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Omphalocyclus is a well-known genus of large benthic foraminifera; species in the genus mainly occur in the argillaceous limestones and carbonates of the Aqra Formation of the early to late Maastrichtian age from Kurdistan foreland basin in Northern Iraq. Its presence is a significant indicator of its paleogeographic distribution in the Middle East. The Aqra formation was divided by lithology into lower, middle, upper, and transitional parts using Google Earth satellite images. Evolutionary changes were documented in successive Omphalocyclus assemblages for the first time in Iraq, and a clear increase in embryon size was found towards the end of the Maastrichtian. This evolutionary development was followed by an increase in the number of epi-embryonic chamberlets. The earliest known Omphalocyclus specimens in the studied strata predominantly have three to four primary epi-embryonic chamberlets and one to two accessory epi-embryonic chamberlets, and these occur in horizons attributable to the Pseudotextularia intermedius zone. The gain of radial stolons in the tritoconch wall may have led to accessory epi-embryonic in consecutive Omphalocyclus populations in horizons attributable to the Racemiguembelina fructicosa zone; accordingly, only a few additional epi-embryonic chamberlets arise from the tritoconch. Epi-embryonic chamberlets tend to be relatively large and comprise a large part of the embryon around its dense external enclosure. Notable differences in embryon size, the number of epi-embryonic chamberlets, as well as other morphological features in successive populations, two prominent species were distinguished: O. cideensis in the early Maastrichtian strata and O. macroporus in the late Maastrichtian. Omphalocyclus specimens exhibited the same evolutionary age and a similar embryonic developmental stage, according to a morphometric analysis of O . macroporus embryon size. However, tests of some of these specimens from the uppermost Aqra Formation were ellipsoidal, biconcave, and centrally depressed, and other tests showed disk forms and central depressions with a well-rounded equatorial margin. These were interpreted as two new subspecies: O . macroporus ellipsoides subsp. nov. and O . macroporus maukabensis subsp. nov. [ABSTRACT FROM AUTHOR]

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 Q 95.7 F 2.8 R 1.4 where 90% of the quartz grains are monocrystalline and texturally supermature. Meanwhile the mean composition of the thickly bedded sandstones is Q 85.4 F 9.7 R 4.8 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. [ABSTRACT FROM AUTHOR]

A combination of high resolution cathodoluminsecnce-spectroscopy (HRS-CL) with spatial electron microprobe analysis and optical microscopy is used to determine paragenesis and history of cementation in the limestones and dolostones of Khurmala Formation which is exposed in many parts of Northern Iraq. Khurmala Formation was subjected to different diagenetic processes such as micritization, compaction, dissolution, neomorphism, pyritization and cementation that occurred during marine to shallow burial stages and culminated during intermediate to deep burial later stages. Five dolomite textures are recognized and classified according to crystal size distribution and crystal-boundary shape. Dolomitization is closely associated with the development of secondary porosity that pre-and postdates dissolution and corrosion; meanwhile such porosity was not noticed in the associated limestones. Microprobe analysis revealed three types of cement, calcite, dolomite and ankerite which range in their luminescence from dull to bright. Cathodoluminescence study indicated four main texture generations. These are (1) unzoned microdolomite of planar and subhedral shape, with syntaxial rim cement of echinoderm that show dull to red luminescence, (2) equant calcite cements filling interparticle pores which shows dull luminescence and weak zonal growth, (3.1) homogenous intrinsic blue stoichiometric calcite with dull luminescence and without activators, (3.2) coarse blocky calcite cement with strong oscillatory zoning and bright orange luminescence which postdates other calcite cements, (4) ankerite cement with red to orange, non-luminescence growth zonation which is the last formed cement. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Ordovician Khabour Formation is the oldest exposed rock unit in Iraq. [•] Its sandstones are characterized silica cementation. [•] Five quartz cement phases are recognized by using SEM-CL. [•] Biogenic silica, pressure solution and hydrothermal fluids were major sources for successive quartz cement phases. [Copyright &y& Elsevier]