A stratigraphic sequence limestone, gypsum, halite indicates what type of environment?

• A. Transgressive marine
• B. Regressive marine
• C. Freshwater lake
• D. Desert dunes

Answer: (B)

A sequence that begins with limestone and progresses to gypsum and then halite records a retreating shoreline and increasingly evaporative conditions in a restricted marine basin. Limestone forms in warm, shallow seas where carbonate sediments accumulate. As sea level falls or basin accommodation shrinks, the environment becomes more restricted and evaporation concentrates salts in the brine. Gypsum precipitates from moderately evaporated brines, and as evaporation intensifies, halite crystallizes. This upward progression shows a regression with decreasing water depth and rising salinity, not a transgression. Transgression would typically yield deeper-water facies overlying shallower ones, rather than an evaporite-rich stack. Desert dunes or freshwater lakes don’t produce this marine carbonate–evaporite sequence, so the best interpretation is a regressive marine setting.