Geology

doi: 10.1130/0091-7613(1999)027<0147:RSPAIT>2.3.CO;2 1999;27;147-150Geology

 Glenn A. Goodfriend and Daniel Jean Stanley A.D. and the demise of the port of PelusiumRapid strand-plain accretion in the northeastern Nile Delta in the 9th century  

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INTRODUCTIONThe northeastern corner of the Nile Delta,

bordering the Gulf of Tineh east of the Suez Canal(Fig. 1), is not traversed by any functioning NileRiver distributaries. However, the Pelusiac branchonce flowed through the region (Toussoun, 1922;Sneh and Weissbrod, 1973; Coutellier and Stan-ley, 1987). A northwest-southeast–trending sandystrand plain, with ~18 low (20–30 cm) beachridges of shelly sand, extends 35 km along thecoast and to 12 km inland (Fig. 1).

Sneh and Weissbrod (1973) delineated thisstrand plain and located the former lower courseof the defunct Pelusiac branch of the Nile River(Fig. 1). In their interpretation, accretion of thestrand plain was responsible for degeneration ofthe Pelusiac distributary and some of its minorbranches. They obtained a bulk radiocarbon dateof 1925 ± 90 yr B.P. (uncorrected for isotopicfractionation or marine reservoir age; the two ef-fects tend to cancel each other), based on shellfrom near the landward edge of the strand plain.On this basis, they concluded that accretion of thestrand plain began in the 1st century A.D. and wascompleted no later than the 13th to 15th century,due to the presence of Mameluke ruins along thepresent coastline.

In this study, we reevaluate the history of thestrand plain of the northeastern Nile Delta usinglithostratigraphic and chronostratigraphic resultsfrom several cores taken on the strand plain. De-tailed dating of the cores was carried out by acombination of amino acid racemization analysisof individual shells and accelerator mass spectro-metric (AMS) 14C analysis. Racemization al-lowed us to carry out numerous analyses of indi-

vidual shells rapidly and inexpensively in orderto determine the actual time of deposition even ifreworked material is present (e.g., Goodfriendand Stanley, 1996). We relate these results on thechronology of growth of the strand plain to his-

torical accounts of the region, and discuss impli-cations of our results for the late Holocene his-tory and geographical evolution of the region, es-pecially the ancient port city of Pelusium and thePelusiac and Damietta branches.

MATERIALS AND METHODSChronological results are presented for cores

S21 and S15 (along the present coast) and S18(near the landward edge of the strand plain) (Fig.1). Lithostratigraphic information from thesecores and cores S12 and S19 are considered(Stanley et al., 1996). Cores were taken using anAcker II drilling machine (Stanley et al., 1996).Because of the thickness and noncoherence of theupper sand, most samples were recovered aswashings over vertical intervals of 50 to 200 cm.

Shells and shell fragments of the small bivalveDonaxspp. (D. trunculusand D. semistriatus)and the gastropod Piranella conicawere pickedor sieved from core samples in the laboratory.

Geology;February 1999; v. 27; no. 2; p. 147–150; 4 figures; 2 tables. 147

Rapid strand-plain accretion in the northeastern Nile Delta in the 9th century A.D. and the demise of the port of Pelusium Glenn A. Goodfriend Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, N.W., Washington, D.C.

20015, USADaniel Jean Stanley Deltas—Global Change Program, Paleobiology E-206, U.S. National Museum of Natural History, Smithsonian

Institution, Washington, D.C. 20560, USA

ABSTRACTAn unusually large (~1 km3) and rapid influx of Nile River sediment in the early 800s

(A.D.) resulted in accretion of an extensive strand plain (6 to 15 m thick, 35 km long, and asmuch as 12 km wide) on the subsiding northeastern Nile Delta margin, Egypt. This event is re-lated to blockage of the Pelusiac branch and breaking through of a new distributary to the westof present-day Port Said, probably representing initiation of the Damietta branch. The sand isof analytically identical age throughout the area and was deposited within less than ~60 yr, asindicated by 14C and amino acid racemization analyses of Donaxshells from a series of cores.Radiocarbon dates, in combination with historical accounts by Al-Jakubi, who found thestrand plain already in existence when he visited the area in the late 800s, place this event in theearly 800s. Nilometer flood records suggest that the sequence of great floods of 813, 816, and820 may have been the triggering events. This sudden displacement of sand caused Pelusium,then the principal port and fortified city of the northeastern Nile Delta located at the mouth ofthe Pelusiac branch, to be cut off from both the Nile and the Mediterranean, and led to its de-cline and eventual abandonment by the 12th century, when the Crusaders arrived.

Figure 1. Map of northeastern Nile Delta (modified from Sneh and Weissbrod, 1973), show-ing strand plain, core locations (S numbers), fault line, and other geographic features. In-set shows location of figure within Nile Delta.

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Donaxis typical of sandy littoral zones, whereasPiranella conicais a brackish-water (lagoonal)species (Bernasconi et al., 1991). Depths ofsamples from the core were corrected to com-pensate for compression of sediments during cor-ing and shrinkage during storage by comparingoriginal and current lengths of core segments. Af-ter cleaning (Goodfriend and Stanley, 1996),shell pieces of 15–60 mg were hydrolyzed, de-salted, and derivatized for amino acid racemiza-tion analysis by gas chromatography (see Good-friend, 1991, for details of procedures). ForD-alloisoleucine/L-isoleucine (A/I) values, ana-lytical errors average ~5%, but additional errormay occur from heterogeneity within the shell(Goodfriend et al., 1997). The reported A/I valueshave been calibrated by multiplying the peak arearatio by 0.87 (Goodfriend and Mitterer, 1993).

Precleaned aliquots of selected shells weresent for AMS 14C measurements to the WoodsHole Oceanographic Institution’s NOSAMS fa-cility. Ages are reported corrected for isotopicfractionation. Calibration of radiocarbon dateswas carried out by the CALIB 3.0 program (Stu-iver and Reimer, 1993).

STRATIGRAPHY AND LITHOLOGY OFTHE STRAND PLAIN

The top of each core from the strand plainconsists of unconsolidated sands that overlie mudor sandy mud of late Holocene age (Stanley et al.,1996). Core S21 (Fig. 2), located along the coast ina rapidly subsiding area (Stanley and Warne,1993), consists of 49 m of Holocene sediment, the

upper 15 m of which are unconsolidated sand(Stanley and Goodfriend, 1997). The other coastalcore, S15, contains 32 m of Holocene sediment,the upper 6.4 m of which are unconsolidatedsands. S18, located near the landward edge of thestrand plain (8 km inland), contains 27 m of Holo-cene sediment; unconsolidated sand comprises theupper 6.1 m. S19, at Tel Farama (Pelusium) at thelandward edge of the strand plain contains 3.6 mof unconsolidated sand at the top. S12, located <1km from the coast, contains 4.6 m of unconsoli-dated sand at the top. The volume of this uppersand unit is estimated to be ~1 km3.

Grain-size analyses using a laser particle sizeanalyzer indicate mean sizes ranging from 75 to270 µm (very fine to medium sand) and poorsorting, resulting from admixtures of quartz withbiogenic carbonate of various sizes. No trend ofgrain size with depth was noted. Composition-ally, the sands are dominated by light minerals,primarily quartz of Nile derivation, and variableproportions of heavy minerals, mica, verdine,and biogenic components (Stanley et al., 1996).Gypsum prevails in the upper sand of core S18,recovered in a salt pan.

CHRONOLOGY OF STRAND-PLAINSANDSRacemization and Radiocarbon Results

Core S21.Amino acid racemization analyseswere carried out on 29 Donaxand 10 Piranellashells over the 15 m span of the upper sand ofcore S21. The majority of the DonaxA/I valuesare within a narrow range of 0.04 and 0.06; there

are a few outliers as high as 0.15 (Fig. 3). Notrend of A/I values with depth is seen over thewhole 15 m interval. AMS 14C analyses of indi-vidual shells having the lowest A/I values (–0.05)at each of three levels spanning 5 to 15 m depthconfirm the lack of a trend of age with depth: allthree radiocarbon dates are identical (1420–1450 yr B.P.) within analytical error (Table 1).Piranellashells appear in several muddier inter-vals within the core. These give a range of A/Ivalues, but at each level, the minimum values(~0.02) are much lower than those seen in Donaxand close to typical values measured for live-collected shells (0.01). AMS 14C analysis ofPiranellashells with the lowest A/I values at 0.6and 7.9 m depth confirms their very young age(275 and 365 yr B.P., before subtraction of thereservoir age; Table 1).

Core S15.With the exception of one anom-alous shell giving a near-modern value at 5.6 mdepth, minimum DonaxA/I values at both the top(0.5 m) and bottom (5.6 m) of the core are ~0.04to 0.05, as in core S21. This indicates that there isno measurable age difference between the topand bottom; thus sedimentation must have beenvery rapid and occurred ~1440 yr B.P. (uncali-brated), as indicated by the radiocarbon dates forshells with the same A/I values in core 21. Oldershells (with higher A/I values) are also present atboth the top and bottom of the sands. The shellwith a near-modern A/I value at the base of thesand is problematic; it may represent artificialdisplacement of a surface shell during drilling.

Core S18.The surface of this core is one ofthe low beach ridges comprising the strand plain.Located at the landward edge of the strand plain,it thus represents the initial progradational phaseof the plain. Radiocarbon analysis of a Donaxshell from the surface of the beach ridge gave an

148 GEOLOGY, February 1999

Figure 2. Core logs of five bor-ings examined (modified fromStanley et al., 1996).

Figure 3. Amino acid racemization (A/Ivalues) for Donax and Piranella shellsin core S21 in relation to depth.

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age of 1460 yr B.P. (Table 1). Racemizationanalyses of Donaxfrom 3.5 m (middle of sandunit) and 5.7 m (bottom of sand unit) gave arange of values with minimum values of 0.04 to0.05, as for the other cores (Fig. 4).

Radiocarbon Reservoir Ages and Calibrationof Radiocarbon Dates

Shallow marine carbonates typically give ra-diocarbon ages several hundred years older thancontemporary atmospheric values (the reservoirage), but the amount varies among different waterbodies (Stuiver and Braziunas, 1993). For theMediterranean, few data are available for reser-voir ages (based on 14C analysis of modern, pre-bomb mollusk shells). These indicate (Table 2)that the values are similar to typical worldwidevalues (the ∆R, or deviation from typical values,is essentially 0), but the variability is considerable.Of the standard deviation of 167 yr calculated forthe four measurements, the average analytical er-ror (53 yr) accounts for only a small proportion,leaving a net standard deviation of 158 yr (totalvariance is the sum of the intrinsic variability [netvariance] plus the analytical error variance). Ra-diocarbon ages were therefore calibrated using a∆R value of 0 with a standard deviation of 160 yr.

Both Piranelladates from core S21 have agesthat are younger than any pre-bomb (pre-1950)14C levels. This may indicate a post-bomb age orcould be the result of reduction of the marinereservoir age by input of fresh water from theNile. The depleted δ13C values of Piranella, ascompared to Donax (Table 1), are strongly sug-gestive of a significant influence of fresh water.

Core Chronologies Based on Radiocarbonand Racemization Results

The unexpected results for core S21, with stratacontaining recent Piranellaappearing at variouslevels down to 8 m (Fig. 3), indicate that these sedi-ments were reworked at least to this depth, prob-ably at the time of construction of the adjacent SuezCanal bypass in the 1970s. Refilling of the excava-tion apparently incorporated adjacent sand withDonax(originally deposited ~1450 yr B.P.), as wellas recent lagoonal mud containing Piranella.

The analyses discussed here indicate that thestrand-plain sand was deposited very rapidly. No

difference in age could be detected between thebase and top of the sand in any of the cores. The ra-diocarbon age for the initiation of strand plaingrowth (1460 ± 25 yr B.P.; S18 in Table 1) is nearlyidentical to that for the termination, as representedby the mean value (± standard error) of S21 Donaxages (1435 ± 25 yr B.P.). These indicate that strandplain accretion must have been completed withinca. 25 ± 35 14C yr (the error is obtained fromadding the variances of the two radiocarbon ages),or less than 60 yr (at 1σ). This event occurred at1450 14C yr B.P.; but when this date is corrected forreservoir age and calibrated, the calendric date israther less precise—A.D. 800 to 1100 (at 1σ). How-ever, historical records allow more precise delimi-tation of the timing of this event.

Historical Records Relating to Strand-PlainChronology

In his work Kitab el Buldan(Book of Coun-tries), written in A.D. 891–892,Al-Jakubi provides

a geographical account of his travels in NorthAfrica (de Goeje, 1892). In the 870s, he visited theeastern Nile Delta coastal plain, including the cityof Farama (former Pelusium). Although now lo-cated at the landward edge of the strand plain,Pelusium in ancient time served as a Mediter-ranean port and as the primary defense position ofthe northeastern delta. Of this city,Al-Jakubi wrotethat “between it and the Green Sea [Mediter-ranean] is three miles” (de Goeje, 1892, p. 330).This distance agrees closely with the present dis-tance of this site from the coast (Fig. 1) and thus in-dicates that at the time he visited Farama, thestrand plain had already been deposited. The ab-sence of any mention of this dramatic depositionalevent in his account suggests that it had occurredsome years before his visit. Between this accountand the 14C measurements, the timing of strand-plain accretion in the northeastern Nile Delta canbe delimited as having occurred some time in thefirst half of the 9th century A.D.

LATE HOLOCENE HISTORY OF THESTRAND PLAIN

Sneh and Weissbrod (1973) interpreted thestrand plain as having accreted gradually, startingin the 1st century A.D. Our amino acid racemiza-tion analyses indicate that age mixtures of shellsoccur in most of the strand-plain sediment, sotheir bulk radiocarbon date would be expected tobe older than the actual age of the deposit.

The presence of Donaxshells of a range ofages (as represented by A/I values) at all loca-tions and levels analyzed in the strand-plainsands is also significant in that it implies that the

GEOLOGY, February 1999 149

Figure 4. Amino acid racemization(A/I values) for Donax shells fromupper sand unit in three cores. S21data from Figure 3. Minimum A/Ivalue for each sample is in range of0.04–0.05, except for bottom of S15.

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sands represent a reworking of a previously ex-isting coastal sand body, and not a large influx ofnew Nile River sands incorporating only contem-porary littoral marine mollusk shells. Becausecoastal currents along the delta sweep sedimentseastward (Carmel et al., 1984), the source of theshell-rich sands of inner shelf derivation must bewest of the Port Said region. The sands mustoriginally have been derived from the formerMendesian and Tanitic branches. We propose thatin the early 800s, the already weakly functioningPelusiac branch finally became blocked and theNile broke through a new distributary to the west,probably representing the origin of the Damiettabranch. Although the origin and early history ofthis branch remain vague (Toussoun, 1922), ourfindings agree with Butzer's (1975) conclusionthat by A.D. 900, a substantially modern patternof Nile distributaries had been established.

Nilometer records compiled by Hassan andStucki (1987), covering A.D. 650 to 1900, providequantitative data on the flood history of the Nile.Among the largest floods recorded during thisentire period were three great floods of the firsthalf of the 9th century, in 813, 816, and 820. Wepropose that these exceptional events triggeredthe sequence of rapid Nile evolution, startingwith the blockage of the Pelusiac branch andopening of the Damietta branch. The floodswould have swept vast quantities of preexistingdelta sediments out to sea as its new courseevolved across the delta. After being carried east-ward by coastal currents, the sands were rede-posited on top of late Holocene near-shore mudsin the “shadow area” of the Gulf of Tineh, down-stream from the coastal protrusion of the arcuatedelta (cf. Carmel et al., 1984). Accommodationspace for rapid accumulation of the ~1 km3 ofsand is provided by marked subsidence related toactive faulting (Stanley and Goodfriend, 1997).

This event would have had a major effect onPelusium, located along the Pelusiac branch of theNile and dating well back into the first millenniumB.C. Following the Arab occupation of the 7th cen-tury A.D., the city (then called Farama) was stillused as a port, but by then significant silting-in ofthe Pelusiac branch had occurred (Fontaine,1951–1952). By the 12th century, the city was de-serted. Its decline is no doubt related to the evolu-tion of the northeastern Nile Delta, having been cutoff both from the coast as well as from the Nile.

This sudden change in the geographic positionof Farama in the early 9th century, related tostrand-plain development, must be taken into ac-count in interpreting the history of this region. Atthe time of the Persian conquest in 616 and alsoduring the Arab occupation starting in 640, thecity would still have been in a coastal position.Historical accounts by Makrizi in the 15th centuryindicate that in 853–854, the sultan El-Moutawakel built fortifications in the region, in-cluding Tineh, which was built “next to the sea”(Bouriant, 1900). Whereas Fontaine (1951–1952)

identifies Tineh as the inland ruins northwest ofFarama (Fig. 1), Tamari (1978) considered these amuch later 15th-century Mameluke structure. Be-cause by 853–854 progradation of the strand plainwould already have occurred, the position of thefortress described by Makrizi should be some-where along the present coast. Indeed, the con-struction of a series of new fortifications along theeastern delta coast at this time may have been aresponse to the then-recent change in the positionof the coastline as a result of strand-plain deposi-tion. Later landings at Farama by the Byzantinesin 859–860 (Casanova, 1906), by the Greeks in954–955 (Bouriant, 1900), and then by the Cru-saders in the 12th century would have occurredwhen Farama was already in an inland position.

In antiquity, many of the major port cities ofthe Mediterranean (e.g., Ostia [the port of ancientRome], Troy, and Ephesus) were located ondeltas. Like Pelusium, they also were subject todramatic geographic changes as a result ofcoastal progradation (e.g., Brückner, 1997); butthese were of a rather more gradual tempo thanthe event we document at Pelusium.

ACKNOWLEDGMENTSWe thank P. E. Hare for providing facilities for the

amino acid racemization analyses, N. Boktor for trans-lating passages from Al-Jakubi, M. Fontugne for pro-viding information on radiocarbon reservoir ages forthe Mediterranean, F. Hassan for confirming the simi-larity of early Arab miles (“amiel”) to English milesand providing Nile flood record information, T. Jorstadfor preparation of figures, S. Hardy and M. Wolf for ob-taining hard-to-find publications, and C. J. Murray andan anonymous reviewer for providing helpful sugges-tions on the manuscript. Support was provided to Stan-ley by the National Geographic Society and the WalcottFund of the National Museum of Natural History.

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