Inorganic geochemistry and origin of bitumen intruded in Euphrates and Fatha formations in Hit area, western Iraq

Abstract EN

The content of redox sensitive trace element (V, Co, Ni, and Mo) in the bituminous limestone of the Euphrates Formation (E.

Miocene) and bituminous gypsum of the Fatha Formation (M.

Miocene) in the Hit Abu-Jir village area, Anbar governorate were determined using Inductively-Coupled Plasma Mass Spectrometer (ICP-MS), in order to infer the origin of the hydrocarbon and the depositional conditions of the organic matter.

Hydrocarbons species by using FTIR technique was identified as aliphatic, aromatic compound, hydroxyl acids, hydroxyl group, sulfoxide and sulfur.

Bitumen occurrences in these formations is a result of the hydrocarbon seepages that moved up under high pressure along the Abu-Jir fault Zone, and then were intruded in the limestone and gypsum beds of Euphrates and Fatha Formations.

A distinctive fractional differentiation in trace elements in the hydrocarbon-bearing fluids was detected, and resulted in enrichment of these trace elements in the carbonates of the Euphrates, rather than in gypsum belonging to the Fatha.

The source of the organic matters located in the Euphrates carbonates is mainly marine planktonic deposited in an anoxic environment, whilst, for that located in the gypsum of Fatha Formation is marine anoxic carbonate-shale, marine terrestrial oxic-dysoxic, and terrestrial oxic.

The original kerogen is estimated as of type- I/ II.

Bitumen precipitated in shallow depth does not exceed 2 km.

The temperature of the ascending hydrocarbons-bearing fluids is computed as 35°C, whereas the burial depth is of 61°C, where the biodegradation was the most probable process responsible for producing bitumen in such depth and temperature