Foster et al. 1989.pdf

GLOEOCAPSOMORPHA PRISCA ZALESSKY, 1 917: A NEW STUDY

PART I : TAXONOMY, GEOCHEMISTRY, AND PALEOECOLOGY

by

CLINTON B. FOSTER*, JACKIE D. REED** & REEl) WICANDER***

ABSTRACT R~SUM~

Gloeocapsomorpha prisca ZALESSKY, 1917 is emended and redescribed and a neotype is designated from Middle Ordovi- clan kukersites of the Baltic Shale Basin, Estonia. Gloeocapso- morpha was a colonial, probably cyanobacterial organism and its fossil remains are represented by at least three morphotypes. These morphotypes result from growth and life cycle stages which are overprinted by post-mortem changes. Gas chromatography of hydrocarbons from pyrolysed kukersite yields a diagnostic low molecular weight, odd- dominated suite of n-alkanes, maximizing at Cl9. The emended diagnosis of Gloeocapsomorpha incorporates these biogeochemical criteria. Morphological and biogeochemical characteristics of Gloeocapsomorpha show strong similarities with certain species of the modern Entophysalidaceae cyanobacteria. Entopby- sails major, a mat-forming, and sometimes stromatolite-for- ruing, cyanobacterium, is suggested as a modern analogue for a. prisca.

Gloeocapsomorpha prisca ZAtESS~, 1917 est amend~e et red&rite ; le n~otype ddsign6 provient des kuckersites de l'Ol"- dovicien moyen, dans la partie schisteuse du Bassin Balte. Gloeocapsomorpha &ait colonial et probablement d'affinit6 cyanobact6rienne ; elle est repr6sentde par au moins trois morphotypes fossiles. Ces derniers correspondent aux phases de croissance et du cycle de vie accentu6es par des change- ments post-mortem. La chromatographie gazeuse d'hydrocarbures de kuckersite pyrolys6e rdv~le une suite de n-alkanes es- sentiellement de faible poids moldculaire, ~t nombre impair de carbones et avec un maximum de C19. La diagnose dmendde de Gloeocapsomorpba tient compte de ces crit~res biogdochimi- ques. Les caract&istiques morphologiques et biogfochimiques de Gloeocapsomorpha ressemblent beaucoup ~t celles de cer- taines cyanobactdries modernes, les Entophysalidaceae. I1 est suggdr6 qu'EntophysMis major, une cyanebact6rie moderne formant des tapis et parfois des stromatolithes, est le corres- pendant moderne de G. prisca.

KEYWORDS : G£OEOCAPSOMORPHA PRISCA, TAXONOMY, KUKERSITE, ORDOVICIAN, PALYNOLOGY MOTS-CLES : GLOEOCAPSOMORPHA PRISCA, TAXONOMIE, KUCKERSITE, ORDOVICIEN, PALYNOLOGIE

* Western Mining Corporation Ltd., 168 Greenhill Road, Parkside, SA 5063, Australia **Arco Oil and Gas Co., 2300 West Piano Parkway, Piano, Texas 75075, U.S.A. *** Dept. of Geology, Central Michigan University, Mr. Pleasant, Michigan 48859, U.SJu

Geobios, n o 22, fasc. 6 p. 735-759, 7 fig., 3 tabl., 3 pl. Lyon, ddcembre 1989

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INTRODUCTION

Gloeocapsomorpha prisca is the principal component of Middle Ordovician oil shales known as kukersites of the Baltic Shale Basin, Estonia (Zalessky 1917). Deposition of kukersite occurred in a marine environment, as indicated by intercalated limestones containing bryozoans, brachiopods, bivalves, gastro- pods, trilobites and ostracodes (Beld~er 1921). Consequently, G. prisca is, prima faaie, a marine microfossil.

Primary productivity must have been high during the Middle Ordovician (478 to 458 million years ago) as indicated by the large cumulative thickness of kukersite and kerogen-rich rocks (20 m over an area of 100,000 kin2). These rocks account for as much as 200 billion tons of organic carbon, 40 to 50 billion of which occur in layers (kukersite), with the remainder dis- persed throughout the associated carbonate rocks (Baukov 1973). Recoverable oil shale reserves for Estonia in 1970 were 3.8 billion tons and, in the adjacent Leningrad area, 0.9 billion tons (Baukov 1973).

The economic and strategic importance of kukersite has been the underlying motive for study of both the deposits and its contained microfossils. In this context, it is noteworthy that Zalessky's (1917) study was galvanized by serious fuel shor- tages in 1916 in Petrograd (Leningrad), and, as a consequence, the heating potential of the oil shale was assessed. The results of his work were initially read on November 16, 1916, by Aca- demician N.I. Andrusov at the meeting of the Physical-Mathe- matical Sciences Section of the Russian Imperial Academy of Sciences. They were subsequently published in Russian, in the

Bulletin of the Academy in 1917, and reappeared in a French translation in January of the following year (Zalessky 1917, 1918) with reorganized text-figures and photomicrographs. Subsequently, kukersite deposits have been reviewed by Ger- man, Estonian, and Russian investigators. However, in spite of its abundance and significant ability to produce hydrocarbons (Table 1), the systematic position of G. prisca remains uncertain and has been vigorously debated since 1917.

Kukersite is very organic rich, with 20% to 60% total organic carbon and has significant hydrocarbon potential (Table 1). Retorting of kukersite produces a hydrocarbon assemblage with a distinctive n-alkane hydrocarbon-signature maximizing at el9 (Klesment 1974, Klesment & Nappa 1980). Recent studies have noted similarities between the geochemistry of several Ordovician oil and organic-rich rocks containing G. prisaa (see Reed et al. 1986 and Hoffmann et al. 1987 for summaries).

In this study we review the morphology, geochemistry, paleoecology, and taxonomy of G. prisca from the type locality Kukrnse "Stage" of the Baltic Shale Basin, Estonia (Fig. 1). The genus and species is redescribed and a neotype designated. Comparisons with modern cyanobacteria suggest that En- tophysalis is a potential modern analogue. The environment of deposition for kukersite is reviewed, and based primarily on the findings presented in this study, a model for its accumula- tion is proposed in a subsequent companion paper (Part I1).

Depth Tmax S 1 S 2 S 3 S 1 & S 2 PI PC TOC HI

Outcrop 421 9.03 329.1 11.17 338.18 0.03 28.18 48.8 674

Table I - Total organic carbon and Rock-Eval pyrolysis data on kukersite (WM 23911{). Rock-Eval par'ametets : Tmax = °C ; Sl = kg hydrocarbons (extractable) per tonne rock ; Sz = kg hydrocarbons (kerogen pyrolysate) per tonne rock ; S3 = kg CO2 (organic) per tonne rock ; S1 & S2 = potential yield ; PI = production index ; PC = pyrolysable carbon, weight % ; TO(; = total organic carbon ; HI = hydrogen index, mg hydrocarbons ($2) per g TOE ; Ol --- oxygen index, mg CO2 ($3) per g TOC. Carbone organique total et donn6es par pyrolyse Rock-Eval de kuckersite (WM 23911{). Param[tres Rock-Eval : Tmax =°C ; St =kg d'hydrocarbures (ex- tractible) par tonne de roche ; $2 = kg d'hydrocarbures (pyrolysat de kdrog~ne) par tonne de roche ; S3 = kg CO2 (organique) par tonne de roche ; S1 & S2 = rende- ment potentiel ; PI = index de production ; PC =carbone pyrolysable, % en poids ; TOE =carbone organique total ; HI =index d'hydrog~ne, mg d'hydrocarbures (SO par g TOC ; Ol = index d'oxyg~ne, nag COx (S3) par g TOE

PREVIOUS STUDIES

Many authors have studied the morphology and geochemistry of G. prisaa in an attempt to classify it and determine its paleoecology. Results and rationale for the conclusions of the

major previous studies need to be summarized before a reclas- sification and paleoecologic interpretation of G. prisca is proposed.

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Fig.l - Locality map. Early-Middle Ordovician paleogeography (Smith etal. 1981) and distribution of reported occurrences ofaloeocapsomorphaprisca. A. Amadeus Basin ; B. Baltic Basin ; C. Canning Basin ; MI. Michigan-Illinois Basin ; S. Southampton Island (see text); W. Williston Basin. Insert is a generalized map of the disMbu- tion of Middle Ordovician kukersites from the Kukruse "Stage" of the Baltic Shale Basin, Estonia (modified from Baukov 1973). KJ l(oht!a-Jarve, K =Kukruse. Carte de lotalit6s. Pal6og6ographie de l'Ordovicien Inf6rieur-Moyen (Smith et alii 1981) et r6partition de Gloeoeapsomorpha prisca. A. Bassin d'Amadeus; B. Bassin Balte ; C. Bassin de Canning ; MI. Bassin de Michigan- Illinois ; S. lie de Southampton (volt texte); W. Bassin de Williston. L'encadM est une carte g6n(~raie de la distribution des kuckersites de l'Ordovicien Moyen de 1' "Etage" Kukruse dans la pattie schisteuse du Bassin Bake (modit~6 d'aprbs Baukov 1973).

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MORPHOLOGY

Based on apparent morphologic similarities with extant species, G. prisca has been previously assigned to either the cyanobacteria (--Cyanophyta =blue-green algae =myxophyceae) or to the Ghlorophyta (=green algae). Zalessky (1917) noted that in its pure form, kukersite was composed only of G. prison and that it occurred as several morphotypes, which presumably were affected by in situ compression (See Appendix 1 for details of compression experiments). He concluded that G. prison was a fossil form of the extant cyanobacterium Gloeo- capsa KfJTZlN~, 1843 because both modern and fossil forms have :

1. cells that are enclosed in a thick, layered or lamellated sheath ; and

2. undergo cell division in one, two, or three dimensions, giving the surface of the colonies a distinct, botryoidal appearance.

This conclusion, however, was challenged by subsequent workers such as Lindenbein (1921) and Riiger (1926) who stated that any supposed morphologic affinity did not reflect phy- logenetic (systematic) relationships and,. moreover, that Za- tessky's (1917) morphologic interpretation was incorrect. They assigned G. prisca to a new class, the "Protophycea," which shared certain characteristics with both the Cyanophyta and Rhodophyta, and noted that specimens displayed radial symmetry.

Fig. 2 - Diagrammatical representation of the morphology of a supereolony of Gloeocapsomorpha prtsca. A colony (a) comprises one to several cell voids enclosed in a lameUated sheath. A mesocolony includes two or more colonies bound by a common wall, while a supercolony is composed of mesoeolonies connected together by mucilaginous layers. Diagramme repr6sentant la morphologie d'une supercolonie de Gloeocapsomorpha 1;risen. Une colonie (a) contient une ~. plusieurs enclaves cellulaires dans une enveloppe lamellaire. Une m6soeolonie in- elut au moins deux colonies euvelopp6es dans une paroi commune ; une supercolonie est form6e de m6soeolonies r6unies par des couches muci- lagineuses.

Eisenack (1960) discussed the apparent affinities of a. prisca, commenting that the cell voids of the fossils are arranged much more regularly than those of extant Gloeocapsa (see P1. 3, figs 7,8), and that they also occur within a common bounding layer delimiting what we refer to as a mesocolony (Fig. 2). Eisenack also rejected the assignment of aloeocapsomorpha to the cyanobacteria on the grounds that gelatinous sheaths would not be chemically stable enough to be fossilized (cf. Knoll et al. 1975, Adamczak 1963). However, experimen- tal studies on fossilization of cyanobacteria by Oehler (1976) and the ecophysiology of some modern taxa (namelx being able to withstand desiccation in a hostile external environment, e.g., members of the Entophysalidaceae) negate Eisenack's pre- mise. Cyanobacteria are capable of being fossilized and, of course, are among the oldest microfossils. They occur in stromatolitic forms in Proterozoic cherts, limestones and dolo- mites (see Walter 1976, Schopf 1983).

The systematic assignment of G. prison has also been influenced by the direction of openings of the cavities. If the voids opened to the surface, perhaps via release of a polysaccharide cap (see Berkaloff et al. 1984, Aaronson et al. 1983, fig. 6), then Gloeocapsomorpha might be considered to be congeneric with the green alga Botryococct~s K0"rZING, 1849 (Harris 1938, Tappan 1980, p. 84:1, fig. 10.28).

However, not all workers accepted inclusion of Gloeocapso- morpha into Botryococctts. Eisenack (1960), Adamczak (1963), Timofeev (1966), Burns (1982), and others, interpre- ted the structure of G. prisaa differently, and considered that the cavities (=ceils) were enclosed in multilayered walls or sheaths and hence aIoeocapsomorpha was not related to Bo- tryococcus. In Botryo¢occus braunii, cells are held in small depressions or cups in the colonial matrix and are surrounded by copious mucilage (see Wake 1983, Berkaloff et al. 1984). However, the outer layer of a. prisca is smooth and entire, while for B. braunii, it is dimpled with the mucilage removed, revealing depressions associated with the cell cups.

It is noteworthy that Tappan (1980 p. 77, 81; fig. 1.41) clas- sified aloeocapsomorpha as a member of the cyanobacteria, yet also stated (p. 841) that Botryococctls, a chlorophyte, is reported under various names such as Gloeocapsomorpha, a point which illustrates the confusion surrounding this microfossil. Both of Tappan's statements have been quoted by prota- gonists to support inclusion into the green alga (Hoffmann et al. 1987) and cyanobacteria (Playford & Wicander 1988).

NUTRIENT REQUIREMENTS Nitrogen requirements for the precursor of a. prisca may

have also influenced earlier systematic interpretations. Many cyanobacteria possess the ability to fix free nitrogen from the atmosphere ; therefore, their gromh is not dependent upon nitrogen sources such as nitrites (Fogg 1969). This ability is ex- ploited by cyanobacteria so that the quantitative composition of the plankton changes in response to changes in nitrogen avai- lability. A 1969 study of Lake Erie (Tappan 1980) showed a

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shift in the plankton from 75% green algae, with high dissolved nitrogen levels, to more than 80% heterocystous cyanobacteria in waters with almost zero dissolved nitrogen (see Khatri 1985 for other examples). Such observations have profound implications for quantitative analyses of fossil algal assemblages in that numerically abundant fossils may reflect changing nutrient patterns rather than gross environmental differences.

The ability of certain heterocystous, filamentous cyanobacteria to fix atmospheric nitrogen has been known or at least suspected since the 1930s (Fritsch 1959), but it was not until recently that a species of living Gloeocapsa was also shown to fix nitrogen (Wyatt & Silvey 1969). Further work by Stanier et aHi (1971) noted that the non-heterocystous, nitrogen fixing strains were "characterized typologically by enclosure of cells in multilaminate sheaths."

The recognition that gloeocapsid forms can fix nitrogen in marine intertidal environments (Stalet al. 1984) has important implications. Prior to 1969, a renewable source of dissolved nitrogen was considered necessary for nitrogen fixation by gioeocapsid forms. Riiger (1926) for example, suggested that aminoacids from decaying marine megafaunas might have been a nitrogen source for G. prisca. However, if the ~. prisca precursor had a nitrogen fixing capacity, it would have had an advantage in colonizing new areas created by transgressing seas (see Foster et al. (in press.)).

GEOCttEMISTRY Hydrocarbons generated from 6. prisca-rich kerogens have

certain distinctive geochemical characteristics that have been used to assess the systematic affinities of a. prisca. Evidence from such biochemistry is discussed below.

Klesment and Nappa (I 980) pyrolyzed kukersite by destruc- tive hydrogenation using water and sodium formate at tempe- ratures of 340 °, 360 °, 380 °, and 430 ° C. They noted an appre- ciable amount of straight-chain hydrocarbons, predominantly Ct3, ClS, and C17, in the derived liquids. They considered that the fatty acids Ct4, Ct6, and Cls, respectively, were tile precur- sors of these normal alkanes (see also Vitorovi~ 1980 for summary).

Reed et aL (1986) studied kukersite and G, prisca-derived oils and identified the same n-alkane characteristics as did Klesment and Nappa (1980). However, Reed et aL (1986) also noted that the isoprenoid alkanes, pristane and phytane, assu- med to be primarily derived from chlorophyll, were essentially absent from their pyrolysis (temperature programmed) analyses. These results were consistent with those for their analyses of other Ordovician G, prisca-bearing rocks and oils. Ba- sed on these data, Reed et aL (1986) suggested that a. prisca was a non-photosynthetic, prokaryotic organism. With the exception of the kukersite samples examined by Reed and coworkers, all their G. prisca examples were recovered from thin laminae in cores, which together with their biogeochemical evidence, led Reed et al. (1986) m suggest that G. prisca was a benthonic, mat-forming, aerointolerant chemoautotroph.

Hoffmann et al. (1987) studied a. prisca-rich Ordovician kerogens from the Canning and Amadeus Basins in Australia. Their pyrolysis (sealed tube, 250 ° C) analyses on a Canning Ba- sin sample (previously reported by Foster et aL 1986) showed the same distinctive C17-Cl9 n-alkane distribution as described previously. However, Hoffmann et al. (1987) also reported occurrences of pristane and phytane which was in marked contrast to the very low abundances reported by Reed et aL (1986) and the low abundance in hydrous pyrolysates of the same sample reported by Foster et aL (1986). Based on their analyses, which also included evidence from sterane abun. dances, Hoffmann et aL (1987) suggested that a. prisca may have been a photosynthetic eukaryote.

Two arguments have subsequently been raised against the findings of Hoffmann et al. (1987) : first, the sample was not composed exclusively of G. prisca, and secondly, the pyrolysis temperature of 2500 C that they used was too low for significant organic maturation. For example, Klesment & Nappa (1980) reported a maximum yield of liquids from kukersite at 3600 C.

Several studies have been made of the hydrocarbons associated with the green alga Botryococcus braunii, a sometimes proposed modem analogue of G. prisca (e.g., Brown & Knight 1969, Murray & Thomson 1977, Wake & Hillen 1981, and Lar- geau et aI. 1986). The n-alkane distribution from a Permian torbanite rich in Botryovo¢cus is shown in Figure 3b (Sum- mons, pers. comm. 1988). This distribution of hydrocarbons is consistent with that reported by other workers, and is clearly distinct from that of G. prisaa.

Although the various studies do not show consistent occurrences of isoprenoids with G. prisca, they do show that the characteristic n-alkane distribution is specifically associated with this species.

ECOLOGY AS discussed above, comparisons between ~. prisca and

certain Cyanophyia and green alga have been based on morphological, rather than ecological considerations. Extant Gloeo- capsa (used by Zalessky 1917) and Botryococczts (used by Harris 1938) are both essentially freshwater genera, while associated faunal evidence as discussed earlier, suggests a nor- real marine environment for ~. prisca.

Modem Gloeocapsa commonly occurs as gelatinous mats on wet rocks In non-martue environments. Thus, its ecology poses a problem when attempting to explain the thick accumu- lations of material in Ordovictan marine rocks (see translation of Zalessky 1917 in Hoffmann etaL 1987).

Botryococcus, however, even though it is a predominantly fresh-water genus, has been reported to be tolerant of brackish- water conditions, and there are rare reports of it occurring in high saline environments. For example, Master (1971) in a Canadian study and P. E. Playford (pers. comm. in Bauld 1981) reported Botryococcua sp. forming stromatolitic mats in a hypersaline lake in Western Australia. However, the

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18 19

20 21

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17

13 19

20

21

22 23

19

1o

2 7

23 25

31

29

Fig. 3 - Gas ehromatograms arranged at C17 peak for (a) Estonian kukersite pyrolysed at 2500 C for 48 hours, (b) Sydney Basin Permian torbanite pyrolysed at 3300 C for 72 hours, and (c) lipids extracted from modern Entopbysalis major. Chromatogram (a) shows the presence of minute amounts of isoprenoids (pr =pristane, ph =phytane) and the distinctive distribution of low molecular weight n-alkanes. This distribution is readily distinguishable from the chromatogram resulting from pyrolysis ofBotryococcus-rieh kerogen (b). Chromatogram (c) shows the dominance of C17 and C19 and the presence of phytane (ph), a similar feature of Gloeocapso- morpbaprisca ; higher molecular weight alkanes are also present. Chromatogrammes gazeux dtstribu~s autour dupic C17 pour (a) kuekersite estonienne pyrolys~e 5. 2500 C pendant 48 h, (b) torbanite du Bassin permian de Sydney pyrolys~e 5. 3300 C pendant 72 h et (c) lipides extraits d'Bntopbysalis major modemes. Le chromatogramme (a) montre la presence de tr~s petities quantit~s d'isopr~no'fdes (pr=pristane, ph-phytane) et la distribution earact~ristique de n-alkanes de faible poids mol~ctllaire. Cette r~partition est ais~ment visible dans le chromatogramme obtenu par pyrolyse de k~rog[ne (b) riche en Botryococcus. Le chromatogramme (c) montre la preponderance de Ct7 et (:19 et la presence de phytane (ph), comme darts le cas de G.prisca ; des alkanes de poids mol~culaire plus ~le% sont ~galement presents.

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identity of the Western Australian taxa have not been confirmed (J. Bauld pers. comm. 1989) and, moreover, neither of these types of environments is similar to that indicated for G. prisca.

OCCURRENCE

Records of G. prisca from Estonian Ordovician deposits are summarized in Figure 4. Other than its type locality, G. prisca has been recorded from Ordovidan sequences throughout much of the world, but not all of the reported identifications of G. prisca are reliable. Figured specimens attributed to G. prisca from the Early Ordovician of the Georgina Basin, Australia (Playford & Wicander 1988, fig. 6G-L), for example, belong to a genus to be described as new by Foster & Wicander (in prep.). On the basis of its age, lithology and apparent paleogeographic position, Foster et aL (1986) suggested that oil shale deposits from Southampton Island, Canada, might also contain G. pris. ca, but recent studies (Foster unpublished data) have shown that G. prisca is extremely rare in the Boas Oil Shale.

a. prisca has also been recorded from Proterozoic and Silu- rian localities. Timofeev (1966, p. 43 [translation]) commen- ted that G. prisca was found in "predominantly Ordovidan and Silurian sediments" and that G. prisca was "significantly rare in the Cambrian and isolated in the Precambrian." lle recorded Gloeocapsomorfiha in the Upper Precambrtan (Vendian), Ordovician, and Silurian (p. 101-103), but details from the line-drawings are not convincing.

Cramer & D~ez de Cramer (1972) recorded G. prisca from 11 localities that were all of Silurian age (ranging from Llando- verian to Ludlovian) and defined a G. prisca microfacies. The type material for their Silurian ~. prisca microfacies is from the Read Bay Formation, a unit that lies close to the Ordovi- cian/Silurian boundary in Canada. Cramer & Diez de Cramer (1972) did not illustrate their material and further comparison cannot be made. We have been unzble to obtain either detailed locality information for these Silurian records or comparative material from the Read Bay Formation.

Chronostratigraphy (1)

-~g o E o '~ Estonia (a) o = oLu 0~

Estonia {b)

Porkun! (Fil) Borkholmer Stufe (F2)

",3 Pirgu {Fic ) =T, a= = ~ Vormsi (F ib ) Lyckholmer Stufe IF I)

~ Nabala (Fla) Rakvere (E) Wesenberger Stufe (E}

{Baltic Limestone)

Locality

Baltic Basin Aust. Can.

1 2 I 3 4 , 5 6 , 7 !

I

g [ 3

I

• ~ 0andu (Oil I) Wasalemmsche Stufe (D 31 - -

Keila (DII) Kagersche Stufe (D 2)

• ~ Johvi (D 1} Jewe'sche Stufe (D 1 ) [~ .*- . . . . . o ~ Idavere Itfer'sche Stufe (C 3) - F = -~ "~ (Clll) i

O ~ Kukruse (CI~) Kuckersehe Stufe (C 2} [ " ~ g l "~ Uhaku [Cic} Revaler Stu|e (C I) [ ~ Lasnarnagi (Ibl

Aseri (Cla) "T

_ _ _~ , | g

l i~ ~ Kunda (Bll I) Vaginatenkalk (B3)

=* ~ '~ Volkhov (BII) Glaukonitkalk (B2) ,~ . - o Leetse {BI)

= ~ ~ Pakerott (A 2 3 } E ~ o *

USA Fig. 4 -

8, B Summary of selected Ordovieian occnrrences ofaloeocapsomor- pht tprisca with special reference to the type locality. (a) Standard division of R66smusoks (1960). (b) After Eisenack (1962, etseq;). (I) Af- ter Tynni (1975). g =Geochemical evidence. See Reed et aL (1986),

• . Foster et al. (1986), and Hoffmann et al. (1987) for summaries. ? =age limits uncertaim 1. Eisenack ~ (1960) ; 12 (1962) ; *(1968). 2.Type locality: Zalessky (191'7, 1918), Burns (1982), this study. 3. Adamczak (1963), fossils recovered from erratics. 4. Combaz & Peniguel (I972). 5, Foster et al. (1986). 6. McGregor & trainer (1971). 7. Foster, Reed & Wi- cander, unpublished data. 8. Tappan (1980). 9. Reed etal. (1986).

g R6sum6 de r6partlttons ordovtciennes s61ectionn6es de aloeocapsomorpha prtsca, ~vec r~f~renee particuli~re ~ la leealit~-

t type. (a) Division standard de R'6~smusoks (1960). (b) d'apr~s Eisenack (1962, et. seq.). (1) d'apr~s Tynni (1975). g =6vidence gdochimique. Voir Reed at at. (1986), Foster et al. (1986), and Hoffmann et al. (1987) pour r&um6s. ? =limites incertaines d'~.ge. 1. Eisenack ~ (t960) ; (1962) ; *(1968), 2. Localit&type : Zalessky (1917, 1918), Burns (1982), cette 6tude. 3. Adamczak (1963), fossiles extraits de blocs erratiques. 4. Combaz & Peniguel 0972). 5. Foster et aL (1986). 6. McGregor & trainer (1971). 7. Foster, Reed & Wicander, donn6es non publi6es. 8. Tappan (1980). 9. Reedetal. (1986).

CLASSIFICATION PROBLEMS Previous assignment to either the cyanobacteria or the Chlo-

rophyta using morphologic criteria alone has posed problems ever since G. flrisca was named, primarily because multilamel- lar wall structm'e and colonial habit are not unique to either group. Frequently taxa of both cyanobacteria and green algae are described as having a gloeocapsid phase in their life cycle.

Among the cyanobacteria, gloeocapsid-like morphotypes are found in Gloeocapsa (PI. 3, figs 7,8) and Chroococcus of the Chroococcaceae, EntophysaIis and Placoma of ~he Entophysa- lidaceae and Siphononema of the Siphononemataceae (see Fritsch 1959, Padmaja 1972, Rippka et aL 1979). Members of the Siphononemataceae, however, are further distinguished by development of baeocytes (reproductive spore-like bodies) in their life cycle.

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are enclosed in thick gelatinous, and sometimes stratified, sheaths. They include species of gloeocystis and Hormotila, both of which belong to the family Palmellaceae. Living taxa are distinguished by the motility of their flagellate zoospores and other criteria not applicable to fossils (see Bold & Wynne 1985).

Previously, most authors have figured examples of G. prisca that most closely resemble the specimens illustrated by Zaless- ky (1917, 1918; morphotype I herein); few have discussed the morphologic variation of the species and so their treatment has paralleled that of most spore-pollen taxonomy.

Because Gloeoeapsomorpha is represented by multiple morphotypes, there is an inherent problem in determining diagnostic criteria for its classification. Cell size and shape of the colony are used in the systematic description, but cell contents, and probably the bounding layer of the protoplasm, are often missing in G. prisca, leaving a void or cavity surrounded by either a multilayered or unstructured wall. The individual void- spaces (= internal cavity of Burns 1982) in undistorted specimens may thus approximate cell size. However, data from extant coccoid species indicates that cell shrinkage following death can be between 55% to 70% of the original volume (Go- lubie & Hofmann 1976) and microbial attack can further alter morphology. Consequently, cell size in fossil studies is not ne- cessarily a diagnostic taxonomic criterion.

Nonetheless, for ease of communication, three morphologic categories are used in this study to describe G. prisca : (1) colony, comprising one to two cell voids (maximum dimensions 0.5 - 8 p.m, 3 i~m average) ; (2) mesocolony (7-41 p~m), a three dimensional spherical or ovoid structure that includes

two or more colonies bounded by a common wall (equivalent to microcolonies recognized in living cyanobacteria by Stanier et al. 1971) ; and (3) 8upercolony (30-210 p~m), a collection of mesocolonies loosely or tightly connected by mucilaginous layers or, more rarely, by short tubular appearing structures (fig. 2).The categories are artificial because they represent growth stages of a colonial organism. Therefore these parame- ters cannot be of diagnostic importance.

These problems of classification of G. prisca are not unlike those experienced by biologists attempting to classify living taxa of algae and bacteria. For modern studies, there is a growing tendency to use living, pure cultures as taxon references, rather than herbarium specimens (Stanier et al. 1971, Rippka et aL 1979). Moreover, because morphologic expression of living algal and bacterial species is modified by both genetic and environmental controls (see, for example, Golubic 1965, Padmaja 1972), morphology is therefore only one of the criteria used to classify living taxa.

Equally important characteristics for classification are biochemistry, physiology, and mode of reproduction (Truper & Kramer 1981 ; Bold & Wynne 1985). Whereas cell walls and contents generally are not preserved in G. prisca, biogeochemical methods can be used to identify the fossil species (see also Nildas & Chaloner 1976). This approach contrasts with the usual taxonomic methods used to classify other fossil palynomorphs, which are based on a single specimen. Moreover spore-pollen classification is based primarily on mature specimens; aborted and immature examples are rarely considered in taxonomic assessments.

SYSTEMATICS OF GLOEOCAPSOMORPHA PRISCA

Almost all of Zalessky's (1917) publication is devoted to the description, comparison, and probable palaeobiology of the then monotyplc genus Gloeocapsomorpha. His treatment is discursive, and there is no formal description of either the genus or species. The name is introduced in the text on page 14 (translation): "But whether the fossil alga is a planktonic or benthic form, it seems more prudent to create a new genus for it, which I propose to name gloeoeapsomorpha, in view of its similarity to our alga Gloeocapsa. Thus it seems to me that Gloeocapsomorphaprisca, as 1 call the alga forming kuker- s i t e . . . " The taxon is illustrated by detailed pencil-drawings (1917, figs 1-3, 8-9) of unlocated specimens; no holotype is designated.

In the French translation, line-drawings and photomicrographs of G. prisca are given (Zalessky 1918, pl. II, figs 1-2, 4- 7; pl. III, figs 1 & 2), but a type is not mentioned. On these grounds, it may be argued that based on a strict interpretation of the International Code of Botanical Nomenclature (ICBN), both the genus and species are nomen nudum (Articles 38.1,

41.2, 43.1 ; Voss 1983). However, in accordance with Articles 14.1 and 14.2 which relate to avoiding disadvantageous no- menclatural changes, we propose that the name should be conserved, and further that Zalessky's (1917) description serve as the initial and valid diagnosis of the monotypic genus and species (Article 42). BeCause no type was originally proposed, a neotype is here designated in accordance with Article 7 (ICBN).

G. prisca is treated here as an organic-walled microfossil that has morphologic attributes of a cyanobacterium, but as a fossil, it cannot yet be accommodated in the International Code of Bacteriological Nomenclature (see Truper & Kramer 1981). It currently remains then, under the taxonomic umbrella of the Botanical Code.

Incertae sedis Cenus aloeocapsomorpha Z~.ss~, 1917 emend.

Foster, Reed & Wicander

TYPE SPECIES (by monotypy) Gloeoeapsomorphaprisaa ZALESS~, 1917.

B - 743 -

Pig.5 -Three views of the neotype of aloeocapsomorpha prises ZAL~SS~, 1917 emend. FOSTER, I~ED & WICANDER. The slide number, coordinates for Olympus light microscope BH2 (no, 69725), and the film and negative numbers are given for the entire holotype figure 5.2. The scale bar for figures 5,1 and 5.3 is 30 ~m and for figure 5.2 is 60 ~Lm. 5.1 - View of portion of the neotype showing the detailed nature of the supercolony, the individual cell voids and the multilayered walls. B points to the location of this view in relation to the entire supercolony illustrated in figure 5.2.5.2 - View of the entire neotype supercolony of G. prisca. The location of detailed portions of the supercdony are indicated by A and B which correspond to figures 5.3 and 5.1 respectively. 2391IVSR, i6.6;142.2, 32/30,32,38; 5.3 - View of portion of the neotype showing the detailed nature of the supercolony. A points to the location of this view in relation to the entire supercolony of figure 5.2. Trois vues du n~otype de Gloeocapsomorpha prtsaa ZA~mSaT, 1917 emend. F o ~ RE~I~ & WlC,~DEI~. Le num6ro de lame, les coordon- n6es pour le microscope optique Olympus Bit2 (no, 69725) ei les num6- ros du film et du n6gatif sont donuts pour la totafit6 de l'holotype, ~t la figure 5.2. Trait = 30 ,t.Lm pour les figures 5.1. et 5.3. et 60 ~m pour Ia figure 5;2, 5.1 - Vue partiefie du n6otype d6taillant: la supercolonie, les enclaves cellulaires individuelles et les parois form6es de p!usieurs couches. B indique sa position dam la figure 5,2.5.2 - Vue complete du n6otype de la supercoionie de G. prisca. La localisation des parties d6taifiees de la supercol0nie est indiqu6e par Ae t B, correspond.ant respectivement aux figures 5.3, et5Ai 23911f/5R, 16.6; 142.2 , 32/30, 32, 38. 5 .3 , Vue par- tielle du n60type d6taiilant la supercolonie. A indique sa position dans la supercolonie en~re de la figure 5.2.

Neotype (here designated): Fig, 5.

EMENDED DIAGNOSIS

Thallus variable ; cells rarely preserved but their position is commonly indicated by circular, hemispherical, lacrimate or irregularly-shaped (highly compressed), empty voids ensheathed by a single or multilamellate wall. Cell voids do not open to surface of thallus. Arrangement of cells dependent upon planes of cell division ; cells dividing in two or three dimensions from round to oval colonies of one to four cells bounded by a common wall or sheath, Repeated cell division within a colony forms a mesocolony, also bounded by a common wall ; number of individual cells in mesocolony difficult to determine. Colonies and mesocolonies may be separate or connected via strands, mucilaginous layers, or irregularly-shaped pa- renchymatous cells that presumably were formed by repeated division in one plane. Mesocolonies may show directional growth. Characterized biogeochemicafiy by a predominantly low molecular weight series of n-alkanes, maximizing at C19 (Fig, 3a).

COMPARISON

Modem Gloeocapsa includes colonies having two to eight cells bounded by a thin, common sheath; the colonies are not connected by cellular material, nor do they form the large multicelled mesocolonies seen in aloeocapsomorpha (PL 3, figs 7,8).

Palaeopleurocapsa KNOLL, BARGHOORN & GOLUBIC, 1975, described from Precambrian rocks, is characterized by a filamentous arrangement of coccoid cells, presumably resulting from cell division occurring mostly within a single plane.

Eoentophysalis HOFMANN, 1976, known from Precambrian sequences, and modern Entophysalis K~TZING, 1843 (PL 3, figs 1-6) have a wall structure that is characterized by a distinctly grainy texture, multilamellate walls that are relatively thin, and cells that almost always contain granular inclusions ; these features are not seen in Gloeocapsomorpha. For the fossil taxa, differences in mode of preservation, i.e., in cherts and in stromatolitic dolostones (Belcher Supergroup, Hofmann I976) ver- sus oil shales, might perhaps explai n some of these morphologic differences (see Knoll & Goiubic 1979), but they are here considered taxonomically significant, since the modern examples of Entophysalis also show these features.

Biogeochemically, hydrocarbons extracted from Entophysa- lis (Fig. 3c) show some similarities with those of Gloeocapso- morphai namely abundances of n.alkanes CI7 and C19, but there are sufficient differences to readily distinguish between the two genera. The emended diagnosis formally incorporates the biogeochemical criterion.

aloeocapsomorphaprtsca ZAL~SS~, 1917 emend. Foster, Reed & Wicander

Pl. 1, figs 1-12, P1. 2, figs 1-16 ; text-figs 2,5,6,7.1,7.3,7,5,7.6

Fig. 6 - Scanning electron micrographs of a cross-section of aloeoca#so- raorpha prtsca ZaLESS~, 1917 emend. FOSTER, RILED & WICAN'D/.R. This specimen is from sample preparation 2391K, mounted on SEM stub 2. The negative catalogue numbers are Kodak 2,3 and are housed in the senior author's permanent illustrative materials collection. 6.1 - Cross-section through a kukersite supereolony ofG. prisca showing the individual cell voids and relationship between cell voids, mesocolonies and the su- pereoiony. The arrow indicates the location of figure 6.2. Scale bar =20 }.Lm. 6.2 - Detail of figure 6.1 cross-section, showing individual cell voids and laminar nature of the colony walls. The arrow corresponds to the location of the arrow of figure 6.1. Scale bar = 5 / £ m Micrographies 61ectroniques ~ halayage de la coupe transversale de Gloeocapsomorl~ha prisca 7~Ess~, 1917 emend. FOSTER, RE~.D & WIOanDEP,. Le sp6cimen provient de l'6chantifion 2391K, mont6 sur la table 2 du MEB. Les n6gatifs portent les numgros Kodak 2 et 3 et sont d6- pos6s dans la collection de types du premier auteur. 6.1 - Coupe transversale d'une supercolonie de G.prisca dam une kuckersite et montrant les lacunes cellulaires, la relation entre celles-ci, les m6soeolonies et la supercolonie, La fl~che indique la position de la figure 6.2. Trait =20 ~m. 6.2 - D6tail de la figure 6.1 montrant les lacunes cellulaires et [a nature lamellaire des parois de la colonies. La fi~che indique la position de celle de la figure 6.1. Trait = 5 }.Lm.

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SELECTED SYNONYMY OF ILLUSTRATED SPECIMENS

1917 - Gloeocapsomorpheprisca ZALESSKY, p.8-14, figs 1-3,6-9. 1918 - Gloeocapsomorpha prisca ZALESSKY, p. 31-36, figs 1,2;

PI. 2, figs 1,2,4-7 ; P1. 3, figs 1-2. 1921 -Gloeocapsomo~ha prisca ZALESSKY, Bekker, Pl. 1, figs

1- 3, ?4a [no formal description, but see p. 26-27]. 1960 - Gloeocapsomorpha prisca ZALESSKY, 1916 (sic)-Eise-

hack, p. 17-18, P1.2, figs 12-15. 1963 - Gloeocapsomorpha prisca ZALESSKY ,1916 (sic)-Adamc-

zak, p. 466-467 ; fig 1, B,C ; P1. 1, figs 1, 2, ?3,4. 71966 - Gloeocapsomorpha prisca ZALESSKY, Timofeev ; Pl. 58,

fig. 1 [no description]. 1971 - Gloeocapsomorpha prisca ZALESSKY, McGregor & era-

met, p. 2 ; Pl. 1, figs 1-6. 1972 - Gloeocapsomorpha cf. prisc~ ZALESSKY, Combaz & Peni-

guel, p. 138, P1. 1, figs 13-15. 1982 -Gloeocapsomorpha prisca ZALESSKY, Burns, p. 172-173 ;

text-fig. 10, figs 19-21. 1986 - Gloeocapsamorpha (sic) prisca ZALESSKY, Foster et al..,

Pl. 1, figs A-E [no description].

DIAGNOSIS

Same as for genus.

NEOTYPE

Figs 5.1-5.3.

DESCRIPTION

Three basic morphotypes are recognized and, for descriptive purposes only, are designated morphotypes I, II, IIL

L Morphotype L In optical section colonies are circular to oval in outline; in three dimensions, supercolonies are botryoidal indicating that cell division may have occurred in two to three planes (H. 1, figs 10-12 ; Pl. 2, figs 15,16 ; fig. 7.6). Cell voids are either hemispherical, lacrimate, crescentic or circular in outline. Careful focusing reveals that some voids taper with depth from the optical section, indicating that cells were elongated within the colony. Colony margins are always entire because they represent an optical-plane section of a spherical/ovoid body. Cell voids are ensheathed by multilayered (usually 2-4 layers) walls typically 1-5 ~m thick, and individual layers usually less than 1 p.m thick. Cell voids are often opaque which may be due to infilling with pyrite. Evidence of directional growth is rare, but some apparent branching is ob- vious in the supercolonies (PI. 2, figs 7-10). These supercolonies may occur singly or be intimately associated with morphotypes ll(A,B) and Ill (q. v.).

2. (a) Morphotype IIA. Colonies are circular to oval in plan view, lobate in three dimensional outline. Void spaces are highly compressed and appear as fine, irregular openings that are enclosed by a multMamellar or unstructured sheath (Pl. 1, figs 4-7). Careful focusing reveals details of wall margins. Out- lines of void spaces are irregular, often modified by microbial attack (perhaps bacteria or fungi initially attacked the ceil

- 745 -

contents). The origin of the colonies may be due to compression of the morphotype 1 cells, or to post-mortem effects on the cells as the enclosing sheath lost turgidity. Morphotypes I and II commonly occur in the same supercolony.

2. (b) Morphotype IIB. Colonies retain the same outline as morphotypes I and I1A above, or are irregularly flattened and elongate. Cell voids are not easily discernible, if at alLThe surface of the colonies appear irregularly "punctate" and both SEM and light microscopy suggest that these features resulted from microbial attack of the ensheathing wall: at high magnification, rod-shaped and coccoid-shaped holes are visible (PI. 2, figs 11-12).They are assigned to morphotype IIB because layers are not discernible and the wall appears as a nearly homoge- neous layer; this, together with irregularly shaped outlines of colonies suggests that either homogenization or polymerization of the wall has occurred (as is evident in certain gymnosper. rebUS pollen grains; see Foster 1979, p. 90) and/or that cell growth became irregular and cell elongation may have resulted from division in one plane (see Padmaja ]972 for modern analogues in coccoid cyanobacteria).

3. Morpholype III. Although relatively rare in the type material, sheaths may have separated or peeled off from the colonies, and been preserved as fiat, sheet-like layers (see Pl, 2, figs 13-14). The layers are irregularly shaped, and exhibit similar "micropunctate" structure as does morphotype IIB. In

other samples, such forms are far more common, and various stages of colonial disaggregation are observed (Foster & Wican- tier unpublished observations). The modern cyanobacterium Chroo¢occus turgidus shows a similar sheath sloughing (Fogg et al. 1973 ; Foster & Wicander unpublished observations)i Wake (1983) recorded similar separation of mucilage from Bo- tryococcus colonies.

The type species has the same diagnostic biogeochemical characteristics as given for Gloeocapsomorpha (Fig. 3a).

DISCUSSION : Many organic-rich Ordovician layers are associated with sty-

lolytic pressure-driven sequences. Therefore, to determine how pressure might affect morphology, preliminary pressure experiments using both pyrolysed and unpyrolysed kukersite-kerogen were attempted (details are given in Appendix 1). The results are difficult to interpret statistically with any degree of certainty because the original sample contains an admixture of morphotypes. Experiment 1 which subjected the kerogens to 7 x 109 dynes/sq cm for 40 hours, and corresponding to a depth of burial of 2000 m, had no noticeable effect on morphology. Only at higher pressures~ corresponding to 10 km burial were changes in morphology evident. In experiment 3, morphotype II specimens were more evident than morphotype I, although cell voids may have been smaller.

OTHER SPECIES ATTRIBUTED TO GLOEOCAPSOMORPHA

~vo other species have been assigned to Gloeocapsomor- pha by Eisenack (1960) and Tfmofeev (1966), and they are reviewed below.

(1) aloeocapsomorpha makrocysta EISENACK, 1960

HOLOTYPE Eisenack (1960, pp. 16-17, P1. 1, fig. 7a).

REMARKS For distinguishing features, see Table 2.

(2) aloeocapsomorpha hebetca TIMOFEEV, ] 966

HOLOTYPE Timofeev (1966, p. 43, PI. 4, fig. 1).

REMARKS G. makrocysta is from the Baltic Ordovician and sub-

sequently reported from the Silurian by Cramer & Dlez de era- met (1972) ; G. hebeica was described from the "Tsuanglin- gou Formation" (translation, p. 43) =Proterozoic (Early Si- nian), Chuanglingkou Formation, Changcheng Group, of Hebei Province, north China. G. hebeica has a lobate outline and lacks cell voids, but there are too few characters for detailed comparison (see Table 2). We consider that inclusion within Gloeocapsomorpha is doubtful, but we draw attention to microfossils subsequently described from the Changcheng Group. Several coccoid genera, recovered from formations im- mediately overlying the Chuanglingkou Formation, show similarities with Gloeocapsomorpha. These include : Eoentophysa- lis HOFMANN, 1976, Coniunctiopbycus Z~NG, 1981 and Gloeo- theceopsis ZHANG, 1988. These genera are distinguished from Gloeocapsomorpha by cell shape, colony size, and the presence of intracellular granules. Zhang (1981, 1988) did not comment on any similarities with G. hebeica, but perhaps Ti- mofeev's species might be more appropriately assigned to one of these genera.

- 746 -

CHARACTER

Super-colony

Outline

Size (~m)*

Void space (um)

Size

Shape

G. prisca

spherical, oval strongly lobate

10-80(1),* * 10-40(2) 40-100, 320)3), 358(4) 10-150(5)

5 x 3 . 5 , 1 x 1

circular, laerimate, bean-shaped, irregular

G. makrocysta

spherical, oval, strongly lobate

690(3)

12-30

rectangular (rare) mostly rounded

G. hebeica

lobate

50-72(6)

not present

not present

Common bounding yes; sometimes not yes; sometimes not not clear layer of mesocolony present present

)?preservation)

Connections between yes; sometimes yes; short not clear mesocolonies short stalks, often stalks

irregula~ mesh

Wall

Lamellate

Thickness OJm)

Planes of contact

mostly yes; can be single-layered or uncertain (2)

1-5

mostly rounded, curved, sometimes linear

not given

2-5

Jinear

not given

not given

curved?

Reproduction

Endospores uncertain suggested not given

Planes of cell yes yes presumably division (I to 3D)

Age (see text) Ordovician, ?Silurian Ordovician, ?Silurian Sinian

Table 2 - Summary of diagnostic characters for species of aloeocapsomorpha ZALESS~, 1917 emend. FOSTEr, REED & WIC,~DE~. * Supercolony size is affected by fossilization and extraction techniques, and is not re- garded as a primary diagnostic feature. **References : (1) Zalessky (1917) ; (2) Bums (1982) ; (3) Eisenack (1960) ; (4) This study;, (5) McGregor & Cramer (1971) ; (6) Timofeev (1966). Re, sum6 des caract~res diagnostiques de aloeocapsomorpha Za. LESS~, 1917 emend. FOSTER, REED & ~,VIc,~E~ *La taille de la supercolonie est modifi6e par ]a fossilisation et les techniques d'extractign. **R6- f6rences : (1) Zalessky (1917); (2) Burns (1982); (3) Eisenack (1960); (4) Cette 6rude ; (5)McGregor & trainer (1971) ; (6) Timofeev (1966).

MICROFOSSILS OCCURRING WITH GLOEOCAPSOMORPHA PRISCA

By far the most abundant microfossils occurring with G. prisca are small, unnamed tetrad-like forms (P1. 2, figs 1-5; text-figs 7.2, 7.7). The relative proportions of these forms within sample WM 2391K is shown in Table 3.

The tetrad-like forms consist of two sizes of cells: (1) thin- walled (<0 .5 ~m) small cells (diameter 1-6 }xm) which often occur in clusters ; the basic structural unit seems to be a tetrad. The wall appears single-layered and is often invaginated, forming a "doughnut-shaped" cell ; (2) thicker-walled (1-2 l.~m) larger cells of similar habit, they appear to intergrade with the thinner-walled cells.

Knoll (1981, fig. 2.29) has illustrated similar tetrad-like, unnamed aggregates of cells which he considered to be mat- dwelling cyanobacteria. They were recovered from laminae in cherts of the Draken Conglomerate of Precambrian age.

The smaller tetrad-like forms encountered are intimately associated with morphotypes I, II and llI. We consider that the smaller tetrad-like forms might be baeocytes or endospores (see Rippka et alit 1979, 1981), and therefore part of the life cycle of G. prisca. Me/nbeps of the modern Entophysalidaceae (e.g., Chlorogloea microcystoides ; Fritsch 1959, p. 818) re- produce via endospores, which are initially formed in clusters

of tetrad-like specimens. However, these cells separate when released from the enclosing membrane and form individual colonies. The tetrad-like forms reported here also occur in other assemblages with gloeocapsid-type microfossils from Australia, Canada and the U.S.A. (Foster unpublished observations), but their systematic position remains uncertain. Hoffmann et al. (1987) suggested that the tetrads might be bacterial remains but from comparison with modern bacteria (e.g. Starr et al. 1981), this is no longer considered likely. They may be symbionts with G. prisca, or, perhaps, unsuccessful G. prisca cells that grew on top of the colony without sufficient pigment and therefore protection from ultraviolet light and subsequently died (J. Bauld peps. comm. 1989). Both possibilities are, however, speculative.

The remainder of microfossils occurring with G. prisca are rare specimens of uncertain affinities, which account for less than four percent of the total assemblage. They include an acritarch (Multiplicisphaeridium sp.) and a multicelled colony in which cell walls remain in a few of the void cavities, and small, single-walled coccoid bodies. No filamentous cyanobacteria are evident in the Estonian material (cf. Bekker 1921).

- 747 -

Fig. 7 - Scanning electron micrographs of 6'loecapsomorpba prlsca ~Lzss~. 1917 emend. FOST~R. REED & WIC&'~DEI~ and associated tetrad-like lbrms. M[ specimens are from sample preparation 2391L The SEM negative number is given for each figured specimen. All gEM negatives are housed in the senior author's permanent illustrative materials collection. Scale bar as indicated for each figure (~m). 7.1 - Outer surface ofG.prisca supercolony. SEM 518, (14 ~Lm), 7.2 - Tetrad-like forms occurring with G, prisca, SEM 927. (6 [,.Lm). 7.3 - Cross-section of G. prtsca supercolony showing cell voids. Arrow indicates layering of wall, SEM 506. (5 [,Lm), 7.4 - Small. single-walled coccoid cell of uncertain ail]nity occurring with G. prisca. SEM 519. (3 [.Lm). 7.5 - Cress-section of G. prisca supercolony with pyrite framboid (arrow), SEM 512. (6 }.Lm). 7.6 - Outer surface of G. prisca supercolony showing how cell division occurs in two to three planes. SEM 503. (16 LLm). 7.7 - Tetead- like forms occurring with G. prisca showing how the invagination of the wails produces a "doughnut-shaped" cell. SEM 118. (3 I.Lm).

Micrographtes ~lectroniques ~ balayage de aloeocapsommTphazOrtsca ZALESSKY, 1917 emend. FeSTEr, REED & WmAm~Ret de fromes associ~es ressemblant des t6trades. Tousles exemplaires proviennent de 1'6chantillon 2391K. Tous les n6gatifs au MEB, dent les uum6ros sent fournis pour chaque sp6,cimen figur6, sent d6pos6s dans la collection de types du premier auteur. Echelle indiqu6e en ~Lm pour chaque figure 7.1 - Surface externe de la supercolonie de G.prisca. MEB 518. (14 [,Lm). 7.2 - Formes ressemblant ~, des t6trades pMsentes avec G.prisca. MEB 927. (6 l.Lm). 7.3 - Coupe transversale d'une supercolonie de a, prisca montrant des lacunes eel[ulaires. La fl~ehe tndique la lamellation de la paroi, MEB 506. (5 ~m). 7.4 - Petite cellule coccoidale ~. paroi simple, d'aFfinit6 incertalne et trouv6e avec G, prisca. MEB 519. (3 ~m) 7.5 - Coupe transversa e de la supercolonie de G.pri$ca avec de la pyrite framboidale (fi~che). MEB 512. (6 l, Lm). 7.6 - Surface exteme d'une supercolonie de G.prisca montrant comment la division cellulalre a lieu dens deux ou trois plans. MEB 503. (16 I, Lm), 7.7 - Formes ressemblant a des t6trades, prdsentes avec G. prisca et montrant comment l'invagination des parois produit une cellule en forme d'anneau. MEB 118. (3 l,Lm),

- 748 -

PARA- METERS

%

n

Total %

Surface Area

Max %

Mean %

% Of Total

Total % (B)

Gloeocapsomorpha prisca

MORPHOTYPEI

wt nt

11.4 10.0

2 5

MORPHOTYPES IIA, B, III

wt n t

21,4 9.0

12,0

3.8

16.3

22 47 20

21.4 --[-- 30.4 /

35.3

14.0 24.0 18.0

3.1 4.94 4.25

19,0 32.7 24.5

-J_ 57.2

L

TETRAD-LIKE FORMS

MISCELLANEOUS TAXA

COCCOID CELLS

44.5 3.7

98 S

44.5 3.7

4:0 1.4

0.62 0.24

5.4 1.9

5.4 1.9

Table 3 - Estimates of numbers (A) and surface area of morphotypes (B) within Estonian kukersite (WM 2391K). Estimates of the surface area account for contributions from organic matter of different sizes. Count (n) of 220 specimens. Associated with tetrad-like forms (wt) ; not associated with tetrad-like forms (nO. Estimations du nombre (A) et de la surface des morphotypes (B) darts la kukersite d'llstonle (WM 2391 K). Les estimations de surface prennent en compte la matiSre organique de diff6remes tailles. Comptage (n) de 220 sp6cimens. Associ6s avec des formes ressemblant ~. des t6tmdes (wt) ; non associ6s (nt).

ENTOPHYSALIS MAJOR • MODERN ANALOGUE FOR GLOEOCAPSOMORPHA PRISCA

At least for part of their life cycle, many cyanobacteria and Chlorophyta taxa (e.g., Gloeocapsa, Chroococcus, Entophysa- lis, Placoma, and Siphononema, Gloeocystis, Hormotila) are superficially similar to G. prisca. They can, however, be rejected as modem analogues of G. prisva because of their ecophysiology. Of the comparable Chlorophyta and cyanobacteria just mentioned, most genera are known from fresh-water or terres- trial habitats. With the exception of Chroococctts (fresh-water) and Entopbysalis (marine), these taxa would not seem to have had the capacity for extremely high productivity, as would be required to have formed pure kukersite beds up to 0.5-0.8 m thick.

EntopbysaIis major is a photosynthetic cyanobacterium that lives in a marine environment and possesses a glo.eocapsid morphology. Modern entophysalids and closely related Precam- brian counterparts (e.g., Eoentophysalis HOFMANtL 1976), have been studied extensively by Golubic and coworkers (Golubic 1973, 1983 ; Golubic & Hofmann 1976 ; Golubic & Barghoorn 1977 ; Knoll et aL 1975 ; Knoll & Golubic 1979). Their results are reviewed briefly below.

MORPHOLOGY E. major has cells 3 to 9 Ixm in diameter that divide either

in one plane (near the center of the colony) or three planes (outer margins). It produces copious amounts of extracellular polysaccharides that hold the cells together in a mat-like colony (Pl. 3, figs 1-6). The polysaccharide envelopes, or sheaths,

have a loose fibrous ultrastrueture, which forms an elastic fa- bric that can expand as cells divide and new polysaccharide layers are added inside the existing cell wall. This creates a multilayered cell. The envelopes are stained brown by a photo- reactive pigment (scytonemine) that may be particularly dense in layers close to the mat surface, depending upon seasonal light intensity. The envelopes are highly hydrated, giving a translucent, gelatinous appearance and consistency, and they provide convenient water storage during times of emmersion and exposure to air (Golubic 1983).

ECOLOGY E. major forms widespread mats in the (1) lower intertidal

zone of Shark Bay, Western Australia (Logan et aI. 1974) ; (2) modern sabkha environments in the Persian Gulf (Kinsman & Park 1976) ; (3) the hypersaline Laguna Mormons, California (see Stuermer et al. 1978). It also forms stromatolites, a phe- nomenon apparently confined to the Shark Bay area (Golubic 1983). The mats gradually disintegrate, perhaps seasonally (cf. Stalet al. 1984). After storms, and other less violent but turbu- lent events, cells from weakened parts of the mats are released by dissolution of the enclosing gel, float to the surface, and are distributed by the tide to start new colonies (Golubic 1983).

E. major is a cosmopolitan species that favors low energy intertidal settings, moderately hypersaline water (greater than three times normal sea water will cause carbonate precipita- tion and obliteration of cell morphology), and periodic alterna-

- 749 -

tion of flooding and emmersion. It does not grow subtidally or in stagnant intertidal pools. Associated filamentous cyanobacterial taxa occurring with E. major are either common or rare, depending on immersion conditions: the greater the depth of water over the mat, the more abundant are associated taxa (,I. Bauld pers. comm. 1989).

PRESERVATION POTENTIAL According to Kinsman & Park (1976), Bauld (1981), and

Golubic (1983), the potential for preservation of E. major in situ is poor. Bauld et al. (1979) lloted that in mats available to their study, E. major did not support in situ bacterial sulfate reduction, and, as a consequence, sulfides, which are usually indicative of an anoxic environment, were not present. Howe- ver, excellently preserved fossils belonging to the Entophysali- daceae do occur in the Precambrian (e.g., Eoentopbysalis HOF- MANN, 1976) and, potentially, Ordovician examples from this study. Moreover, the presence of framboidal pyrite, which is often intimately associated with the G. prisca microfossils, indicates that reducing conditions existed at some time. It seems reasonable therefore, that Entopbysalis colonies are preserved only when they are transported into suitable reducing environments.

Fossilization potential may also be enhanced by growth or deposition in highly saline environments. With increasing sali- nity there is a decrease in oxygen solubility, which would re- duce productivity of aerobic grazing organisms,

BIOGEOCHEMISTRY Hydrocarbons extracted from mats of E. major by R.E.

Summons (written comm. 1988) show a dominance of C17 and C19 n-alkanes and is therefore similar to the signature of G. prisca (Fig. 3c). However, higher molecular-weight aikanes are also present. It is nevertheless noteworthy that these taxa show similar biogeochemical characters.

As discussed earlier, the lsoprenoid content of G. prisca remains controversial. However, Ihe low isoprenoid content dis. cussed by Reed et aL (1986), may be explained in the comext of this proposed modern analogue. Within modern mat-forming communities of E. major, tile geiosic mass of connecting tissue is volumetrically greater than cells bearing chlorophyll and consequently a dilution effect could be expected because of this inbalance (Bauld et al. 1979 ; Fig. 3c). However, despite this possible explanation, it remains clear that further work must be completed on the abundance and role of isoprenoids in G. prisca - derived hydrocarbons.

CONCLUSIONS

1. aloeoaapsamorpha ZALESS~, 1917 is emended and a neotype is selected for G. prisca ZALESS~, 1917. Gloeocapso- morpha was a coionial, probably cyanobacterial organism, and its fossilized remains are represented by at least three morphotypes. These morphotypes probably reflect normal growth patterns, as well as changes resulting from post-mortem causes, such as microbial attack, degradation, and compression. Cell division occurred either in two or three planes, giving rise to spherical to ovoid mesocolonies that are bounded by a common wall or sheath. Collections of mesocolonies and colonies (one to four cells bounded by a common wall) form supercolonies often with a botryoidal or hummocky appearance. The colonial cells seem to have been enclosed within a parenchyma- tous-iike mass, presumably resulting from cell division occurring in one plane.

2. Ceils of G. prisca often represented by empty voids, are completely ensheathed by a multilamellate or unstructured sheath or wall. When intact, voids do not open to the surface of the thallus.

3. Pyrolytic products of kukersite, and of other G. prisca-

bearing kerogens, have a diagnostic low-molecular weight, odd- dominated suite of n-alkanes that maximize at C19. This

biogeochemical signature is formally added to the emended generic diagnosis of Gloeovapsomorpba.

4. Some doubt remains as to the origin of the small amount of isoprenoids found in extracts and pyrolytic products of G. prisca-bearing rocks and kerogen. Further biogeochemical characterization of kukersite is needed to confirm their occurrence and quantitative abundance.

5. Morphologically, particularly in the arrangement of cells, a. prisca is most closely comparable with members of the marine cyanobacteria assigned to the Entophysalidaceae. Moreo- ver, there is a close biogeochemical similarity with the extant, mat-forming and stromatolite-forming marine cyanobacterium Entophysalis major.

6. Other organic-walled microfossfls occurring in the kukersite are rare and this is consistent with some modern ecosys- tems with E. major. Coccoid cells and thin-wailed tetrad=like forms are the most common associates of G.prisca.; they may be symbionts or remnants of unsuccessful cells of G. prisca.

Acknowledgments

We thank the following people for their assistance in various Dr. S. Golubic (Boston University, Boston, Massachusetts, aspects of thiswork. For comparative data on modern algae, U.S.A.), Dr. D.E. Wujek (Biology, Central Michigan University

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[CMU], Mr. Pleasant, Michigan, U.S.A., Dr. L.C. Saha (Botany, Bhagalpur University, India), the late Dr. G.W. Prescott (Wyo- ming, U.S.A.) ; Dr.John Bauld (Bureau of Mineral Resources [BMR], Australia) provided modem examples of Entophysalis major from Shark Bay, Western Australia and discussed their biology; Dr. J. Lampky (Biology, CMU) provided help in bacteriological techniques and discussed aspects of the study ; Dr. K. Lindfors (Chemistry, CMU) arranged for pressure experiments on G. prisca ; Dr. R. E. Summons (BMR) did pyrolysis experiments on G. prisca and made available comparative gas chromatographic data on an Early Permian torbanite, and modern E. major ; Ors. C. Rothfuss (Modern Languages, CMU) and G. Wood (Amoco, Houston, Texas, U.S.A.) made available transla- tions of relevant Russian and German papers ; Dr. F. Martin (Institut Royal des Sciences natnrelles de Belgique, Brussels,

Belgium) kindly translated relevant portions of the paper into French ; Dr. A. Hutton (University of Wollongong, Australia) provided one of the samples of Estonian kukersite used in this study ; Professor Li Xingue (Academia Sinica, Nanjing, China) kindly provided geologic details of Timofeev's (1966) locality for G. hebeica. Dr. W.A.S. Sarjeant (Geology, University of Sas- katchewan, Canada), Dr. A. Le Heriss6, (Pal6ontologie Lab., Universit6 de Bretagne Occidentale, France), Drs. ILChristo- pher, D. Goodman (&'co Oil and Gas, Plano, Texas, U.S.A.), and Dr. W. Vollscheimer (Museum of Argentina, Buenos Aires, Ar- gentina) critically read and offered valuable suggestions for im- proving this paper ; Martha Brian (Geology, CMU) labored significantly with the manuscript. This work was completed while C.B.F. was a Visiting Scholar on a WMC Study Fellowship in the Department of Geology, C.M.U.

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APPENDIX 1 :PROCEDURES

MICROSCOPY Kukersite samples were processed without oxidation using

standard palynological techniques. Samples were crushed and carbonates were removed using warm dilute hydrochloric acid; any silicates and fluorosilicates were removed by successive treatments of 30% hydrofluoric acid and warm dilute hydrochloric acid. Before each change of acid, residues were neutra- lized by repeated washing with distilled water. For routine fluo- rescence and light microscopy, residues were mounted in either Zeiss "Eukitt", glycerin jelly, or Fischer Permount media under No. 0 glass cover slips. Coordinates of figured specimens are from Olympus light-microscope BH2, (no. 69725), housed at the Department of Geology, Central Michigan University, Mt. Pleasant, Michigan, U.S.A. Both strew mounts and individually picked specimens were studied using scanning electron microscopy (SEM). Wall morphology was determined on freeze-frac- tured specimens using a Hitachi $530 SEM unit, housed at the

Department of Earth Sciences, University of Toronto, Canada. All photographic negatives remain with the catalogued illustrative material in the senior author's collection.

GEOCHEMISTRY Standard Rock-Eval pyrolysis of 60 mg of unextracted, pow-

dered kukersite was undertaken at the Australian Mineral De- velopment Laboratories (AMDEL), South Australia, using a Gir- del IFP-Fina Mark 2 instrument. Total organic carbon (TOC: also analyzed by AMDEL) was determined using an acidified sample combusted with a Leco IR-12 Carbon Determinator.

Gas chromatography-mass spectrometry (GCMS) analysis was performed on a. prisca-rich kerogen. Approximately 25-50 mg of solvent-extracted kukersite-kerogen was washed exhaus- tively with dichloromethane, dried, and pyrolyzed in sealed

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sate was subsequently extracted with dichloromethane and sa- turates separated by liquid column chromatography (SiO2, pe- troleum ether) for analysis. Details of instrument-type and ex- perimental conditions used in GCMS analyses are given by Hoffmann et at. (1987, p. 2683-2684). The analyses were car- ried out at the Bureau of Mineral Resources, Canberra, Austra- lia, by Dr. R. E. Summons.

PRESSURE EXPERIMENTS Following pyrolysis (250 o C for 48 hours), the kerogen was

recovered to see if any significant morphological changes had occurred. The same pyrolyzed kerogen was then used in burial simulation experiments to assess the effect of pressure on morphology. For the pressure experiments, microfossils were mixed with potassium bromide (KBr2) because they could be readily recovered, and because salts of halites are common, naturally occurring constituents of Phanerozoic sequences. Ex- periments were done without heating although both pyrolyzed and unpyrolyzed kukersite-kerogen was used. Burial pressures at 2 kin, and 10 km were calculated using the following formu- la:

Pressure (dynes/sq cm) = SG x depth of burial (cms)x G, where SG is the average density of the enclosing rock (gr/cm3), G is the gravitational constant in cm/sec 2, and depth of burial is in cm. Three experiments were run using a 30 tonne press C-30 (Research & Industrial Instruments Company, London)

fitted with hydraulic pressure control. The three experiments were designed as follows :

t. pyrolysed kerogen : 7 x 109 dynes/sq cm for 48 hours 2. pyrolysed kerogen : 35 x 109 dynes/sq cm for 168 hours 3. unpyrolysed kerogen : 35 x 109 dynes/sq cm for 24

hours

BACTERIOLOGICAL TECHNIQUES Gram staining, using crystal violet, iodine, ethanol, and sa-

franin (Bartholomew 1981, p. 378 wet method), characterizes bacteria as either Gram-negative (stained red or pink) or Gram- positive (blue-black; see Beveridge 1988 for discussion). Because cyanobacteria are Gram-negative (Rippka et aL 1979), this inexpensive technique was used to assess the biolo- gic composition of kerogen. However, because most eukaryotes are also Gram-negative (Bartholomew 1981) the technique is not a definitive test but the results are useful in supporting other criteria used to distinguish between bacteria and eukaryotes. Although fungicides such as copper sulfate are routinely used to prevent growth in stored palynological residues, they had not been used on our material. The surfaces of many of the G. prison mirofossils show evidence of microbial attack. To test ifliving bacteria were present in the acid residues, kerogen samples were plated on nutrient agar ; no growth was recorded (Dr.J. Lampky pers. comm. 1988)

M anuscrit ddpos6 le 03-02-1989 Manuscrit ddfinitif re~u le 01-07-1989

PLATE 1

'Light photomicrographs of specimens of Gioeocapsomorpha prtsca ZALESSK¢, 1917 emend. FosTEP~ REED & WICANDEIL The slide number, coordinates for Olympus light microscope BH2 (n ° 69725), and the film and negative numbers are given for each specimen. The scale bar = 20 ixm.

Photomicrographies optiques de sp6cimens de aloeocapsomorpha prlsca ZALESSK¢, 1917 emend. FOSTER, REED & WICANDER. Le numdro de lame, les coordonndes pour le microscope optique Olympus BH2 (n ° 69725) et les num6ros du films et du n6gatif sont indiquds pour chaque sp6cimen. Trait =20 I~m.

Fig.1 - Supercolony of 6. prisca, with focus on a mesocolony, (morphotype I), illustrating the individual cell voids and wall layering. Morphotypes I and II visible. 3491/5R, 20.0 ; 132.3, 17/34. Supercolonie de 8. prisca avec raise au point sur la mdsocolonie (morphotype I) montrant les lacunes cellulaires individuelles et les couches de la paroi. Morphotypes Iet II visibles.

Fig. 2 - Supercolony of (7. prisca. Morphotypes I and II visible. 2391K/6R, 3.5 ; 148.0, 20/15.

Fig.3 - Supercolony of 8. prisca showing the three dimensional growth of the colony and the lameUate nature of the wall. 2391K/6R, 16.0 ;129.2, 10/36. Supercolonie de 8. prisca montrant sa croissance selon trois dimensions et la nature lamellaire de sa paroi.

Fig. 4 - Morphotype IIA. 2391K/6R, 5.2 ;147.8, 20/16.


Fig.6 - Morphotype IIA. Different focus from same location of G. prisca supercolony of figure 5. 2391K/SR, 13.4 ;131.5, 17/36. Diffdrentes mises au point du m~me endroit de la supercolonie de G.prisca de la figure 5.


Fig. 8 -View of entire G. prisca supercolony. 2391K/6R, 6.9 ;148.1, 19/36. Vue de l'enti~re supercolonie de G. prisca.

Fig. 9 - Detail of G. prisca supercolony. 2391K/7R, 23.4 ;150.5, 19/14. Ddtail de la supercolonie G. prisca.

Fig.10 - Morphotype I. Arrow points to lamellate nature of the wall. 3699/1, 20.3 ;135.4, 20/35. Morphotype I. La fl~che indique la nature lamellaire de la paroi.

Fig.11 - Morphotype I. Focusing on individual mesocolony. 2391K/7R, 17.6 ;147.7, 21/23. Morphotype I. Mise au point sur une m6socolonie isol6e.

Fig.12 - Morphotype l.Same location as figure 11, but different focusArrow points to tetrad-like cells attached to mesocolony 2391K/7R, 17.6 ;147.7, 21/24. Morphotype I. M~me endroit que la figure 11 avec raise au point diffdrente. La fl/~che indique des cellules ressemblant A des t~- trades et attachdes ~ la mdsocolonie.

Geobios n ° 22, fast. 6

PL 1 C.B. Foster, J.D. Reed & R, Wicander

PLATE 2

Light photomicrographs of specimens ofGloeocapsoraorphaprtsca ZAtESSrt, 1917 emend. FOSTER, REED & WICANDER and associated tetrad-like forms. The slide number, coordinates for Olympus light microscope BH2 (n o 69725), and the film and negative numbers are given for each specimen. The scale bar =20 ~m.

Photomicrographies optiques de sp6cimens de aloeocapsomorpha prtsca ZALESS~, 1917 emend. FOSTER, REED & WICANDER et de formes associ6es ressemblant it des t6trades. Le numdro de lame, les coordonndes pour le microscope optique Olympus BH2 (n o 69725) et les numdros du film et du n6gatif sont indiqu6s pour chaque sp6cimen. Trait = 20 ~m.

Fig. 1 - Tetrad-like forms. 2391K/TR, 22.4 ;151.3, 31/38. Formes ressemblant it des tdtrades.

Fig. 2 - Tetrad-like forms. Arrow indicates small, thin-walled cell associated with more typical larger, thick-walled cells. 2391K/5R, 18.5 150.0, 29/5. Formes ressemblant it des tdtrades. La fi~che indique de petites cellules it fine paroi associ6es avec des cellules typiquement plus larges "~ paroi 6paisse.

Fig. 3 - Tetrad-like forms. Same colony as figure 2, but different focus. 2391K/5tL 18.5 ;150.0, 29/7. Formes ressemblant it des tdtrades. M~me colonic que la figure 2, avec mise au point dlffdrente.

Fig. 4 - Tetrad-like forms. Typical thick-walled cells forming the basic tetrad structural unit. 2391K/6R, 5.5 ;148.2, 19/35. Formes ressemblant it des tdtrades. Cellules il paroi typiquement ~paisse et formant une unit6 fondamentalement organis6e en t6trade.

Fig. 5 - Tetrad-like forms. Typical thick-walled cells forming the basic tetrad structural unit. 2391K/7R, 17.3 ;151.2, 31/35. Formes ressemblant it des tdtrades. Cellules it paroi typiquement 6paisse et formant une unit6 fondamentalement organis6e en t~trade.

Fig. 6 - G. prisca colony showing lamellated wall layers. 23911(/5R, 21.8 ;151.8, 30/28. Colonic de G. prisca montrant les couches lamellaires de la paroi.

Fig. 7-9 - G. prisca supercolony showing branching. Each figure is at different focus of supercolony. 3699/1, 20.5 ; 130.2, 21/11,10, 9. Supercolonie de G. prisca avec embranchements. Mise au point diffdrente pour chaque figure,

Fig. 10 - Directional growth of a G. prisca supercolony. 2391K/5R, 12.0 ;131.4, 17/43. Croissance orient6e de la supercolonie de a. prisca.

Fig. 11-12 - M orphotype liB at different foci. Rod and coccoid- shaped holes are visible (arrow in figure 11). Those holes give the surface of the colony a "punctate" appearance and are the result of microbial attack of the ensheathing wall. 2391K/5R, 23.5 ;152.3, 30/31, 32. Diff6rentes raises au point du morphotype liB. Des trous en forme de b~tonnets et de coccoides sont visibles. Ces trous donnent une apparence "perfor6e" ii la surface de la colonic et sont peut-~tre le r6sultat d'une attaque microbienne de Ta paroi envelop- pante.

Fig.13-14 - Morphotype 111 at different foci showing where a bounding layer or sheath has been peeled off the colony leaving a void. The sheath seems to have enclosed a radially symmetrical supercolony as shown in figures 15, 16. 2391K/5R, 19.9 ;152.1, 30/23, 32. Diffdrentes raises au point du morphotype lI1 montrant un vide A l'endroit o~ une couche de la colonic a 6t6 61iminde,

Fig. 15-16 - M orphytype I showing the botryoidal and radial pattern of the G. prisca supercolony. 2391K/5R, 22.4 ; 151.7, 30/29, 30. Morphotype I montrant la nature botryo'fdale de la supercolonie de G. prisca.

Geobios n ° 22, fasc. 6

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PI. 2 C.B. Foster, J.D, Reed & R. W~eander

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PLATE 3

Nomarski interference phase contrast light photomicrographs of wet mount living specimens of Entophysalis major (figures 1-6), and aloeocapsa sp., University of Texas (UTEX) Culture LB 1938 (figures 7,8). The film and negative numbers are given for each specimen. The scale bar =10 p,m except for figure 6 =20 p,m.

Photomicrographies en contraste interf6rentiel selon Nomarski. Sp6cimens d' Entophysalts ~najor, vivants et en milieu humide (figures 1-6) et de aloeoca1Osa sp. (figures 7, 8). Oniversit6 du Texas (UTEX) Culture LB 1938. Les num6ros de film et de n6gatif sont donn6s pour chaque sp6cimen. Trait = 10 p,m saul figure 6 =20 p,m.

Fig.l-4 - Wet mount of living colony of Entophysalis major at different loci levels. The individual cells are surrounded by multiple poly saccharide layers which delineate a supercolony. 27/6, 7, 8, 9. Diffdrentes raises au point d'un montage en milieu humide d'une colonie vivante d' Entophysalis major. Les cellules individuelles sont entourdes de multiples couches de polysaccharides d6limitant la supercolonie.

Fig. 5 - Different portion of the Entophysalis major colony showing the multllayered nature of the cells. 27/10. Autre pattie de la colonie d' Entophysalis major montrant les multiples couches des cellules.

Fig. 6 - Low magnification view of Entophysalis major colony. 26A/24. The scale bar =20 ~m. Faible grossissement de la colonie d' Entopbysalis major. Trait = 20 p,m.

Fig. 7 - Gloeocapsa sp. (UTEX LB 1938) showing cells of individual colonies bounded by a common sheath (arrow). The colonies, howe ver, are not connected by cellular material, nor do they form the large multicelled mesocolonies seen in Gloeocapsomorpha. 26A/10. Cellules de colonies individuelles de Gloeocapsa sp. (UTEX LB 1938) limitdes par une enveloppe commune (fl~che). Toutefois les colonies ne sont pas r~unies par du materiel cellulaire et ne forment pas de larges colonies multicellulaires comme dans Gloeocapsomorpha.

Fig. 8 - Gloeocapsa sp. (UTEX LB 1938) showing cells bounded by a common sheath. 26A/2. Gloeocapsa sp. (UTEX LB 1938) avec des cellules limitdes par une enveloppe commune.

Geobios n ° 22, fasc. 6

Pl. 3 C.B. Foster, J.D. Reed & R. Wicander

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