Ruhpolding-Formation
In a broader sense, all radiolarites of Oberbajocs, Calloviums, Oxfordian, Kimmeridgiums and Untertithons be summarized in the Northern Limestone Alps now to Ruhpolding - radiolarite Group ( RRG ).
Occurrence
The eponymous type locality forms part of the ceiling of the Lech Valley oberostalpinen Bajuvarikums. The formation occurs from the Allgäu Alps and the Lech Valley Alps in the west to the Chiemgau Alps in the east. The Ruhpolding Formation in the strict sense but is found also in the south adjoining the Bajuvarikum Tirolikum and thus also extends to the eastern part of the Northern Limestone Alps.
The Ruhpolding - radiolarite group still has a much wider -ranging occurrence ( spatial and temporal) and will appear in the Karawanken and in the Southern Alps. In the Austroalpine it is also to be found, but it is here already metamorphosed before ( examples are the Austroalpine as part of the Tauern Window and the Grisons ). Indeed, even still in the Pennine area (Piedmont zone) occurs on the group.
Stratigraphy
In Bajuvarikum the Ruhpolding Formation follows concordant layers of the Chiemgau - siliceous, capel leading spätige limes - or in the Allgäu Alps, the gray, marly younger Allgäu layers. They will in turn overlaid conformably by Aptychenschichten the Oberammergau formation (dense, yellowish to greenish - gray marly limestones of the Tithonian to Berriasian ). The transition to the Aptychenschichten with Lamellaptychus lamellosus and Punctaptychus punctatus is gradual. In the central portion of the Northern Limestone Alps follows the Oberalm formation of Kimmeridgiums to Berriasian to the Ruhpolding Formation, in places with a base conglomerate; mostly, however, the transition is gradual and is characterized mainly by increasing calcium content.
In the northern Tirolikum, such as in Tauglboden Basin, the Ruhpolding Formation is a significant Bankfuge on the subjacent, bulbous ( the tubers consist of manganese - iron oxide) Rotkalken Klaus lineup. The Bankfuge is here emphasized by several centimeters powerful pitch. About the Ruhpolding Formation then sets the Tauglboden formation of Kimmeridgiums and Untertithons.
Occasionally, the Ruhpolding Formation down access also to the Adnet Formation or the Vilser lime.
In Sillenkopf Basin of southern Tirolikums the Ruhpolding Formation is under - and overlain by the Strub mountain formation of the simultaneous formation of Tauglboden Sillenkopf lineup.
Lithology
Lithologically is the average of around 50 meters (range 5 to 100 meters) thick expectant Ruhpolding Formation of black - green and red radiolarites, Kieselkalken, siliceous marls and siliceous clays. It is substantially originated from Radiolarienschlick. The silt solidified to a uniformly finely layered and banded Chertformation, which is composed of chert, siliceous limestone and chert layers. The individual siliceous layers are usually separated by the slimmest of pitches. The resulting cyclicality is to bring possibly with Milankovitch cycles in conjunction. A possible diagnetisch conditional segregation as an explanation of the banding can be excluded by cycles across Rutschungsstrukturen.
The color of the fine-grained, very hard, splintery to conchoidal breaking and weathering of solid rock is predominantly red, but also green- light gray to black colors are found. The shade of color ( hematite) goes to the complete oxidation of iron compounds contained by oxygen-rich deep water back (ratio of Fe3 / Fe2 > 1). In the greenish radiolarites is the ratio of Fe3 / Fe2 < 1, bound to the minerals sericite and chlorite. The FeO ratio is very high, also likely pyrite play a role in the coloring.
In thin section it can be seen that the siliceous matrix of diagenetically converted, a maximum of 0.1 mm Radiolarienskeletten composed. The chemically almost 100% SiO2 existing Chertgestein is crossed by some net-like organized columns and crack systems that auskristallsierten with secondary calcite. These fault systems have been caused by the occurrence of later tectonic stresses. Mafic Tuffitlagen are pretty common at the base of Ruhpolding lineup. This should already be associated with the Ehrwalditmagmatismus.
Fossils
The Ruhpolding Formation consists mainly of microfossils ( radiolarians ), macrofossils are extremely rare, with the exception of poorly preserved Aptychen, crinoids as Saccocoma, needle debris and filaments. Benthic foraminifera are rare planktonic foraminifera and missing completely. Of the considerable diversity of radiolarians some taxa were singled out:
- Entactinaria - Saturn Alidae: Acanthocircus
- Nassellaria - Amphipyndacidae: Triversus
- Nassellaria - Archaeodigtyomitridae: Archaeodictyomitra apiarium, Archaeodictyomitra minoensis, Archaeodictyomitra mitra and Archaeodictyomitra rigida
- Nassellaria - Bagotidae: Droltus galerus
- Nassellaria - Canoptidae: Cinguloturris carpatica
- Nassellaria - Eucyrtidiellidae: Eucyrtidiellum nodosum, Eucyrtidiellum ptyctum
- Nassellaria - Eucyrtidiidae: Cyrtocapsa, Stichocapsa naradaniensis and Stichocapsa trachyostraca
- Nassellaria - Hsuidae: Hsuum brevicostatum
- Nassellaria - Parvicingulidae: Dictyomitrella, Parvicingula dhimenaensis
- Nassellaria - Sethocapsidae: Gongylothorax favosus
- Nassellaria - Williriedellidae: Williriedellum carpathicum
- Nassellaria -: Tricolocapsa funatoensis
- Spumellaria - Angulobracchiidae: Angulobracchia, Paronaella
Deposition conditions
The Ruhpolding Formation is clearly high marine origin and were deposited in the pelagic area, recognizable by quite rare ammonite finds such as Hibolites semisulcatus Münster. At what water depth, the sedimentation was ultimately remains controversial. Aktuogeologisch to Radiolarienschlamme form below the compensation depth for calcite (English calcite compensation depth or CCD) in a water depth of 4,000 to 5,000 meters. To be considered here, however, that the CCD in the Upper Jurassic was much higher (probably between 2000 and 3000 meters).
The blossoming of radiolarians may have been triggered by volcanic activity and / or by changes in the water circulation. The silica needed may have been delivered alongside volcanic entry with cold water buoyancy. Indirectly, may thus also be closed on extensive intra- oceanic changes in the spatial conditions of the then Tethysraumes.
Ruhpolding turn
The sedimentation of the radiolarites the Ruhpolding Formation means a sudden and drastic cut in Sedimentationsgeschehen the Northern Limestone Alps, which is called the turn of Ruhpolding. This change of Sedimentationscharakters was not of a temporary nature. With the appearance of radiolarites (and later the Aptychen layers) sediments spread out, which differed significantly and consistently from the under - and Middle Jurassic.
This was preceded by a rapid decrease in sedimentation rates and widths in the Dogger. So piled up in the upper Klaus lineup the Omissionsflächen and sedimentation was generally slower and incomplete. The starvation of sedimentation was probably due to a continuous downward movement.
During the Ruhpolding turning the existing seabed relief was accentuated tectonically and single threshold ranges rose up into the zone of shallow water on. In these raised thresholds, the limited to the deeper basin areas Ruhpolding lineup did not come the way to the deposit, but it was here continue Rotkalke sediments, such as the Agathakalk ( a Cephalopodenkalk the Tiefseeschwellenfazies from the Oxfordian to Kimmeridgian ), or Hasselberg - lime ( a clayey Flaserkalk from the Tithonian ). Only later, with the onset of sedimentation of Aptychen layers, the tectonically -related contrasts were then balanced again slowly.
The Ruhpolding turn is characterized next to tectonic movements also by volcaniclastic deposits ( tuffites ), which are expected to basic, Upper Jurassic Magmenpuls.
With the Ruhpolding turning the frequency increased autokinetischer sediments such as turbidites, Fluxoturbidite, mudflow breccias, grain flows, mud wrinkle and slide blocks. Also Olistolithen are encountered. This subheading includes the light brown, allodapischen limestones Barmsteins ( with Eingleitungen Hallstatt Faziesbereichs ), the Sonnwendbrekzie and Tauglboden and the Strub mountain formation. Most of the fall caused by tectonic movements mass movements either in the period shortly before or shortly after the turn of Ruhpolding. A good example was during the turn of mass movements is the Grubhörndlbrekzie, a Megabrekzie ( with a 300 -foot block of limestone! ), Which slid off in a north-south trending fault to the west and toothed in the basin with the Ruhpolding Formation.
The gradually taking place Radiolarienschlamms displacement of the Ruhpolding Formation by Coccolithenschlamm the overlying Aptychenschichten can either be attributed to a further deepening and / or can be explained by a flourishing of calcareous Nannoplanktons.
Age
The Ruhpolding Formation in the narrow sense was deposited in the Upper Oxfordian, ie to around 157-155 million years BP. This biostratigraphic age ( maximum age ) is based on ammonite finds in the top Klaus lineup.
In the meantime, however, the Diachronicity the Ruhpolding Formation is generally recognized. A recent study by Wegener, Suzuki & Gawlick (2003) was based on the Radiolarienstratigraphie an age of Middle Oxfordian to Lower Kimmeridgian for the upper Red radiolarite, ie 159 bis 154 million years BP.
For the Ruhpolding - radiolarite group give Suzuki & Gawlick ( 2003a) an age of Bajocian to Untertithon, ie the period 171-147 million years BP.