FACIES, DIAGENESIS AND SEDIMENTARY ENVIRONMENTS OF MIDDLE JURASSIC FROM CENTRAL SINAI, EGYPT.
NADIA. M. ABDEL MAGUID
Faculty of Sciences,Menoufia University,Egypt |
The Middle
Jurassic succession exposed in Wadi Tarifah and Wadi Bark, central Sinai is described on the basis
of microfacies investigations.The miciofacial characteristics
demonstrate similarities within age-equivalent units of different
areas. Most facies varieties are caused by changing rates of
terrigenous input- due to different synsedimentary tectonics.
The recorded clays are mainly kaolinite with a minor amount of illite. The kaolinite
exhibits three morphological habits: vermicuIar, blocky and
lath-shaped. The vermicular kaolinite is dominant and was interpreted to have
formed by dissolution of feldspar grains. The blocky kaolinite was observed with
a textural relationship, indicating that it was neomorphosed after vermicular kaoIinite.
The mineral assemblages in the Clastic facies, epidote, amphibole,
staurolite, kyanite and garnet are indicative of initial provenance dominated
by metamorphic and acid igneous rocks. Direct derivation of some
clastics in Safa and Masajid formations are from the basement rocks of
Central Sinai.
Petrographic analysis revealed that the original composition and textural characteristics were largely
modified by cementation, replacement,. neomorphism and to a lesser extent
dissolution and compaction. The cementation of the carbonates with
different calcite fabrics denote diagenetic environments of
relatively deeper marine depleted δ18O sea water and relatively high
temperature conditions .
The origin of carbon in the calcite cement is maily of marine origin. The simiIarity between the isotopic
composition δ18O and δ13C
of the analyzed ooids and their associated calcite
cement denote stabilization of the ooids with fluids similar to those
from which the cement precipitated.
Repeated and oscillating marine conditions of sedimentation, which were
varying between shallow tidal flat (sandstones) and intertidal to
very shallow sub-tidal environmental conditions (carbonates) rhythmically interrupted with
fluviomarine sediment are here suggested for the Middle Jurassic,
Safa and Masajid formations at Wadi Tarifah and Wadi Bark in Central Sinai
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