الفهرس 
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Abstract
The present study is mainly concerned with paleoenvironmental interpretation and mineralogical study of the exposed Nile terraces of Quaternary point bar sediments. Ten geologic sections were measured and described in the field. These sections are Hammra I, Hammra II, Hammra III, Quarry IV, Quarry V, Quarry VI, Sand sheet, Torrent VII, Torrent VIII and Torrent IX. Hammra I, II and III sections belong to the Middle Pleistocene, Quarry IV, V and VI sections belong to Late Pleistocene, Sand sheet belongs to the Holocene and Torrent VII, VIII and IX sections belong to the Holocene (Recent).
The Middle Pleistocene (Hammra I,II and III) sections are characterized by coarse sand and the internal structure of lamination and planar cross bedding indicating that these units were deposited by medium to high energy water current. Also, the occurrence of tufa as a spring fed up by carbonate lake indicates that they were deposited in highly evaporative environment with warm paleoclimatic and wet conditions as well. The Late Pleistocene (Quarry IV, V and VI) sections are characterized by medium sand and the internal structure of lamination, wedging shape and planar cross bedding which indicate that these units were deposited by medium energy water current. The Holocene Torrent (VII, VIII and IX) Sections are characterized by medium sand and the internal structure of lamination indicating that these units were deposited by medium energy water current.
Fifty five samples were collected from the study area. Histograms of the studied sediments revealed that most of the studied sediments are considered of bimodal distribution pattern with a little unimodal and polymodal distributions indicating more than one source. The modes of these samples nearly lie in the medium sand classes. The cumulative curves of the studied sediments reveal that poorly sorted traction and saltation are considered the predominant populations of these cumulative curves. In some curves, saltation population is divided into two segments which indicate two different transport conditions or variation in the energy of the depositional current. Most of curves indicate that the exposed Quaternary point bar sediments were deposited by defunct braided Nile channel. The presence of little amount of silty sand grain sized in the Middle and Late Pleistocene exposed Nile sediments reveals that it will be easy to cultivate.
94 grains of gravel size were collected from Hammra III section. The average shapes of gravels are mainly rod-shaped (37.23 %), spheroidal shape (25.53 %), disc shape (23.40 %) and bladed shape (13.83 %) which indicate that these gravels were transported and deposited by the water river channel.
Nine grains were selected from the gravels and tufa from Hammra III section to be examined under the polarizing microscope. The investigated thin sections revealed that most of them are of sedimentary origin (88.30 %) beside few igneous clasts (11.70 %). These observations indicate that the provenance of these gravels is the older formations (Eocene, Oligocene and Miocene). Also the occurrence of basalt refers to the Oligocene basalt provenance. The recorded quartz grains display unit extinction may indicate that the source rock is volcanic igneous rock.
Fifty five sand sized portions from the collected samples were used for the separation of the heavy and light minerals. The light fractions consist of sub-rounded to sub-angular quartz with a little amount of feldspar. The investigated heavy minerals are zircon, tourmaline and rutile from the ultrastable group. Epidote, staurolite, kyanite, monazite and garnet from the metastable group. Amphibole is represented by hornblende and pyroxene is represented by augite from the unstable group. ZTR index for the studied samples lies below 25 % which indicating mineralogically immature sediments. The dominance of subangular to subrounded heavy mineral grains with low ZTR index in the studied sediments reflect instability of the sediments. Also, the presence of prismatic ultrastable heavy minerals such as zircon, tourmaline and rutile in the studied sediments indicates sources of igneous and metamorphic rocks and they were derived by the Nile water from pre-existing sedimentary sources.
The examined X-ray samples revealed that the predominance minerals are quartz, gypsum, albite and little amount of orthoclase was detected only in Quarry V section. The presence of albite indicates that the sediments were derived from acidic igneous contribution, and gypsum was derived from Miocene evaporites.
Regarding to the X-ray fluorescence of tufa, the high amount of Sr (587.7 ppm) indicating the occurrence of tufa as a spring fed up by carbonate lake because the Sr amount increases with less diagenesis in carbonates.
The hazardeous flash flood in the depression shows prominent alluvial fans with a cone-shaped of coarse stream sediments, sheet-flood deposits and debris flows that formed as a result of the November 4, 2015 flash flood. The exposed Quaternary Nile sediments was flushed out and transported in three ways: stream flow, debris flow and mud flow. Stream flow is the most prominent that occurs in flash floods.
Regarding to salinization, the lakes with high salinity dry up lefting large amounts of salts on top which are used in several industries. The accumulation and precipitation of the salt and natrun crystals affect drastically the fertile soils and turn it into bad land.