Palynofacies and paleoenvironment of late Jurassic early cretaceous formations at Duhok basin, Northern Iraq

Abstract EN

This study was covered palynofacies and paleodepositional environment of the Chai Gara, Garagu, Sarmord and Qamchuqa formations along Atrush, Shaikhan and Sarsang oilfields in Duhok Region northern Iraq.

Six main types of palynofacies were recognized within the studied formations.

The palynofacies one (PF.1) and two (PF.2) are appeared in Chia Gara Formation, these two types of palynofacies are characterized by dominant amorphous organic matters (AOM), especially in PF.2 which reaches to 90%, moderate palynomorphs content ranges between 5 – 59%, whereas the phytoclasts are relatively low percentages (1 – 5%).

The identified palynofacies indicate that the paleodepositional environment of the Chia Gara Formation is distal suboxic-anoxic basin (IX) to dysoxic-anoxic shelf (VII).

Garagu Formation is represented by palynofacies three (PF.3) and palynofacies four (PF.4), the former one is characterized by the abundant of palynomorph, ranges between 41 – 85% (comprised mainly of pollen, spores, foraminifera test lining and few dinoflagellates), while the latter one is rich by amorphous organic matter which is between 55 – 63%, in both palynofacies the percentage of phytoclast is low to moderate ranges change from 7 – 19, and 3-35% respectively.

Paleodepotional environment of the Garagu Formation is oxic shelf (V, VIII).

The Sarmord Formation is represented by palynofacies five (PF.5), this palynofacies is characterized by high percentage of phytoclasts which reaches to 74%, with moderate palynomorphs and amorphous organic matter ranges between 11 – 31%, 12 – 38% respectively.

Shelf to basin transition (IV) is the claimed environment for the Sarmord Formation.

Qamchuqa Formation is represented by palynofacies six (PF.6), this facies is also high percentage of phytoclasts content but more than PF.5, which the range is 48 – 85% with a moderate percentage of palynomorphs (12 – 43%) and a low percentage of amorphous organic matter (3 – 15%).

The Qamchuqa Formation was deposited under proximal oxic shelf (III) condition