Sedimentary cycles and biological zones in the Marun oil field (upper part of the Pabdeh Formation and lower part of the Asmari Formation)
Document Type : Original Article
Author
Geology Department, Earth Sciences Faculty, Lorestan University, Khoram Abad, Iran
Abstract
In the present study, 275.5 meters of deposits from the upper part of the Pabdeh Formation and the lower part of the Asmari Formation were studied in one of the wells of the Marun oil field. In this well, the boundary between the Pabdeh Formation and the Asmari Formation is gradual and continuous, and their dominant lithology is shale, marl, calcareous shale, and limestone. Biostratigraphic study led to the identification of three Assemblage biozones of Late Eocene-chattian age. The first biozone (Globigerina spp - Turborotalia cerroazulesis - Hantkenina Assemblage Zone) is in the Late Eocene time period and is related to the upper part of the Pabdeh Formation, and the second biozone (Lepidocyclina - Operculina - Ditrupa Assemblage Zone) are of Rupelian, chattian - chattian age and are related to the base of the Asmari Formation, and the third biozone (Archaias asmaricus - Archaias hensoni - Miogypsinoides compalanatus Assemblage Zone) is related to the lower part of the Asmari Formation and is determined to be of chattian age. In this well, based on the cyclolog study, five negative boundary levels and four positive boundary levels were identified, and based on the identified boundary levels, two sedimentary cycles were introduced. The first sedimentary cycle was between NB1000 -1000 PB levels and based on the biostratigraphic study, the age of this sedimentary cycle was determined to be late Eocene and the second sedimentary cycle was between NB2000 - 2000 PB levels and based on the fossil data, its age was determined to be Rupelian, chattian - chatian. The Eocene-Oligocene boundary in this well coincides with PB1000 and also the maximum sea level coincides with NB2000.
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