THE IMPACT OF PALEOCENE EOCENE BOUNDARY EVENTS ON MIDDLE NERITIC BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EGYPT/

A 25 m upper Paleocene to lower Eocene marry sequence exposed at Gebel Duwi, (Quseir, Red Sea coast of Egypt) provides a good opportunity fo r studying Paleocene/Eocene (P/E) boundary stratigraphy and events. Va rious bio-, eco-, and isotope stratigraphic correlations accurately de lineate the position of the P/E boundary (i.e. the level of stable iso topic excursions and deep-sea benthic extinctions) in the middle part of this section, within Zones P5 and NP9. In this paper the impact of P/E boundary environmental perturbations on benthic foraminiferal comm unities of the shallow Tethyan shelf is examined. Benthic foraminifera l assemblages from Gebel Duwi, characterized by large Frondicularia ph osphatica and F. nakkadyi in addition to a number of other neritic tax a, but without any typical outer neritic-bathyal taxa, suggest middle neritic (75-100 m) deposition throughout the studied interval and only minor relative sea-level variations (perhaps some 10-20 m). Across th e boundary sea-level appears to have been stable. Yet, a distinct faun al turnover marks the P/E boundary of this shallow site, which, in con trast to deep-sea records, is less abrupt, being preceded by a gradual diversity decrease starting some four meters below the boundary. More over, most exits are either local or just temporary and thus not true extinctions: many (Lazarus) taxa reappear at some point above the boun dary, while all but one of the disappearing taxa are known from other lower Eocene neritic deposits in Egypt. In general, benthic foraminife ral assemblages display low diversities and high dominance values (not ably Anomalinoides aegyptiacus: up to 74%), suggesting high levels of environmental stress at the sea-floor. In combination with occasionall y very high P/B ratio's (up to 98%P), and generally laminated sediment s, the character of the benthic assemblage points to a strong influenc e of recurrent dysoxia and/or anoxia. We suggest that these resulted f rom surface eutrophication by (intermittent) coastal upwelling and red uced ventilation of the bottom environment. Although these conditions prevailed during most of the time-interval studied, they were most sev ere during the latest Paleocene and early Eocene when eutrophication i ntensified, and the organic carbon flux to the sea-floor increased. En hanced atmospheric contrasts between the Tethys seaway and the African continent, resulting in intensified longshore tradewinds, may have co ntrolled these changes. At the P/E boundary the bottom environment bec ame minimally ventilated, perhaps due to reduced oxygen advection from deeper waters. Three meters above the boundary a succession of increa singly diverse assemblages indicate a gradual decrease environmental s tress and a return to more normal conditions, although the organic car bon flux to the sea-floor remained high.