess timing and amount of uplift and erosion of the Alpine Foreland Basin. The combination of the different techniques allows us to discriminate the effects of two different erosion events during the Neogene: (1) Seismic stratigraphy and isopach maps indicate a Karpatian (Early Miocene) regional tilting of the basin to the west (slope of about 0.5 %) and a minor erosion phase. (2) Moisture content of lignite combined with fission track data provides evidence for extensive regional uplift after deposition of Late Miocene fluvial deposits. It is estimated that sediments, 500 to 900 m thick, have been eroded. Shale compaction data derived from sonic logs indicates additional uplift of the eastern part of the basin (near the river Enns). Here, 300 to 1000 m of sediments were additionally eroded (giving a total erosion of about 1000 to 1900 m!), with a general increase of erosion thickness towards the northeast. While the regional uplift is probably related to isostatic rebound of the Alps after termination of thrusting, the local uplift in the east could be affected by Late Neogene E-W compressional events within the Alpine-Pannonian system. Both, tilting and erosion influence the hydrocarbon habitat in the Molasse Basin (tilting of oil-water contacts, PVT conditions, biodegradation).

Garuti G.,Peter Tunner Strasse | Zaccarini F.,Peter Tunner Strasse | Cooper R.W.,Lamar University
Geologica Acta | Year: 2012

Nineteen chromite crystals from the A, B, E, G, H, J and K chromitite layers of the Peridotite Zone of the Stillwater Complex (Montana, USA) have been studied by means of X-ray single crystal diffraction and microprobe analyses. The results show that samples from the basal A layer are quite different from the others showing very high oxygen positional parameter u (0.2633-0.2635) and Ti- contents (0.059-0.067apfu). Mg# values are within the range 0.21-0.23 while for the other chromites it is in the range 0.45-0.47. Moreover, for the other samples, according to the structural parameters, two groups have been identified. The first one comprises samples of layers B, E and G, the second includes H, J and K layer samples. It is supposed that high Fe 2+ and Ti contents of A layer samples are due to the post-crystallization reaction with interstitial liquid. This fact allowed a very slow cooling rate as evidenced by the high u values. The fractionation of evolved magma from within the intrusion and pulse of a new magma bringing more chromium into the chamber lead to Cr- and Fe 3+ -rich compositions and consequently to the increase of the cell edges. The decrease of u values seems to be related to the Cr+Fe 3+ and/or Al contents.

Discover hidden collaborations