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

Abstract

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.