The first detailed calcareous nannofossil and planktonic foraminiferal
biostratigraphic and integrated lithofacies analyses of the Eocene–Oligocene
transition at the Qa’ Faydat ad Dahikiya area in the Eastern Desert of Jordan, on
the border with Saudi Arabia, is presented. Three calcareous nannofossil zones
namely: Discoaster saipanensis (NP17), Chiasmolithus oamaruensis (NP18) and
Ericsonia subdisticha (NP21), and three planktonic foraminiferal zones: upper part
of Truncorotaloides rohri (E13), Globigerinatheka semiinvoluta (E14) and Cassigerinella
chipolensis/ Pseudohastigerina micra (O1) are identified.
Calcareous nannofossil bioevents recorded in the present study show numerous
discrepancies with the Standard biostratigraphic zonal schemes to detect
the Middle/Upper Eocene boundary (e.g. the highest occurrences (HOs) of
Chiasmolithus solitus, C. grandis, and lowest occurrences (LOs) of C. oamaruensis,
Isthmolithus recurvus are not considered reliable markers for global correlation). The
Middle/Upper Eocene boundary occurs in the current study above the extinctions
of large muricate planktonic foraminifera (large Acarinina and Truncorotaloides
spp.) which coincide within the equivalent calcareous nannofossil NP18 Zone.
These microplanktonic bioevents seem to constitute more reliable markers for the
base of the Upper Eocene in different provinces. The uppermost portion of the
Middle Eocene is characterized by an observed drop in faunal content and, most
likely, primarily denotes the effect of the major fall in eustatic sea level.
A major unconformity (disconformity) marked by a mineralized hardground
representing a lowstand is recorded in the present study at the Eocene–Oligocene
transition that reveals an unexpected ca. 2.1 Myr duration, separating Eocene
(NP18/E14 zones) from Oligocene (NP21/O1 zones). Furthermore, the microfossil
turnover associated with a rapid decline of the microfossil assemblages shows
a distinct drop in diversity and abundance towards the Eocene/Oligocene
unconformity and is associated with a sharp lithological break marked, at the
base, by a mineralized hardground representing a major sequence boundary.
These bioevents, depositional sequences and the depositional hiatus correlate
well with different parts of the Arabian and African plates, but the magnitude of
the faunal break differs from place to place as a result of intraplate deformation
during the regional Oligocene regression of Neo-Tethys on the northern Arabian
Plate. The presence of the Lower Oligocene shallow-marine calcareous planktonic
assemblages in the study area indicate that communication between the eastern
and western provinces of the western Neo-Tethys region still existed at this time