Faunal analyses in the Interpretation of the Submergence of Substrates beneath Heracleion and Eastern Canopus.

The ancient Greeks built the cities of Herakleion and Eastern Canopus as major navigational gateways at mouths of the Canopic branch of the Nile River in Egypt. Although originally built on the coastal margin of the northwestern Nile delta (Toussoun, 1934; Bernand, 1970), these recently rediscovered cities now lie in Abu Qir Bay (Fig. 1) where they are now completely submerged in marine waters at depths of about 5 to 7 m (Goddio et al., 2003). Herakleion, the older settlement, remained above sea level from about the 6th century BC to the 1st century AD, and Eastern Canopus was active from Greek/Ptolomaic time until the mid-8th century AD (Stanley et al., 2001; Stanley and Warne, 2003). To date, relatively little is known of the sediment substrate on which the cities were built, except that these once lay at elevations of little more than 1 m above sea level and subsequently were submerged by a series of both gradual and sudden events. Some preliminary information on submergence of the cities and failure of their sediment substrate has been obtained as a result of recent geological and geophysical surveys. These provide new insight on the triggering mechanisms and on how and when the two cities subsided in Abu Qir Bay (Stanley et al., 2003 a, b). The purpose of this study is two-fold: (1) to determine whether correlation by cores can be established between now-submerged substrates in different geographic localities at and near the submerged sites; and (2) to interpret the environmental evolution recorded in the cores in order to gain additional information on the nature of lowering of the sediment substrates upon which the two ancient cities were originally built. It is anticipated that an investigation focusing on these two aspects could provide some clarification of sea-level changes and sin- and post-depositional conditions affecting these substrates during the past 2500 years. To achieve these goals, we examined various faunas from a series of radiocarbon-dated vibracores collected at nine localities beneath the two cities (Fig. 1). Emphasis herein is on molluscan assemblages, including bivalves, gastropods and scaphopods, and on microfossils, including foraminiferal and ostracod faunas. The approach used is based on the a priori expectation that most faunas encountered in Holocene core sections recovered in the study area presently live in the Mediterranean. Thus, an assessment of molluscan and microfossil assemblages in core sections would likely shed new light on depositional conditions through time on the vertically mobile Nile delta margin. It is important for study of the now-submerged cities that we focus herein on faunal changes through time, i.e. prior to, during and following subsidence of both cities into the sector that has only recently evolved as a fully marine bay.