Cretaceous / Paleogene Boundary Analysis by Planktic Foraminiferal Biozonation in the Western Zagros Fold- Thrust Belt (Smaquli valley), Sulaimani Governorate, NE-Iraq

The current work focuses to study the foraminifera assemblages within the Cretaceous/Paleogene (K/PG) boundary outcropped in the High Folded Zone in Smaquli valley (Gali section), Kurdistan Region, and Northeastern Iraq. The boundary is nearly located between Tanjero and Kolosh Formations and their exposure mainly consists of thick succession of deep marine turbidities (flysch) and hemipelagic sediments. The study aims to indicate biological fossils assemblages and physical expressions that inherited from globally important events of the end of cretaceous. The study has extraited expressions of the well exposed successions of fine grains from which 8 biozones are identified in the uppermost section of Shiranish formation, the ShiranishTanjero transition area and the Tanjero formation through biostratigraphy (biozonation) and lithostratigraphic analyses. These zones, from the bottom to top, are upper part of Globotruncana aegyptiaca Interval Zone (CF8), which belongs to Upper part of Shiranish Formation, (Early Maastrichtian) and lower part of Tanjero Formation. The second, third, fourth and fifth zones are Gansserina gansseri Interval Zone (CF7), Contusotruncana contusa Interval Zone (CF6) (Early Maastrichtian) and Pseudotextularia intermedia Interval Zone (CF5), Racemiguembelina fructicosa Interval Kirkuk University Journal /Scientific Studies (KUJSS) Volume 15, Issue 3, September 2020 , pp. (45-81) ISSN: 1992-0849 (Print), 2616-6801 (Online) Web Site: www.uokirkuk.edu.iq/kujss E-mail: kujss@uokirkuk.edu.iq, kujss.journal@gmail.com 46 Zone (CF4) respectively and all belong to lower part of Tanjero Formation (Early Maastrichtian). The sixth, seventh and eighth zones are Pseudoguembelina hariaensis Interval Zone (CF3), Pseudoguembelina palpebra Interval Zone (CF2), Plummerita hantkeninoides Total Range Zone (CF1) respectively that belong to upper part of Tanjero Formation (Late Maastrichtian). Moreover, four biozones of Danian (Early Paleocene) are recorded in the lower part of Kolosh Formation which are Guembelitria cretacea Interval Zone (p0), (base of Danian), Parvularugoglobigerina eugubina Total Range Zone (pα), (base of Danian), Parvularugoglobigerina eugubina-Subbotina triloculinoides Interval Zone (P1a) (Early Danian), Subbotina triloculinoides–Praemurica inconstans Interval Zone (P1b), (Middle Danian). The lithostratigraphic and biostratigraphic study revealed that no physical events (conglomerate, erosional surface, paleosoil and hardground) and has a conformable and gradational existence, which is evidenced by continuous sedimentation of the same sediments and no chronostratigraphic gaps within K / PG boundary. Biologically, it shows the gradual extinction of the Cretaceous planktic foraminifera and the sudden emergence of the Paleogene ones.


Introduction:
The study of the K / PG boundary over the last few decades was contentious and one of the most frequently discussed problems in stratigraphy. This controversy is obvious in literature in which many authors suggested many hypotheses to explain the events and character of the boundary see [1][2][3][4]. The key event is the cause of the international mass extinction of many organism groups across this boundary and the distribution and number of other marine and terrestrial species have been inclined. Many authors such as [5 -7] attributed this extinction to the multiple causes, such as plate tectonics (continental rifting), the asteroidimpact and volcanisms.
For various purposes, the K / PG boundary has been explored in different locations and regions of the world by specific methods such as tectonic, geochemical, stratigraphic and biological tracts. This boundary is not entirely studied in northerly Iraq (Kurdistan Region) particularly in the area of Sulaimani that shows important exposed sedimentary record

Materials And Methods:
To identify the K/PG boundary, the authors sampled about 230 m of the succession and extended the sampling into part of Maastrichtian and Paleocene, across the Gali section, they excavated 152 fresh samples at 1m interval to find the approximate stratigraphic position of the boundary. After approximate location, 20 additional samples have taken at 10 cm intervals to conduct high-resolution study of the boundary. On all samples, the procedure includes picking of the index species and fixing them directionally on slides for identification under stereomicroscopes and electronic scanning. The research photographed the described species for further analysis and comparison with previously published photos. The results are valid for precise planktic foraminiferal zonation to indicate location and events associated with the studied section boundary of K / PG, in addition to similarities and contrasts with local and global studies .Fresh samples and residues are stored at the Department of Geology, Sulaimani University.  Stratigraphic distribution of the planktic foraminifera in the studied section is shown in Fig. 6  . Hence, the biozone is limited geographically and environmentally in these situations. it is easier to avoid an unpredictable first and last data extinction scenario from being replaced by other biozones. Figs. 6 -part1 and 9.

Zonation of the Upper Cretaceous sediments:
In the present analysis, eight biozones were reported in accordance with the established planktic foraminifera assemblages in the upper part of the Shiranish Formation, Shiranish-Tanjero transition Zone and Tanjero Formation. The identified biozones from older to younger have been defined as below.     Fig. 4.13.
The foraminiferal assemblages are the same as that of the underlying Racemiguemblina fructicosa zone, as shown in the stratigraphic range chart Fig. 6 Figure 8 shows the relative and corresponding current zones.  The decline in the number of species inside the plummerita hantkeninoides zone is reliable and has persisted at the end of this zone at the K/PG contact. In Gali Section, from (37) to (28) this is observed. The planktic foraminipheral assemblages of Maastrichtian at the stratigraphic stage corresponding to upper part of this biozone have unexpectedly disappeared. The K/PG limit is based on paleontological criteria for the mass extinction of the foraminifera planktic assemblages, as in the portion under discussion, as well as the first occurrence of the Paleocene species. Fig. 8 shows similar and related zones to the present one.

Zonation of the Early Paleocene sequence:
The current study represents four biostratigraphic zones in the studied section from bottom to top in accordance with defined foraminiferal planktic assemblages within the Kolosh Formation: -Guembelitria cretacea interval Zone (P0, Earliest Paleocene, Danian) The boundary contact between Tanjero and the Kolosh Formation was situated in this area to last friable brown fine sandstone (1m) beds. This layer is without of foraminifera bearing except for few forms of Guembelitria cretacea Cushman Fig.7.1-2

Discussion:
The The physical events for the bolide are also not observable in Iraq according to current research and are also recorded by [62]and [66], respectively in the Dokan and Higran sections, on the progressive turnover of foraminifera assemblages for relatively long periods.
The absence of unconformity in current study as well as its inclusion in additional studies thus suggests seven potential explanations or evidence. The first due to remoteness of the extraterrestrial bolide object near Mexico, the physical effect of the event was not recordable in marine sediments of the Iraq and only a gradual biological effect had imprinted. The second is possibility of asynchronous mass extinction in different places of the world; therefore, the biostratigraphic event is not coincided with physical events. The third one is possibility of mass extinction by other factor such biota evolution, the flood basalts of Deccan in India and competition or environmental changes, especially [67] in particular concluded that the influence of Chicxulub 300 ka predates this boundary mass extinction. The proposed stratigraphic and micropaleontological data from the Gulf of Mexico show 3 impacts during period of time spanning the boundary with the Chicxulub effects predating the K/PG boundary by ~300 ka [68]. However, this multiple impact hypothesis has not gained support from other K/PG boundary locations free from stratigraphic complexities of near-impact sites.
In addition, over 350 K/PG boundaries currently known display a distinct trend in which the thickness of ejecta deposits declines with a decreasing distance from the Chicxulub crater and thus represents a special source of ejecta at the K/PG boundary [69]. According to this later article, the mass extinction by asteroid bolide is more probable than other factor due to its environmental perturbations.
The fourth fact is missing of one or two biozones not necessarily due to unconformity (erosion or non-deposition) but it may result from diagenesis, environmental constrains, method of sampling and fossil extraction. Therefore, the fossil absence is not unique evidence for absence of sediments but it is only a circumstance condition. This condition needs several conjugate sets of unique evidence to prove unconformity, which include detail boundary condition study in ten of sections.
The fifth fact is a possible excessive enthusiasm of some authors to previous ideas due to which may neglect the effective precautions in the sampling and identification of the crossboundary index fossils. The sixth fact is the environment refreshments proceeded through late  [72]. Nevertheless, the causal mechanisms of this cooling period are still unclear. While some researchers mainly propose oceanographic shifts, others thought that ephemeral glaciation is related to a eustatic decline. The relative timing and changes of the ocean oxygen and the carbon isotope are mostly not yet known in the eustatic sea level. This Cooling mainly reflects shifts in ocean circulation due to plate movements that cause progressive deep water sharing between deep ocean basins and a corresponding decrease in concentrations of atmospheric carbon dioxide [73]. The seven fact is the (the most important one) is the dilution of index fossil in shallow and in deep environments to the degree that their recording becomes impossible in some case. It is attributed to high rate of dilution of sedimentation in proximal deep turbidities and in carbonate or clastic dominated shelves.
Therefore, this study is important because it could change with unquestionable evidence, the balance between conformable and unconformable communities in Iraq and world in favor of the first of all.