AN ACID PERENNIAL SALINE LAKE SYSTEM FROM THE TRIASSIC MERCIA MUDSTONE GROUP IN THE CARNDUFF 02 CORE, NORTHERN IRELAND
Flooding events in shallow lakes and surrounding mudflats are interpreted from dissolution pipes/pits, dissolution surfaces, and climbing ripple cross-bedding. The presence of bedded evaporites is evidence of evapoconcentration. Chevron halite crystals suggest shallow water depths. There is no evidence of desiccation within shallow saline lake lithofacies. Lake waters were saturated with respect to Na, Cl, Ca, and SO4. Shallow groundwaters in saline mudflats were NaCl-rich, interpreted from displacive halite. Mudcracks, dewatering structures, circumgranular cracks, and soil slickensides are interpreted products of wetting and drying within the dry mudflat lithofacies. The massive mudstone deposits may have been deposited by eolian processes or may have chemically precipitated from lake waters. The lack of carbonates and abundance of halite, gypsum, hematite, and kaolinite are lithologically similar to known acid saline lake systems. A related studied on bedded halite of the Mercia Mudstone Group suggests lake pH less than 1.
Terrestrial redbeds and evaporites may be good analogs for Mars strata. More work is needed on redbed and evaporites on Earth to better understand the past lakes on Mars.