Geology

Biography

Biography: Muhamed Fakhri Omer

Abstract

Advanced techniques such as scanning electron microscope hot- cathodoluminescence (SEM-CL) and electron microprobe analysis (EMPA) as well as petrography are applied to investigate the paragenetic sequence and provenance of intertidal-tidal flat sandstones of the Ora formation which is exposed in northern Iraq. The formation consists mostly of supermature quartzarenites with subordinate immature subarkoses and sublitharenites. The mean framework composition of the thinly bedded sandstones of Ora Formation is Q95.7F2.8R1.4 where 90% of the quartz grains are monocrystalline and texturally supermature. Meanwhile the mean composition of the thickly bedded sandstones is Q85.4F9.7 R4.8 with 84% of the quartz grains are monocrystalline and texturally immature. The provenance of the Ora sandstones is dominantly craton interior and less recycled orogeny. The Ora formation has undergone intensive and complex episodes of eogenesis, mesogenesis, and telogenesis. Compaction and quartz cementation is more dominant than other diagenetic processes evident from tight grain supported fabric which predated authigenic illite formation; this is also evident from close packing of detrital framework that resulted in reduction of primary porosity. Albitization has postdated eogenesis of K-feldspar cements. Cathodoluminescence study indicated four main distinctive fabrics in quartz grains, (1) healed fractures, (2) mottled textures, (3) low-intensity dark CL streaks and patches, and (4) shocked quartz. The results indicate the dominance of brown to dark blue CL for quartz of low-temperature metamorphic origin; bright blue colors for the felsic plutonic and high-temperature metamorphic quartz; with considerable amounts of detritus that has originated from felsic and mafic volcanic rocks and are characterized by red, violet colors luminescence.