Quaternary shoreline development: the northwestern coast of Egypt
Introduction
A well-developed sequence of coastal sediments, aeolionites and paleosols are developed on the Mediterranean coast of northwest Egypt (Fig. 1), along with well-developed evidence of former sea levels. The area includes numerous geomorphic features developed in limestone bedrock (notches, caves, platforms) and coastal dunes, and currently has a low tidal range.
The northwestern Mediterranean coast of Egypt forms the northern extremity of the Miocene Marmarican homoclinal plateau, which extends west of Alexandria for about 500 km. This confines the coastal plain of a narrow western province which extends from El-Salum to Ras El-Hekma, and an eastern province which extends from Ras El-Hekma to Alexandria. The eastern region is wider than the western province and is affected by the synclinal Arab's Gulf embayment (Fig. 1A). The eastern province is characterised by the development of successive ridges running parallel to the present coast. These have been described by Shata (1971) and interpreted as of Sicilian to Monasterian age (1600–70 ka). These features have variously been interpreted as having formed as shallow marine bars, mixed beach and aeolian ridges (Philip, 1953, Philip, 1976; Ismail and Selim, 1969; Hassan et al., 1986; El-Asmar, 1991, El-Asmar, 1994; Hassouba, 1995), or as non marine coastal dunes (Hilmy, 1951; Paver and Pertorius, 1954; Shata, 1955). The presence of the beach boulders at the bottom of the Gebel Maryut ridge exposed at the drainage ditch of Bahig, together with the presence of the foraminiferal limestones and molluscs in their life position support the marine origin of the ridge core, while the development of aeolianites and paleosols around the core suggests that wind action and soil processes contributed to further development of the ridges during periods of lower sea-level (El-Asmar, 1991, El-Asmar, 1994; Hegab and El-Asmar, 1995).
Although Quaternary stratigraphy and its relation to paleoclimate and sea level changes have been well studied in many areas of the Mediterranean, little work has been done on the northern Mediterranean coast of Egypt. This paper reports some of the results of a long-term programme on this subject (El-Asmar, 1994, El-Asmar, 1997, El-Asmar, 1998; Hegab and El-Asmar, 1995; El-Asmar and Gheith, 1995). It concentrates on the coastal area between Burg El-Arab and El-Omayid (Fig. 1A). Four distinct ridges have been distinguished: the Coastal (first) ridge, the El-Max-Abu Sir (second) ridge, the Gebel Maryut (third) ridge and the Khashm El-Ish (fourth) ridge (Fig. 1B–E). This area is presently characterised by an arid to semi-arid climate, having a mean annual temperature of 20°C, and annual rain fall less than 100 mm/yr, with moderate to high relative humidity (65–80%).
This paper records the results of the research including the findings from Optically Stimulated Luminescence (OSL) and Electron Spin Resonance (ESR) dating of the sediments along with previous radiometric and amino acid determinations. This paper also records a new fossiliferous bed overlying the Cardium limestones and underlying the boulder beach at the core of the third ridge.
Section snippets
Field work
All the sedimentary units constituting the coastal ridges have been sampled. The morphology of the ridges, the sedimentary structures and the fossil content have been studied. Accordingly three formations are identified, these are from younger to older; the Alexandria oolitic limestone Formation (Attia and El-Ghazawy, 1984) of Late Pleistocene to Holocene age, the Burg El-Arab fossiliferous limestone Formation, and the El-Hammam bioclastic limestone Formation of Middle to Late Pleistocene age (
El-Omayid
Two sections were studied at El-Omayid. One section cuts across the first ridge, closest to the present coastline and acts as a barrier at the landward end of the present beach (Fig. 2A and B). This section is represented by two units <8 m thick, dipping both north and southwards, composed of ooids with minor presence of quartz grains, and characterised by low angle cross bedding (Fig. 2A) (Alexandria Fm., Attia and El-Ghazawy, 1984). These units are separated by a conspiciuous surface of
Age of the coastal ridges.
The results of the dating programme are listed in Table 1, and shown in Fig. 1; to record the relationship with the stratigraphy.
Conclusions
The Quaternary deposits of northwest Egyptian coastal zone between El-Omayid and Burg Arab are described in detail and age determinations have been carried out on rock and fossil samples using radiocarbon, U-series, OSL, AAG and ESR.
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The OSL dates of ooids and paleosols give ages for the younger ridge which appear to agree with other radiometric and AAG determinations.
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The paleosols at both the northern flanks of the second and third ridges are complex resulting from development over several wet
Acknowledgements
The authors would like to express their gratitude to the anomyous reviewers and Prof. J. Rose, Department of Geography, Royal Holloway, University of London, for fruitful discussion, continuous help, support, analytical facilities provided and revision of the manuscript.
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