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7th Middle East Geosciences Conference and Exhibition
Manama, Bahrain
March 27-29, 2006
1 Saudi Aramco, Dhahran, Saudi Arabia, phone: 96638747892, [email protected]
2 Geological Technical Services, Saudi Aramco, P.O. Box 12311, Dhahran, 31311, Saudi Arabia
3 British Geological Survey, Keyworth, United Kingdom
4 Varol Research, Colwyn Bay, United Kingdom
Conventional biostratigraphy based on palynology and nannofossils provides broadly spaced datums for age
control within
the Aptian – Albian deltaic sequences represented by the Khafji and Safaniya members of the Wasia Formation. Higher
resolution stratigraphy is achieved by using multidisciplinary biofacies that contribute to recognition of higher order marine
flooding events, associated with within the world's largest offshore oilfield reservoirs of Saudi Arabia. Integration with
sedimentology is an ongoing part of this project.
The intervals between biostratigraphic
datums based on the appearances of elaterate palynomorphs (late Albian), pollen,
dinoflagellate cysts and selected nannofossil control (late Albian and Aptian) are characterized by diversity/abundance
peaks of dinoflagellate cysts, fresh water algae, foraminifera, coccolith and ascidian spicule nannofossils.
Benthic agglutinating foraminifera define the upper and lower estuarine and marine settings. This control has been
developed from Recent assemblages from the Sedili River, Malaysia where foram assemblages were calibrated to ebb and
flood salinities from the South China Sea to 32 km upstream.These Recent assemblages form the basis for understanding
paleoecology of Trochammina, Ammobaculites and Orbitolina biofacies of the Khafji and Safaniya members. Dinocysts also
show similar patterns to the foraminifera responding to salinity, of which Subtilisphaera dominates brackish environments
with assemblages diversifying with increasing salinity. Pteridophyte spores dominate the terrestrial successions. The
integrated biofacies display isolated but distinct evidence of marine flooding events of variable extent within a depositionally
complex thick succession Khafji and Safaniya deltaic sediments.