Ages of Cenozoic Strata of NE Iraq
Cenozoic strata are important reservoirs and seals for oil and gas in NE Iraq. They were deposited in various settings while the Tethys Ocean closed. Traditionally, ages were based mainly on larger benthic foraminifera, although many rocks are unfossiliferous. We are revising the ages using planktonic and nannofossil biostratigraphy and Sr-isotope dating of carbonates and anhydrites.
Paleocene-Eocene strata were deposited in shelfal to basinal environments, with major prograding shelf margins. These strata lap onto the Cretaceous unconformity, with basal ages ranging from Danian to Ypresian. Bartonian and Priabonian shelfal and shelf-margin carbonates locally are eroded below the Miocene Fatha Fm.
The overlying Kirkuk Group is composed of 3 sequence sets of prograding shelfal and shelf-margin carbonates of early Rupelian, middle to late Rupelian, and Chattian age.
The overlying shelfal Euphrates Fm. and basinal Serikagni Fm. have traditionally been considered Lower Miocene. Our data indicate that they are Chattian-Aquitanian in age.
The overlying basin-filling anhydrites of the Dhiban Fm. are dated Aquitanian by Sr isotopes. They are overlain by platformal carbonates of the Jeribe Fm., traditionally considered Middle Miocene, but which we date as early Burdigalian (Bur1 and Bur2 sequences).
The Fatha Fm. also has been considered Middle Miocene, but Sr-isotope dating yields Burdigalian ages (Bur3 to Bur5 sequences). The influx of nonmarine sediments of the overlying Injana Fm. is due to continental collision and formation of the Zagros Foldbelt, which is no older than Langhian.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009