Holocene Sequences Distributed across the Northern Nile Delta, Egypt, as a Function of Tectonic, Eustatic, and Climatic Controls
STANLEY, DANIEL JEAN, DIDIER ARBOUILLE, and HELENE HOWA, Mediterranean Basin Program, Smithsonian Institution, Washington, DC
Analysis of the laterally variable lithofacies distributions in the Nile delta, Egypt, in recent time provides an opportunity to model the evolution of a very active depocenter, the largest on the North African margin. Of particular interest is the interplay of major factors controlling sedimentation. The changes of Holocene facies in time and space across the northern Nile delta have been mapped by means of sediment cores. This study is based on extensive petrological, geochemical, and biogenic analyses of more than 2000 samples in 65 cores. Most cores (length to 60 m) are radiocarbon dated, indicating that Holocene deltaic progradational sequences began to accumulate about 7500 years ago. The delta plain has been subsiding (from 0.04 to 0.50 cm/yr) and also tilting toward the northe st during this period.
As a consequence, sediments have accumulated at long-term averaged rates of 0.1 to 0.5 cm/year, from west to east. Marked variations in temporal and lateral lithofacies distributions and sequence thicknesses are in part a direct consequence of asymmetric lowering of the delta plain surface during the period of sediment accumulation. Other factors affecting deposition include eustatic sea-level rise (about 15 m during the past 7500 years), change from humid to arid climate (about 5000-4000 years ago), which altered sediment input to the delta from East African and Ethiopian source areas, and strong easterly directed longshore currents that erode the coast. On the one hand, classic complete deltaic coarsening-upward sequences consisting of open marine prodelta to coastal facies are rest icted to the northeastern delta; this is largely a response to accelerated subsidence in this region. In contrast, sediment sections are reduced in thickness and comprise lithologically more irregular successions of delta plain deposits (distributary channel, marsh, lagoon) over most of the tectonically more stable north-central sector of the delta.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)