Dolomia Principale Formation

The main dolomite is called a up to 2200 meters thick lithostratigraphic unit in the Northern and Southern Limestone Alps, in parts of western and central eastern Alps and the Apennines, which is composed primarily of dolomite. The rocks were mostly in shallow lagoon areas in the period of late Karniums and Noriums deposited (both Upper Triassic ).

History

The term, Hauptdolomit ' comes from the German geologist Carl Wilhelm von Gumbel, who used it for the first time in 1857 in his essay examinations in the Bavarian Alps between the rivers Isar and Salzach. Richard Lepsius, the son of Karl Richard Lepsius, the term introduced in 1876 for the Southern Alpine area. The term Dachstein dolomite was partially used as a synonym to main dolomite. Today, upper portions of the main dolomite are called Dachstein dolomite.

Lithostratigraphic classification

Despite his often large cardinality of the main dolomite is not divided on many geological maps and shown as gray surface. In the description of the stratigraphic commission of Italy Italy in the principale as Dolomia designated Hauptdolomit the rank of a formation is awarded. For the northern Alpine region, there is the proposal to regard the here up to 2200 meters thick Hauptdolomit as a group .. Also about the 1992 published Geological map of Zirl in scale 1,50,000 points within the main dolomite from different subunits, but without ever explicitly stratigraphic concepts of use group or formation.

Education Area

The main dolomite is a formation of very shallow and wide lagoon regions and areas of shallow water. Sometimes there were at times falling dry Wadden Sea areas. The bituminous rocks of the Seefeld lineup have emerged in embedded therein basins, bays and kolkartige wells.

Geomorphology

The main Dolomite is a Hauptgipfelbildner the Limestone Alps of the Austroalpine because of its high resistance to erosion. In the northern Alps, he is due is through an intensive convolution with a small scale changing gap directions, so usually no powerful, very steep rock walls ( except eg Trettachspitze ), but above approximately 2000 m complex structure, brittle, ravines, small cliffs, talus slope, bands and channels criss-crossed Schrofenwände and studded with small turrets ridges are typical. Lower mountains in the main dolomite, however, are often strongly influenced by pines and forest -covered, heavy-handed, less impressive mountains. In the Southern Alps, where the rock is less folded, can develop impressive mountains, with favorable gulf course, such as the famous Three Peaks. Because of its strong fracturing is the main dolomite of the strongest Schuttbildner the Alps. Huge scree slopes and level areas of debris in the valley (so-called Griese, such as Frieder Gries near Garmisch -Partenkirchen ) testify to this.

Occurrence

Northern Limestone Alps

In the Northern Calcareous Alps of the main dolomite, especially in the western area is making summit, as in the Lech Valley Alps, the Lechquellengebirge and the Allgäu Alps with mountains known as high bird or Mädelegabel. The highest main dolomite peak in the Northern Limestone Alps, the 2889 m high Vorderseespitze in the Lech Valley Alps dar. Overall, the main dolomite is the areally most important rocks of the Northern Limestone Alps. The Karwendel is especially the Erlspitzgruppe from main dolomite. On the black horse in the southeastern tip Karwendel the greatest known thickness of the main dolomite of 2200 meters was measured. Further to the east of the main dolomite is also still common, especially in the northern areas of the Limestone Alps, but he also appeared on the southern edge again. However, in the Eastern Limestone Alps he no longer reaches thicknesses as in the Karwendel. He is about 500 meters thick in the Ötscherdecke in Southwestern Lower Austria.

For more detailed subdivisions of the main dolomite there is room for Seefeld and the Lech Valley Alps. In the Erlspitzgruppe in Seefeld formations Lower Hauptdolomit Middle Hauptdolomit ( Freiung Formation), Seefeld layers ( Seefeld Formation) and Upper Main Dolomite ( Dachstein dolomite) (Castle Brook Formation), distinguished.

In the eastern Lech Valley Alps W. Müller- Jungbluth in 1970 made ​​a subdivision of the main dolomite into three sections, a Lower, Middle, and Upper Main dolomite. The lower main dolomite with a thickness of 250 to 350 meters is characterized by finely laminated, dark - bituminous and pyrite containing dolomite. The Middle Hauptdolomit achieved with 400 to 900 meters, the largest size, is lighter, fine gebankt to dense and rich in detritus. The Upper Main dolomite reaches about two thirds of the thickness of the Middle Main Dolomite. Here there is a greater diversity of rocks such as Brekzienlagen, Algenstromatolithe or Onkolithe. In addition to a richer fossil guide ( Dasycladaceen and Megalodonten ) here will also dry cracks or rain tracks.

Under Superimposed is the main dolomite of Raibler layers, but the limit can be fuzzy. In Lunzer facies, extending approximately over the southeastern Upper Austria and parts of southern Lower Austria, is the main dolomite above the Opponitz lineup but is allowed, this replacing, engage more deeply. Towards the top of the main dolomite passes into Noricum also still Plattenkalke.

Central Eastern Alps

In the central eastern Alps there is Hauptdolomit in various sediment conditions on the crystalline basement, so in the Kalkkoegel or in the Radstadt Tauern. In the Semmering region occur colorful slate, called Bunter Keuper and in his monograph on the Northern Limestone Alps also associated with the geologist Alexander Tollmann as a special form of the main dolomite.

Western Eastern Alps

In the western Eastern Alps ( Dolomites Arosa, Montafon Mountains, the Lower Engadine Dolomites ) reached the main dolomite only a comparatively small thickness. There is debris on the crystalline basement of the Silvretta blanket. The rocks are often verfaltet by overhead transport, sheared and broken.

Southern Alps

While in the area east of Lake Maggiore on the go mitteltriadischen sediments directly into Jurassic sediments, is the main dolomite in the eastern Lombardy and extends to Slovenia. In the Italian Southern Alps of designated here as dolomia principale Hauptdolomit widths reaches up to 1500 meters. Nonetheless, he is out here as a formation. But some members are locally defined, in the Brenta which characterized by breccias Membro di Malga Flavona. As well as in the northern Alps of the main dolomite generally of Carnian sediments is underlain, in the Lombardy region of the Formazione di Castro Sebino, east of Raibler layers.

In the Lienz Dolomites of the main dolomite as in the Northern Limestone Alps of Raibler is underlain layers and layers of Solnhofen.

Arise, for instance, large parts of the Brenta, the upper floor of the sella or the Three Peaks from main dolomite in the Southern Alps.

Apennines

In the Apennines the main dolomite occurs in the central and southern part. The massif of the Gran Sasso d' Italia, he reached thicknesses around 600 meters.

Fossil guide

The main dolomite is generally considered poor fossil rock. At macro fossils are found algae as Gyropella or Dasycladaceen, Megalodonten or snails as Worthenia. The microfauna is relatively poor. Local foraminifera but can occur en masse. Is known, however, the fish faunas of Seefeld layers.

Properties

The rock is light gray or brownish- gray color with clear layered structure and strong fracturing. It is extremely brittle and hard. The fractures are often subsequently healed with calcite, recognizable by white veins in the rock.

Use

The main dolomite is because it is cheap and somewhat harder than lime (eg, as a base for road construction ) is used as a building material, as well as grit for walkways it is known. The brittleness of the rock, however, can be only a few applications as gravel in the technical sense.

The cleft- rich rock is also responsible for the supply of drinking water is important. If its layers were folded by the Alpidic orogeny to larger troughs, they are followed by the development of groundwater; so the underground catchment area can also be estimated in unclear source areas.