Daniel Jean Stanley

Worldwide initiation of Holocene marine deltas by deceleration of sea-level rise

Radiocarbon-dated deltaic sequences of Holocene age from different parts of the world began to accumulate within a restricted time range, from about 8500 to 6500 years ago. Evaluation of major delta processes indicates that deceleration in sea-level rise was the key factor in Holocene delta formation. Within many deltas, there is as much as a 2000-year age range between basal deposits in seaward and landward cores. This age difference records the progressive landward migration of near mean sea-level depositional environments during the lower to mid-Holocene. Establishment of a chronostratigraphic framework for Holocene delta development provides a fundamental global baseline for distinguishing sea-level change from vertical land motion by tectonism and isostasy, and for evaluating rates of future marine incursion into low-lying deltas.

Nile Delta: Recent Geological Evolution and Human Impact

Few countries in the world are as dependent on water from a single source as Egypt. The natural Nile cycle of flow and sediment discharge has been disrupted by human intervention, including closure of the High Aswan Dam; this intervention has resulted in a series of responses that now threaten the northern Nile delta. Erosion, salinization, and pollution are inducing a marked decline in agricultural productivity and loss of land and coastal lagoons at a time when the population is expanding exponentially. Geological analyses of radiocarbon-dated cores across the northern delta are used to interpret the interaction of sea-level changes, climatic oscillations, subsidence, and transport processes during the past 35,000 years. Recognition of long-term trends of these natural factors provides a basis to evaluate the profound impact of human activity and to assess future changes in the Nile delta ecosystem.

Subsidence in the northeastern nile delta: rapid rates, possible causes, and consequences.

Holocene fluvial and marine deposits have accumulated in a graben-like structure on the northeastern margin of the Nile delta. This part of the delta, which includes Lake Manzala, Port Said, and the northern Suez Canal, has subsided rapidly at rates of up to 0.5 centimeter per year since about 7500 years ago. This subsidence has diverted at last four major distributaries of the Nile River into this region. The combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100. The impact of continued subsidence, now occurring when sediment input along the coast has been sharply reduced because of the Aswan High Dam, is likely to be substantial, particularly in the Port Said area and as far inland as south of Lake Manzala.

Nile delta: extreme case of sediment entrapment on a delta plain and consequent coastal land loss

Abstract Accelerated erosion of Egypts Nile delta coast during this century has generally been attributed to construction of two dams at Aswan, entrapment of sediment in Lake Nasser behind the High Dam, and effects of barrages and river control structures on River Nile deposition below Aswan. Also considered important are natural factors, including delta subsidence, rising sea level and strong coastal current processes. This study proposes that more influential in controlling coastal land loss is the near-complete entrapment of modern and reworked Nile sediment on the Nile delta plain. Sediment is primarily retained in an extremely dense network of irrigation and drain channels, and also in wetlands in the northern delta. The increased number of artificial canals, more than 10,000 km of waterway, is a response to Egypts drive to augment its much-needed agricultural production by perennial irrigation. The drastically reduced amount of sediment now reaching the sea, discharged primarily from lagoon outlets and several canal mouths, is removed by strong, easterly-directed coastal and innermost shelf currents. The Nile delta is an extreme example of a depocenter which has been completely altered by man, from an active prograding delta to a locally eroding coastal plain.

Late Quaternary stratigraphy and paleogeography of the eastern Nile Delta, Egypt

Abstract A petrological study of numerous sediment borings identifies the late Pleistocene and Holocene lithofacies in the northeastern Nile Delta of Egypt. A coarsening-upward sequence characterizes the major Holocene depocenters located along the northern margin of the present Delta. Stratigraphic correlation of radiocarbon-dated sections and mapping of key facies such as delta-front mud reveal the locations of four major Holocene delta lobes related to former distributary branches of the Nile River: Mendesian, Pelusiac, Tanitic and pre-modern Damietta. These lobes, formed primarily of marine prodelta and delta-front deposits, interfinger geographically, but radiocarbon dating indicates that their bases are not synchronous. Lobes developed for the most part since 8000 years B.P., i.e. as the rate of eustatic sea-level rise began to decrease. Climatic and sediment-discharge fluctuations, lateral migrations of distributaries, and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes. Paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic-plain environments (marsh, lagoons), and concomitant displacement of the coastline. Holocene sediment accumulation rates to 500 cm per 1000 years are calculated. This is 10 times greater than that on the Nile Cone and 50 times greater than on the Egyptian continental shelf. The delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years, an average progradational rate of up to 10 m per year. The general configuration of the present delta developed during the past millennium. The major changes recently induced by man in this region, coupled with a series of continuing natural phenomena (slow rise in sea level, coastal erosion, subsidence) have markedly affected the evolution of the delta. Petrological study of the Nile Delta sediments provides baseline reference information to help recognize changes in the recent geological past, to help identify those taking place at present, and possibly to help predict those likely to occur in this region in the future.

Recent subsidence and northeast tilting of the Nile delta, Egypt

Abstract 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.

Neolithic settlement distributions as a function of sea level–controlled topography in the Yangtze delta, China

Combined geological and archaeological data sets indicate that sea level–controlled topography best explains the timing of Neolithic settlement onto the southern Yangtze delta plain, almost 1500 yr later than inland China. Information on settlement patterns of the three major Neolithic cultures (Ma-Jia-Bang, Song-Ze, Liang-Zhu), dated from ca. 5500 to 2200 B.C., is provided by petrologic study of habitat bases of sites and of sediment cores recovered near the sites. In the early Holocene, rising sea level induced decreased relief and an aggrading silt mantle on the low-lying delta surface. Changes of sea level and climate from early to mid-Holocene initiated a fertile delta plain at ca. 6000–5500 B.C., and settlement and cultivation, including rice, began within only 500 yr of delta formation. Rate of sea-level rise decelerated by mid-Holocene time, resulting in rising ground-water level and poor drainage, and a reduced delta plain area suitable for human occupation and agriculture. As a consequence, Neolithic settlements shifted progressively eastward toward higher, more restricted areas of the Yangtze delta chenier plain.

Unifites: structureless muds of gravity-flow origin in Mediterranean basins

Unifite is the descriptive term applied to a structureless or faintly laminated, often thick, mud layer revealing a fining-upward trend. Study of Mediterranean basins suggests this mud type represents rapid, single event deposition from low-density gravity flows. This interpretation is based on unifite restriction to basin plains, distinct vertical and lateral petrologic trends, and lithofacies association with mud turbidites. Deposition involves accumulation in small, topographically restricted depressions, basinward displacement involving repeated failure and redeposition, slope-relief bypassing resulting in progressive fining and homogenization downslope, and modification by hyraulic jump effects at the base-of-slope.

Deltas, radiocarbon dating, and measurements of sediment storage and subsidence

In Holocene marine deltaic sequences there is no simple relationship between radiocarbon age and depth of sampling. The Nile and Ganges-Brahmaputra deltas show remarkably similar radiocarbon age-depth relationships: (1) most radiocarbon dates, by conventional and accelerator mass spectrometric (AMS) analyses, are older (some by 4000 yr) than reasonably expected; (2) dates are commonly inverted (i.e., older upcore); and (3) sample dates at delta surfaces commonly exceed 2000 yr B.P. These anomalous age-depth phenomena are in part a response to reservoir effects, introduction of old carbon, and, emphasized herein, influence of sediment storage and remobilization that prevail in fluvial and delta plains. In fluvial systems, sediment generally is not transported in a single episode from its original source area to the sea. Rather, material transported from upland reaches and river valley to coast is subject to a repeated series of depositional, burial, and erosional events induced by episodic flooding, overbank sedimentation, and channel migration. Because sediment is likely to be temporarily stored in the delta plain, it is difficult to determine the time of a sediment9s final deposition and burial at a delta site. A successful strategy requires use of several independent dating methods, including AMS analyses of in situ basal peats and fossils and, where possible, archaeological evaluation of associated artifacts that are in place. Accurate dates are needed for reliable measurement of rates of delta plain aggradation and land subsidence, information to help implement effective coastal protection measures.

Metal pollution loading, Manzalah Lagoon, Nile Delta, Egypt: Implications for aquaculture

High cultural enrichment factors are found for Hg (13×), Pb (22.1×), and other potentially toxic metals (e.g., Sn, Zn, Cu, Ag) in the upper 20 cm of sediment cores from the southeastern Ginka subbasin of Manzalah lagoon, Nile delta, Egypt. Cores from other areas of the lagoon show little metal loading. Metal loading followed the closure of the Aswan High Dam, the availability of abundant cheap electricity, and the development of major power-based industries. Industrial wastes containing potentially toxic metals are dumped into the Nile delta drain system. The load carried by Bahr El-Baqar drain discharges into the Ginka subbasin, which acts as a sink and results in metal loading of the sediment deposited there. Further development of aquaculture in this subbasin, of food-stuff agriculture on recently reclaimed lagoon bottom, or where irrigation waters come from Bahr El-Baqar drain or its discharge should be halted or strictly limited until potentially toxic metals in the drain waters and sediment are removed and polluted input drastically reduced. This environmental assessment of heavy metals in aquaculture or agriculture development should extend to other waterbodies in the northern Nile delta, particularly Idku lagoon and lake Mariut, where industrial metal-bearing wastes discharge into the waterbodies.