A non-clastic limestone characterized by loosely consolidated, earthy calcium carbonate and clay containing deposits of shell is called what?

A non-clastic limestone characterized by loosely consolidated, earthy calcium carbonate and clay containing deposits of shell is called what?

• A. Chalk
• B. Marl
• C. Limestone
• D. Dolostone

Answer: (B)

Marl is a calcareous clay-rich mudstone. It forms from fine carbonate sediments mixed with clay minerals and often includes shell fragments, giving it an earthy, loosely consolidated texture. This combination—calcium carbonate with clay and biogenic inputs like shells—fits the described rock: a non-clastic limestone that is earthy and clayey. Chalk, while also a non-clastic carbonate rock, is mainly composed of microfossil shells (coccoliths) and tends to be very pure calcite with little clay, giving a finer, whiter, more uniform appearance. Limestone is the broad category for calcium carbonate rock, but the specific clay-rich, shell-bearing nature points to marl rather than a general limestone. Dolostone has dolomite as the main mineral and is not characteristically clayey or shell-bearing in the same way.

Marl is a calcareous clay-rich mudstone. It forms from fine carbonate sediments mixed with clay minerals and often includes shell fragments, giving it an earthy, loosely consolidated texture. This combination—calcium carbonate with clay and biogenic inputs like shells—fits the described rock: a non-clastic limestone that is earthy and clayey.

Chalk, while also a non-clastic carbonate rock, is mainly composed of microfossil shells (coccoliths) and tends to be very pure calcite with little clay, giving a finer, whiter, more uniform appearance. Limestone is the broad category for calcium carbonate rock, but the specific clay-rich, shell-bearing nature points to marl rather than a general limestone. Dolostone has dolomite as the main mineral and is not characteristically clayey or shell-bearing in the same way.