--> ABSTRACT: Rapid Subsidence in the Nile Delta and the Effects of a Mobile Depositional Surface on Stratigraphic Facies Development, by Daniel Jean Stanley; #91030 (2010)

Datapages, Inc.Print this page

Rapid Subsidence in the Nile Delta and the Effects of a Mobile Depositional Surface on Stratigraphic Facies Development

Daniel Jean Stanley

Radiocarbon-dated late Quaternary sedimentary sections serve as a base to quantify high rates of subsidence in the northern Nile delta of Egypt. Measurements of recent vertical shifts of land relative to the sea, coupled with eustatic changes, are used to interpret temporal and spatial facies distribution patterns and delta lobe migration in the major recent depocenter in the eastern Mediterranean. The study is based largely on cores, collected during two drilling expeditions, which recovered material deposited during the past 30,000 years. These borings, plus an additional 50 core logs, allow good correlation for the region around Lake Manzala. There, variable thicknesses of Holocene marine and fluvio-marine units lie above transgressive coastal sands (upper Pleistocene o lower Holocene) and older alluvial delta-plain deposits. Mapping of these facies shows that the top of the transgressive sand becomes younger (to ~ 7,000 years ago) and shallower toward the south of the present coastline. Progradation of delta lobes began about 8,000 years ago, and the coastline has advanced northward at a rate of approximately 1 km/100 years.

Lake Manzala lies almost directly above, and is clearly related to, a 60-km long, narrow, linear northwest-southeast region of rapid subsidence; its axis trends parallel to, but is 10-15 km inland of, the present coastline. Holocene coastal and marine sediments lie at depths of 50 m, suggesting a lowering of land relative to the sea of about 40 cm per century. This linear zone, probably the surface expression of a growth fault, has been highly active during deposition. Similar neotectonic dislocation of sedimentary sections underlying the other lakes and lagoons in the northern delta is postulated. Facies patterns have been more extensively affected by rapid subsidence in the Nile delta than previously indicated.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.