Holocene rock varnish microstratigraphy in the Dead Sea basin and Negev Desert: Chronometric application and climatic implication

Abstract

Rock varnish microstratigraphies from Holocene geomorphic and geoarchaeological features in the Dead Sea basin and Negev Desert of the Middle East record past millennial-scale wetness variations. Age calibration of the varnish record indicates six major wet phases between 11 and 4.9 ka during the early to mid Holocene and six minor wet phases between 3.7 and 0.3 ka during the late Holocene. The earliest (11 ka) and late (2.8, 1.5, 0.3 ka) Holocene wet phases appear to be correlated with Holocene millennial-scale cooling events in the North Atlantic, with a cold/wet (warm/dry) regime corresponding with the influence of the North Atlantic and Eastern Mediterranean climates. The early to mid Holocene (9.9–4.9 ka) wet phases in the varnish record altogether constitute an extended moist interval that is broadly concurrent with the African Humid Period (10.5–4 ka). Such a warm/wet (cold/dry) regime reflects a possible northward incursion of the African monsoonal moist air masses over the Dead Sea basin and Negev Desert. These findings suggest a climatic interplay between the African monsoon circulations and the westerly circulation/Eastern Mediterranean cyclones in the Southern Levant during the early to mid Holocene.

The Holocene varnish microstratigraphy, once radiometrically calibrated, can be used as a correlative dating tool to estimate surface exposure ages of geomorphic and geoarchaeological features in the study region. Varnish microlamination (VML) dating of abandoned shorelines of the Dead Sea yields new insights into the Holocene lake level fluctuations. The Dead Sea attained its Holocene highest stand at 369 mbsl (meters below mean sea level) around 11 ka and transgressed to the levels of 370–380 mbsl four times at ca. 9.9, 8.8, 7.6, and 6.2 ka. It rose intermittently to 383, 385, 387.5, and 389 mbsl around ca. 4.9, 2.8, 2.1, and 1.5 ka, respectively, and has remained below 389 mbsl since 1.5 ka. VML dating of an ancient water diversion channel system at Bortot Hazaz and a quarry site at Masada yields minimum-limiting age estimates of 2.6 and 1.9 ka, both in accordance with the OSL and relative archaeological dating of the sites. VML dating of a stone artifact from the 11 ka highstand shoreline brackets the timing of the tool abandonment at 10.5–10 ka, suggesting an early Pre-Pottery Neolithic B (10.5–8.25 ka) site occupation in the Dead Sea basin. These geomorphic and archaeological applications demonstrate that the Holocene varnish microstratigraphy documented in this study has great potential as a unique chronometric tool in the Southern Levant.