Evolution of Nile and Other Mediterranean Deltas During Holocene: Depocenter Architecture and Eustatic Sea Level Factor

Daniel Jean Stanley

Deposition of deltas along margins of the Mediterranean Sea resulted from the interplay of climatic effects, transport processes, and tectonics. Fluctuating eustatic sea level is one of the dominant controls. This conclusion is based on the finding that the beginning of deposition of Mediterranean deltas during the Holocene was amazingly consistent, although their geologic and geographic settings were diverse. The data base available for the modern deltas is uneven, with more information available for the Nile delta as a result of petrologic study of more than 100 drilled borings, radiocarbon dating of 210 core samples, systematic mapping of lithofacies, and close-grid correlation of core sections. Land-to-sea core traverses show that the Nile delta began to form 7,000-8, 00 years ago. Published studies indicate that the Po, Rhone, and Ebro deltas also began to form about 7,000 years ago. Moreover, geometry of the lithofacies sequences detailed in this study (basal transgressive sands overlain by marine, coastal, deltaic, and fluvial deposits) are generally comparable in the four deltas.

The surface configurations of the four deltas are distinct, largely as a function of different tectonic settings, provenance and dispersal patterns, and physical oceanographic conditions affecting the four coastal sectors. Of note, however, is the similar internal architecture/anatomy of the four depocenters, i.e., comparable facies sequence distributions in time, space, and thicknesses. A likely explanation for the near coincidence of timing of delta progradation in four regions is the slowing of eustatic sea level rise in the mid-Holocene (~ 7,500-7,000 years ago) as determined in the Mediterranean and other continental margins. This deceleration occurred during a more humid period characterized by increased river flow and accelerated transport of bed load and suspensates to the coa ts. This coupling resulted in the initiation of delta-lobe migration on recently submerged inner shelves. Until recently, the four deltas prograded rapidly as sea level continued to rise slowly. Renewed acceleration of eustatic sea level rise predicted for the next century and continuation of man-induced changes in drainage basins, along river channels, and in delta plains are likely to modify the late Holocene depocenters. Thus, in years ahead, we will have an opportunity to measure these eustatic sea level changes and quantify their effects on lithofacies distributions in Mediterranean deltas.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.