الفهرس 
MATERIAL AND METHODOLOGYOnly 14 pages are availabe for public view
 |  | from | 189 |  |  |
| | | from | 189 | | |
Abstract
Myos Hormos lies at the head of a bay, behind which is a silted lagoon. The small inlet cuts the Late Pleistocene coral reef that runs parallel to the shore. Rainfall water is catched from the upstream oriented northwest and distributed through the two main stream valleys, Wadi Anz and Wadi Quseir El Qadim, into downstream (the bottom of silted lagoon and its inlet) then in the sea. The two main valleys bring flash floods in winter annually. The prevailing wind is NW-SE direction.
Geomorphologically, the upper stream of Thebes limestone Plateau (about 200m above sea level) is washed through alluvial fans slopped down to the bay. The bay is particularly well sheltered by two southwest Plio-Pleistocene and Holocene coralline coastal terraces that flank southwestern side on the Quseir El Qadim Red Sea Coast. The entrance to the embayment faces the southwestern side. Bed load sediments is supplied by the two stream valleys Wadi Anz and Wadi Quseir El Qadim.
The catchment area of Wadi Anz and Wadi Quseir El Qadim is about 47.53 square km. Its width is about 7 km from east to west and its length about 5 km from north to south. The upstream area is about 200m above sea level where downstream found a few dozen centimeters above mean sea level.
Occasionally, the fringing reefs form a platform-like barrier against the open sea, behind which shallow protected lagoons are developed, particularly at the mouths of these wadis. Also, they form elongated narrow framework running in the general direction of the Red Sea and are about 1-2 m below sea level, which allows exchanging the water between the sea and the lagoon.
Myos Hormos harbor is incised in Quaternary sediments as it lies at the head of a bay or sharm, behind which is a silted lagoon. The small inlet cuts the Late Pleistocene coral reef that runs parallel to the shore. The silted lagoon extends some 700 m inland to the west and is approximately 2 km long (north to south) and is linked to the back of the bay by a silted channel.
Our palaeoenvironmental reconstruction is based upon the litho- and biostratigraphical study of three cores taken from the palaeo-lagoon surrounding the site of Myos Hormos. Coring sediments play an important role in palaeoenvironmental reconstruction as it is used to demarcate the shape, size, depth, and aspect of Myos Hormos harbor basin and understand the sedimentological history of this area as well as to use the changes in sediment delivery to the site as a proxy for studying environmental changes. Thus, a maximum depth of nine meters below the surface was reached using mechanical coring of Vibracore COBRA auger.
136 samples were taken from three cores Quseir core 1, Quseir core 2, and Quseir core 3, at regular 10 cm intervals. Quseir core 1 (9 meters) lies in the center of the silted lagoon while Quseir core 2 (3meters) and Quseir core 3 (3meters) are situated in the boundary of the silted lagoon. Preliminary core descriptions and log drawings were undertaken in the field, before analysis of the various lithoclastic and biological indicators under laboratory conditions in which samples retained were subjected to grain size analysis and ostracod examination to assess the nature of the sediments.
Lithostratigraphically, 124 samples were investigated from the 3 cores. The grain size analyses of the samples of the first core (26º 09’ 03.7” N & 34º 14’ 32.9” E) consists of 0-9.6 % gravel, 3.2-83 % sand and 8.7-96.8% of silt and clay. The grain size analyses of the samples of the second core (26º 09’ 16.8” N & 34º 14’ 17.7” E) consists of 0.37-89.75% gravel, 6.37-75.31% sand and 3.89-83.41% of silt and clay. The grain size analyses of the samples of the third core (26º 09 ’07.1”N &34º 14’ 42.1” E) consists of 0-76.63% gravel, 0.66-70.51% sand and 2.92-99.34% of silt and clay.
Chronostratigraphically of the cores is constrained by a series of AMS radiocarbon determinations undertaken upon in situ marine macrofauna shells and charcoal fragments. These were performed on three samples in Quseir core 1and two samples of Quseir core 3. In Quseir core 1 samples, at 838-840 cm is dated as 7180-7420 cal. years BP and 5475-5230 cal. years BC, while 629 cm is dated as 2110-2540 cal. years BP and 590-160 cal. years BC and at 273 cm, it is dated as 2000-2290 cal. years BP and 340-50 cal. years BC, consistent with the Graeco-Roman period.
While in Quseir core 3 samples, at 370-380 cm is dated as 6715-7130 cal. years BP and 5180-4765 cal. years BC, and 270-280 cm is dated as 3390-3780 cal. years BP and 1830-1440 cal. years BC.
Sedimentologically, the calculated ”Mz” values of Quseir core 1 sediments range from 3.15 Ø to 3.27Ø (Very fine sand), while Quseir core 2 sediments range from 1.13 Ø to 1.86 Ø (Medium sand). Also, Quseir core 3 sediments range from 1.5 Ø to 1.96 Ø (Medium sand).
The calculated values of inclusive graphic standard deviation of Quseir core 1 range between 0.55 to 0.69 Ø (Moderately well sorted), while Quseir core 2 range between 0.91 to 1.22 Ø (Poorly sorted) and Quseir core 3 range between 1.12 to 1.28 Ø (Poorly sorted).
The calculated ”SkI” value of Quseir core 1 range from -0.37 to -0.3 Ø (Very coarse skewed), while Quseir core 2 range from 0.06 to 0.46 Ø (Fine skewed) and Quseir core 3 range from 0.64 to 0.81 Ø (Fine skewed).
Grain size of Quseir cores 1, 2, and 3 could be classified into two subpopulations according to the mean grain size and the sorting of the samples as follows:
The mean grain sizes of the sediments of Quseir core 2 and Quseir core 3 are medium sand (averaging1.5 Ø) and the main clustering values of standard deviation fall is poorly sorted (averaging 1.09 Ø). So, the subpopulation 1 is described as medium poorly sorted sand indicates initial high energy depositional environment.
The mean grain size of the sediments of Quseir core 1 is very fine sand (averaging 3.21 Ø) and the main clustering values of standard deviation is moderately well sorted (averaging 0.62 Ø). So, the subpopulation 2 is described as very fine moderately well sorted sand indicates initial low energy depositional environment.
The histogram of Quseir core 1 and 2 are unimodal while that of Quseir core 3 is bimodal. Histograms point out that most of the samples are bimodal. It means that the sediments were deposited by more than one source. It is most likely to be deposited fluvially and by sea level rise. It is important to note that brackish water are accessible for harboring the ships.
Paleoenvironmentally, shifts in the granularity of ancient harbor sediments translate the degree of harbor protection, often characterized by a rapid accumulation of sediments following a sharp fall in water competence brought about by artificial harbor works. There are three distinct facies of note:
(1) Middle-energy beach sands at the base of each unit (i. e. the pre-harbor phase).This may be expressed at units A and B in each of Quseir cores 1, 2, and 3 samples,
(2) Low-energy silts and gravels (i. e. the active harbor phase). This may be expressed at units C, D, and E in Quseir core 1 samples, unit C in each of Quseir cores 2 and 3 samples.
(3) Coarsening beach sands or terrestrial sediments which cap the sequences (i.e. the post-harbor facies). In the broadest terms, this stratigraphic pattern translates a shift from natural coastal environments to anthropogenically-modified contexts, before a partial or complete abandonment of the harbor.
Biostratigraphically, a total of 5849 individuals of ostracods constituting fifteen species of ostracod species have been collected from the region from Al-Quseir. The recorded species belong to order Podocopida. The collecting ostracod species were Loxoconcha ghardaqensis, Loxoconcha ornatovalve, Loxoconcha gisellae, Loxoconchella dorsobullata, Xestoleberis sp., Paranesidea fracticorallicola, Neonesidea schulzi, Mosella stariata, Hiltermannicythere rubrimaris, Cyprideis sp., Tanella gracilis, Callistocythere arcana, Leptocythere arinecola, Quadracythere borchersi and Alocopocythere reticulata. The most common species in the collecting region are Loxoconcha spp., and Xestoleberis sp.
The lagoon of Myos Hormos provides a clear evidence for widespread landscape changes during the Holocene that can be linked to sea-level transgression, sediment forcing agents and human impacts.
The litho- and biostratigraphical data during Middle Holocene marine transgression (" ~ " 7000 cal.BP) demonstrate that as sea level continued to slowly rise during the approach to the mid-Holocene, marine waters penetrated inland, creating a large palaeobay at " ~ "7000 cal. BP
At the boundary of the harbor in Quseir cores 3 and 4 samples (3m thick), the presence of marine species Callistocythere arcane, and Semicytherura sp. and coastal species Hiltermannicythere rubrimaris is consistent with a semi-protected environment indicating a connection to open sea. Furthermore, peaks of coastal taxon Aurila convexa are concomitant with a proximal shoreface attest to continued connection with the open sea and offshore marine dynamics.
In the middle of the harbor in Quseir core 1, the increase of marine lagoonal species (Loxoconcha spp., Xestoleberis sp.) marks a semi- protected environment.
A more rapid fall in sea level during the late lagoonal (estuarine) environment Holocene combined with eolian sedimentation and infrequent riverine inputs forced complete closure of the paleo-bay.
Stratigraphic evidence implies higher sediment inputs from the adjacent wadi system, Wadi Anz and Wadi Quseir El Qadim, during the development of this paleo-bay, constraining its size and forcing partial closure despite ongoing sea-level rise.
The late Roman and Byzantine periods are marked by transition to a fine grained silty sand facies. This phase of harbor is consistent with highly sophisticated port infrastructure creating a brackish lagoon type environment isolated from the sea.
In the middle of the paleobay, Quseir core 1 samples consist of very fine sand indicating lagoon environment. While in the boundary of the paleobay (Quseir cores 3 and 4), in a landward direction from the bottom 3m to " ~ "1m, the sediments grains becomes finner upwards containing medium sand indicating lagoon environment. Then, these lagoon sediments are overlained by very fine grained sediment (mud) rich unit indicating wadi environment.
The sedimentological proxies all point to medium to low energy marine dynamics, and are further corroborated by the increase of the brackish lagoonal water species Cypredeis sp. to the detriment of marine lagoonal species (Loxoconcha spp., Xestoleberis sp.).The increase of the brackish lagoonal water species Cypredeis sp. is consistent with a sheltered, well protected harbor.