Lithology and Geochemistry of the Chert Beds in the Qulqula Radiolarian Formation From Zalan and Kaolos Sections NE-Iraq

Chert beds occur as thick successions of about 5 – 30 m thick in the middle part of the Qulqula Radiolarian Formation (ORF). They have studied geochemically in two sections for decoding the origin of silica, the provenance of clastic fraction, and the redox conditional environment. These successions are several and comprise about 25% thickness of the formation. For these purposes, 27 samples are quarried regularly from two exposed outcrop sections; Zalan and Kaolos in northeastern Iraq, located 20 Km north of Chwarta and 7 Km north of SaidSadik towns, respectively. These samples were analyzed for the major oxides, trace and rare earth elements, and total organic carbon. The thin section study indicated that most cherts have fine grain texture with ghosts of silicified detrital grains with few radiolarian tests. The discriminant function and binary diagrams of major oxides of samples indicated that these beds belong to the arc and diversional tectonic settings. The ratios of the trace elements indicate several origins of silica of QRF such as felsic and wind-blown detrital grains which are deposited under oxic to suboxic conditions and fairly biogenic. The discrimination diagrams and PAAS-normalized trace and rare earth elements indicate several sources of silica such as Mid-Oceanic-Ridge. High quantities of silica are released by sub-marine weathering and quartzose dust influx from the western desert as the primary source of silica. This condition is similar to the influx of silica-rich dust from the African Desert to the Amazon Forest. The radiolaria tests and sponges, whose siliceous remains are observed as a minor fraction of the silica in the bedded cherts. These sources supersaturated the environments QRF and developed bedded chert in deep basins below CCD where silica is stable instead of carbonates and falls within the range of felsic rock.