Figure 17 Tombolo sedimentation rates from cores T13 and T14.
Related Figures (26)
Fig. 1. Tyre’s tombolo set against some of the Mediterranean’s better known examples. Fig. 2. Location of core sites on the Tyrian peninsula (black dots denote the sites). Fig. 3. Location map of core sites at Alexandria. Radiocarbon dates for Tyre (no shading) and Alexandria (shading) Table 1 Fig. 4. Core T18 marine macrofauna. Fig. 6. Core T13 lithostratigraphy and grain size analyses. Fig. 9. Core T14 lithostratigraphy and grain size analyses. Fig. 13. Wave heights for 225°, 270° and 315° propagated swells (adapted from Marriner et al., 2007). Inset 3: Reconstructed island dimensions around 4000 BP. The bathymetry has been calculated on the basis of a 4.5m RSL change. Inset 1: Reconstructed island dimensions around 8000 BP. The bathymetry has been calculated on the basis of a7m RSL change. A north—south transect comprising three cores, T13, T14 and T15, elucidates the tombolo’s stratigraphy. In this area, leeward of the island breakwater, the Maximum Flooding Surface (MFS) is dated to ~8000 BP (Fig. 15). The litho- and biostratigraphic signatures of this transgression comprise silt and sand rich in molluscan shells. Fine-grained sediments and brackish and marine-lagoonal faunas translate shallow, low- energy waterbodies during this period. Shelter was afforded by Inset 2: Reconstructed island dimensions around 6000 BP and maximum marine ingression. The bathymetry has been calculated on the basis of a5 m RSL change. nset 4: Reconstructed island dimensions around 300! 3P. The bathymetry has been calculated on the basis o a 4m RSL change. Inset 5: Reconstructed island dimensions around 330 BC. The bathymetry has been calculated on the basis of a3m RSL change. Inset 6: Present day coastal morphology and bathymetry Core T18 was drilled between Tell Mashuk and El Bass , the oldest portion of the continental salient sensu stricto. Two contrasting facies record the early growth of the tom bolo margin. The clay substratum is transgressed by fine-bedded marine sand dated to ~ 6000 BP (Figs. 4—5). After 5500 BP, the transition from marine sand to choked lagoon sedimen s is concurrent with the accretion of the salient, culminating in the isolation of the back-barrier lagoon. This rapid coastal accretion is explained by the mid-Holocene stillstand regime and high sediment supply, inducing a loss of accommodation space. Although the density of core networks does not allow the precise spatial dimensions of the lagoon to be established, local The Hellenistic causeway led to a human-induced metamor- phosis of Tyre’s coastal system accentuating many of the proto- tombolo genetic processes. After ~ 330 BC, the city’s bays were definitively segmented into two coves characterised by two isolated littoral cells. A cessation of longshore currents is linked to human impacts and subaerial growth of the isthmus. During After 3000 BP, the chronostratigraphic data provide evidence of very rapid rates of sedimentation, >0.3 cm/year (Fig. 17). We link this to human-induced erosion of surrounding watersheds, namely the expansion of agriculture and deforestation, which delivered increased sediment supply to coastal depocentres. Climate records from the Levantine basin evoke a transition to a cool wet climate during the Late Bronze Age/Early Iron Age and the Late Roman/Byzantine periods (Bar-Matthews et al., Fig. 18. Morphodynamic evolution of the Alexandria and Tyre isthmuses since antiquity. Fig. 19. Chronostratigraphy of tombolo cores C9 and C2 at Alexandria. Fig. 20. Top: Palaeogeographical reconstruction of Alexandria’s tombolo around 5500 BP. The reconstruction factors in a relative sea-level change of 7 m since this time. Note the existence of an extensive 14 km breakwater ridge that shielded Alexandria’s western bay. We hypothesise that a number of breaches existed in the sandstone ridge creating a low-energy lagoon environment on the leeward side at this time. Middle and bottom: Palaeogeographical reconstruction of Alexandria’s tombolo at 330 BC. The reconstruction factors in a 5 m relative sea-level change since the Ptolemaic period that has significantly reduced the dimensions of Pharos island.
