Question

Which of the following is classified as a mechanically formed sedimentary rock?

• A. Potash
• B. Chalk
• C. Halite
• D. Loess

Answer 1

Answer:

D. Loess

• Loess is a type of sediment, specifically an aeolian (wind-deposited) silt that is typically uniform in particle size and is usually yellow or tan in color.

• It is formed by the accumulation of fine dust, primarily silt-sized particles (0.02 to 2.0 mm in diameter), carried by wind from sources such as desert margins, glacial outwash plains, or river floodplains.

• This process of accumulation over vast areas is known as aeolian deposition.

Geological Significance

• Loess deposits are significant because they are often highly fertile and form some of the best agricultural soils in the world, such as the Chernozems found in parts of Russia, Ukraine, and North America.

• The unique properties of loess, such as its vertical permeability and ability to form steep bluffs when undercut, are a result of the way the silt particles are arranged and cemented.

• Notable loess deposits are found in:

  • China (Yellow River Valley): The thickest and most extensive loess deposits are found here, covering over 300,000 square miles.

  • United States (Midwest): Significant deposits are present in states like Iowa, Nebraska, and Kansas.

  • Europe: Found in countries such as Russia, Ukraine, Romania, and Germany.