cap rock

Or caprock

noun

Geology.

1. a mass of anhydrite, gypsum, or limestone immediately above the salt of a salt dome.

2. an impervious stratum overlying an oil- or gas-bearing structure.

cap rock

noun

1. a layer of rock that overlies a salt dome and consists of limestone, gypsum, etc

2. a layer of relatively impervious rock overlying an oil- or gas-bearing rock

Word History and Origins

Origin of cap rock¹

An Americanism dating back to 1865–70