Jean-Daniel Stanley

Nile Delta vegetation response to Holocene climate variability

A 7000 yr palynologic record from Burullus Lagoon, Nile Delta, Egypt, is assessed to investigate changes in terrestrial vegetation in response to Nile flow. Previous studies in this region have shown that sea-level rise in the early to mid-Holocene, and markedly increased human land use during the past several centuries, altered vegetation in and around the lagoon. The pollen record from this study documents changes in delta vegetation that likely reflect variations in Nile flow. We suggest that Cyperaceae pollen is a sensitive marker of precipitation over the Nile headwaters and the resultant Nile flow. Decreases in Cyperaceae pollen, interpreted as a marker for diminished Nile flow, as well as the increase in relative abundance of microscopic charcoal, occurred at ca. 6000–5500, ca. 5000, ca. 4200, and ca. 3000 cal. yr B.P. (calibrated years before present). These correspond to extreme regional and global aridity events associated with a more southerly mean position of the Intertropical Convergence Zone. These changes, also recorded by other proxy studies, indicate that several marked regional drought events affected the Nile Delta region and impacted ancient Egyptian and Middle Eastern civilizations.

Ancient Archaeological Sites Buried and Submerged along Egypt's Nile Delta Coast: Gauges of Holocene Delta Margin Subsidence

Abstract For calculating subsidence rates along the Nile Delta coastal margin, archaeological site data provide more accurate temporal and elevation control relative to Holocene sea levels than chronostratigraphic analyses of radiocarbon-dated sediment cores. Recently acquired data on the depth and age of 11 buried and/or submerged levels of human activity at seven ancient sites serve to calculate average annual rates of subsidence along the northern Nile Delta margin during the middle to late Holocene. Subsidence rates range from 0.9 to 4.3 mm/yr, varying irregularly from west to east along the northern delta coast, and averaging ∼2.5 mm/yr for 11 data points on the margin as a whole. Subsidence rate is directly related to thickness of sediment section, with highest values in the eastern part of Manzala lagoon and at coastal promontories of the Damietta and Rosetta branches. This, in large part, is a function of underlying sediment compaction plus sediment loading and readjustment of strata at depth. Short-term natural events such as earthquakes, tsunamis, Nile floods, and winter storm surges also serve as triggers of subsidence. An additional important factor is human activity, such as construction of large structures on water-saturated substrates. Most modern towns along this increasingly populous delta margin are located in low-lying vulnerable settings presently subject to subsidence, a phenomenon that warrants close monitoring and increased implementation of protective measures.

Geoarchaeological Interpretation of the Canopic, Largest of the Relict Nile Delta Distributaries, Egypt

Abstract The Canopic branch, the largest relict Nile distributary, once flowed across the NW Nile delta of Egypt to the Mediterranean. This study focuses on the Canopics evolution at the delta margin and in Abu Qir Bay seaward of the coast. Information from historic documents, integrated with data from geographical, geological, and archaeological exploration in the bay, indicates that the Canopic distributary was active from ∼4000 B.C. to the end of the 1st millennium A.D. Fluvial discharge persisted through pre-Dynastic, Dynastic, Greek, Roman, Byzantine and early Arabic time. The channel flowed to two sites, Herakleion and Eastern Canopus, established by the Greeks as navigational gateways for trade in the delta and surrounding region. Eastern Canopus functioned until the mid-8th century A.D. At that time, flow in the Canopic had decreased markedly, and Nile water was diverted to the east, through the Bolbitic-Rosetta branch. By the end of the first millennium A.D., Nile water was channeled in the Rosetta and Damietta distributaries, and the Canopic branch eventually converted to a canal and drain system. The Canopic promontory across which the branch flowed, and the 2 ancient sites located at the promontory coast near Canopic channel mouths, subsided beneath the waters of the bay after the 8th century. Submergence was a response to interaction of eustatic sea-level rise, annual floods, growth-faulting, soft-sediment deformation and other natural processes. As the Canopic promontory subsided, Abu Qir Bay attainted a marked concave-seaward shape and its shoreline shifted southward. This geoarchaeological investigation helps distinguish the long-term impact of natural events from that of increased human activity. This distinction is of practical importance for the highly populated and vulnerable delta margin that continues to experience submergence and erosion.

Holocene Depositional Patterns and Evolution in Alexandria's Eastern Harbor, Egypt

Abstract This investigation focuses on sedimentological attributes and the litho- and chronostratigraphic framework of Holocene sediment core sections recovered in Alexandrias Eastern Harbor in Egypt, for many centuries the major port in the southeast Mediterranean. Holocene sediment trapped in the harbor, formed of marine calcareous sand, muddy sand, and mud, are examined to define major depositional patterns that developed before and after expansion of Alexandria in the 4th Century BC. Petrologic and radiocarbon data indicate that the harbor formed between two Pleistocene carbonate sandstone (kurkar) coastal ridges and was flooded by seawater during the transgression at about 8000 years before present (BP). Sediments accumulated at an average rate of 1–3 mm/y largely by wave- and wind-driven currents driving material from the Egyptian shelf into the high-energy basin. The association of distinct biological components, failed slump-like sediment strata, and important hiatuses (time gaps) record the episodic influence of powerful events, such as large storm surges, seismic tremors, and tsunamis. These events likely transported marine biota and sediment from the kurkar ridge and inner shelf north of the harbor and also eroded and displaced substantial amounts of older deposits laterally within the basin. In addition to natural processes, the influence of human activity is detected in harbor sediments after ∼2400 years BP, following development of Alexandria by the Ptolomies and their successors, the Romans. Among important components in cores are artifacts and lithoclasts. The development of important mud-rich deposits from ∼2200 to 1800 years BP is attributed in part to construction of the Heptastadion, the large causeway and aquaduct system built to connect Alexandria with Pharos Island to the north. Structures such as breakwaters have modified sedimentation patterns but do not fully protect the quasi-closed harbor. Ongoing geoarcheological investigations hold promise to more precisely distinguish effects of natural processes from those of human-related activities.

Pelusium, an Ancient Port Fortress on Egypt's Nile Delta Coast: Its Evolving Environmental Setting from Foundation to Demise

Abstract This study documents the evolution of the coastal site on which an ancient port fortress, Pelusium, was positioned in the NE corner of Egypts Nile Delta. Focus is on the stratigraphy, petrology, and faunal assemblages of radiocarbon-dated core sections recovered at major ruins at the site. The late Holocene development of this margin surface is unusual in that it has been subject to important geologically recent uplift since the citys founding, in contrast to predominant subsidence and relative sea-level rise that characterize most of the delta margin west of Pelusium. Vertical tectonics resulted from displacement along the Pelusiac Line, a major structural feature several kilometers south of Pelusium. The geoarchaeological survey shows the was built with ready access to the Mediterranean, after tectonic uplift, from ∼1000 to 800 BC. It was then, when Egypt was subject to Assyrian control, that the margin evolved from an open shallow marine (prodelta, delta-front) setting to a coastal one. The citys progressive decline was influenced by warfare with Persians and other invaders from the east, effects of plague, and diminished role of its commercial and trade activities following construction of Alexandria by the Greeks. However, Pelusiums eventual demise also resulted from natural factors, especially tectonically controlled motion of the lower delta plain. Vertical shifts around 800–850 AD and subsequent periods resulted in rapid coastal build-out north of Pelusium. This caused a cutoff of the city from the sea and the Niles Pelusiac branch, the major navigational byway into the delta. Pelusium, after approximately 800–850 AD, continued as a commercial center for an additional three to four centuries prior to its abandonment by the time of the Crusades. Submergence of the city on the delta margin by rise of relative sea level has been effectively counteracted by episodic fault-related uplift of this lower plain sector and continued subaerial exposure since Byzantine time.

Benthic biofacies to interpret Holocene environmental changes and human impact in Alexandria's Eastern Harbour, Egypt:

Holocene molluscan and foraminiferal faunas, sensitive ecological markers, are statistically treated to define their temporal and spatial distributions in radiocarbon-dated cores in Alexandrias Eastern Harbour. Up-core variations of these benthic biofacies record the evolution of depositional environments during the past 8000 years in this long-occupied Eastern Mediterranean port. The most important change occurred in the mid-Holocene between 6300 and 4300 yr ago, a time of lower sea level and minimal human activity. This faunal change, indicating a transition from a somewhat protected to a more open and higher-energy marine environment, resulted primarily from rise of sea level, lowering of the harbour floor and diminished shielding by Pleistocene coastal ridges and reefs near the bay mouth and within the harbour. Since that time, faunal assemblages have remained generally constant, except during the period from 2100 to 1800 yr ago when Greeks and Romans built the Heptastadion that connected Alexandria to Pharos Island; this construction effectively separated the Eastern from the Western Harbour. Absence of a well-marked faunal change during the past 18 centuries is unexpected, particularly in light of the much-increased population and associated human effects. The harbours overall large size, rise in relative sea level and continued exchange of marine water between the open shelf and port have maintained an active circulation pattern. The strong current regime and reworking of bottom sediments have generally masked short-term human effects and altered the harbours late-Holocene sediment stratigraphy. These factors help explain why benthic biofacies primarily record influences of natural processes that prevailed in this relatively unconfined, high-energy marine setting rather than those of a more constricted and anthropogenically impacted port.

Alexandria, Egypt, before Alexander the Great: A multidisciplinary approach yields rich discoveries

Historic records refer to Rhakotis as a settlement on Egypt’s Mediterranean coast before Alexander the Great founded the famous Mediterranean port city of Alexandria in B.C. 332. Little is known of Rhakotis, however, because the site has yet to be clearly identified beneath the modern city. This problem motivated a geoarchaeological investigation of sediment cores from Alexandria’s East Harbor, from which radiocarbon-dated sections of pre-Alexander age (>2300 yr B.P.) have been obtained for study. These core sections comprise a number of critical components, five of which are emphasized here: ceramics, rock fragments derived from Middle and Upper Egypt, and sediment with markedly increased contents of lead, heavy minerals, and organic matter. A multidisciplinary approach, by which archaeological, stratigraphical, petrological, and geochemical methodologies are applied to study the five distinct core components, reaffirms that a sum can be greater than its parts. Together, the diverse markers in the dated core sections enable us to confirm human activity to at least seven centuries before B.C. 332 on the mainland coast, where Alexandria would later be established. Alexander’s city, it now appears, rose from a preexisting town whose inhabitants had long before recognized the favorable harbor potential of this Egyptian coastal sector. The discoveries, providing direct evidence of the settlement’s early (to ca. B.C. 1000) existence, are intended to prompt new exploratory efforts on land and offshore to further delineate that center’s actual position and history.

Alexandria's Eastern Harbor, Egypt: Pollen, Microscopic Charcoal, and the Transition from Natural to Human-Modified Basin

Abstract STANLEY, J.-D. and BERNHARDT, C.E., 2010. Alexandrias Eastern Harbor, Egypt: Pollen, microscopic charcoal, and the transition from natural to human-modified basin. Pollen and microscopic charcoal examined in Holocene sediment core samples record major environmental modifications affecting Alexandrias Eastern Harbor through time. We assess whether such changes on Egypts coastal margin were influenced primarily by natural, or natural plus human, or primarily human factors. We focus on (1) the times when pollen assemblages and microscopic charcoal content changed in the core, (2) how they changed, and (3) why this occurred. The analysis takes into account the cores stratigraphy, regional climate variability, human history, and local archaeological record. Four pollen–microscopic charcoal zones are identified. The earliest change occurred at ca. 6000 YBP, during Egypts earlier Predynastic (Neolithic) period, coinciding with a lithologic break from sand to muddy sand. Pollen during this time indicates a transition to a much drier climate rather than effects of human activity. The second change in pollen occurred 3600–2900 YBP, during a period of continued aridity with no lithologic variation in this core interval. Pollen (cereal taxa, agricultural weeds, grape) and a sharp increase in microscopic charcoal indicate that human activity became prevalent at least 700 y before Alexander the Greats arrival in this region, and these results highlight the transition from a largely natural climate–controlled environment to one influenced by both climate and anthropogenic activity. The third shift up-core in pollen assemblages is dated at ca. 2300 YBP, at the boundary between a sand and mud unit. It coincides with construction by the Ptolemies of the Heptastadion between Alexandria and Pharos Island. From this time onward, harbor sediment in the nearly enclosed catchment basin indicates a near-continuous record of dominant proximal human activity.

Clay Distributions, Grain Sizes, Sediment Thicknesses, and Compaction Rates to Interpret Subsidence in Egypt's Northern Nile Delta

ABSTRACT Stanley, J.-D. and Clemente, P.L., 2014. Clay distributions, grain sizes, sediment thicknesses, and compaction rates to interpret subsidence in Egypts northern Nile Delta. This study focuses on the role of clay on subsidence of Holocene sedimentary sequences in the northern Nile Delta. Proportions of clay in 1262 samples from 87 cores are much higher here than elsewhere in the delta and along the Nile in Egypt. The northern third of the delta lies at a low, near-horizontal elevation (∼1 m above mean sea level), but clay content and total thickness of Holocene deposits in subsurface vary considerably in time and space. Greatest clay content (to >60%) and mud-rich thickness (to 47 m) are concentrated near Manzala lagoon. The volume of Nile water and sediment discharged annually on the delta diminished during the past two millennia as a result of climate change and intensified human activity. During the past two centuries, barrages and dams placed across the Nile and increased water diversion activities further reduced Nile flow and sediment delivery to the northern delta. Lowering at the coastal margin has also resulted from interplay of sediment compaction, regional sea-level rise, and intermittent readjustment of strata at depth. These events are ongoing, as indicated by increased erosion of extensive stretches of delta coast, salinization that affects large areas of agricultural land and groundwater, and major changes in recent sediment textural patterns as mapped in the present survey. Formerly dominant fluvial S-to-N transport during much of the Holocene has become distinctly shore parallel, recording landward shoreline advance and W-to-E sediment displacement along the delta margin. Implementing extensive coastal protective measures should take into account zones most prone to effects of subsidence, where (1) clay-rich subsurface sequences are thickest, (2) these strata are subject to high compaction rates, (3) sediment replenishment is insufficient, and (4) readjustment at depth of pre-Holocene sequences is continuing. These factors will cause the deltas NE and north-central sectors to experience continued significant surface lowering.

Measuring Strata Thicknesses in Cores to Assess Recent Sediment Compaction and Subsidence of Egypt's Nile Delta Coastal Margin

ABSTRACT This study develops a method to determine compaction and subsidence of Holocene fluviomarine sections along Egypts northern Nile Delta coastal margin based on variations of strata thickness with depth. Thicknesses of 3183 oxidized layers in 85 long cores (10 to 45 m) are examined to determine the nature of down-section and spatial patterns. The thickest layers are at depths of 1 to 2 m (dating to <1000 y BP) and become significantly reduced within the next meter due to (1) rapid expulsion of interstitial pore water from overburden compression of sediment and (2) evaporation in near-surface deposits in this hyperarid setting. Thicknesses decrease more irregularly to depths of 5 to 6 m and then more gently to the base of the sections. The more gradual compaction of strata at mid- and lower-core depths accounts for more than 50% of total Holocene compaction. The derivatives of regression curves determine the strata thickness reduction rate, which is treated as a proxy for compaction rate. Average compaction rates for Holocene sections vary along the approximately 225-km-long coastal margin: about 8.4 mm/y in the NE, about 7.7 mm/y in the NC, and about 3.7 mm/y in the NW sectors. These rates, somewhat higher than those previously proposed for this delta, are within the range for land subsidence obtained from recent satellite surveys. The interaction of natural factors, such as moderate to high compaction rates and rising global sea level, with human activities, especially those reducing sediment supplied to the lower delta, presents serious concerns for the deltas future. Without emplacement of a continuous network of protective structures along the coast, a marked landward retreat of about 30 km by the Mediterranean coast is projected in little more than a century, resulting in submergence and loss of agricultural and wetland terrains vital to Egypts rapidly expanding population.