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

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Carbonaceous Bodies of Debatable Organic Provenance in the Banded Iron Formation of the Wadi Kareim Area, Eastern Desert, Egypt Journal of African Earth Sciences, Vol. 19, No. 1/2, pp. 125-133, 1994 Pergamon Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0899-5362/94 $7.00 + 0.00 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 4 8 Figure 3.1-4
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