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 Kfeldspar 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.
Keywords: Cathodoluminescence; Sandstone petrography; Provenance; Ora Formation;
Northern Iraq.