by Akmal M. Marzouk, Tanta
MARZOUK, A.M. (2004): Biostratigraphy and palaeoecological significance
of calcareous nannofossils from Upper Cretaceous of Gabal Oneigah in the Northeastern
Sinai (Egypt). Freiberger Forschungshefte, C 502: Paläontologie, Stratigraphie,
Fazies (12): 51-76; Freiberg.
The calcareous nannofloras of about 70 samples from the about 200 m thick Upper
Cretaceous of Gabal Oneigah (NE Sinai) have been analysed quantitatively in order
to determine compositional variations and to improve paleoecological interpretations
as well as biostratigraphic resolution. The biostratigraphic zonation recognized
in the studied section is compared with those established in other regions. The
Cretaceous nannofloras of the NE Sinai are similar to other regions of the Tethys.
The two solution-resistant species Micula decussata and Watznaueria barnesae are predominant in most samples. Watznaueria barnesae reaches its highest abundance during the Late Santonian-Campanian followed by a sharp decrease during the Maastrichtian. Micula decussata is more abundant in the Maastrichtian than in the Campanian. During the Late Santonian-Campanian dissolution led to a marked increase in the abundance of Watznaueria barnesae (< 70% of total assemblage). However, dissolution has generally not altered the composition of the nannofossil assemblages as evidenced by the good preservation of even delicate species such as Zeugrhabdotus spp. under the SEM and the presence of species susceptible to dissolution, such as Tranolithus phacelosus and Prediscosphaera spinosa.
The large Total Organic Matter content (TOM < 14.6%) indicates enhanced productivity during most of the Campanian and Earliest Maastrichtian, whereas productivity decreases during the Middle-Late Maastrichtian. Calcareous nannofossil species are grouped into high- and low productivity indicators, which allows the determination of the Nannofossil Index of Productivity (NIP) to record paleoproductivity changes. The NIP curve indicates relative rise in productivity through the later Santonian to Campanian followed by a decrease during most of the Maastrichtian. The Upper Cretaceous sequence of the NE Sinai has been deposited in a regional high productive regime associated with a large-scale upwelling system along the southern margins of the Tethys active from the Late Santonian to the Late Maastrichtian.