Late Maastrichtian litho- and ecocycles from hemipelagic deposits of eastern Sinai, Egypt

A biostratigraphical and palaeoecological survey employing calcareous nanno fossils and planktonic and benthonic foraminifera has been carried out in f our sections of hemipelagic marls and chalks of the Late Maastrichtian Abat homphalus mayaroensis Zone of eastern Sinai, in order to evaluate the mecha nisms controlling the composition of the well preserved microfauna and nann oflora. The Abathomphalus mayaroensis Zone in eastern Sinai can be easily identifie d by the wide occurrence of the index fossil A. mayaroensis and can be furt her subdivided by the first occurrences of Plummerita reicheli (ex. P. hant keninoides) and Micula prinsii. Microfossil abundances and lithologies are characterised by pronounced repetitive distribution patterns. These include tow and high frequency fluctuations of the planktonic/benthonic (P/B) fora miniferal ratio, repetitive changes in the abundance of calcareous nannofos sils and benthonic foraminifera, as well as the development of chalk-mart c ouplets and thinning upward chalk packets. Both microfossil distribution pa tterns and the occurrence of rhythmites are attributed to changes in primar y palaeoproductivity. Semiquantitative investigations of calcareous nannofo ssils and a few selected benthonic foraminifera yield evidence of the prese nce of high (HP) and low (LP) productivity assemblages. The interpreted HP assemblage is dominated by Glaukolithus diplogrammus, Ma nvitella pemmatoidea, Microrhabdulus decoratus and Micula murus and the ben thonic foraminifera Neoflabellina jarvisi; the LP assemblage is characteris ed by Lithraphidites quadratus and Bolivinoides draco. However, further qua ntitative studies are necessary to reconstruct the exact composition of the se assemblages and to explain deviatory developments. The chalk-marl couple ts, thinning-upward chalk packets and the high frequency P/B patterns are i nterpreted to reflect productivity changes related to orbital forcing. Thes e hemipelagites were deposited during the latest phase of the southern Teth yan upwelling system, which was active from the Santonian to the Late Maast richtian with a peak in the Campanian. Termination of upwelling just before the K/T boundary also provides a good explanation for the change towards a palaeobathymetric control on foraminiferal distribution, as observed for t he Palaeocene of central east Sinai. (C) 1998 Elsevier Science Limited. All rights reserved.