SHALLOW MARINE SEDIMENTS, RED SEA, EGYPT: RESTRICTED DISTRIBUTION
OF CORAL DEBRIS
ABBAS M. MANSOUR, AHMED H.
NAWAR1, and AHMED W. MOHAMED1
Geology Dept.. Fac. Sciences, South Valley Univ., 83511 Qena; 1National
Inst. Oceanography and Fisheries, Red Sea Branch, Hurghada, Egypt. |
One hundred and forty two samples were collected from transects perpendicular to the Red Sea coast of Egypt to a distance exceeding 4000m from shoreline, and ab. 60m deep.
Grain size distribution shows that sand-size sediments cover wide areas, mostly
the high topographic ones with coral reefs. Muddy sediments occupy the lows between high reef areas or in the nearshore zone to ab. 200m offshore. Grain size characteristics
reflect the restriction of sands rich with coral debris in coral reef areas due to the low rate of transportation.
Major constituents present are: Coral debris in reef areas; quartz and rock fragments in the beach and nearshore zone; a mixture of
foraminifers, molluscs, a d corals in sand areas near or within coral reefs. a mixture of quartz and rock fragments, foraminifers. molluscs in muddy areas; and a mixture of foraminifers, quartz and rock fragments, molluscs in muddy areas rich with seagrass. The variation of terrigenous amount depends on the nearness to the valley mouth. This composition shows the scarcity of coral debris in muddy basins not far from coral reefs, and coral is significant only in the reef areas due to the low rate of transportation. Minerals from high topographic areas show dominance of aragonite related to the abundance of corals, whereas the abundance of high Mg-calcite and calcite in low topographic areas reflects the occurrence of molluscs and foraminifers. Sedimentation of grains coarser than
3Ø (Phi) within the basins between coral reef is the resuIt of in situ organic production combined with low hydrodynamic control.
However, sedimentation of low topographic areas in the nearshore zone is affected by the terrigenous input from the nearby
Wadies.
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