Origin of red color in the gercus formation (eocene), Northeastern Iraq

Al-Rawi, Yehya T.

doi:10.1016/0037-0738(83)90037-4

Cited by 20 publications

(21 citation statements)

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“…In the Hüdai Formation, the reddening is restricted by bedding surfaces and repeats in the sequence, representing syn-sedimentary or early diagenetic colouration. The reddening is caused by finely dispersed hematite (Fe 2 O 3 ; Van Houten, 1973;Turner, 1980;Al-Rawi, 1983;Einsele, 1992;Friedman et al, 1992;Eren and Kadir, 1999). The XRF and XRD analyses showed that very small quantities of hematite pigment caused reddening in the sediments (Tables 1 and 2; Figures 6d-6g; see also Walker, 1967;Tucker, 1991 ).…”

Section: Discussionmentioning

confidence: 97%

“…Ferrous iron (Fe 2+ ) is oxidised to ferric form (Fe 3+ ) at neutral or alkaline pH conditions (Stumm and Morgan, 1996;Mamet et al, 1997). Chemical weathering of primary minerals in the red beds is characterised by an iron (oxyhydr)oxide halo around biotite (Walker, 1967) in the thin sections ( Figure 6c), which indicates intrastratal alteration (Walker et al, 1981;Al-Rawi, 1983). Hematite crystallisation requires very high temperatures or environments wherein the water activity is considerably reduced.…”

Section: Discussionmentioning

confidence: 99%

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Colour origin of red sandstone beds within the Hüdai Formation (Early Cambrian), Aydıncık (Mersin), southern Turkey

EREN¹

2013

Turkish J Earth Sci

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Colour origin of red sandstone beds within the Hüdai Formation (Early Cambrian), Aydıncık (Mersin), southern Turkey

EREN¹

2013

Turkish J Earth Sci

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“…It has been noted that the Gercus Formation clastics (sandstones and mudstones) have a uniform distribution of pigment suggesting that the origin was either predepositional or syndepositional. Indeed, Al‐Rawi (1983) suggested that the red colour was most probably the result of detrital ferric hydroxides coating the grains (Al‐Rawi, 1983). However, the present SEM study showed that various morphologies of haematite were mainly formed authigenically (Figures 7c,f, 8d, 9a,b, 10d,f, and 11).…”

Section: Discussionmentioning

confidence: 99%

“…The succession was deposited under arid to semi‐arid conditions (Al‐Rawi, 1980; Hussain & Aghwan, 2015). Initial studies on the petrography and the origin of the red colour in the Gercus Formation were provided by Al‐Rawi (1980, 1983) suggesting that the source of the red pigment on the detrital grains was partly predepositional and/or syndepositional and most probably diagenetic. He also noted that the sediments were mainly derived from carbonate and metamorphic (mainly serpentinite) rocks.…”

Section: Introductionmentioning

confidence: 99%

“…(b) Tectonic provinces of Iraq (modified from Numan, 1997) [Colour figure can be viewed at wileyonlinelibrary.com] (Khurmala) and Middle-Upper Eocene Pila Spi formations. Although, as noted above, the source of the red pigment within the Gercus Formation was previously investigated by Al-Rawi (1983), his work was based on traditional petrographic microscopy. The present study will examine a range of clastic (including sandstones and mudstones) and nonclastic 'carbonate' units ( Figure 2) using a variety of analytical tools [scanning electron microscopy (SEM), X-ray diffraction (XRD), and Xray fluorescence (XRF)] in addition to standard petrography, in order to determine the origin of the red pigment within the sediments and thus to detail the diagenetic and authigenic history of clay and non-F I G U R E 2 Sedimentary logs depicting vertical succession with lithology and sample locations of the three studied sections (modified after Hussain and Aghwan (2015) [Colour figure can be viewed at wileyonlinelibrary.com] clay mineral phases in the clastic unit of the Gercus Formation.…”

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Clay mineral diagenesis and red bed colouration: A SEM study of the Gercus Formation (Middle Eocene), northern Iraq

et al. 2020

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Detailed high magnification scanning electron microscopic (SEM) study supported by petrographic, mineralogical, and geochemical (major and trace element) analysis of the Gercus Formation clastics (sandstones and mudstones) from northern Iraq shows that the main authigenic components are carbonate (dolomite and calcite), clay and haematite minerals with rare quartz, feldspar, and gypsum. The carbonates and sulphate minerals were the main early diagenetic phase in the Gercus Formation and were produced from the post-depositional breakdown of ferromagnesian minerals. These latter are unstable in the oxidizing conditions of the interstitial waters below the desert surface. The main authigenic clay minerals are illite, illite-smectite, and palygorskite. The presence of tangential illite coating and illite-smectite in the sandstones can be related to their desert origin. Palygorskite is associated with dolomite, calcite, and haematite. These mineral associations may indicate early diagenesis in evaporitic and saline conditions. It also confirms the syndepositional and diagenetic origin for the clayey-haematitic matrix and pigment of the Gercus Formation. Haematite occurs as extremely fine-grained crystals mixed with authigenic clays and exhibits a range of shapes (e.g., fibrous to lath-shaped aggregates, small spherical grains, specularite crystals, blade-shaped, rosette-like clusters, and a lump of bright spheroidshaped haematite/goethite). The arid to semi-arid conditions together with the oxidizing and alkaline interstitial water favoured the noted mineral assemblage within the Gercus Formation.

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Petrography and geochemistry of siliciclastic rocks of the Middle Eocene Gercus Formation, northern Iraq: Implications for provenance and tectonic setting

2020

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Red coloured Middle Eocene Gercus Formation is a widely exposed rock unit in northern Iraq, southeastern Turkey, and northwestern Iran. Siliciclastic rocks (mudstones and sandstones) are the predominant rocks of this formation which were studied petrographically and geochemically. The Gercus Formation also contains a few beds of limestone, gypsum, and conglomerate. The sandstones are of two types, red and white, mostly immature litharenites, consisting of lithics (85%), quartz (12%), and feldspars (3%). The rock fragments consist dominantly of angular chert and rounded limestone and smaller amounts of sedimentary, magmatic, volcanic, and metamorphic lithics indicating proximity of their source rocks. The provenance discrimination diagrams of the detrital grain counts in sandstones show recycled and collision orogen sources. Petrographic, heavy minerals and major and immobile trace element (e.g. La, Th, Sc, Zr, Hf, and Ti) discrimination diagrams indicated that the Gercus Formation was originated under a collision tectonic setting above a subduction zone as part of an Oceanic Island Arc (OIA), where its sediments were derived from mixed sources, including recycled sediments of chert-and carbonate-rich formations and igneous-metamorphic ophiolitic complexes of north to north-east Iraq and adjacent Iranian and Turkish counterparts. The results also indicated a mixed marine (lacustrine and deltaic) and non-marine (fluviatile) origin for the Gercus Formation. The red sandstones, white sandstones, and mudstones show minor differences in their major, trace, and rare-earth element (REE) contents and have generally similar Post Archean Australian Shale (PAAS)-, Upper Continental Crust (UCC)-, and CI-chondrite-normalized distribution patterns indicating their common origin. The average of elements in the siliciclastic rocks is depleted in the high-field-strength elements (HFSE), the large-ion lithophile elements (LILE), and REE; and enriched in some rock-forming elements (RFE) and mantle rock-forming elements (MRFE) (Mg, Ca, Cr, Co, Ni) and depleted in others (Si, Al, Fe, Cu, Zn, Ga) relative to PAAS and UCC; whereas, they are depleted in Fe, Mn, Mg, Co, Ni, Cu, Zn, Ga, Na, and P, and enriched in all other RFE, MRFE, LILE, HFSE, and REE compared to CI-Chondrite. The REE content of these rocks is very low (23-34 ppm) and their LREEs are enriched six times relative to HREEs. These geochemical characteristics suggest a provenance dominated by basic/ultrabasic rocks. The U/Th, V/Cr ratios and the authigenic U values show an oxic depositional environment for the studied siliciclastic rocks.

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Origin of red color in the gercus formation (eocene), Northeastern Iraq

Cited by 20 publications

References 18 publications

Colour origin of red sandstone beds within the Hüdai Formation (Early Cambrian), Aydıncık (Mersin), southern Turkey

Colour origin of red sandstone beds within the Hüdai Formation (Early Cambrian), Aydıncık (Mersin), southern Turkey

Clay mineral diagenesis and red bed colouration: A SEM study of the Gercus Formation (Middle Eocene), northern Iraq

Petrography and geochemistry of siliciclastic rocks of the Middle Eocene Gercus Formation, northern Iraq: Implications for provenance and tectonic setting

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