Pergamon Journal of African Earth Sciences, Vol. 19, No. 1/2, pp. 125-133, 1994

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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. M A H M O U D

Geology Depar tment , Faculty of Science, Assiut University, Assiut 71516, Egypt

(Received 26 January 1994 : accepted 12 Augus t 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-organismes lors 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.

I N T R O D U C T I O N

Woese (1985) believed that the first organisms to arise on this planet , in an ocean rich in organic compounds , w e r e ex t r eme ly he te ro t roph ic anaerobes , and that au to t rophy and p h o t o t r o p h y were later evolut ionary developments . Knoll (1985) states that the oldest known organic remains occur in the Fig Tree Group of southern Africa (~3400 Ma), whilst the Bitter Springs Format ion (-850 Ma) f rom Austral ia contains cyanobacterial and p o s s i b l e a lga l r e m a i n s of s t r i k i n g l y m o d e r n m o r p h o l o g y . The m i c r o b i o t a of the Gunf l i n t I roh F o r m a t i o n , O n t a r i o , C a n a d a , a p p e a r to be b o t h temporal ly and morphological ly intermediate between the other two units, the overall picture which emerges being one of g radua l evolut ion over vast stretches of geological time. Knoll (1985) states that compar isons be tween the Neoproterozoic and m o d e r n Earth reveal m a n y m o r e s imilar i t ies than differences. H o f m a n n (1985) states that carbonaceous compressions have been k n o w n for more than a century in rocks n o w assigned to the Precambrian. These compress ions include both remains wi th regular rounded outl ines and irregular a n g u l a r f r a g m e n t s . The i r g e o g r a p h i c d i s t r i bu t i on includes all continents. Almost all these compress ions

are cons idered to be r ema ins of p h o t o s y n t h e s i z i n g organisms. Jackson et al. (1986) recorded the presence of extensive u n m e t a m o r p h o s e d carbonaceous shales, widespread microbial remains and repor ts of binLrnen and gas in the McAr thur Basin of nor thern Australia. The Precambrian, however , exhibits abundan t fossils o f g r e a t t a x o n o m i c d i v e r s i t y , the f i ve m o s t b i o s t r a t i g r a p h i c a l l y u s e f u l b e i n g s t r o m a t o l i t e s , oncolites and s u n d r y megafossi ls , microfossi ls and trace fossils (Hofmann 1987).

The re la t ion b e t w e e n biological ac t iv i ty and the deve lopmen t of Banded Iron Format ion (BIF) has been invest igated by several authors since the p ioneer ing work of Leith (1903), w h o was the first to sugges t a poss ib le b iological or ig in for the BIF of the Lake Supe r io r region. Par t i c ipa t ion of o r g a n i s m s in the deposi t ion of iron format ions was also sugges ted by Moore (1918), Grou t and Broder ick (1919), H a r d e r (1919) and Gruner (1922, 1923, 1925). Extensive studies of microfossils in the 1000-2000 Ma Gunflint Formation, O n t a r i o h a v e b e e n c a r r i e d o u t b y T y l e r a n d B a r g h o o r n (1954), M o o r e h o u s e a n d Beales (1962), Edgell (1964), Barghoorn and Tyler (1965), Cloud (1965, 1968, 1973) and Cloud and Hagen (1965). Glaessner (1962) stated that bacterial activity has been p roposed

125

126 G.H. EL-HABAAK and M.S. MAHMOUD

to account for the precipitation of certain iron-rich and calcareous sediments. Cloud (1968) suggested that iron is precipitated as a result of oxygen production by photosynthetic organisms. LaBerge (1973) noted that some organisms may act as silica precipitators, and that precipitation of chert in the iron formations was biologically controlled. Beukes (1983) stated that the primitive proterophytic oceans probably served as a source of iron and silica. Records of well preserved microflora in Egyptian Precambrian rocks in general and the BIF in particular are rare (e.g. Shimron and Horowitz 1972; Khalifa et al., 1988; Aboul Ela 1989).

Inorganic sources of iron and silica have also been sugges ted . Iron and silica could be de r ived by weathering (James 1954, 1983; Lepp and Goldich 1964; Belevtsev et al., 1983). Iron and silica also originate during volcanic activity (Goodwin 1956; Trendall and Blockley 1970; Cloud 1973; Beukes 1983). Cairns-Smith (1978) ascribed BIF to the photo-oxidation of ferrous ions in sea water. Eugster (1969) and Eugster and Chou (1973) suggested that magadiite or a sodium silicate gel are to be considered the most likely precursors of banded chert. Hol land (1973) postulated that the derivation of iron from the sea floor in quantity is possible if deep ocean water, Containing a few mg/1 of dissolved iron, wells up, is oxidized in a near surface environment and is deposited in the basin.

The following work presents the results of the investigation of the possible role of biogenic activity on the deposition and development of the BIF at Wadi Kareim in the Eastern Desert of Egypt. Potential organic remains were separated. Replacement textures and m e t a m o r p h i s m have ob l i t e ra ted most p r imary struc~res rendering taxonomic classification uncertain.

Preserved palynomorphs and other possible organic remains extracted from the BIF are illustrated.

GEOLOGICAL SETTING

The Wadi Kareim area is located within the Pan- African basement complex and is accessible through a desert track starting at 18 km from Quseir on the Qift- Quseir asphalt road (Fig. 1). The basement complex is covered mainly by weakly metamorphosed subaqueous and subaerial tholeiitic and calc-alkaline lava flows and volcaniclastics of island arc affinity (Stern 1979, 1981; Hafez and Shalaby 1983; Khudier et al., 1988; E1-Habaak 1992) forming an elongate belt, which are locally interbedded with iron ore bands (i.e. BIF), either as thick stratified layers up to 10 m thick or lenticular bodies. The BIF-bearing unit occupies an area of about 5 km 2 and attains a maximum thickness of about 160 m. The BIF bands are comprised of a number of contrasting facies, namely oxide, carbonate, silicate and suphide dominated which are either laminated, massive or granular (E1-Habaak 1992). The stratigraphic setting is shown in Fig. 2. In general, little radiometric dating has yet been carried out for Egyptian BIFs; the island arc metavolcanics point to 825 Ma (Hashad 1980) and, recently, 712&24 Ma (Stem et al., 1991).

MATERIAL A N D M E T H O D

In order to study the possible biological activities and their influence on the precipitation of the BIF, twenty samples comprising lean-ore, chert and jasper, all containing carbonaceous debris, were selected for 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

V V ~ V V V V

• imI4o~

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50 m

Figure 2. Stratigraphic setting of the BIF, Wadi Kareim area',

subjected to a standard palynological maceration technique in order to separate out the carbonaceous material (hydrofluoric and hydrochloric acid treatment and sieving). Some samples y i e lded potent ia l palynomorphs. Glycerine jelly was used as a mounting medium to prepare permanent palynological slides.

MICROBIOLOGICAL NATURE OF THE WADI K A R E I M BIF

Some brilliant red, pigment-poor, jasper micro- and

Andesite

Andesitic tufts

Andesitic lappill- tufts

Volcanic breccia

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Eastern Desert, Egypt.

BIF

Metavolcanics

submicrolaminae are particularly rich in spherical bodies attributable to Eosphaera tyleri (Barghoorn and Tyler 1965). Those occur as more or less clear spherules of quartz surrounded by thin veneers of very fine hematite granules. There are two distinct varieties of E. tyleri, one of which attains about 15 ~tm in diameter and the other measures about 60 ~tm. The smaller are commonly scattered throughout the jasper laminae but are sometimes segregated in discrete submicrolaminae. LaBerge (1967, 1973) described E. tyleri from many Archaean and Proterozoic BIF.

128 G.H. EL-HABAAK and M.S. MAHMOUD

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4

8

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,-like palynomorph 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

Spheroida l bodies of un i fo rm size (30 ~tm in diameter) are very common in the algal chert (Fig. 3: 1,2). They occur in in t imate associat ion with fi lamentous forms interpreted as algal in origin (Barghoorn and Schopf 1966). These spheroids are noncolonial and are preserved as black carbonaceous matter in a groundmass of chert pigmented by hematite and containing pyrite and greenalite particles. These spheroidal bodies resemble those recorded from the Fig Tree Group, which were identified as algae-like microfossils (Schopf and Barghoorn 1967) and were subsequen t ly des igna ted Archaeosphaeroides barbertonensis (Engel et al., 1968). Knoll (1990) stated that simple carbonaceous spheroids of varying size were reported from several horizons in the Onverwacht (3500 Ma) and over lying Fig Tree Groups though the biogenicity of many of these structures is open to question. During 1970-1980, several authors reported popula t ions of sphero ida l ca rbonaceous microstructures that show a number of features more consistent with a biological interpretation.

These spheroidal bodies were replaced by magnetite (Fig. 3: 2) with any organic structures being obliterated. Direct replacement of organic material by hematite is evidently uncommon (LaBerge 1973). It is suggested that decaying organic mat ter on the bot toms of restr icted basins, held wi thin the interspaces of unconsolidated sediments on the basin bed, reduces accumulating ferric iron oxide to magnetite. These spheroids are not restricted to any particular facies (LaBerge 1967). The sphero ids are c o m m o n l y concentrated in spots (Fig. 3: 3,4), where they usually undergo recrystallization into skeletal crystals bounded by one or more crystal faces and terminated ultimately by the d e v e l o p m e n t of ra ther coarse, euhedra l magnetite crystals which are free from inclusions.

Algal chert contains filamentous structures 5-12 ~tm in diameter. These probably originated as carbonaceous matter, which is now preserved in stilpnomenalane and magnetite. Minute magnetite granules are usually associated with these filaments. They are commonly unevenly distributed but are mostly arranged in a pattern subparallel to the bedding planes. They also form a network of branched filaments (Fig. 3:1 and Fig. 4: 1-4). Undoubted fi lamentous microfossils have recently been described from cherts of the Warrawoona Group (Schopf and Packer 1987) where they occur in association with clusters of spheroidal unicells encased in multiple extra cellular envelopes. Well-preserved filamentous forms (Gunflintia minuta) occur in silicified carbonates from the Palaeoproterozoic Duck Creek dolomite, western Australia (Knoll et al., 1988).

Indeterminate globular to ovoid forms (10-30 ~tm) are composed of hyaline to microcrystalline cherty cores surrounded by thin shells composed of minute magnetite granules. In some instances carbonaceous matter is partly replaced by magnetite with siderite as an intermediate stage. Chert is commonly pigmented with spheroidal bodies of stilpnomenalane which are

equal in size and shape to the chert spherules (10-30 ~tm in diameter, Fig. 4: 4) as in those associated with the filaments (e.g. Fig. 4: 1). It is assumed that the carbonaceous matter was replaced by Fe silicate, which gave rise in turn to stilpnomenalane, with partial to complete olbiteration of any carbonaceous structure (LaBerge 1967). Pigmented silicate structures have been observed in samples from the Robe River area in the Western Hammersley range, Western Australia and the Biwabik, Gurflint, Temiscamie and Kipalu Iron Formations in North America. All structures of this size, shape and mineralogy are replacement products of unknown organic forms (LaBerge 1967).

Cherts and associated very fine andesitic tufts of the Wadi Kareim area contain s t ructures s imilar to Melasmatosphaera sp. A and Melasmatosphaera sp. B. (1989) Aboul Ela. The Precambrian of Belcher Island, Canada (Hofmann 1976) and the metasediments of Gabel E1Hadid, central Eastern Desert (Aboul Ela 1989) have structures similar to primitive algal growths. Cherts of the Wadi Kareim area, on the other hand, are composed of uniform red-blood spheroidal particles (10-40 btm in diameter), commonly with thin veneers of hematite, magnetite, pyrite and stilpnomenalane dust particles, and contain structures related to the growth of primitive algae, particularly cyanophytes.

Carbonaceous debris includes abundant opaque material in addition to the spore-like bodies (Fig. 3: 5- 10). These are dominant, though terminal apertures and markings are not observed. These bodies possess the morphological e lements of Late Silurian spores (Visscher 1974), having wall patterns limited to general outlines and ornamentation insufficient for detailed taxonomical and biostratigraphical resolution. These bodies are of uncertain biological affinity, as are other, quadrangular, polygonal and scarce rounded forms, which mimic pol len grains. Forms s imilar to Melasmatosphaera sp. A Aboul Ela and Melasmatosphaaera sp. B Aboul Ela from the Neoproterozoic of Gebel E1- Hadid figured by Aboul Ela (1989), occur in Wadi Kareim. Indeterminate quadrangular forms comparable with those of Wadi Kareim, are also figured from the Gebel E1-Hadid assemblage. There is, however, a marked contrast between the two assemblages with the Gebel assemblage being much more diverse. Aboul Ela (op. cit.) recorded Myxococcoides inornata (Schopf), Oscillatoriopsis media (Mende lson and Schopf), Cephalophytarion sp., Eomycetopsis robusta (Schopf), Eomycetopsis sp., Siphonophycus sp. A (Aboul Ela) and Siphonophycus sp. B (Aboul Ela) in addition to other oscillatoriacean forms, which are evidently lacking at Wadi Kareim.

A POSSIBLE BIOLOGICAL RELATIONSHIP WITH BIF DEPOSITION

It is suggested that biogenic activity played (directly or indirectly) a role in the deposition and development of the BIE Direct involvement of iron bacteria in the

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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. However the following points can be considered:

i) Cloud (1965) suggests that the transformation of soluble ferrous iron into insoluble ferric iron was achieved through biological activity. He assumed that free O 2 was not available from primary sources but was provided only as a product of photolytic dissociation or of photosynthesis. Belevtsev et al. (1983) suggested that pe r iod ic burs t s of in tense p h y t o p l a n k t o n "blooming" in the Precambrian did not lead to an increase of oxygen content in the atmosphere, but to the oxidation of Fe 2÷ iron to Fe 3÷ in the water, thus causing the precipitation of insoluble iron hydroxide. A considerable release of oxygen under photosynthesis was accompanied by a corresponding increase of biogenic mass and CO 2 absorption, which in turn led to a local decrease in pCO 2 and rise in pH. The resulting Fe(OH) 3 prec ip i ta t ion was accompan ied by the accumulation of carbonate.

ii) The production of magnetite in the replacement of pre-existing organic remains.

iii) Chert is normally microcrystalline (20 ~tm in diameter) and of un i form size. Chert bands are frequently enriched in organic remains and forms. Silica replaces cellular structures of micro-organisms, algal filaments, tissues and other organic remains. This observation, together with the recrystallization of the original siliceous forms, argues for the biogenic origin of the chert bands. LaBerge (1973) suggested that since chert formed in a wide range of physical environments, is always composed of spheroidal bodies of uniform size similar to that of the recorded organic forms, this argues for a common biological origin. He added that bacteria and certain forms of algae may precipitate silica. Some radiolarians and diatoms metabolize silica to build skeletons therefore the association of recent algae with siliceous sinters of volcanic origin, e.g. in Yellowstone Park, USA, may be even more relevant (Weir pers. comm.)

iv) In the oxide-silicate association of Wadi Kareim, greenalite is the chief iron silicate mineral occurring as tiny spherules and featureless isotropic pellets or granules up to 1500 ~tm in diameter. Gruner (1922) conc luded that t iny si l icate spheru les of the Paleoproterozoic Lake Superior region are of organic origin.

v) It is questionable whether the prevalence of mechanical over chemical weathering can provide a basin of deposition with the volume of iron and silica required for the accumulation of the BIF at Wadi Kareim (El Habaak 1992).

SUMMARY

The present work is a study of the possible relation between biological activity and the development of the banded iron formation of the Wadi Kareim area, Eastern Desert, Egypt. Twenty samples of lean-ore, chert and jasper conta in ing ca rbonaceous debr is were

microscopically studied in detail, some yielding forms resembling palynomorphs. Red jasper micro- and submicrolaminae are rich in forms comparable with Eosphaera tyleri (Barghoorn and Tyler 1965), which cccur as clear spherules, surrounded by very fine hematite granules. Spheroidal bodies resembling Archaeosphaeroides barbertonensis (Engel et al., 1968), are very common in the algal chert and occur in intimate association with the filamentous forms. These spheroidal bodies are indirectly replaced by magnetite. The algal chert contains filaments preserved as stilpnomenalane and magnetite. These are also indeterminate globular to ovoid forms composed of chert cores surrounded by thin shells composed of minute magnetite granules. Chert is commonly p igmented with spheroidal stilpnomenalane bodies equal in size and shape to the chert spherules. It is assumed that the organic matter was rep laced by Fe si l icate which gave rise to stilpnomenalane. Chert is also composed of uniform spheroidal particles with thin veneers of hematite, magnetite, pyrite and dust-sized st i lpnomenalane particles and contains structures resembling primitive algae. The carbonaceous content includes abundant opaque material and spore-like bodies, the latter of uncertain provenance. It is therefore tentat ively suggested that biogenic activity played a role (direct or indirect) in the deposition and development of the BIF. Direct invo lvement of iron bacter ia in the precipitation of iron is considered questionable.

Acknowledgements The authors wish to express their deepest gratitude

to Prof. Dr Samir E1-Gaby, Geology Department, Assiut University, for reading the manuscript. The authors would like also to acknowledge Prof. A.H. Knoll, Botanical Museum, Harvard University and Dr. J.A. Weir, Department of Geology, University of St Andrews for revising and improving the manuscript.

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