Iraqi National Journal of Earth Science

The present study deals with the biostratigraphy of the Aquitanian -Lower Early Langhian successions age in Kor Mor well No.3 at Kirkuk area.
The studied section includes six formations with a total thickness of about (430) meters.These are: Ibrahim, Azkand, Anah, Euphrates, Dhiban and Jeribe formations.
Eighteen species and subspecies of planktonic foraminifera and twenty one species and subspecies of benthonic foraminifera are recognized.
Also some forams of benthonic foraminifera to the genus level are identified.
Fragments of mullosca shell, echinoderm, green and red algae were recognized from the studied succession.They permit an identification of five biostratigraphic zones and are from younger to older:
Borelis melo curdica Total Taxon - Range Zone.
Miogypsina globulina Total Taxon - Range Zone.
Miogypsinoides complanatus Total Taxon - Range Zone.
Catapsydrax dissimilis Partial - Range Zone (N.5).
Globigerinoides primordius Partial - Range Zone (N.4).
The first two zones are withen Ibrahim Formation, of Early Miocene (Early Aquitanian) age.Whereas, the third zone affilated to Azkand and Anah formations of Early Miocene (Late Aquitanian) age,The fourth zone is related to Euphrates and Dhiban formations of Early Miocene (Late Burdigalian) age. The last zone represent Jeribe Formation of Middle Miocene (Lower Early Langhian).

The biometric analysis on Miogypsina from bioclastic limestone (Azkand Formation) in Kirkuk area, Iraq reveals that the evolutionary trend based on a distinct overall change in morphology of the nepiont, which change is in agreement with the principle of nepionic acceleration as defined by Tan Sin Hok,1936. The oldest species of Miogypsinoides represented by Miogypsinoides complanata and Miogypsinoides formosensis accompanied by the association Miogypsina gunteri which exhibit in the lower part of Azkand Formation of Late Oligocene age (Chattian). The early Miocene association of Miogypsina s.s. represented by Miogypsina gunteri-tani are often accompanied by Miogypsinoides. Most of these are close to Miogypsinoides bantamensis

Biometric invesgation of the megalospheric individuals of nephrolepidina assemblages from several sections in Kirkuk area, iraq led to recognize three morphometically defined species by the combination of two parameters. The degree of embracement of the protoconch by deuteroconch (factor A ) and number of accessory auxiliary chambers on the deuteroconch (factor C ) on the basis of generally accepted theory which is called embryonic and nepionic acceleration. The succession of these three species corresponds to the phylogenitic lineage in the European-medierranean area which started at some level in the middle part of the Oligocene and continued upward into the early Miocene. The slow numerical progress in this lineage and especially the double morphometric definition of the species limits have led to the recognition of a wide array of morphologically intermediate assemblages.

The present study has processed the gravity measurements which were prcviously reduced to sea level, using a constant density of 0.22 along two parallel traverses located to the north east of Guwair city near Upper Zab River. A geophysical model for each traverse was designed according to available geological data taking in consideration the lateral mass variation due to folding of the sedimentary sequences above the reduction plane.
The removals of the negative resultant gravity anomaly effects by the above processing have enhanced the gravity high. Furthermore, the geophysical models show the continuity of folding of stratigraphic sequence down to cretaceous rocks. This anticline (East Zab Anticline) seems to have the same structural characteristics of khurmala dome within Kirkuk Oil field. In addition, the study reveals that the axis of Zab structure is shifted to the north east due to the possible existence of strike slip fault trending NE-SW which causes the swinging of the surrounding fold axes.