RECENT SUBSIDENCE AND NORTHEAST TILTING OF THE NILE-DELTA, EGYPT

Sediment borings collected in the Nile delta of Egypt, many of them radiocarbon dated, indicate that the entire northern sector of this major depositional center in the eastern Mediterranean is presently subsiding. Mapping of the base of the Holocene deltaic facies, which is dated at about 8000-6500 yrs B.P., reveals that differential lowering of the northern delta plain is preferentially accentuated toward the northeast. Long-term subsidence rates at or near the coast, averaged for the mid- to upper Holocene, range from about 0.1 to 0.25 cm/yr between Alexandria and the north-central delta margin. Rates increase markedly eastward to a maximum of about 0.5 cm/yr in the Port Said-Manzala lagoon region, and this rapid lowering explains the presence of thick marine delta lobe sequences of Holocene age in cores in the northeastern delta. In contrast, only reworked remnants of Holocene marine delta lobe deposits of the earlier River nile branches which once flowed to the north and northwest are preserved seaward of the present north delta coast. Subsidence has induced marked environmental changes, particularly with respect to coastal erosion and salt water incursion. The asymmetric pattern of saline ground water, here attributed in part to the northeast tilt of the delta plain, has serious implications for agricultural development in this intensely cultivated region. © 1990.