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PETROLOGY, GEOCHEMISTRY AND DEPOSITIONAL ENVIRONMENT OF THE KHABOUR FORMATION IN ORA AND KHABOUR LOCALITIES, NORTHERN IRAQ | ||
| Iraqi Bulletin of Geology and Mining | ||
| Article 1, Volume 6, Issue 2, 2010, Pages 71-94 | ||
| Author | ||
| Khaldoun S. Al-Bassam | ||
| Abstract | ||
| The Khabour Formation, the oldest exposed rock unit in Iraq (Ordovician), was sampled in two exposed sections at Ora and Khabour localities. It is comprised of about 800 m thick sandstone-shale cyclic alternations. Petrographic study showed that quartz arenite and phyllarenite are the main textural varieties of the sandstone with mica and silt-size quartz dominating the shale. The sandstones are texturally mature and mineralogically mature to submature. The mineralogy includes: quartz (dominant), muscovite, illite, glauconite, chlorite/serpentine (mixed layer), francolite (conodont) and heavy minerals (opaques and ZTR). Silica cementation is the main diagenetic process, resulted from pressure solution of silica and lead to an interlocking quartz mosaic texture. Alteration is of minor intensity. The chemical composition is characterized by high SiO2/Al2O3 and K2O/Na2O ratios. The geochemical associations are controlled by the mineralogy and three groups were recognized by factor analysis, namely the sheet alumino-silicates, phosphate and heavy minerals (ZTR). All of which are diluents to the major mineral constituent: quartz. Mineralogical analysis of the studied samples suggests recycled granitic plutonic rocks and more proximal low-grade metamorphic rocks as source of the clastics. The whole sequence of the Khabour Formation seems to have deposited in marine environment extending from shallow intertidal to deep outer shelf, under variable conditions of sea-level fluctuation, subsidence rate, and detritus supply. The whole sequence may have resulted from deposition from turbidity currents; the proximal part is rich in coarse clastics and the distal part is rich in micaceous shale. Complete Bouma sequence was not recognized, but the sedimentary facies of the Khabour Formation may be considered as an example of a passive plate margin turbidities. | ||
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