Keweenawan System

Keweenawan System

      division of late Precambrian rocks and time in North America (the Precambrian began about 3.8 billion years ago and ended 540 million years ago). Rocks of the Keweenawan System are about 10,700 metres (about 35,000 feet) thick, overlie rocks of the Huronian System, and underlie rocks of the Cambrian System; it has been suggested that the youngest Keweenawan rocks actually may be Cambrian in age. In the Lake Superior (Superior, Lake) region, Keweenawan rocks consist of reddish sandstones, siltstones, shales, and some conglomerates. Great thicknesses of lava flows also occur; it has been estimated that about 100,000 cubic kilometres (24,000 cubic miles) of lava were produced. The burden of the great weight of lava caused the crust beneath to sag and produced the basin that Lake Superior now occupies. The Keweenawan System has been divided into Lower, Middle, and Upper series; the lavas are primarily concentrated in the Middle Keweenawan Series, whereas the Lower Keweenawan Series is dominated by sediments. The Keweenawan System is named for prominent exposures studied at Keweenaw Point, Michigan.

* * *


Universalium. 2010.

Игры ⚽ Нужен реферат?

Look at other dictionaries:

  • Midcontinent Rift System — Geological map of North America showing (in white) the Midcontinent Rift, here labeled Keweenawan Rift. Lake Superior occupies the apex of the rift. The Midcontinent Rift System (MRS) or Keweenawan Rift is a 2,000 km (1,200 mi) long… …   Wikipedia

  • Beaver-Bay-Komplex — Das schattierte Reliefbild zeigt den Duluth Komplex, der sich bogenförmig von Duluth zum Pigeon Point zieht und dabei die Mesabi Range und die Gunflint Range unterbricht Der Duluth Komplex, der damit verbundene Beaver Bay Komplex (der oft als… …   Deutsch Wikipedia

  • North Shore Volcanic Group — Das schattierte Reliefbild zeigt den Duluth Komplex, der sich bogenförmig von Duluth zum Pigeon Point zieht und dabei die Mesabi Range und die Gunflint Range unterbricht Der Duluth Komplex, der damit verbundene Beaver Bay Komplex (der oft als… …   Deutsch Wikipedia

  • Duluth Complex — Shaded relief image showing Duluth Complex arcing from Duluth to Pigeon Point, interrupting and splitting the Mesabi and Gunflint Ranges The Duluth Complex, the related Beaver Bay Complex (often treated as part of the Duluth Complex),[1] and the… …   Wikipedia

  • Duluth-Komplex — Das schattierte Reliefbild zeigt den Duluth Komplex, der sich bogenförmig von Duluth zum Pigeon Point zieht und dabei die Mesabi Range und die Gunflint Range unterbricht Der Duluth Komplex, der damit verbundene Beaver Bay Komplex (der oft als… …   Deutsch Wikipedia

  • igneous rock — Any of various crystalline or glassy, noncrystalline rocks formed by the cooling and solidification of molten earth material (magma). Igneous rocks comprise one of the three principal classes of rocks, the others being metamorphic and sedimentary …   Universalium

  • Volcanism in Canada — Canada has examples of almost every type of volcano found on earth, including stratovolcanoes, calderas, cinder cones, shield volcanoes, maars, submarine volcanoes and tuyas. Most of Canada s volcanoes are located in British Columbia. Several… …   Wikipedia

  • Precambrian time — Interval of geologic time from с 3. 8 billion years ago, the age of the oldest known rocks, to 544 million years ago, the beginning of the Cambrian Period. This interval represents more than 80% of the geologic record and thus provides important… …   Universalium

  • Lake Nipigon — Location Ontario Coordinates …   Wikipedia

  • Columbia River Basalt Group — The Columbia River Basalt Group (including the Steen and Picture Gorge basalts) extends over portions of five states. The Columbia River Basalt Group is a large igneous province that lies across parts of the Western United States . It is found in …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”