On the basis of the biocontents, lithological features and analysis of the microfacies, an attempt is made to establish the nature of paleoecology and depositional environments of some Upper Cretaceous formations from northwest and middle Iraq ,of which the successions are represented by the formations from the oldest to the youngest are Khasib, Tanuma, Sa'di, Mushorah, Hartha and Shiranish.A wide spectrum of environmental types distributed between deep and shallow marine environments. The implication of paleoecological interpretations for different Ostrscode species and other fossils recorded in the studied sections highlights the strong correlation between the environmental parameters in particular the depths and the lifestyle of these organisms including specific morphologies and faunal abundance.In addition to that from palaeocological point view the identified biocontents represent a southern shelf tythes fauna.
Fifteen samples of limestone, marls and, clay from the Fat'ha Formation are obtained from the location of Bashiqa village, Bashiqa anticline, Northeastern Iraq. A detailed investigation is carried out, during which twenty-four species of calcareous nannofossils identified, twenty- one are descried from other regions while three are left under an open name because of lack of material or insufficient samples. Besides, seventeen species of Ostracoda fossils were picked and diagnosed, including two subspecies, belonging to ten genera, and four subgenera.
The recorded calcareous nannofossil assemblages include two biozones which are from the lower to the upper part of the section: (1) Helicosphaera ampliaperta Interval Biozone (CNM6); (2) Discoaster signus Interval Biozone (CNM7). These biozones are correlated with other calcareous nannofossils biozones from both local and regional sections that lead to conclude the age of the Middle Miocene(Burdigalian to Laghian).
The paleoenvironment of the Fat'ha Formation was determined through the use of the environmental evidence of the Ostracoda fossils, which indicated oscillating periods which vary from normal salinity to brackish and saline environments, with shallow lagoonal environment and sometimes deep lagoonal environment that do not exceed the margin of shelf zone.
The Paleocene-Eocene Thermal Maximum (PETM) event, which represented a sudden and abnormal rise in temperature during the early Cenozoic Era, is regarded as one of the most important global geologic phenomena. Two important index microfossils (nannoplankton and Ostracoda) were utilised to understand and predict the paleoenvironment and describe the changes during this period. The basis of the study was 12 cutting samples taken from Aaliji and the lower part of Jaddala formations of a subsurface section of (Ba-8) borehole in central Iraq. Some geophysical data were used to determine the upper and lower contacts of the Aaliji Formation and define the shale rate in the studied formations. The micropaleontologic investigation reveals twenty-four nannoplankton species and twenty species belonging to seven genera of Ostracoda. The use of Nannoplankton fossils led to the identification of two types of biozones based on two species belonging to the genus Discoaster, which are ordered from bottom to top as follows; 1- Discoaster nobilis Interval Biozone (CP7) and 2- Discoaster multiraditus Interval Biozone (CP8). The biozones were compared locally and regionally with their equivalent biozones, which deduced the age of the Aaliji Formation as (Late Paleocene-Lower Early Eocene) whereas (Early Eocene) for the studied part of the Jaddala Formation. The determination of the upper and lower boundaries was determined by interpreting the geophysical logs. Ostracoda fossils were used to predict paleoecology and its changes in the area during the PETM episode. The transmutation of nanoplankton fossils from the Paleocene to the Eocene indicates an abnormal rise in global temperatures, flourishing and high diversity of some nanoplankton, such as some species belonging to Discoster, especially those in the CP8 zone.
Through a comprehensive taxonomic study of the ostracoda fossils in Fat'ha Formation in the stratigraphic section exposed within the eastern limb of Butmah anticline northwestern Mosul city, several genera and their belonging species of ostracoda have been identified from this previously unexamined section in terms of fossils. However, the focus in this research is on the genus Paijenborchellina and its species as it indicates an important environmental, age and geographical indications Six species belonging to this genus have been diagnosed as follows:
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