Geomorphic, environmental, and archeological significance of Last Glacial Maximum to middle Holocene dune damming, northwestern Negev dunefield margin, Israel

Abstract

Aeolian-Fluvial (AF) stratigraphic sequences record the bilateral impact of aeolian and fluvial systems upon each other. Along dunefield margins, AF sequences document shifts from fluvial-dominated environments to aeolian-dominated environments mainly in the form of dunes damming and impounding fluvial systems. We report on a 200 m-long exposure, documenting AF sequences in a medium-sized (64 km2) basin along the northwestern Negev desert dunefield margins.Remains of five dune morphologies abutted and overlapped by ever-emptying dune-dammed waterbody deposits record three major OSL-dated dune encroachment phases. Two distinct dune encroachments dated to the Last Glacial Maximum (LGM) at 27–21.5 ka constructed a dune-dammed environment, maintained by post-LGM encroachments at 19.3–17.3 ka and 14.5–13.1 ka. The dune-damming of the ancient basin led to the formation of short-term waterbodies, which accommodated two types of deposits: (i) basal massive clay-silty loam units whose buildup decreased the fluvial accommodation space; and (ii) overlaying event-based sedimentary couplets deposited in shallower waterbodies, which led to upstream widening of a playa-like alluvial plain during the early to middle-Holocene (9.8–5 ka). Epipalaeolithic and Chalcolithic campsites upon these deposits chronologically correlate to the post-LGM development and persistence of these waterbodies.The uppermost early to middle Holocene deposition of couplets that lags the last recorded dune encroachment indicates that the transition from aeolian to fluvial domination was gradual and lasted more than 5 kyr. The onset of the Holocene characterized by regional dune stabilization and shallow accommodation space upstream of the damming-dune, records a climatic shift and a geomorphic response to diminishing loess at the upper basin which increased hydrological regime. AF palaeo-archives thus provide us with indirect evidence of palaeoclimate transitions and both aeolian and fluvial geomorphic responses, that also complement and compensate inherent OSL dating constraints involved with OSL-dating of dunefields.