Carbonaceous Bodies of Debatable Organic Provenance in the Banded Iron Formation of the Wadi Kareim Area, Eastern Desert, Egypt

0899-5362(95)00016-X

Carbonaceous bodies of debatable organic provenance in the Banded Iron Formation of the Wadi Kareim area, Eastern Desert, Egypt

GALAL H. EL-HABAAK and MAGDY S. MAHMOUD

Geology Department, Faculty of Science, Assiut University, Assiut 71516, Egypt

(Received 26 January 1994 : accepted 12 August 1994)

Abstract - The role of micro-organisms in the precipitation of the Precambrian Banded Iron Formation is discussed. The discovery of life in the Archaean rocks is described (cf. Gruner 1925), noting that the sedimentary record documents more than 3000 Ma of Archaean and Proterozoic time. Stromatolites, microfossils and geochemical markers provide fragmentary but critically important evidence for early evolution (Knoll 1990). Precambrian microfossils (mainly microflora) have recently been extracted and described from the clastic sediments of the Hammamat Group. In the present work we introduce the first identified microfossils occurring in chert bands in the Banded Iron Formation (BIF) of The Wadi Kareim area, Eastern Desert, Egypt. Replacement and reaction textures between the postulated organic remains and both iron oxide and silica are described and an explanation offered.

R~sum4 - Le r61e des micro-organismeslors de la pr6cipitation des itabirites pr6cambriennes est discut6. La d6couverte de l'existence de la Vie dans les s4dlments arch6ens est rappel6e (cf Gruner 1925) en notant que l'enregistrement s6dimentaire concerne plus de 3000 Ma d'Arch6en et de Prot6rozoique. Les stromatolites, les microfossiles et les marqueurs g6ochimiques fournissent des preuves fragmentaires mais essentielles de son 6volution pr6coce (Knoll 1990). Les microfossiles pr6cambriens, surtout ia microflore, ont 6t6 pr61ev6s des s6diments clastiques du Groupe de Hammamat et d6crits. Dans ce travail, nous d6crivons pour la premi6re fois les microfossiles provenant des niveaux de cherts des itabirites de la r6gion de Wadi Kareim dans le d6sert oriental 6gyptien. Les textures de remplacement et de r6action entre les restes organiques pr6sum6s avec les oxydes de fer et la silice sont d6crites et une explication propos6e.

INTRODUCTION are considered to be remains of photosynthesizing organisms. Jackson et al. (1986) recorded the presence Woese (1985) believed that the first organisms to arise of extensive unmetamorphosed carbonaceous shales, on this planet, in an ocean rich in organic compounds, widespread microbial remains and reports of binLrnen were extremely heterotrophic anaerobes, and that and gas in the McArthur Basin of northern Australia. autotrophy and phototrophy were later evolutionary The Precambrian, however, exhibits abundant fossils developments. Knoll (1985) states that the oldest known of great taxonomic diversity, the five most organic remains occur in the Fig Tree Group of southern biostratigraphically useful being stromatolites, Africa (~3400 Ma), whilst the Bitter Springs Formation oncolites and sundry megafossils, microfossils and (-850 Ma) from Australia contains cyanobacterial and trace fossils (Hofmann 1987). possible algal remains of strikingly modern The relation between biological activity and the morphology. The microbiota of the Gunflint Iroh development of Banded Iron Formation (BIF) has been Formation, Ontario, Canada, appear to be both investigated by several authors since the pioneering temporally and morphologically intermediate between work of Leith (1903), who was the first to suggest a the other two units, the overall picture which emerges possible biological origin for the BIF of the Lake being one of gradual evolution over vast stretches of Superior region. Participation of organisms in the geological time. Knoll (1985) states that comparisons deposition of iron formations was also suggested by between the Neoproterozoic and modern Earth reveal Moore (1918), Grout and Broderick (1919), Harder many more similarities than differences. Hofmann (1919) and Gruner (1922, 1923, 1925). Extensive studies (1985) states that carbonaceous compressions have been of microfossils in the 1000-2000 Ma Gunflint Formation, known for more than a century in rocks now assigned Ontario have been carried out by Tyler and to the Precambrian. These compressions include both Barghoorn (1954), Moorehouse and Beales (1962), remains with regular rounded outlines and irregular Edgell (1964), Barghoorn and Tyler (1965), Cloud (1965, angular fragments. Their geographic distribution 1968, 1973) and Cloud and Hagen (1965). Glaessner includes all continents. Almost all these compressions (1962) stated that bacterial activity has been proposed

125 126 G.H. EL-HABAAK and M.S. MAHMOUD to account for the precipitation of certain iron-rich and Preserved palynomorphs and other possible organic calcareous sediments. Cloud (1968) suggested that iron remains extracted from the BIF are illustrated. is precipitated as a result of oxygen production by photosynthetic organisms. LaBerge (1973) noted that GEOLOGICAL SETTING some organisms may act as silica precipitators, and that precipitation of chert in the iron formations was The Wadi Kareim area is located within the Pan- biologically controlled. Beukes (1983) stated that the African basement complex and is accessible through a primitive proterophytic oceans probably served as a desert track starting at 18 km from Quseir on the Qift- source of iron and silica. Records of well preserved Quseir asphalt road (Fig. 1). The basement complex is microflora in Egyptian Precambrian rocks in general covered mainly by weakly metamorphosed subaqueous and the BIF in particular are rare (e.g. Shimron and and subaerial tholeiitic and calc-alkaline lava flows and Horowitz 1972; Khalifa et al., 1988; Aboul Ela 1989). volcaniclastics of island arc affinity (Stern 1979, 1981; Inorganic sources of iron and silica have also been Hafez and Shalaby 1983; Khudier et al., 1988; E1-Habaak suggested. Iron and silica could be derived by 1992) forming an elongate belt, which are locally weathering (James 1954, 1983; Lepp and Goldich 1964; interbedded with iron ore bands (i.e. BIF), either as thick Belevtsev et al., 1983). Iron and silica also originate stratified layers up to 10 m thick or lenticular bodies. during volcanic activity (Goodwin 1956; Trendall and The BIF-bearing unit occupies an area of about 5 km 2 Blockley 1970; Cloud 1973; Beukes 1983). Cairns-Smith and attains a maximum thickness of about 160 m. The (1978) ascribed BIF to the photo-oxidation of ferrous BIF bands are comprised of a number of contrasting ions in sea water. Eugster (1969) and Eugster and Chou facies, namely oxide, carbonate, silicate and suphide (1973) suggested that magadiite or a sodium silicate gel dominated which are either laminated, massive or are to be considered the most likely precursors of granular (E1-Habaak 1992). The stratigraphic setting is banded chert. Holland (1973) postulated that the shown in Fig. 2. In general, little radiometric dating has derivation of iron from the sea floor in quantity is yet been carried out for Egyptian BIFs; the island arc possible if deep ocean water, Containing a few mg/1 of metavolcanics point to 825 Ma (Hashad 1980) and, dissolved iron, wells up, is oxidized in a near surface recently, 712&24 Ma (Stem et al., 1991). environment and is deposited in the basin. The following work presents the results of the MATERIAL AND METHOD investigation of the possible role of biogenic activity on the deposition and development of the BIF at Wadi In order to study the possible biological activities and Kareim in the Eastern Desert of Egypt. Potential organic their influence on the precipitation of the BIF, twenty remains were separated. Replacement textures and samples comprising lean-ore, chert and jasper, all metamorphism have obliterated most primary containing carbonaceous debris, were selected for struc~res rendering taxonomic classification uncertain. detailed microscopic studies. These samples were

0 ~ 2, km

Figure 1. Geological map of the Wadi Kareim area, Eastern Desert, Egypt. Carbonaceous bodies of debatable organic provenance in the Banded Iron Formation of the Wadi Kareim area, Egypt 127

50 m

Andesite • imI4o~ Andesitic tufts

Andesitic lappill- N tufts Volcanic breccia

VV~VVVV PT-/ BIF Gi}ii'':" Metavolcanics

Figure 2. Stratigraphic setting of the BIF, Wadi Kareim area', Eastern Desert, Egypt. subjected to a standard palynological maceration submicrolaminae are particularly rich in spherical technique in order to separate out the carbonaceous bodies attributable to Eosphaera tyleri (Barghoorn and material (hydrofluoric and hydrochloric acid treatment Tyler 1965). Those occur as more or less clear spherules and sieving). Some samples yielded potential of quartz surrounded by thin veneers of very fine palynomorphs. Glycerine jelly was used as a mounting hematite granules. There are two distinct varieties of medium to prepare permanent palynological slides. E. tyleri, one of which attains about 15 ~tm in diameter and the other measures about 60 ~tm. The smaller are MICROBIOLOGICAL NATURE OF THE WADI commonly scattered throughout the jasper laminae but KAREIM BIF are sometimes segregated in discrete submicrolaminae. LaBerge (1967, 1973) described E. tyleri from many Some brilliant red, pigment-poor, jasper micro- and Archaean and Proterozoic BIF. 128 G.H. EL-HABAAK and M.S. MAHMOUD

l) 320p-- 2

Figure 3.1-4 Thin sections of: 1-Filamentous and unidentified spheroidal organic bodies in algal chert. 2-Unidentified circular to oval forms composed of an inner hyaline core and surrounded by a thin shell composed of minute spherial magnetite cluster in algal chert. 3,4 Organic spheroidal bodies associated with filamentous forms in algal chert. 5,9 Spore-like palynomorphs 5-Slide IG: 118.2/21.3; diameter 64 ~tm. 9 Slide ID: 108.0/8.9; diameter 55 p.m. 6 Spol~a,-likepalynomorph Slide IA: 114.4/24.8; diameter 47 ~m. 7,10 Unidentified hexagonal palynomorphs 7 Slide I (photographed from the temporary test slide). 10 Slide IG: 113.5/4.8; diameter 39 ~m. 8 Diad of unidentified palynomorph Slide IG: 126.5/10.1; diameter of the larger one 75 ~tm. Carbonaceous bodies of debatable organic provenance in the Banded Iron Formation of the Wadi Kareim area, Egypt 129

Spheroidal bodies of uniform size (30 ~tm in equal in size and shape to the chert spherules (10-30 diameter) are very common in the algal chert (Fig. 3: ~tm in diameter, Fig. 4: 4) as in those associated with 1,2). They occur in intimate association with the filaments (e.g. Fig. 4: 1). It is assumed that the filamentous forms interpreted as algal in origin carbonaceous matter was replaced by Fe silicate, which (Barghoorn and Schopf 1966). These spheroids are gave rise in turn to stilpnomenalane, with partial to noncolonial and are preserved as black carbonaceous complete olbiteration of any carbonaceous structure matter in a groundmass of chert pigmented by hematite (LaBerge 1967). Pigmented silicate structures have been and containing pyrite and greenalite particles. These observed in samples from the Robe River area in the spheroidal bodies resemble those recorded from the Western Hammersley range, Western Australia and the Fig Tree Group, which were identified as algae-like Biwabik, Gurflint, Temiscamie and Kipalu Iron microfossils (Schopf and Barghoorn 1967) and were Formations in North America. All structures of this size, subsequently designated Archaeosphaeroides shape and mineralogy are replacement products of barbertonensis (Engel et al., 1968). Knoll (1990) stated that unknown organic forms (LaBerge 1967). simple carbonaceous spheroids of varying size were Cherts and associated very fine andesitic tufts of the reported from several horizons in the Onverwacht (3500 Wadi Kareim area contain structures similar to Ma) and overlying Fig Tree Groups though the Melasmatosphaera sp. A and Melasmatosphaera sp. B. biogenicity of many of these structures is open to (1989) Aboul Ela. The Precambrian of Belcher Island, question. During 1970-1980, several authors reported Canada (Hofmann 1976) and the metasediments of populations of spheroidal carbonaceous Gabel E1Hadid, central Eastern Desert (Aboul Ela 1989) microstructures that show a number of features more have structures similar to primitive algal growths. consistent with a biological interpretation. Cherts of the Wadi Kareim area, on the other hand, are These spheroidal bodies were replaced by magnetite composed of uniform red-blood spheroidal particles (Fig. 3: 2) with any organic structures being obliterated. (10-40 btm in diameter), commonly with thin veneers Direct replacement of organic material by hematite is of hematite, magnetite, pyrite and stilpnomenalane dust evidently uncommon (LaBerge 1973). It is suggested particles, and contain structures related to the growth that decaying organic matter on the bottoms of of primitive algae, particularly cyanophytes. restricted basins, held within the interspaces of Carbonaceous debris includes abundant opaque unconsolidated sediments on the basin bed, reduces material in addition to the spore-like bodies (Fig. 3: 5- accumulating ferric iron oxide to magnetite. These 10). These are dominant, though terminal apertures and spheroids are not restricted to any particular facies markings are not observed. These bodies possess the (LaBerge 1967). The spheroids are commonly morphological elements of Late Silurian spores concentrated in spots (Fig. 3: 3,4), where they usually (Visscher 1974), having wall patterns limited to general undergo recrystallization into skeletal crystals bounded outlines and ornamentation insufficient for detailed by one or more crystal faces and terminated ultimately taxonomical and biostratigraphical resolution. These by the development of rather coarse, euhedral bodies are of uncertain biological affinity, as are other, magnetite crystals which are free from inclusions. quadrangular, polygonal and scarce rounded forms, Algal chert contains filamentous structures 5-12 ~tm which mimic pollen grains. Forms similar to in diameter. These probably originated as carbonaceous Melasmatosphaerasp. A Aboul Ela and Melasmatosphaaera matter, which is now preserved in stilpnomenalane and sp. B Aboul Ela from the Neoproterozoic of Gebel E1- magnetite. Minute magnetite granules are usually Hadid figured by Aboul Ela (1989), occur in Wadi associated with these filaments. They are commonly Kareim. Indeterminate quadrangular forms comparable unevenly distributed but are mostly arranged in a with those of Wadi Kareim, are also figured from the pattern subparallel to the bedding planes. They also Gebel E1-Hadid assemblage. There is, however, a form a network of branched filaments (Fig. 3:1 and Fig. marked contrast between the two assemblages with the 4: 1-4). Undoubted filamentous microfossils have Gebel assemblage being much more diverse. Aboul Ela recently been described from cherts of the Warrawoona (op. cit.) recorded Myxococcoides inornata (Schopf), Group (Schopf and Packer 1987) where they occur in Oscillatoriopsis media (Mendelson and Schopf), association with clusters of spheroidal unicells encased Cephalophytarion sp., Eomycetopsis robusta (Schopf), in multiple extra cellular envelopes. Well-preserved Eomycetopsis sp., Siphonophycus sp. A (Aboul Ela) and filamentous forms (Gunflintia minuta) occur in silicified Siphonophycus sp. B (Aboul Ela) in addition to other carbonates from the Palaeoproterozoic Duck Creek oscillatoriacean forms, which are evidently lacking at dolomite, western Australia (Knoll et al., 1988). Wadi Kareim. Indeterminate globular to ovoid forms (10-30 ~tm) are composed of hyaline to microcrystalline cherty A POSSIBLE BIOLOGICAL RELATIONSHIP cores surrounded by thin shells composed of minute WITH BIF DEPOSITION magnetite granules. In some instances carbonaceous matter is partly replaced by magnetite with siderite as It is suggested that biogenic activity played (directly an intermediate stage. Chert is commonly pigmented or indirectly) a role in the deposition and development with spheroidal bodies of stilpnomenalane which are of the BIE Direct involvement of iron bacteria in the 70

?igure 4. Thin sections of: 1,2 Filamentous structure in algal chert. 3 Algal chert pigmented by organic matters (note variation of oxidation of organic matter into magnetite). 4 Algal chert pigmented with ~pheroidal bodies of stilpnomenalane. Carbonaceous bodies of debatable organic provenance in the Banded Iron Formation of the Wadi Kareim area, Egypt 131 precipitation of iron cannot be denied or verified. microscopically studied in detail, some yielding forms However the following points can be considered: resembling palynomorphs. Red jasper micro- and i) Cloud (1965) suggests that the transformation of submicrolaminae are rich in forms comparable with soluble ferrous iron into insoluble ferric iron was Eosphaera tyleri (Barghoorn and Tyler 1965), which cccur achieved through biological activity. He assumed that as clear spherules, surrounded by very fine hematite free O 2was not available from primary sources but was granules. Spheroidal bodies resembling Archaeosphaeroides provided only as a product of photolytic dissociation barbertonensis (Engel et al., 1968), are very common in or of photosynthesis. Belevtsev et al. (1983) suggested the algal chert and occur in intimate association with that periodic bursts of intense phytoplankton the filamentous forms. These spheroidal bodies are "blooming" in the Precambrian did not lead to an indirectly replaced by magnetite. The algal chert increase of oxygen content in the atmosphere, but to contains filaments preserved as stilpnomenalane and the oxidation of Fe 2÷ iron to Fe3÷ in the water, thus magnetite. These are also indeterminate globular to causing the precipitation of insoluble iron hydroxide. ovoid forms composed of chert cores surrounded by A considerable release of oxygen under photosynthesis thin shells composed of minute magnetite granules. was accompanied by a corresponding increase of Chert is commonly pigmented with spheroidal biogenic mass and CO 2 absorption, which in turn led stilpnomenalane bodies equal in size and shape to the to a local decrease in pCO 2 and rise in pH. The resulting chert spherules. It is assumed that the organic matter Fe(OH) 3 precipitation was accompanied by the was replaced by Fe silicate which gave rise to accumulation of carbonate. stilpnomenalane. Chert is also composed of uniform ii) The production of magnetite in the replacement spheroidal particles with thin veneers of hematite, of pre-existing organic remains. magnetite, pyrite and dust-sized stilpnomenalane iii) Chert is normally microcrystalline (20 ~tm in particles and contains structures resembling primitive diameter) and of uniform size. Chert bands are algae. The carbonaceous content includes abundant frequently enriched in organic remains and forms. Silica opaque material and spore-like bodies, the latter of replaces cellular structures of micro-organisms, algal uncertain provenance. It is therefore tentatively filaments, tissues and other organic remains. This suggested that biogenic activity played a role (direct observation, together with the recrystallization of the or indirect) in the deposition and development of the original siliceous forms, argues for the biogenic origin BIF. Direct involvement of iron bacteria in the of the chert bands. LaBerge (1973) suggested that since precipitation of iron is considered questionable. chert formed in a wide range of physical environments, is always composed of spheroidal bodies of uniform Acknowledgements size similar to that of the recorded organic forms, this The authors wish to express their deepest gratitude argues for a common biological origin. He added that to Prof. Dr Samir E1-Gaby, Geology Department, Assiut bacteria and certain forms of algae may precipitate University, for reading the manuscript. The authors silica. Some radiolarians and diatoms metabolize silica would like also to acknowledge Prof. A.H. Knoll, to build skeletons therefore the association of recent Botanical Museum, Harvard University and Dr. J.A. algae with siliceous sinters of volcanic origin, e.g. in Weir, Department of Geology, University of St Andrews Yellowstone Park, USA, may be even more relevant for revising and improving the manuscript. 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