Keywords : Early Turonian

Sedimentological, Paleontological and Mineralogical Evidences for Oceanic Anoxic Event-2 (OAE-2) in the Gulneri Formation (Early Turonian), Northeastern Iraq

Safwan Al-Lhaebi; Ali Al-Jubory; Falah Al-Miamary

Iraqi National Journal of Earth Science, 2020, Volume 20, Issue 2, Pages 105-125
DOI: 10.33899/earth.2020.170373

In the current work, the Gulneri Formation (Early Turonian) is studied in three surface sections (Degala, Dokan and Azmir) from northeastern Iraq. The formation is characterized by grey to black color limestone and marly limestone in the Degala and Dokan sections, whereas in Azmir section, fissile marl and marly limestone with pale to reddish color are dominated in addition to few beds, which occasionally contain fish remains, with distinct gray color reflecting the very few amount of total organic carbon in these beds. Microfacies analysis revealed that the formation consists of three microfacies: mudstone, wackestone and packstone. The predominance of dwarfish planktonic foraminifera (Heterohilex) and thin shell filaments particularly in packstone microfacies represent Heterohelix shift event and filament event respectively. In addition to these events, fish remains, radiolarian pyritization, planktonic foraminiferal chambers elongation and glauconite are all refer to anoxic environmental conditions that may have been coincided with the Global Cenomanian-Turonian Oceanic Anoxic Event (OAE-2).

The Effect of Dolomitization on Mergi Formation Sequences (Cenomanian- Early Turonian ) at The Type Section, Northern Iraq

Rafi I. AL-Homadi; Ibrahim S. Al- Okli

Iraqi National Journal of Earth Science, 2018, Volume 18, Issue 1, Pages 149-164
DOI: 10.33899/earth.2018.159282

In order to study the effect of dolomitization on Mergi Formation sequences (Cenomanian – Early Turonian), Field and petrographical examinations were carried out on fourty six meters (46m) of the type section of this formation. It has been observed that the formation is highly affected by diagenesis processes, especially dolomitization. On the other hand, the effects of other processes such as. cementation, dissolution, micritization and compaction in its both types, physical and chemical were less than dolomitization. Dolomite crystals appeared as rhomb-shaped euhedral to subhedral. The main diagnosed fabrics were Aphanotopic, Contact-rhomb porpherotopic, fogged mosaic, Sutured mosaic, Saddle dolomite and Cloudy-centered clear-rimmed dolomite fabrics. It is concluded that formation of dolomite was by the mechanism of mixing zone model and subsurface dolomitization model.(.