The Qreiya Beds that record the ‘mid-Paleocene
event’ at Gabal Nezzazat occur within the Igorina albeari
(P3b) Zone and constitute part of a 14-m thick shale succession
that ranges in age from Early to Late Paleocene. They are
composed of four alternating dark grey and brown shale
beds, which are thinly laminated, phosphatic, organic-rich
and extremely sulphidic. They are characterized by distinct
enrichment and high peak anomalies in chalcophiles (Zn, Co,
Ni, Cu and Pb) and organic association elements (V and Cr),
especially within the brown organic-rich beds. It is concluded
that these elements are incorporated into the phosphatic debris,
sulphides and organic matter. In contrast, the grey beds are
enriched in clay minerals and quartz. Clay mineral assemblages
indicate alternating periods of warm/humid climate (high
kaolinite) and dry climate (low kaolinite) during the formation
of the grey and brown beds, respectively. The sediments of
the Qreiya Beds yield lithological, biotic, geochemical and
mineralogical data indicative of suboxic/anoxic marine environments
as a result of high productivity and/or upwelling.
The top metre of the succession below the Qreiya Beds is
characterized by a progressive change from faunas dominated
by praemurcurids to faunas dominated by Morozovilids, and
by a progressive upward decrease in δ13Ccarb and δ18Ocarb
values. The foraminiferal faunal change may reflect shallowing
and warming preceding deposition of the Qreiya Beds. The
change in isotopic values is inferred to be the result of surface weathering, fluvial input and diagenesis with no evidence of
any primary change that could support presence of a hyperthermal
event.