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2014-10-15 07:28:56
Earth Sciences Geology

Geological terms defined by Wikipedia (or other web-sources)
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  1. Agglomerate
    Agglomerates (from the Latin 'agglomerare' meaning 'to form into a ball') are coarse accumulations of large blocks of volcanic material that contain at least 75% bombs. Volcanic bombs differ from volcanic blocks in that their shape records fluidal surfaces: they may, for example, have ropy, cauliform, scoriaceous, or folded, chilled margins and spindle,[clarification needed] spatter, ribbon, ragged, or amoeboid shapes. Globular masses of lava may have been shot from the crater at a time when partly molten lava was exposed, and was frequently shattered by sudden outbursts of steam. These bombs were viscous at the moment of ejection and by rotation in the air acquired their shape. They are commonly 1 to 2 feet (30 to 60 cm) in diameter, but specimens as large as 12 feet (3.7 m) have been observed. There is less variety in their composition at any one volcanic centre than in the case of the lithic blocks, and their composition indicates the type of magma being erupted.
  2. Peperite
    A Peperite is a sedimentary rock that contains fragments of igneous material and is formed when magma comes into contact with wet sediments. The term was originally used to describe rocks from the Limagne region of France, from the similarity in appearance of the granules of dark basalt in the light-coloured limestone to black pepper. Typically the igneous fragments are glassy and show chilled-margins to the sedimentary matrix, distinguishing them from clasts with a sedimentary origin.
  3. Fanglomerate
    When a series of conglomerates accumulates into an alluvial fan, in rapidly eroding (e.g. desert) environments, the resulting rock unit is often called a fanglomerate. These form the basis of a number of large oil fields, e.g. the Tiffany and Brae fields in the North Sea. These fanglomerates were actually deposited into a deep marine environment but against a rapidly moving fault line, which supplied an intermittent stream of debris into the allochthonous pile. The sediment fans are several kilometers deep at the fault line and the sedimentation moved focus repeatedly, as different sectors of the fault moved.