Short-Term Sea-Level Changes and Sequence Stratigraphy of the Mid-Cretaceous Kharita Formation Reservoirs in Egypt: Insights from Geochemical and Palynological Data

Widespread deposition of siliciclastic sediments with
consequent
alternations between fine-grained siltstones and shales versus coarse-grained
sandstones in the north Western Desert of Egypt provides an archive
for mid-Cretaceous sea-level oscillations. This study presents elemental
geochemical data as well as palynofacies and palynomorph components
of upper Albian reservoirs in the Abu Gharadig Basin, north Western
Desert. During the mid-Cretaceous, the studied area is located in
the transition zone between the fluvio-deltaic and shallow marine
settings at the southern margin of the Tethys Ocean. Thirty rock cutting
samples were collected from the Kharita Formation and analyzed for
major and trace elements, total organic carbon, and palynological
composition. These data, together with geophysical gamma ray log values
and lithological composition, allowed us to reconstruct the changes
in relative sea level at this time in the framework of a third-order
transgressive–regressive (T–R) sequence stratigraphic
model. Palynomorph composition, represented by a fairly diverse assemblage
of terrestrial plant spores and pollen grains versus marine dinoflagellate
cysts and other microplankton, was employed along with the variation
in the particulate organic matter composition. Chemical proxies, including
Si, Ti, and often K and Fe, and their ratios normalized to Al, as
well as the carbonate content and the Sr/Ca ratio, provided significant
stratigraphic variations with respect to sea-level changes. The above
proxies allowed for the subdivision of the studied reservoir intervals
into three T–R sequences.