Biostratigraphic, mineralogical, geochemical and isotopic analyses of
the Gebel Qreiya section in the Asyut Basin of central Egypt indicate a
depositional environment interrupted by periods of erosion due to local
tectonic activity exacerbated by eustatic sea-level fluctuations, and by
high-stress environmental conditions akin to those normally experienced
during the Cretaceous-Tertiary boundary transition. During the late
Maastrichtian (66.8-65.4 Ma) this region experienced a breakdown of the
biologically mediated surface to bottom gradient of the C-13/C-12 ratio
with planktic delta(13)C values 0.2-0.8parts per thousand lighter than
benthic values. Planktic foraminiferal species diversity was reduced by
more than 50%, with faunal assemblages dominated (75-90%) by the
opportunistic disaster species Guembelitria cretacea, which alternate
with abundance of small, low oxygen-tolerant heterohelicids (Heterohelix
navarroensis, H. dentata, H. globulosa). This prolonged breakdown in
ocean primary productivity occurred during a time of global climate
cooling and sea-level regressions (at 66.8 and 65.5 Ma), though clay
mineralogy suggests that locally low seasonality warm, wet, tropical and
subtropical conditions prevailed. The high detrital influx suggests that
the biologically high-stress environment was primarily linked to the
existing shallow shelf conditions in southern Egypt, and possibly to
local tectonic activity and restricted circulation. A normal carbon
isotope gradient was briefly re-established during the short climate
warming and rising sea level between 65.4 and 65.2 Ma, a time of
increased species diversity, peak abundance of rugoglobigerinids and
common heterohelicids. During the last 200000 years of the
Maastrichtian, increased precipitation and terrestrial runoff (increased
phyllosilicates and kaolinite) and increasing total organic carbon
values are associated with Heterohelix-dominated planktic foraminiferal
assemblages. The K/T boundary is marked by a red clay layer and Ir
anomaly of 5.4 ppb. During the early Danian, planktic foraminiferal
populations and stable isotope data indicate that similarly fluctuating
high-stress conditions prevailed in central Egypt as elsewhere in the
marginal eastern Tethys. (C) 2002 Elsevier Science B.V. All rights
reserved.