|
Seyed Ali Moallemi, Shahid Beheshti University and Research Institute of Petroleum Industry (Islamic Republic of Iran)
Mohammad Hossain Adabi, Shahid Beheshti University and Research Institute of Petroleum Industry (Islamic Republic of Iran)
Abbas Sadeghi, Shahid Beheshti University and Research Institute of Petroleum Industry (Islamic Republic of Iran)
|
|
In order to determine the depositional environment and age of the carbonaceous Jahrum Formation, benthic foraminiferal assemblage of upper Eocene in the Jahrum Formation carbonates, located in Gisakan Mountain, north of the Bushehr city (south of Iran) and adjacent fields, were studied. Based on the foraminiferal distribution and abundance, the paleogeography and sedimentary environment were reconstructed. Due to the presence of Nummulites fabianni and based on strontium isotopic analyses, the age between 33.7-35Ma (Priabonian) were determined. The mean sedimentation rate of ∼ 2 m/10000 yr. was calculated. The sedimentation was occurred gradually during three regressive cycles. Asmari Formation deposited after a hiatus, more than four million years (Rupelian stage). Gradual decreases of the sea level and hence the distribution of large benthic foraminifer resulted in deposition of six sedimentary facies along the inner-middle to outer ramp system. These facies, from deep to shallow parts of the basin, include argillaceous carbonates containing planktonic foraminiferal that were deposited in a hemipelagic to pelagic environment (which is the transition zone from the Pabdeh to Jahrum Formation), carbonate facies of operculina wackestone to packstone related to the outer ramp, discocyclina /nummulite wackestone to packstone facies deposited in the middle to outer ramp environment, nummulite wackestone facies occurred in the middle ramp environment, nummulite orbitolites wackestone to packstone belong to the middle to inner ramp, and finally the orbitolites/milliolide packstone deposited in the inner ramp environment
|
