| Popis: |
The bioturbated chalky limestones of the Khasib Formation (Upper Turonian - Lower Coniacian) furnish an extensive reservoir rock of several oil fields in central Iraq including: Tikrit, Balad, Samarah, and East Baghdad oil fields. Investigation of these rocks by means of microfacies analysis and electrofacies correlation as well as sequence stratigraphic analysis indicate that it had being deposited in a ramp setting sloping east- southeastwards forming part of the Arabian passive margin. The inner ramp is characterized by a bioclastic packstone of a carbonate bank with green shale intercalations of peri-bank sediments. The middle ramp which dominate the Khasib Formation section is consist of white- beige, porous, bioturbated, chalky and dolomitic bioclastic wackestone. Bioclasts includes; shelf faunal debris with variable mixture of benthic and planktonic forams. Intensive Thalasionodes and Palaeophycus bioturbations significantly contributed to the high porosity of this part. The outer ramp is consists of intercalations of boiturbated bioclastic chalky limestone and basinal argillaceous limestone. The latter is characterized by the occurrence of planctonic forams, calcispheres, dwarf rotalids and sponge spicules. The Khasib section represents a third order cycle with lower sequence boundary of type one separating Khasib sequence from the underlaying LST of the Kifl Formation. The TST is consist of thin and basinal facies. The HST is the thickest and represented by the bioturbated chalky limestone of the middle ramp facies. The maximum flooding surface is idicated by a thin horizon dominated by intensive Paleophycus bioturbation within the middle ramp facies. The boundary with the overlaying Tanuma Formation is of type two and represented by the transition to the LST of the next cycle. |
