The Eocene rocks in the Shabrawet area (north Eastern
Desert, Egypt) have been subdivided into three formations
that are from base to top: the Minia Formation (Late Ypresian),
the Sannor Formation (Bartonian) and the Maadi Formation
(Priabonian). These three formations are disconformable with
each other. In addition, the whole Eocene succession is
disconformably overlain by the Oligocene rocks and is underlain
by the Cretaceous rocks with an angular unconformity
surface. The Sannor Formation has been subdivided into three
informal units: lower, middle and upper units. The overall sedimentary
nature of the Eocene rocks in the study area is dominated
by carbonate-siliciclastic rocks. Detailed microfacies
analysis has enabled discrimination of 22 sedimentary
microfacies types, which are grouped into six facies associations,
equivalent to six depositional environments sited on an
inner ramp setting. These depositional environments are
floodplain-dominated fluvial, lacustrine/palustrine, tidal flat, restricted
inner lagoon, shoal bar and outer lagoon with open
circulation. A suitable depositional model of the Eocene rocks
is given. In addition, four discrete benthonic foraminiferal
biozones were reported in the Eocene succession, arranged
from base to top: (1) Alveolina frumentiformis biozone (Late
Ypresian), (2) Orthoplecta clavata biozone (Bartonian), (3)
Dictyoconus aegyptiensis biozone (Bartonian) and (4)
Discorbis vesicularis biozone (Priabonian). In terms of sequence
stratigraphy, the studied Eocene succession exhibits
three superimposed depositional sequences, each of which
shows retrogradational (transgressive systems tract) and aggradational
(highstand systems tract) to progradational (lowstand
systems tract) packages of facies. The retrogradational package
displays a predominance of outer lagoon and restricted inner
lagoon facies. The aggradational package shows an increase of
shoal bar and tidal flat facies, whereas the progradational package
marks the occurrence of continental facies (floodplaindominated
fluvial and lacustrine deposits). In this study, it is
noticed that there are lateral and vertical changes in the depositional
environments of the Eocene rocks, between shallow
marine and continental environments. Also, many unconformities
have been recorded in between and within these rock
units. Such remarks indicate that the Eocene rocks were deposited
within a highly tectonically active area that was consequently
influenced by the transgression and regression of the
Neo-Tethys. Such tectonic activity could be related to the Syrian
Arc System that was renewed and enlarged several times
during the Late Cretaceous up to the Neogene in the eastern and
southeastern Mediterranean domain. |
