Geosciences Dept. Seminar: Paleo-hydrologic Interpretation of a Late Pleistocene/Holocene sediment-core archive ( Nizzanim, Israel)

Abstract:

A 20 meter long sediment core, reaching to the top of the water table, was collected along the southern coastal plain of Israel at Nizzanim. The alternation of the core mineralogy of quartz sand, clay, and carbonate reflected climate changes. Radiocarbon dating of the organic carbon showed two age groups.   Ages of in situ carbon indicating the time of deposition, which increase linearly with depth (r2 =0.99).  A smaller group of  ex situ  ages deviated  from the age-depth line, being younger than expected are due to the subsequent intrusion of plant roots (e.g., at 3m a live Retamia root was found and a live rootlet at 10.5m)which can penetrate beneath  the extant surface an average  of 8.6±2.6m. The dating of the core made possible attributing geologic information to different depths: The Little Ice age, the flooding of the Black Sea, and the Younger Dryas, as well as suggesting important local paleo- hydrologic information. For example, a radiocarbon age of 14K years is measured for the depth at 12m. At this time the global sea level was approximately 100m below the present sea surface, while the sediment surface was about 11m lower than that of today (The exposed coastal plain sediment buildup preceded at a rate of approximately 0.8 mm/y).  The coastal plain aquifer is phreatic, and is in direct contact to the sea, to which it drains. With lowering of sea level not only was the shore line extended westwards (seawards), but the aquifer discharge initially increased due the increased flow gradient. The sea level lowering caused streams draining to the sea to incise their water courses, while increased groundwater discharge to the sea lowered the water table. A lowering of the water table of such magnitude should have had an inhibiting effect on permanent human settlement, probably restricting settlement to the vicinity of incised river courses or eastwards to the mountain springs; for, the digging of inordinately deep wells would have been required to reach fresh water.  At approximately 8K BP the rise in sea level with the concomitant   water table rise would have made   the digging of fresh water wells feasible. Continuous sea level rise would have at first led to increasing salinization of these wells  followed by full sea water flooding, causing human migration eastwards.

Seminar Organizer: Prof. Eyal Haifetz