Abstract

Coarse, clear halite from synsedimentary dissolution pipes in the Permian Salado Formation in southeastern New Mexico (USA) yielded viable halotolerant bacteria and well-preserved cellulose believed to be Permian in age. Here, we show that geologic and hydrologic conditions have isolated these rocks since Permian time. Pipes were dissolved, most likely along cracks (created by thermal contraction or desiccation) and the boundaries of salt polygons (saucers), on exposed Salado Formation salt-pan surfaces down to the level of the water (brine) table. Macropores developed at the brine level in some horizons. As the water level rose, coarse halite cemented the open space. Fluid inclusions (millimeter-scale) trapped bacteria, which were probably in a spore state, as well as cellulose. Inclusion water from pipes in some cycles may have isotopic values reflecting Permian meteoric water, while other cycles may show evaporated Permian seawater.

Exposure surfaces are more prominent in the upper part of Salado Formation depositional cycles due to basin desiccation, as indicated by cracks and dish-shaped laminae. Clays were concentrated on many exposure surfaces by floods, wind, and dissolution. Dissolution pipes formed from these surfaces, and a synsedimentary age is confirmed by undisturbed overlying halite beds. Salado Formation halite has very low permeability (∼10−22 m2), effectively preventing significant fluid flow and passage of fluids through the formation, either to recrystallize salt or to introduce modern bacteria. Stratigraphic relationships, halite textures, fluid inclusion chemistry, and hydraulic properties are all consistent with a synsedimentary origin of the dissolution pipes, their crystals, and the bacteria and cellulose recovered from the Salado Formation.

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