Assiut university researches
UPPER DAKHLA FORMATION ( BEIDA
SHALE MEMBER) AT G. DUWI, RED SEA,
EGYPT: MINERALOGICAL AND
GEOCHEMICAL ASPECTS
Mamdouh F. Soliman and Mahmoud A. Essa
Abstract:
This study deals wi th the mineralogy and geochemistry of the
mineralogical phases found in the Beida Shale Member
belonging to the Dakhla Formation and exposed at G. Duwi
section, Red Sea, Egypt. The sediments of the upper Dakhla
Formation (85 m thick) are composed mainly of grey, dark
greyto black shales as well as grey marly shales and pink
marl. These sediments are intercalated by many thin layers
(30-50 cm thick) of brown and reddish brown marl. The marl
and marly shale are slightly to moderately dolomitic. The
stereoscopic microscopy and the SEM survey of the insoluble
residues of these sediments have revealed the presence of
Mn-oxides (mainly manganite), dolomite, goethite
pseudomorphs (after pyrite and pyrite framboids), goethite,
few Fe-Ti oxides and organic carbon particles. The
mineralogical and geochemical investigations indicate that
the manganese oxides, dolomite, goethite and goethite
pseudomorphs are of diagenetic origin. However, the Fe-Ti
oxides are of detrital origin. These mineralogical contents
suggest that the Beida Shale Member is a normal marine
sediment deposited in oxygen- containing bottom waters,
except for the middle part which is composed of dark grey
shale and contains pyrite and pyrite framboids. This part
reflects an euxinic marine environment and deposition in
anoxic, H2S- containing bottom water. X-ray diffraction
analysis of the clay fraction revealed that the sediments
under investigation are composed of detrital kaolinite,
smectite and illite. The fluctuation in frequencies of these
minerals within the sediments indicates a warm / humid
climate with high rain falls at the K/T boundary and during the
Danian periods as indicated by the abundance of kaolinite.
This is followed by a temperate or cool and dry climatic
conditions during the Selandian-lowermost Thanetian and a
sea level rise in the early Thanetian as indicated by the low
kaolinite content and the relative abundance of smectite.
Published in:
THE THIRD INTERNATIONAL CONFERENCE ON THE
GEOLOGY OF AFRICA,2,283-305