THE SEDIMENTOLOGY AND STRATIGRAPHY OF AN ANNUALLY-RESOLVED 20TH CENTURY HALITE SEQUENCE ACCUMULATED UNDER DEAD SEA LEVEL FALL

Although halite sequences recognized in the geological record have accumulated in deep hypersaline basins, commonly their interpretations are based on observations from modern halite deposits in shallow hypersaline environments. Recently, halite deposition in the deep, hypersaline Dead Sea has been studied coevally with its environmental and limnogeological forcing. This is the closest and only modern analog for deep-water halites. Therefore, to better interpret the global laminated halites, we explored the stratigraphy, sedimentology, and petrography of a well-dated, sub-annually-resolved modern Dead Sea halite sequence. It was deposited under an ~30-meters, lake-level decline since the 1980-onset of modern halite deposition, and compared with measured lake levels, precipitation and flood records. The sedimentology of the sequence documents the trend of shallowing water depth and individual floods during its accumulation. The sequence base is composed of alternating bottom growth-cumulate halite annual couplets, typical of deep hypolimnetic water deposition. Up-sequence, these couplets disappear and towards its top they are composed of cumulate layers with dissolution features, typical of shallow epilimnetic water deposition. Summer undersaturation leads to ‘halite focusing’ in depocenter, reducing deposition rate by 60% at the shallow lakefloor compared with the deep lakefloor. The top of the sequence contains shoreline deposits, halolites, and polygonal surface cracks, indicating subaerial exposure. Here, partially dissolved crystals indicate summer thermal dissolution in contrast with dissolution features by floods during relatively wet winters causing regional truncation surfaces. Systematic spatial variations in halite thickness and respective facies indicate much thinner and spatially limited halite units when compared with units modelled based on mass-balance considerations. These observations provide criteria for: (i) recognizing water depths and shallowing lake-level trends recorded in halite sequences throughout the geological record, and (ii) interpreting paleolimnology, water column structure, and the association between stratigraphic horizons and corresponding shorelines.