THE DEPOSITIONAL ENVIRONMENT OF MARINE EVAPORITES: A CASE FOR SHALLOW, CLASTIC ACCUMULATION

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Abstract
The Upper Miocene Solfifera Series of Sicily contains very coarse, massive selenite; parallel laminated gypsum; wavy, stromatolitic laminated gypsum; planar‐ and ripple cross‐laminated gypsum‐skeletal calcite sandstones; flat‐pebble and fining‐upward gypsum conglomerates; and nodular gypsum. The assemblage of sedimentary features indicates deposition—much of it detrital—in a shallow lagoon‐littoral flat complex.Using modern tidal flats as a guide, we interpret the laminations to form when onshore storms flood the shore‐line area with sediment‐charged seawater. Algal mats bind the newly deposited gypsiferous layer. Flat‐pebble conglomerates are formed when storm waves rip up mudcracked, algally‐bound laminated sediment. The gypsum nodules are similar to the anhydrite nodules of the modern Persian Gulf sabkhas. They form within sub‐aerially exposed skeletal sand just above the groundwater table. The gypsum sandstones accumulated periodically in very shallow shoals formed by wind‐driven currents. Large selenite crystals grew in increments during deposition, as indicated by flat‐topped pockets of gypsum sand between selenite crystals, selenite crystals draped by algal laminations, and intraformational conglomerates of selenite fragments.We believe this model of very shallow strand‐line lagoonal accumulation, partly detrital and partly diagenetic, may apply to the early stages of many ancient marine evaporite deposits.